Biology

BIOLOGY Chapter 2 Cell structure and organization Cell  The basic unit of life  Extremely small (10 – 20 microns)  Made up of living material called protoplasm consisting of water, proteins, carbohydrates and fats  Contains many compartments called organelles

Organelles  Cellulose cell wall o Present in plant cells o Rigid outermost layer of plant cells which provide mechanical support o Prevents plant cell from bursting when absorbing water o Made up of cellulose, a type of carbohydrate o Fully permeable o Gives the cell a fixed shape due to its rigidity  Cell surface membrane o Present in plant and animal cell o Made up of a double layer of phospholipids with some carbohydrates and proteins o Forms boundary of cell o Outermost layer in animal cell and is located beneath the cell wall in plant cells o Partially permeable o Protects the cell, controls movement of substances in and out of cell `

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Nucleus o Present in both plant and animal cells o Controls all cellular activities o Darkly stained, prominent in microscopic slide images o Most cells have diploid nucleus. Sex cells have haploid nucleus. Red blood cells do not have a nucleus  Cytoplasm o Present in plant and animal cells o Contain organelles such as nucleus and mitochondria and more o Site where most cell activities occur Nucleus contains o Nuclear envelope  separates the contents of the nucleus from the rest of the cytoplasm o Nucleoplasm,  the dense material within the nucleus o Nucleolus  plays a part in protein synthesis by producing ribosomes o

Chromatin  a mass of long thin thread-like structure made up of proteins and a compound called deoxyribonucleic acid (DNA)

Cytoplasm contains:  Endoplasmic reticulum (ER) o Present in both plant and animal cells o Involved in lipid synthesis and breakdown of toxins o System of membranes inside the cell which is continuous with the nuclear membrane o Divided into 2 components – rough ER (RER) and smooth ER (SER)  RER  A sheet-like structure with surface studded with ribosomes  Involved in protein synthesis and modifications  SER  Tube-like structure and its surface does not have ribosomes  Synthesises fats and steroids  Converts harmful substances into harmless substances in a process called detoxification o Sheet-like and tube-like structures of RER and SER increases its surface area to volume ratio to carry out their functions more efficiently  Ribosomes o Present in both plant and animal cells o Made up of proteins and ribonucleic acid (RNA) o Small, spherical and numerous. Mainly concentrated on the RER surface, but some lie freely in the cytoplasm o Make polypeptides from amino acids which eventually form proteins o Make proteins used within the cytoplasm of the cell o RER transports proteins made by ribosomes to the golgi apparatus for secretion out of the cell  Golgi apparatus `

Present in both plants and animal cells Made up of several stacks of curved flattened membranes arragned in sacs called cisternae o Membranes are usually surrounded by spherical bodies called vesicles o Vesicles transport immature proteins made in RER to Golgi body for further processing o Chemically modifies substances made in ER o Stores and packages these substances in vesicles for secretion out of the cell o Set of membranes that make up Golgi body is not continuous with nuclear membrane or ER  Vesicles get pinched off RER, fuses with Golgi body, and substances in vesicles released into golgi body  Golgi apparatus may modify these substances  Secretory vesicles containing this modified substances pinched off Golgi apparatus and fuse with cell surface membrane to be released out of the cell Mitochondria (singular mitochondrion) o Present in both plant and animal cells o Small oval shaped organelle which are the powerhouse of the cell o Aerobic respiration occurs in mitochondria, food substances are oxidised to release energy in the form of adenosine triphosphate (ATP) o ATP used by cell to perform cell activities such as growth and reproduction o Has 2 layers of membrane, inner membrane highly folded into structures called cristae o Cells that require more energy usually have more mitochondria Chloroplasts o Present only in plant cells o Contain a green pigment called chlorophyll, which is essential for photosynthesis o Cells in the leaves of the plant usually has highest concentration of chloroplasts Vacuoles o Present in both plants and animal cells o Fluid-filled space enclosed by a membrane o Animal cells contain numerous small vacuoles that contain water and food substances t o These vacuoles exist temporarily o Plant cells have a large central vacuole containing water and a liquid called cell sap o Cell sap contains dissolve substances such as sugars, mineral salts and amino acids o This large vacuole is enclosed by a partially permeable membrane called tonoplast o o

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Specialised cells, tissues, organs and systems  Red blood cell (RBC) o Most abundant cell type in blood (45 % of total vol. of blood) o Contains haemoglobin which binds reversibly to oxygen and transport it to other parts of the body o Absence of nucleus allows RBC to carry more haemoglobin o Biconcave shape increases surface area to volume ratio to absorb oxygen at a faster rate o Flexible enough to squeeze through blood capillaries  Root hair cell o Lines the outer surface of plant roots o Has a long finger-like projection along its length to increase its surface area to volume ratio for faster rate of water and mineral absorption `

Central vacuole contains concentrated cell sap, decreasing vacuole’s water potential. More water can be absorbed by osmosis, as water moves from a region of higher water potential (the soil) to a region of lower concentration (the root cell) o Does not contain chloroplasts as it is usually not exposed to sunlight, hence does not need to photosynthesise Xylem vessel o Transports water and dissolved minerals from plant roots to leaves o Made up of dead cells with thick walls o Narrow and have no cross walls to obstruct water flow through the lumen o No protoplasm to offer resistance to water flow o Walls are thickened with lignin to prevent collapse of the vessel o Xylem vessel provides mechanical support for plants tissues, organs and systems Group of similar cells working together to perform a specific function is a tissue Simple tissues are made up of cells of the same type. Complex tissues are made up of more than one type of cell Different tissues combine to form an organ Organs work together in organ systems. A multi-cellular organism is made up of many organ systems working together o

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Cells,    

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Chapter 3 Movement of substances Diffusion    

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Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient Occurs passively, no external energy needed Takes place as long as a concentration gradient is present, even through a partially permeable membrane Rate of diffusion depends on concentration gradient, size of diffusing substance and temperature o Higher concentration gradient, faster diffusion rate o Bigger particle, lower diffusion rate o Higher temperature, higher diffusion rate E.g. of diffusion o Movement of oxygen and carbon dioxide between alveoli and blood capillaries in lungs

Osmosis  Osmosis is the net movement of water particles from a region of higher water potential to a region of lower water potential down a water potential gradient across a partially permeable membrane  Occurs passively  Takes place only through a partially permeable membrane Terminology Isotonic

Description 2 solutions are isotonic with respect to each other if they have equal water potential A solution is hypertonic with respect to the other if it has lower water potential (lower water potential) A solution is hypotonic with respect to the other if it is less concentrated (higher water potential)

Hypertonic

Hypotonic

 A solution that contains more dissolved substances has a lower water potential than a solution with less dissolved substances

Animal cell `

Hypotonic solution Entry of water

Isotonic solution No change

Hypertonic solution Water exits the

Plant cell

into cell. Cell eventually ruptures Entry of water into the cell. Cell becomes turgid

No change

cell. Cell becomes crenated Water exits the cell. Cell becomes flaccid, then plasmolysed

Active transport  Movement of substances from a region of lower concentration to a region of higher concentration against a concentration gradient  Requires energy from respiration, in the form of ATP (adenosine triphospate)  Rate of active transport depends on the availability of energy  More energy, higher rate of active transport  Active transport is important because it allows cells to obtain nutrients that are in low concentrations outside the cell

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Chapter 4 Biological Molecules Food  Provides energy for vital activities  Food provides raw material to make new protoplasm; needed for growth and repair of worn out tissues  Keeps organism healthy Water 

Solvent for chemical reactions  Water is needed for many chemical reactions taking placing in living things  Key component in tissues  Controlling body temperature  Via perspiration  Medium for transporting dissolved substances  E.g. digested food products and waste products Carbohydrates

 Carbohydrates are organic molecules made up of the elements carbon, hydrogen and oxygen. Hydrogen and oxygen are present in the ratio 2:1  Made up of primary units called monosaccharides (simple sugars)  Cannot be further digested into simpler molecules  E.g. glucose, fructose, galactose. Same formula C 6H12O6, but arranged differently within the molecule  2 monosaccharides combine chemically to form disaccharides, which are complex sugars  E.g. maltose, sucrose, lactose. Same formula of C 12H22O11, but arranged differently within the molecule  Multiple monosaccharides combine chemically to form polysaccharides, which are complex macromolecules  E.g. starch, glycogen, cellulose

Monosacchari de Disaccharide

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Polysaccharid e Condensation reaction is a chemical reaction in which 2 simple molecules are joined together to form a larger molecule with the removal of 1 molecule of water Glucose + Glucose Maltose + water Condensati on reaction

Hydrolysis or hydrolytic reaction is a reaction in which a water molecules is needed to break up a complex molecule into a smaller one Maltose + water Glucose + Glucose Maltase Hydrolytic reaction

Test for starch Procedure Add a few drops of iodine solution into sample

Results Iodine remains yellowishbrown Iodine turns dark blue

Conclusion Starch is absent Starch is present

Test for reducing sugar Procedure Results Conclusion Add an equal volume of Solution remains blue Reducing sugars are absent Green/orange precipitate Low concentration of reducing Benedict’s solution to the forms sugars present sample in a test tube. Place Brick red precipitate forms High concentration of test tube into hot water bath reducing sugars present for a few minutes  Just remember color of rainbow. Brick red is high conc., blue is low        

Glycogen and starch are stores of glucose Plants store glucose as starch Animals store glucose as glycogen Glycogen and starch are suitable storage materials because They are insoluble in water, thus does not change the water potential in cells They are large molecules which are unable to diffuse through cell membranes, so they will not be lost from cell They can be easily hydrolysed to glucose when needed Their molecules have compact shape so they occupy less space than all the individual glucose molecules that make up a starch or glycogen molecule

Hydrolysis of starch

Part of a starch molecule amylase Maltose molecules maltase Glucose molecules

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Functions of carbohydrates

Fats

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Substrate for respiration, provide energy for all activities Form supporting structures (e.g. cell walls in plants) Formation of nucleic acid (DNA) Synthesise lubricants (mucus) Converted into other organic compounds such as amino acids and fats

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Fats are organic molecules made up of the elements carbon, hydrogen, oxygen. Unlike carbohydrates, fats contain much less oxygen in proportion to hydrogen Fats are made up of 1 molecule glycerol and 3 molecules of fatty acids Serve as storage of energy and heat insulation Used to synthesise the lipid bilayer component of cell membranes

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lipase + 3H2O

+

glycerol

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lipas Fat + water Sources of fats  Butter  Cheese  Nuts

3 fatty acid Glycerol + fatty acid

Fat molecule

Test for fats Procedure Add an equal volume of ethanol to the sample in a test tube. Mix thoroughly and add an excess of water

Results Contents of test tube remain clear A cloudy white emulsion formed

Conclusion Fats are absent Fats are present

Proteins    

Proteins are organic molecules made up of elements carbon, hydrogen, oxygen and nitrogen. Another element, sulfur, may also be present Made up of primary units called amino acids which have (-NH 2), a (-COOH), an R group and a hydrogen atom attached to a central carbon atom Many amino acids are linked by peptide bonds to form polypeptides Polypeptides are further modified to form proteins

R

NH `

C

COOH

2

Amino group

Acid group

Test for proteins Procedure Results Conclusion Add an equal volume of Solution remains blue Proteins are absent NaOH solution to the Proteins are present sample in a test tube. Add Solution turns violet a few drops of 1% CuSO4 solution. Shake and mix well  Proteins are found in  Milk, seafood, meat such as chicken  Plants foods such as soya beans, nuts, grains  Functions of proteins  Synthesis of new protoplasm, for growth and repair of worn-out body cells  Synthesis of enzymes and some hormones  Formation of antibodies to combat diseases

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Chapter 5 Enzyme Enzymes        

Enzymes are biological catalysts, which speed up the rate of chemical reactions without themselves being chemically changed at the end of the reaction Since enzymes are not consumed by the reaction they catalyse, they can continue to catalyse more reactions after a reaction is complete Enzymes are protein in nature Work by lowering the activation energy of reactions they catalyse Contain active sites which are the reactive portions of the enzyme and act on specific substrates Enzymes can catalyse reversible reactions o From complex molecules to simpler molecules and vice versa Almost all reactions are catalysed by enzymes Without enzymes, reactions in the body will be too slow to sustain life Energy

1

2

3 time

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1. Activation energy with enzyme 2. Activation energy without enzyme Enzymes are classified as o Carbohydrases digest carbohydrates o Proteases that digest proteins o Lipase that digest lipids (fats)

Characteristics of enzymes  

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Enzymes speed up chemical reactions o Enzymes speed up the rate of chemical reactions that occur in the cell by lowering the activation energy needed to start a reaction Enzymes are required in minute amounts o Because they remain unchanged at the end of the reaction o Same enzyme can be used over and over again to catalyse a large amount of chemical reactions Enzymes are specific in action o Highly specific in nature. E.g. amylase on acts on starch, not proteins or fats. o Specific due to its 3-D shape. ‘Lock and key’ hypothesis explains how the shape of an enzyme affects the way it functions

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Enzymes catalyse reversible reactions o E.g. CO2 + H2O ⇌ H2CO3

‘Lock-and-key’ hypothesis  

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Carbonic anhydrase

Substances which substrates act on are called ‘substrates’ Active sites are depressions on the surface of an enzyme molecule into which the substrate molecule can fit – like a lock-and-key (Enzyme is lock, substrate is key) o Enzyme has specific 3-D shape, and a specific active site o Only a specific substrate which is complementary to the active site can fit into the enzyme. This results in the formation of an enzyme-substrate complex o While substrate is attached to the active site, chemical reactions occur. Substrate is converted into products and later leaves the active site. Enzyme remains unchanged General equation is E + S ⇌ ES ⇌ E + P Where E = enzyme, s = substrate(s), P = product(s)

Factors affecting enzymes 

Temperature o Every enzyme has an optimum temperature at which it is most active. (Usually 4045oC) o Enzymes are inactive at low temperatures. The kinetic energy is low, hence chances of substrate molecule colliding with enzyme is low o As temperature increase, frequency of collisions increases, resulting in higher rate of reaction o Enzymes become denatured at very high temperatures, resulting in little or no catalysis, hence rate of reaction decreases Rate of enzyme activity

temperature Optimum Denaturation is the change of temperature 3D structure of an enzyme or any other soluble proteins, caused by heat or chemicals such as acids or alkalis  

Denaturation results in loss or alteration of the enzyme’s active site. Substrate no longer fits into enzyme active site and no reaction will occur pH o Each enzyme can only operate within a narrow range of pH  E.g. pepsin in stomach can only work in acidic environment o Beyond the optimum pH range, enzymes become denatured, resulting in little or no catalysis o Highest rate of activity of an enzyme is at its optimum pH

Rate of enzyme activity ` pH Optimum

Chapter 6 Nutrition in Humans Nutrition is the process by which organisms obtain food and energy for growth, repair and maintenance of the body Alimentary canal     

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Consists of mouth, oesophagus, stomach, duodenum, small intestine (ileum, jejunum, duodenum), large intestine (colon) and anus Includes salivary gland, pancreas, gall bladder and liver as accessory organs Breaks down food from large portions into smaller soluble substances that can be carried in the bloodstream Digestion : Process of breaking down food Assimilation : Process of making new molecules from simple substances absorbed by the body o Liver plays a major role in the assembly of biological molecules using substances absorbed via alimentary canal Egestion : Process of removing waste products Salivary gland toungue Mouth cavity epiglottis oesophagu spancreas stomach Gall Bile duct Pyloric sphincter pancreas duodenu m jejunum ileum colon Rectu m anus

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Mouth     

Breaks up food by chewing to increase surface area to volume ratio for faster rate of digestion Saliva lubricates food particles to move through oesophagus Tongue mixes food with saliva and rolls food into a bolus Salivary glands produce salivary amylase Amylase turns starch into maltose

Oesophagus   

Food is pushed through oesophagus by rhythmic contractions along its length Peristalsis is the rhythmic, wave-like contractions in the wall of the alimentary canal Oesophagus has 2 layers of muscles o Longitudinal muscles (outer layer) o Circular muscles (inner layer)

Longitudinal muscles Circular muscles

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Longitudinal and circular muscles are antagonistic o When circular muscles contract, longitudinal muscles relax. Oesophagus constricts, becoming narrower and longer o When longitudinal muscles contract, circular muscles relax. Oesophagus dilates, becoming wider

Stomach `

Circular muscles contract

Circular muscles relax

Longitudinal muscles

Longitudinal muscles contract

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Distensible muscular bag which can hold food for a long period of time to allow digestion to take place Strong muscles contract rhythmically to churn and break down food Secretes high concentration of HCl(aq) acid which kills microorganisms that enter the digestive system Also secretes pepsin which are activated and work optimally at low pH Secretes mucus, which lines the inner walls of the stomach and protects it from acid and digestive juices Pyloric sphincter opens periodically to allow food into the duodenum Partially digested food that leaves stomach is called chyme

Small intestine 

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Consists of duodenum, jejunum and ileum o Duodenum  Connects stomach to small intestine  Entry of food controlled by pyloric sphincter  Site of entry of pancreatic juice and bile from bile duct  Alkaline environment neutralises acid from stomach and denatures stomach enzymes, preventing damage to duodenum wall Bulk of digestion takes place in small intestine (ileum and jejunum) Secretes intestinal juice which contains digestive enzymes such as lipase and maltase Pancreatic and intestinal enzymes work optimally in alkaline pH Most food substances are fully digested into simple substances and absorbed into the bloodstream Intestinal wall is highly folded with villi and microvilli to increase surface area to volume ratio for more efficient absorption Well supplied by blood and lymphatic capillaries to transport away absorbed substances

Intestinal villi (singular villi)        

On the surface of the small intestinal wall, there is a high density of finger-like projections called villi Epithelial cells on each villus also have projections that are called microvilli Villi and microvilli greatly increase surface area to volume ratio for more efficient absorption of digested food substances Each villus has a dense network of blood capillaries and a lacteal Blood capillaries carry glucose, amino acids and minerals from the small intestine Lacteals carry fatty acids, glycerol and fat-soluble vitamins from the small intestine Blood capillaries from the villi of the intestine eventually combine and form the hepatic portal vein Epithelium only one cell thick

Large intestine    

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Receives undigested food from the small intestine No digestion takes place in the large intestine Prevents excessive loss of water and mineral salts through the faeces by reabsorbing them Leads to rectum where faeces are expelled through anus

Part Hepatic portal vein

Description  Connects capillaries from small intestine to the liver  Carries blood rich in absorbed glucose, amino acids and minerals for processing and storage in the liver  Harmful microorganisms and toxins might cross the intestinal walls to the bloodstream but are eliminated when they reach the liver  Blood that leaves liver has fairly constant concentration of glucose despite large fluctuations in the hepatic portal vein, especially after a starchy meal 

Pancreas

  Gall bladder Liver Hepatic artery Hepatic vein

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Hepatic portal vein Smalll intestine

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Secretes pancreatic juice containing digestive enzymes such as trypsin, amylase and lipase Pancreatic juice is released into the duodenum via bile duct Secretes hormones such as insulin and glucagon which regulate blood glucose levels Bile is stored temporarily in the gall bladder When gall bladder contracts, bile flows into duodenum via bile duct Receives nutrient-rich blood from the small intestine via hepatic portal vein Produces bile which is necessary to emulsify fats o Bile is stored temporarily in gall bladder and released into duodenum Regulates blood glucose concentration o Too much glucose makes liver secrete insulin, converting glucose into glycogen for storage o Too little glucose causes liver to secrete glucagon, converting glycogen into glucose Iron storage o Breaks down haemoglobin from worn-out RBC and stores the iron that is released Protein synthesis o E.g. prothrombin and fibrinogen Deamination of amino acids o Deamination is the process by which amino groups are removed from amino acids and converted into urea Detoxification o Converting harmful substances into harmless substances

Alcohol 

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Harmful to digestive system o Alcohol stimulates acid secretion in stomach. Excess stomach acid increases the risk of gastric ulcers

Prolonged alcohol abuse leads to cirrhosis of liver – liver cells get destroyed and replaced with fibrous tissue, making liver function less efficiently Harmful effects on the nervous system o Depressant. Slows down some brain functions. Varies from person to person o Reduced self-control o Effect on reaction time. Slowed reaction time, poor vision, slurred speech, slower reflex actions o

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Enzyme Salivary amylase Pepsin Pancreatic amylase Pancreatic lipase

Produced by Mouth Stomach Pancreas Pancreas

Substrate Starch Proteins Starch Lipids

Trypsin Intestinal lipase

Pancreas Small intestine

Proteins Lipids

Maltase Peptidase

Small intestine Small intestine

Maltose Polypeptides

Products Maltose Polypeptides Maltose Glycerol and fatty acids Polypeptides Glycerol and fatty acids glucose Amino acids

Big fat droplets are broken up into smaller fat droplets by the process of emulsification, which increases the surface area to volume ratio of the fats, speeding up their digestion by lipase

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Chapter 7 Nutrition in plants Photosynthesis is the process in which light energy absorbed by chlorophyll is transformed into chemical energy. The chemical energy is used to synthesise carbohydrates from water and carbon dioxide. Water and carbon dioxide is released during the process Conditions for photosynthesis   

Sunlight Carbon dioxide Chlorophyll

Stages of photosynthesis 

There are 2 stages for photosynthesis: Light dependent stage and Light independent stage 1. Light dependent stage o Light energy is absorbed by chlorophyll and then converted into chemical energy Light energy Chemical energy chloroph o Light energy is used to split H2O molecules into hydrogen and oxygen molecules in yll the process called photolysis 2. Light independent stage o Hydrogen produced in photolysis is used to reduce carbon dioxide into carbohydrates such as glucose. Energy required from this process is taken from the light dependent stage o Enzymes play a part in both light dependent and light independent stages

Overall equation for photosynthesis Light  6 CO2 + 12 H2O energy  

C 6H12O6 + 6 O2 + 6 H20

6 CO2 + 6 H2O Chlorophyl C 6H12O6 + 6 O2 (simplified equation) Carbon dioxide + water  glucose + oxygen

Limiting factors for photosynthesis   

Light intensity Concentration of CO2 Temperature

Rate of

Rate of

A

B

A

B

CO2 concentration Light intensity O – AO: Light intensity/CO 2 concentration Ois the limiting factor

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A – B : Light intensity/CO2 concentration is no longer the limiting factor, because other factors are limiting the rate of photosynthesis Rate of

Temperature   

At low temperature, rate of photosynthesis is low As temperature increase, rate of photosynthesis increase At high temperature, rate of photosynthesis decreases rapidly due to denaturation of enzymes and proteins involved in reactions

Fates of glucose after photosynthesis 1. Used immediately  For cellular respiration to provide energy for cellular activities 2. a) In daylight, rate of photosynthesis is high, amount of glucose produced is faster than amount of glucose used. Excess glucose is converted into starch b)In darkness, photosynthesis stops. Starch converts back into glucose 3. Converted into sucrose  Transported to other parts of plant or to storage organs such as seeds, stem tubers, root tubers via phloem  Converted into starch or other forms of storage compounds at storage organs, depending on plant  Might be converted back into glucose 4. Reacts with nitrates and other mineral salts absorbed in soil  To form amino acids in leaves i. Used to form proteins for synthesis of new protoplasm in leaves ii. Excess is transported to other parts of plants for synthesis of new protoplasm or for storage as proteins  Forms fats i. For storage ii. Used in cellular respiration iii. For synthesis of new protoplasm Photosynthesis is important because:   

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Makes chemical energy available to animals and other organisms Removes CO2 and provides O2 Energy is stored as fossil fuels through photosynthesis

Internal structure of lamina cuticle Upper epidermal layer

Palisade mesophyll layer

xylem

phloem

Spongy mesophyll layer Lower epidermal layer

Upper epidermis  

Stomatal pore

One cell thick Covered by a waterproof waxy layer called the cuticle which prevents water loss

Mesophyll layer 

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Consists of 2 layers : Palisade mesophyll and Spongy mesophyll o Palisade mesophyll  Consists of one or two layers of closely packed enlongated cynlindrical cells  Higher concentration of chloroplasts than in spongy mesophyll as it is more exposed to sunlight o Spongy mesophyll  Cells are irregular in shape  Packed loosely  Numerous large intercellular air spaces among the cells allows for diffusion of CO2 and O2 within the leaf

  

Lower concentration of chloroplasts than palisade mesophyll Cells covered with a thin film of moisture Contains the transport tissues, xylem and phloem. These are grouped to form vascular bundles

Lower epidermis 

Like the upper epidermis, one-cell thick and covered by an outer layer of cuticle which reduces water loss through the epidermal cell

Stomata (singular : stoma)    

Lower epidermis contains numerous stomata Regulates exchange of gases Each stoma surrounded by 2 guard cells which control opening and closing of stoma Guard cell contain chlorophyll and can photosynthesise, unlike the rest of the epidermal layer

Adaptations of leaf for photosynthesis Adaptation Petiole (leaf stalk) Thin broad lamina

Waxy cuticle on upper and lower epidermis layer

Stomata present in epidermal layer Chloroplasts containing chlorophyll found in all mesophyll cells More chloroplasts in upper palisade tissue Interconnecting system of air spaces in spongy mesophyll Veins containing xylem and phloem situated close to mesophyll cells

Function Holds leaf in position to absorb maximum light energy Thin lamina provides short diffusion distance for gases and enable light to reach all mesophyll cells Broad lamina provides large surface area for max absorption of light Reduces water loss through evaporation from the leaf Transparent to allow light to enter leaf Open in presence of light, allowing CO 2 to diffuse in and O2 to diffuse out of the leaf Chlorophyll absorbs and transforms light energy to chemical energy used in manufacturing of sugars More light energy can be absorbed near the leaf surface Allows rapid diffusion of CO2 and O2 in and out of mesophyll cells Xylem transports water and mineral salts to mesophyll cells Phloem transports sugars away from leaf

Vascular bundle 

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Consists of xylem and phloem o Xylem carries water and mineral salts from the roots to the leaves o Phloem carries sucrose manufactured from the leaves to the other parts of the plants

Xylem phloem CO2 enters leaf through stomata 1. In daylight, when photosynthesis occurs, the CO 2 ion the leaf is quickly used up a. CO2 concentration in leaf becomes lower than atmosphere b. CO2 diffuses from surrounding air through stomata into the air spaces of the leaf 2. Surface of mesophyll cell surrounded by a thin film of water to allow CO 2 to dissolve in it 3. Dissolved CO2 diffuses into the cells Xylem transports water and mineral salts to the leaf 1. Xylem transports water and dissolved mineral salts to the leaf from the roots (Chpt 9) 2. Once out of veins, water and mineral salts move from cell to cell right through the mesophyll of the leaf 4.

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Chapter 8 Transport in humans

Pulmonary artery

Pulmonary vein

Vena Cava Aorta

Deoxygena ted blood Heart Hepati c vein

Oxygenated blood Hepatic artery

Hepatic portal vein Renal vein

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Renal artery

: represents flow of blood Blood   

Contains red blood cells (RBC), white blood cells (WBC), and platelets suspended in plasma Transports nutrients, dissolved gases and waste products around the whole body Protective function against infections by immune system and prevents blood loss by clotting

RBC (Erythrocytes) Biconcave surface

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Produced by bone marrow Most abundant cell type in blood Contains haemoglobin, which combines reversibly with oxygen. This enables RBC to transport oxygen from the lungs to the rest of the body Contains enzymes which catalyse the rate at which CO 2 dissolves in plasma Flexible enough to squeeze through lumen of narrow capillaries No cell nucleus, which allows cell to carry more haemoglobin and transport oxygen more efficiently Biconcave in shape, increasing surface area to volume ratio to absorb and release oxygen at a faster rate

WBC (Leucocyte)      

Produced by bone marrow and lymph gland Takes up 1% of total vol. of blood Clolorless and does not contain haemoglobin Irregular in shape and contains a nucleus Can move, change shape and squeeze through thin capillary walls nucleus 2 kinds of WBC o Lymphocytes  Large, rounded nucleus  Nearly round in shape  Produces antibodies that help deactivate toxins and harmful microorganisms o Phagocytes  Has a lobed nucleus and irregular in shape  Break down and remove foreign pathogens by engulfing them and ingesting them in a process called phagocytosis

Platelets (Thrombocytes)   `

Fragments of cytoplasm from bone marrow cells Not true cells

granule s Lobed nucleu s

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Damaged platelets release an enzyme called thrombokinase which intiates the clotting process

Plasma      

Pale, yellowish liquid, consisting of 90% water and complex mixture of various dissolved substances such as fibrinogen, prothrombin and antibodies Functions as a transport medium Contain dissolved mineral salts such as chlorides, sulfates and phosphates of calcium, sodium, potassium. All these occur as ions in plasma Contains food substances such as glucose, amino acids, fats, vitamins Contains excretory products such as urea, uric acid, creatinine Contains hormones such as insulin

Blood groups     

Surface of RBC contain special proteins called antigens Blood plasma contains antibodies Natural antibodies will not react with your own antigens, but may react with others, causing clumping of blood (agglutination) People can be classified into blood groups according to the antibodies and antigens present The 4 blood groups are A, B, AB, O. Named after antigens present

Blood group A B Antigen present A B Antibody present b a A antigen reacts with a antibody, causing agglutination

AB A and B No antibodies

O No antigens a and b

A

B

AB

+ + - : no agglutination

+ + -

+ + + -

B antigen reacts with b antibody, causing agglutination Recipient Donor O A B AB + : agglutination

O

O is a universal donor, while AB is a universal recipient. Functions of blood 

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Transport function Substances transported Digested food - Glucose, amino acids, mineral salts, fats, vitamins

Carried from Intestines

Excretory products – Nitrogenous wastes : Urea, uric acid, creatinine

All parts of the body

To Other parts of the body Excess mineral salts transported to kidney for excretion To kidneys

Carbon dioxide : carried as hydrogen carbonate ions (HCO3- in plasma) Hormones Heat

Glands Respiring body tissues (E.g. muscles)

Oxygen (transported by Lungs haemoglobin in RBC) How oxygen is transported to the cells of the body 

To lungs, where HCO3- is converted to CO2 to be expelled Target organs All parts of the body to maintain a uniform body temperature All parts of the body for cellular respiration

Haemoglobin in RBC binds reversibly to form oxyhaemoglobin

Protective functions of the blood:   

Blood clotting Phagocytosis Antibody production

Clotting/coagulation of blood

(Inactive)

Calcium + thrombokinase (thrombokinase produced by damaged tissue and blood Thrombin platelets) (active) (soluble) Fibrinogen thrombin (insoluble) Fibrin threads

Phagocytosis is the process of engulfing or ingesting foreign particles, such as bacteria, by the WBC Tissue rejection is caused by the patient’s lymphocyte responding to the transplant by producing antibodies to destroy the transplant Prevention of tissue rejection – 

Immunosuppressive drugs o Inhibits the responses of the recipient’s immune system o However, the recipient would have lower resistance to many kinds of infection o Recipient has to continue taking the drugs for life

Circulatory system 

  

`

Heart o A muscular pump o When relaxing, heart fills up with blood o When contracting, heart forces out blood o Blood circulates around the whole body Arteries o Carry blood away from the heart Arterioles o Arteries branch again to form arterioles Capillaries o Arterioles branch out to form capillaries

Microscopic blood vessels made up of a single layer of flattened cells called endothelium o Endothelium is partially permeable. Enables substances to diffuse through quickly o Capillaries branch repeatedly, forming a large surface area for exchange of substances between blood and tissue cells Venules o Capillaries unite to form venules o

 

Veins o Venules unite to form veins o Carries blood back to the heart

Structure

Arteries Thick elastic muscular walls help to withstand high blood pressure exerted by the heart  Elasticity helps artery wall to stretch and recoil. Helps to push blood in spurts along the artery, giving rise to a pulse

Veins Thinner elastic muscular layer than arteries because blood moves more smoothly in veins, less pressure needed to withstand

Capillaries One-cell thick walls, no muscular/elastic tissue allows diffusion of substances between blood and tissue fluid

Small lumen relative to diameter Semi-lunar valves absent

Large lumen relative to its diameter Semi-lunar valves absent

Function

Carry blood away from the heart Carry oxygenated blood (except pulmonary arteries)

Large lumen relative to diameter Semi-lunar valves present to prevent backflow of blood Carry blood towards the heart Carry deoxygenated blood (except pulmonary vein)

Flow

Blood under high pressure

Blood under low pressure

Blood moves in pulses, reflecting the rhythmic pumping action of the heart

No pulse

`

Links arteries and veins Blood changes from oxygenated in arterioles to deoxygenated at venule Blood pressure reduced as blood flows from arteriole to venule end No pulse

Blood flows rapidly

Blood flows slowly

Blood flows slowly

Transfer of materials between capillaries and tissue fluids 1. When blood enters capillaries from arteries, it is at relatively high pressure 2. Some blood plasma, excluding blood plasma proteins, is forced out of the capillary into the tissue surrounding it 3. Fluid that escapes from capillaries is called tissue fluid, and bathes every cell in that tissue 4. At the end of the capillary, blood pressure is relatively low, fluid enters from the back into the capillaries where it forms blood plasma 5. This way, freshly supplied tissue fluids containing nutrients and dissolved oxygen constantly replaces tissue fluid containing dissolved wastes   

Mammals go through double circulation, unlike other animals which only go through single circulation In double circulation, blood flows through the heart twice in one circuit Mammals have a double circulation consisting of pulmonary and systemic circulations o Pulmonary circulation: blood pumped from heart to lungs and back o Systemic circulation: blood flows from heart to rest of the body and back

Pulmonar y arteries

Aorta

Superior vena cava

Right atriu

Left atriu

Semi-lunar valves

Inferior vena cava

Tricuspid valve

 

`

Pulmoary veins

Right ventricl e

Left ventricl e

Bicuspid valve

Median septum 2 upper chambers called atria (singular : atrium) o Comparatively thin muscular walls since they only need to force blood into ventricles, does not require high pressure 2 lower larger chambers called ventricles o Comparatively thick muscular walls, especially the left ventricle, since it has to pump blood to the rest of the body, requiring high pressure

Right ventricle has thinner walls than left as it only has to pump blood to the lungs which is close to the heart and requires less pressure, compared to the left ventricle having to pump blood to the rest of the body Right and left sides of the heart separated by a muscular wall called median septum, runs down the middle of the heart o Median septum prevents mixing of deoxygenated blood in the right side with oxygenated blood in its left side o Mixing of deoxygenated blood with oxygenated blood reduces the amount of oxygen transported to the tissue cells o



Cardiac cycle 1. Begins with relaxation of the atria, resulting in blood flowing from the vena cava into the right atrium and from the pulmonary vein into the left atrium 2. Atria contraction increases pressure and forces blood to flow into their respective ventricles 3. Atria relaxation and ventricular contraction cause the closure of the bicuspid and tricuspid valves resulting in the ‘lub’ sound 4. Closure of the bicuspid and tricuspid valves prevent the backflow of blood from the ventricles back to the atria 5. Blood from the right ventricle enters the pulmonary artery 6. Blood from the left ventricle enters the aorta 7. Relaxation of the ventricles causes the closure of the semi-lunar valves, resulting in ‘dub’ sound 8. Closure of semi-lunar valves prevent backflow of blood from the arteries to ventricles when ventricles relax 9. Each cardiac cycle consists of an atrial and ventricular contraction Contraction of ventricles is called ventricular systole Relaxation of ventricles is called ventricular diastole

1 cardiac cycle `

Main arteries of the body:  



The arteries leaving the heart are o Pulmonary artery from the right ventricle o Aorta from the left ventricle From the aortic arch o Arteries to the head, neck, arm o Aortic arch curls backwards towards the left side of the heart and continues downwards as the dorsal aorta Dorsal aorta distributes blood to regions of the body below the heart. It supplies oxygenated blood through o Hepatic artery to the liver o Arteries to the stomach, intestines o Renal arteries, one to each kidney

Main veins of the body 



Blood o o o

is returned to the heart by Pulmonary vein brings blood from the lungs to the left atrium Superior vena cava returns blood from the head, neck and arns to the right atrium Inferior vena cava runs upwards parallel to the dorsal aorta and brings blood to the right atrium Inferior vena cava collects blood from o Renal veins from the kidneys o Hepatic vein from the liver o Veins from the gut do not open directly into the inferior vena cava. Instead, leads to the hepatic portal vein which leads into liver

Coronary heart disease  

 

`

Coronary arteries supply oxygenated blood to the heart muscles Narrowed lumen of coronary arteries caused by fatty deposits causes o Atherosclerosis o This results in an increase of blood pressure o Such affected arteries develop rough inner surface, increasing the risk of a blood clot trapped in the artery o A blood clot formed in an artery is called a thrombosis o When it occurs in the coronary artery, supply of oxygen to heart muscles is reduced or cut off completely o Without oxygen, heart muscle cells may be damaged, heart attack occurs Stress, smoking, alcohol and fatty diets increase the risk of developing heart diseases Leading a smoke-free, healthy lifestyle with regular exercise decreases the risk of developing heart disease

Chapter 9 Transport in plants

xylem

phloem

Xylem    

Transports water and mineral salts from the roots to the leaves of the plant Provides mechanical support to the stem Empty lumen with no cross walls or cytoplasm reduces resistance to water flowing through the xylem Walls thickened with lignin to prevent collapse of the vessel

Phloem  

  `

Transports manufactured food such as sucrose and amino acids from the leaves to the other parts of the plant Consists of sieve tube cells and companion cells o Sieve tube cells only have a thin layer of cytoplasm with perforated cross walls o Companion cells rich in mitochondria, which provide energy to keep sieve tubes alive for active transport Transport of substances occurs by diffusion and active transport Holes in sieve plates allow for rapid flow of manufactured food substances through the sieve tubes

Root hair cells    

Form the epidermal layer of roots Have a long and narrow projection which increase surface area to volume ratio for more efficient water absorption Central vacuole contains concentrated cell sap, which helps to draw water into the cell from the soil by osmosis Have the ability to transport minerals via active transport since they are living cells

Translocation   

Transport of manufactured food substances such as sugars and amino acids in plants Occurs in phloem vessels which are made up of living cells Involves active transport and diffusion

Translocation studies 



`

Using aphids in translocation studies o Aphids penetrates leaf or stem and feed on phloem o Anaesthetising the aphid with CO2 and cutting off the body, leaving the feeding stylet, and examining the liquid that exudes from the cut end of the proboscis shows that it is inserted into the phloem sieve tube, and the liquid is sucrose and amino acids o This shows that translocation of sugars and amino acids occurs in the phloem Using carbon-14 isotopes o Plant is provided with CO2 containing radioactive carbon, 14C o When photosynthesis occurs, the sugars formed contain the radioactive carbon. Stem is cut out and exposed onto an X-ray photographic film. o Radioactive substances are present in the phloem, showing that translocation of sugars occur in the phloem

Entry of water into a plant     

Each root hair cell is a fine tubular outgrowth of an epidermal cell Sap in root hair cell is a relatively concentrated solution of sugars and various salts. Water enters root hair cell by osmosis, moving from a region of higher water potential (from soil) to region of lower water potential (root hair cell) Water drawn into the root hair cell by osmosis creates a pushing force called root pressure Narrow xylem vessels allow water to creep upwards via capillary action Water loss through the stomata of leaves creates a suction force to pull water upwards resulting in transpiration pull

1 2

3

1. Water enters the root hair cell by osmosis 2. Because there is a higher water potential in the root hair cell than the neighbouring cells, water moves to it by osmosis 3. This repeats until the water enters the xylem vessels and moves up the plant `

Root hair cells absorb ions or mineral salts by active transport 

When the concentration of ions in the soil is lower than in the cell sap, it moves into the cell by active transport, using energy from cellular respiration in the root hair cell

Capillary action 

Water tends to move up very narrow tubes due to interactions between molecules of water and surfaces of the tube

Transpiration pull       

Transpiration is the loss of water vapor from a plant, mainly through the stomata of the leaf Spongy mesophyll cells have a thin layer of moisture around them for gases to dissolve and diffuse into the cell Evaporation causes water surrounding the cells to be lost as water vapor through the stomata of the leaves when the stomata is opened Therefore, loss of water in plant via transpiration is a consequence of gaseous exchange in plants Loss of water causes water potential to decrease due to an increase in concentration of dissolved solutes in the cell Water then moves from neighbouring cells by osmosis and eventually creates a suction force at the xylem vessels called transpiration pull Transpiration is important because it also helps to cool the leaves on the plant

Factors affecting rate of transpiration    

Air movement (Wind removes saturated air filled with water vapor) o Increased air movement  increased transpiration rate Humidity (Humid air has high concentration of water vapor) o Increased humidity  decreased transpiration rate Light intensity (increasing light intensity causes stomata to open) o Increased light intensity  increased transpiration rate Temperature (Temperature increase increases rate of evaporation) o Increased temperature  increased transpiration rate

Wilting    

`

Occurs due to excessive transpiration and insufficient water uptake, resulting in net loss of water from the plant Cells of plants become flaccid, resulting in wilting Flaccid guard cells close stomata, preventing further water loss from leaves Leaves fold up, reducing surface area for water loss

Chapter 10 Respiration in Humans 

Respiration is the breakdown (oxidation) of food substances with the release of energy in living cells

2 forms of respiration:  

Aerobic respiration Anaerobic respiration

Aerobic respiration   

Aerobic respiration is the breakdown (or oxidation) of glucose in the presence of oxygen with the release of a large amount of energy. Carbon dioxide and water are released as waste products C6H12O6 + 6O2  6CO2 + 6 H2O + Large amount of energy Occurs primarily in mitochondria of cells

Anaerobic respiration       

`

Anaerobic respiration is the breakdown of glucose in the absence of oxygen. Anaerobic respiration releases less energy than anaerobic respiration Occurs when there is a lack of oxygen/energy provided for muscles by blood to respire, such as vigorous exercise C6H12O6  2C3H6O3 + Small amounts of energy Glucose  lactic acid + small amount of energy Occurs primarily in the cytoplasm of cells Accumulation of lactic acid in muscle cells results in muscle pains and fatigue Lactic acid is gradually removed from the muscles and transported to the liver o In the liver, some lactic acid is oxidised to release energy, which converts the remaining lactic acid into glucose

Respiratory tract    

Air enters from the nose to the nasal cavity, where nostril hairs help remove large dust particles Mucus glands along trachea and bronchi produces mucus which helps trap dust and microorganisms Ciliated cells on the inner surface of trachea and bronchi sweep upwards to remove mucus Mucus also helps warm and moisten air before entering lungs

Alveoli  

Forms a very large exchange surface for gases in the lungs Surrounded by a dense capillary network for efficient gaseous exchange Thin film of moisture

Continuous blood flows from pulmonary

`

Alveola r cavity

To pulmonary vein

1. Deoxygenated blood from pulmonary arteries enter the lungs and into the capillaries at alveoli 2. Concentration of O2 alveoli is higher than in capillary, thus O2 diffuses into capillaries and binds to haemoglobin in the RBC to be carried back into the heart 3. At the same time, CO2 concentration in the capillary is higher than alveoli, thus CO2 diffuses out of the capillary into the alveoli to be exhaled  Alveoli is one-cell thick to minimise distance for diffusion  Surface of alveoli in contact with air is lined with a layer of moisture to allow gases to dissolve and diffuse across Breathing Action

Ribs

Lungs

Diaphragm

Inhaling

Moves upwards and outwards Moves downwards and inwards

Volume increase

Contracts and moves downwards Relaxes and moves outwards

Exhaling

Volume decrease

External intercostal muscle Contract

Internal intercostal muscle Relax

Relax

Contract

Removal of CO2   

CO2 is a waste product of cellular respiration Carbonic anhydrase is an enzyme found in RBC which catalyses the conversion of CO2 and H2O into H+ and HCO3- ions CO2 + H2O ⇌ HCO3- + H+ CO2 CO2 + H2O

CO2

⇌ H2CO3 ⇌ HCO3- + H+

 

`

HCO3-

HCO3-

These ions are water soluble, carried by blood plasma When ions reaches the lungs, ions move back into RBC and are converted back into CO2, which leaves the lungs as a gas during exhalation

Smoking and respiratory diseases Chemicals Nicotine

Properties Addictive Makes blood clot easily

Carbon monoxide

Combines with haemoglobin to form carboxyhaemoglobin Increased rate of fatty deposits on arterial wall Causes uncontrolled cell division Paralyses cilia lining

Tar and irritants

Effects Increased blood pressure Increase risk of blood clots Increases risk of coronary heart disease Lowered supply of O2 in the body Increased blood pressure Increases risk of cancer in lungs Tar accumulates in respiratory airways, obstructing it

Diseases caused 





`

Chronic bronchitis o Epithelium lining on airways inflamed o Excessive mucus secreted o Cilia and epithelium paralysed. Mucus and dust particles unable to be removed o Obstructed air passages, making breathing difficult o Persistent coughing to clear air passage Emphysema (by violent coughing due to bronchitis) o Partition wall in alveoli break down due to coughing o Decreased surface area for gaseous exchange o Lungs lose elasticity and become inflamed with air o Difficulty in breathing – wheezing and severe breathlessness results Lung cancer o Caused by carcinogens in tobacco smoke

Chapter 11 Excretion in humans 

Excretion is the process by which metabolic waste products and toxic substances are removed from the body of an organism

The sum of all chemical reactions within the body of an organism is known as catabolism 

Metabolism = Catabolism + Anabolism

Human urinary system 

Contains: o Kidneys o Ureters o Urinary bladder o Urethra

Ureter  `

Narrow tube which connects the kidney to the urinary bladder, and where urine passes through

Urinary bladder  

An elastic muscular bag located in front of the rectum Stores urine

Urethra 

A duct which urine passes from bladder to outside of body

Sphincter muscles 

Located at bottom of bladder, controls urination by contraction and relaxation

Kidney



`

Cortex o Contains many malphigian corpuscles  Malphigian corpuscle is a single nephron o Outer dark red region, granular texture







o Covered by fibrous capsule Medulla (pyramids) o Inner pale red region o Renal pyramids located in this region o Striated (Striped) texture containing many tubules Renal pyramids o Conical structure in the medulla o Human kidney has 12-16 pyramids o Redial stripes on medulla pyramids indicate numerous kidney tubules called nephrons  Urine is formed in nephrons Renal pelvis o Renal pyramids project into a funnel-like shape called renal pelvis o The enlarged portion of the ureter inside the kidney

Structure of a nephron

 

`

Bowman’s capsule o Each nephron begins in the cortex as a cup like structure called the Bowman’s capsule Proximal convoluted tubule o Bowman’s capsule leads into a short, convoluted tubule which straightens out as it passes into the medulla



 

Loop of Henle o In the medulla, tubule extends into the renal pyramid and U-turns back into the cortex o Consists of both the ascending and descending loop of Henle Distal convoluted tubule o The part of the tubule after the loop of henle which is convoluted again Collecting duct o Tubule opens into a collecting duct that runs straight through the medulla to the renal pelvis

Ultrafiltration    





Occurs at the Malphigian corpuscle of each nephron Blood enters kidneys by renal artery, branching into many arterioles Each afferent arteriole branches into a small ball of capillaries called the glomerulus Blood enters glomerulus at high hydrostatic forces (high blood pressure) and most of the blood plasma, excluding proteins and large molecules are filtered out of the capillary o All blood cells are too large to pass through the basement membrane and are retained in the capillaries. Presence of blood in urine may indicate kidney problems The filtrate passes into the Bowman’s capsule and travels in another set of tubules. Filtrate contains water and small molecules (such as glucose and amino acids, mineral salts and nitrogenous waste products). Blood cells, platelets and large molecules such as proteins and fats retained in glomerular capillary Filtered blood leaves the glomerulus by an efferent arteriole instead if a vein

Reabsorption 

  

`

Most of the mineral salts and all of the glucose and amino acids reabsorbed through the walls of the proximal convoluted tubule into the surrounding blood capillaries o These solutes are reabsorbed by diffusion and active transport. This reabsorption is highly selective, only the substances required by the body would be reabsorbed o Water in the filtrate is reabsorbed by osmosis Water is reabsorbed at the loop of henle At the distal convoluted tubule, some water and mineral salts are reabsorbed At the collecting duct, some water is reabsorbed o Excess water, excess salts and metabolic waste products (e.g. urea, uric acid, creatinine) pass out of the collecting duct into the renal pelvis as a mixture called urine

Ultrafiltration occurs Selective reabsorption

Unwante d material

Osmoregulation is the control of water and solute concentration in the blood to maintain a constant water potential in the body Amount of water in blood plasma is controlled by anti-diuretic hormone (ADH), produced by hypothalamus, released by the pituitary gland 1. Lower water potential than normal of blood plasma detected by hypothalamus and stimulates pituitary gland to release ADH 2. ADH released into bloodstream causes constriction of blood vessels, increasing blood pressure 3. Reaches the kidney and causes more water to be reabsorbed, hence conserving water and increasing water potential of blood a. Regulation of water potential is important to prevent dehydration or cells bursting Kidney failures   

Kidney failure results in the inability of the kidney to remove wastes from the blood or to reabsorb useful substances effectively Commonly caused by high blood pressure, damaging the glomerular filtration membranes or caused by diabetes mellitus, which results in excess glucose being filtered and not reabsorbed by the kidney Patient is usually treated by dialysis, where a machine takes over the kidney’s job of removing wastes from blood

Drinking more water Increase

Less ADH secreted Increased More

Water potential Stimulates hypothalamus Pituitary gland secretes Reabsorption of water Urine

Drinking less water Decrease

More ADH secreted Decreased Less

Dialysis  

`

Blood from patient passes through partially permeable tubes inside the dialyser Tubes are bathed in dialysis fluid containing salts and glucose in approximately equal concentrations with that of blood

  

Only urea and unwanted wastes will diffuse across the membrane into the dialysis fluid to be removed Blood and dialysis fluid flow in opposite directions to maintain a high concentration gradient for the diffusion of wastes o This is known as counter-current flow Useful substances, proteins and blood cells, remain in the tubes and are pumped back to the patients

Chapter 12 Homeostasis    

Homeostasis is the maintenance of a constant internal body environment, which is essential for survival Important parameters include body temperature and blood pH Huge fluctuations in these parameters affect enzymatic activities, which affect many of the body’s chemical reactions Homeostasis involves o Thermoregulation – maintenance of a constant body temperature o Osmoregulation – the maintenance of a constant water potential and pH

Corrective mechanism     

Changes in the internal environment of the body are detected by receptors as a stimulus Receptors send information regarding the stimulus to a processor which is usually part of the brain The processor then sends signals to the effectors which initiate changes in the body to counter the stimulus Receptors continue to monitor the internal environment and send information to the processor until the stimulus is removed The process of correcting the internal environment through this corrective mechanism is known as negative feedback

Receptor (Detect

Stimul us `

Effectors (Implements corrective

As condition returns to normal, negative feedback is sent to receptor to continue monitoring stimulus until normal condition is achieved

Response (Condition starts to return to

Normal condition

Corrective mechanism

Regulating blood glucose concentration

Islets of Langerhans secrete insulin

Receptor Islets Langerhans pancreas



of in



Stimulus

As blood glucose levels decreases, Blood negative feedback is sent to islets glucose of Langerhans to continue concentrati monitoring stimulus until normal on above condition is achieved Normal condition Stimulus Blood glucose concentrationAs blood glucose levels increases, below normalnegative feedback is sent to islets



Insulin is transported to liver and muscle cells Insulin increases permeability of cell surface membrane to glucose. Glucose absorbed more quickly Insulin causes liver and muscles to convert excess glucose to glycogen,

Blood glucose concentration decreases. Blood glucose concentration increases

of Langerhans to continue monitoring stimulus until normal condition is achieved Corrective mechanism Islets of Langerhans secrete glucagon Receptor Islets of Langerhans in pancreas

  

`

Glucagon transported to liver and muscle cells Glucagon causes the conversion of stored glycogen to glucose From liver, glucose enters bloodstream

Corrective mechanism

Regulating blood water potential



Receptor

 

Hypothalamus stimulated

 Stimulus Water potential increases

As water potential decreases, negative feedback is sent hypothalamus to continue monitoring stimulus until normal condition is achieved Normal condition

  

Less ADH released by pituitary gland into bloodstream Less ADH transported to kidney Cells in walls of collecting duct become less permeable to water Less water reabsorbed into bloodstream More water excreted Urine is more diluted More urine produced

Water potential decreases.

Stimulus

Water potential Water increases potential As water potential increases, below normalnegative feedback is sent to hypothalamus to continue monitoring stimulus until normal condition is achieved Corrective mechanism  Receptor hypothalamus stimulated

  

`

 

More ADH secreted by pituitary gland into bloodstream More ADH transported to kidneys Cells in walls of collecting duct become more permeable to water More water reabsorbed into bloodstream Less water excreted Urine more concentrated

Skin 

Functions o Protect the body from foreign organisms and UV rays from sunlight o Prevent excessive water and heat loss o Have nerve receptors which contribute to the sense of touch o Production of Vitamin D in the presence of sunlight

Component Receptor

Organ Thermoreceptor in skin

Processor

Hypothalamus

Effectors

Arterioles in skin

Sweat glands

Thyroid glands

Hair erector muscles Component Receptor

Organ Thermoreceptor in skin

Processor

Hypothalamus

`

Function Detect rise in temperature of skin and sends signals to hypothalamus Detects rise in temperature and sends signals to effectors Vasodilation occurs to allow more blood to reach the skin and lose more heat Produce sweat which will take away heat when it evaporates from the skin Decrease in metabolic rate of the body to reduce heat production Relax to make hair lay flat to lose more heat Function Detect fall in temperature of skin and sends signals to hypothalamus Detects fall in temperature and sends signals to

Effectors

Arterioles in skin

Muscles in body Thyroid glands

Hair erector muscle

effectors Vasoconstriction occurs to allow more blood to reach the skin and lose more heat Shivering occurs to produce more heat Increase in metabolic rate of the body to increase heat production Contracts to allow hair to stand, trapping air and reducing heat loss (air is a poor conductor of heat)

Chapter 13 Coordination and response in humans Human nervous system 

   

Human nervous system consists of o Central nervous system (CNS) containing the brain and the spinal cord o Peripheral nervous system (PNS) consisting of nerves connecting the central nervous system and the rest of the body. Function of PNS is to conduct sensory and motor signals between the CNS and the limbs and organs (receptors and effectors) Stimulus is a change in the environment that causes an organism to react. Detected by sensory neurons Response is a change in the body as a result of the stimulus. Effectors cells are muscle cells or gland cells which carry out the response to the stimuli Receptors collect information from the external and internal environments and send information to the CNS via sensory neurones Nerve impulses from the CNS reach the muscles via motor neurons

Nervous tissue   

`

Nerve impulses are transmitted by nerves, which are bundles of neurones wrapped in connective issue A neurone is a nerve cell o Neurones have a cell body, an axon, and a dendron o Cell body contains nucleus and cytoplasm 3 main types of neurones o Sensory neurones – transmit nerve impulses from the receptors to the relay neuron in the central nervous system o Relay neurones – transmit nerve impulses from the sensory neurones to the motor neurones. Found within CNS

o Motor neurones – transmit nerve impulses from relay neurone to effectors muscle cells or gland cells How impulses are transmitted around the body 1. Stimulus detected by receptors 2. Information is converted into nerve impulses 3. Sensory neurones transmits nerve impulses from sensory neurones to relay neurones in the CNS 4. Brain processes nerve impulses 5. Brain sends other nerve impulses based on the received information from relay neurones to motor neurones 6. Motor neurones sends nerve impulses to effectors 7. Effectors carry out intended action

receptor Sensory neurone Nerve impulse

Relay neuron

Effectors

Motor neurone

Structure of neurones

`

Central nervous system

Cell body

Dendrite of dendron

Myelin shaft

      

Dendrons are nerve fibres that transmit nerve impulses towards the cell body Dendrites of dendrons receive nerve impulses from other neurones Axons are nerve fibres that carry nerve impulses away from the cell body Dendrites of axon transmit nerve impulses to other neurones Myelin shaft is a layer of fatty substance that shields and insulates the nerve fibre. Myelin sheath is surrounded by a thin membrane known as the neurilemma Nodes of Ranvier are regions where the myelin shaft is absent. They speed up transmission by allowing impulses to jump from node to node Motor end plates (in motor neurone) is the junction between the dendrite and muscle fibre

Smooth and circular cell body Long dendron, short axon Transmits impulses from receptor to CNS

Motor neurone

`

Dendrite of

Nodes of Ranvier

Sensory neurone

  

axon

Cell body Axon

Dendrite

Dendro

  

Irregularly-shaped cell body Short dendron, long axon Transmit nerve impulses from the CNS to the nerve effectors

Synapse   

The junction or connection between 2 neurones Impulses are transmitted from an axon to a dendron across a synapse Transmission across a synapse is by chemical means (through a neurotransmitter)

Nerves   

A nerve is a bundle of nerve fibres enclosed in a sheath of connective tissue Nerves that emerge from the brain are called cranial nerves, nerves that emerge from the spinal cord are spinal nerves Spinal nerves contain mixed fibres. They are made up of sensory and motor nerve fibres

Nerve impulse transmission  



Relay neurones lie within the grey matter of the spinal cord Relay neurones transmit nerve impulses from o Sensory neurones  brain o Brain  motor neurones o Sensory neurones  motor neurones Relay neurones form synapses with sensory and motor neurones

Voluntary and reflex actions 

`

Reflex actions  Reflex action is an immediate response to a specific stimulus without conscious control  These actions are involntary and are not under the control of a person’s will  Shortest pathway of nerve impulses from the receptor to the effectors is known as the reflex arc  E.g. of reflex actions





`

o Touching a hot object 1. Heat stimulates receptors in your skin 2. Nerve impulses are produced and they are transmitted along the sensory neurone to the spinal cord 3. In the spinal cord, nerve impulses are transmitted to the relay neurone, and then to the motor neurone. At the same time, nerve impulses are transmitted to the brain 4. Upon receiving nerve impulses from relay neurone, motor neurone transmits nerve impulses to effector 5. Effector muscles contract, resulting in withdrawal of hand from the object Types of reflex actions o Spinal reflex  Reflexes that are controlled by the spinal cord  Withdrawal reflexes, knee-jerk reflexes o Cranial reflex  Reflexes that are controlled by the brain, but occur without a person’s consciousness  Pupil reflex, salivation Reflex arc o The shorter pathway which nerve impulses travel from the receptor to the effector in a reflex action

Chapter 14 The Human Eye 

The eye is a receptor

Cornea 

A dome-shaped transparent layer that is able to refract light rays into the eye

Sclera  

Tough white outer covering, protects eyeball from mechanical damag Continuous with the cornea

Conjunctiva  

A mucus membrane, covering the sclera Secretes mucus to keep front of the eyeball moist

Pupil 

`

A hole in the center of the iris, allowing light to enter the eye

Iris  

A circular sheet of muscles, consisting of 2 sets of involuntary muscles – cicular and radial muscles Also contains a pigment which gives the eye color

Eyelid   

Protects cornea from mechanical damage Squinting prevents excessive entry of light Blinking spread tears over the eyes so that dust can be wiped off

Eyelash 

Shields eye from dust particle

Tear gland 

Secretes tears to o Wash away dirt o Keep cornea moist for atmospheric oxygen to dissolve o Lubricate the conjunctiva, reducing friction when the eyelids move

Internal structure of eye 



  

`

Wall of the eyeball has 3 layers o Sclerotic coat (Sclera) – outermost layer  Tough, white outer covering of eyeball which is continuous to cornea  Eye muscles attached to this layer facilitates the movement of the eyeball o Choroid – middle layer  Black pigmented middle layer which prevents internal reflection of light  Contains blood vessels that carry oxygen and nutrients to eyeball and remove metabolic waste products from the eyeball o Retina – innermost layer  Contains light-sensitive cells known as photoreceptors which consists of rods and cones  Connected to nerve fibres from the optic nerve Fovea (yellow spot) o A small yellow depression where images are focused o Contains cones but not rods o Enables a person to have detailed color vision in bright light Blind spot o Region where optic nerve leaves the eye o Does not contain photoreceptors, therefore not sensitive to light Optical nerve o Transmits impulses to the brain where photoreceptors are stimulated Lens o Transparent, circular and biconvex structure o Shape or thickness can change in order to refract light onto the retina

  



Suspensory ligament o Attaches the edge of the lens to the ciliary body Ciliary body o Contains ciliary muscles which control the curvature and thickness of the lens Aqueous chamber o Space between the lens and the cornea o Filled with aqueous humour, a transparent watery fluid o Aqueous humour keeps front of the eyeball firm, and refracts light into the pupil Virtreous chamber o Space behind the lens o Filled with vitreous humour, a transparent jelly-like substance o Vitreous humour keeps eyeball firm and refracts light onto the retina o More dense liquid that aqueous humour

Photoreceptors in the retina



`

Cones o Three types of cones  Red



 Blue  Green o Each type contains different pigments, which absorbs light of different wavelength o Work together to enable us to see a variety of colors in bright light Rods o Rods are stimulated even by very dim light, but only in black or white o Contains a pigment called visual purple o Visual purple is bleached when exposed to bright light and impulses cannot be sent to brain

Focusing light by the lens (accommodation reflex)  



An image is focused in the eye by changing the thickness of the lens, thus able to refract light into fovea accurately Nature of image o Vertically inverted o Laterally inverted o Smaller image than the object Role of brain  Inverted image formed on retina  Light sensitive cells(rods and cones) are stimulated  Nerve impulses generated are transmitted through the optic nerve  Nerve impulses reach the optic centre of the brain  Brain interprets information and forms an upright image  Brain has a corrective function  Image is upside down in retina, but brain makes it upright

Distance of object Near

Far

  

Action of the eye Ciliary muscles contract

Result Suspensory ligaments slacken, relaxing pull on lens, lens becomes thicker and more convex, decreasing focal length Ciliary muscles relax Suspensory ligament become taut, pulling on edge of lens, lens becomes thinner and less convex, increasing focal length By increasing/decreasing focal length, light rays are sharply focused on the retina, stimulating the photoreceptors Nerve impulses generated are transmitted to brain via optic nerve Brain interprets impulses, person sees object as distant/near

Response to light intensity by the pupil (pupil reflex)  `

Light enters eye through a hole called the pupil

 

Iris controls diameter of pupil, hence controls the amount of light that enters the eye and prevents damage to the retina The iris controls the amount of light passing through 2 type of muscles: Circular and radial Radial muscles Circular muscles

 

These 2 muscles are antagonistic Work together to control size of pupil Light intensity Low High

  

`

Action of eye Iris circular muscles relax Iris radial muscles contract Iris circular muscles contract Iris radial muscles relax

Result Pupil dilates and allows more light to enter eye

Pupil becomes smaller to prevent excessive light from entering the eye and damaging the retina Pupil reflex protects eye from excessive light exposure, which could damage the retina Pupil becomes larger when light levels are low, and smaller when light levels are high The reflex arc of the pupil reflex  Stimulus (change in light intensity)receptor(retina)sensory neurone in optic nerve relay neurone to brainmotor neuroneeffector(iris)

Chapter 15 Hormones Hormones   

  



A hormone is a chemical substance produced in minute quantities by an endocrine gland. It is transported in the bloodstream to target organ(s) where it exerts its effects(s). After hormones have performed their functions, they are eventually destroyed by the liver Hormone production is controlled by the nervous system, produced by endocrine glands  Endocrine glands are ductless glands that transport their secretion through the bloodstream  Exocrine gland have ducts present to transport secretion to target organs Hormones can have an effect on multiple target organs Hormones influence the growth, development and activity of an organism E.g. of hormones are  Insulin and glucagon, produced by the islet of Langerhans in the liver, released directly into the bloodstream Too much of a hormone could harm the person  E.g. hyperthyroidism is the overproduction of thyroid hormones in the thyroid. Results in increased metabolic rate, high body temperature, can result in heart failure

Endocrine glands and their hormonal secretion Endocrine gland Islets of Langerha ns in the pancreas Islets of Langerha ns in the pancreas

Hormone released Insulin

Action 

Increases glucose uptake and cell metabolism by making cells more permeable to glucose  Decreased blood glucose concentration

Glucagon



Adrenal medulla in the adrenal gland

Adrenaline

  

Pituitary

Anti-

       

Stimulates the conversion of glycogen to glucose  Increased blood glucose concentration Stimulates the conversion of fats and amino acids into glucose Stimulates the conversion of lactic acid to glucose Speeds up glycogen breakdown  Increased blood glucose concentration Increases metabolic rate Increases heart rate and blood pressure Increases rate and depth of ventilation Increases rate of blood clotting Constricts arterioles in skin Causes pupils to dilate Contracts hair muscles, producing goose bumps Increase permeability of kidney to water

`

gland

diuretic hormone Ovaries Oestrogen Progestero ne Testes Testostero ne Adrenaline secretion: 1. 2. 3. 4. 5. 6.

   

Water potential of blood increase

Oestrogen controls development of breasts and broadening of pelvis Progesterone helps maintain a healthy pregnancy Causes deepening of voice and growth of facial hair

Stimuli activate hypothalamus in the brain Transmission of impulses down the spinal cord Motor neurone transmits impulses to adrenal gland Adrenal gland secretes adrenaline into bloodstream Blood transports adrenaline to target organs Target organs respond to adrenaline

Diabetes mellitus 

A disease in which the blood glucose concentration cannot be controlled within normal limits. Usually due to low insulin production, lack of insulin secretion or the failure of target cells to respond to insulin

Type 1 diabetes Develops early in a person’s life. Known as juvenile or early-onset diabetes

Type 2 diabetes Occurs later in a person’s life. Known as late-onset diabetes

Islets of Langerhans unable to secrete sufficient insulin

Insulin is produced but target cells, such as muscle cells, do not respond well to insulin

Inject insulin directly into their bloodstream. They ensure that they have a supply of sugary food such as sweets in case blood glucose levels get too low

Control blood sugar levels by carefully controlling dietary intake and exercising



Signs of 1. 2. 3.

diabetes Persistently high blood glucose levels Presence of glucose in urine after a meal Healing of wounds is slow and difficult

Comparing endocrine and nervous controls 

 `

Similar in that 1. Both help to coordinate the activities in the body 2. Both activated by the stimulus 3. Both exert effects on target organ(s) Differences:

Endocrine control Involves hormones (chemical substances) Hormones are transported by the blood Usually slow responses Responses may be short-lived (e.g. adrenaline) or long-lived (e.g. growth hormones) Always involuntary May affect more than one target organ

Nervous control Involves nerve impulses (electrical signals) Impulses are transmitted by neurones Usually quick responses Responses are short-lived

May be voluntary or involuntary Usually localised

Chapter 16 Cell division Mitosis 

  

Mitosis is a form of nuclear division that produces 2 daughter nuclei containing the same number of chromosomes as the parent nucleus. The daughter nuclei are genetically identical 1. Parent cell containing x chromosomes 2. DNA replicates 3. Mitosis 4. 2 genetically identical daughter cells form (with x chromosomes each) Mitosis is important for organism growth and tissue repair Since identical cells are produced, new cells can replace worn out cells during repair to perform the functions of the old cells Mitosis occurs during asexual reproduction

Mitosis Phase Interphas e

Prophase

Metaphas e Anaphase

`

Process  Not part of mitosis, cells carry out their normal activities  Just before mitosis, chromatin threads replicate producing 2 identical chromatin threads joined at a centre called a centromere. These 2 chromatin threads are called sister chromatids  Disintegration of nuclear membrane  Asters form around centrioles, and the pair of centrioles move to the opposite poles of the cell  Spindle fibres extend from centrioles  Chromatins condense and DNA replicates, forming X-shaped chromosomes and they migrate towards centre of cell  Chromosomes are attached by spindle fibres at the centromere to the centrioles  Chromosomes are aligned at the centre plane of the cell  Sister chromatids of each chromosome separate and each of them become a distinct chromosome  Spindle fibres holding the chromosomes shorten and pull the daughter chromosomes towards the centrioles

Telophase

Cytokines is

    

Spindle fibres break down Each set of chromosomes unwinds and uncondenses Nuclear membrane reforms Now there are 2 diploid daughter cells Not part of mitosis, cleavage forms in cell and deepens until cell splits into 2

Mitosis in plants 

Mitosis in plant cells are similar to animals except that  Centrioles are absent in plant cells  Cleavage of cytoplasm does not occur during cytokinesis. Instead, a cell plate is formed between the 2 daughter nuclei, dividing cell into 2. Cell plate is formed by the fusion of small fluid-filled vesicles produced by the Golgi Apparatus

Chromosomes   

Every diploid cell has 2 sets of chromosomes in its nucleus One set of chromosomes come from the mother, other one comes from the father Each chromosome in a paternal or maternal set has a corresponding chromosome in the other set that is approximately the same and contains the same genes  The pair of corresponding chromosomes is called a homologous chromosome 

22 pairs of homologous chromosomes in a male cell (XY) and 23 pairs of homologous chromosomes in a female cell (XX)

Meiosis      

Meiosis is a form of nuclear division that produces 4 daughter nuclei containing half the number of chromosomes as the parent nucleus Consists 2 sets of divisions Chromosome number is reduced by half during the first division (from 2n to n) Results in the formation of 4 haploid cells which will participate in reproduction All 4 cells produced from the single parent cell are genetically different Meiosis occurs in the production of gametes  Gametes are haploid reproductive cells  Diploid parent cell contains 2 pairs of chromosomes (2n = 4)  Replication of chromosomes  Meiosis I occurs, each daughter cell contains 2 chromosomes, but each chromosome consists of 2 chromatids  Meiosis II occurs, 4 haploid gametes containing 2 chromosomes (n = 2)

Process in meiosis Phase Interphas `

Process  Not part of meiosis, cell does its normal activities

e



Prophase I

    

 Metaphas eI Anaphase I

   

Telophase I

Cytokines is Prophase II

        

Metaphas e II Anaphase II Telophase II

Cytokines is `

        

Just before meiosis, chromatin threads replicate, producing 2 identical sister chromatids attached at the centromere Disintegration of nuclear membrane Asters form around centrioles and the pair of centrioles move to opposite poles of the cell Spindle fibres extend from centrioles Homologous chromosomes pair up (this process is called synapsis) Crossing over occurs, the homologous chromosomes twist around each other, and may break and exchange parts (this results in genetic variability between daughter cells) (the point where they cross each other is called chiasma) Chromatins condense and DNA replicates, forming X-shaped chromosomes and they migrate towards centre of cell Homologous Chromosomes are attached by spindle fibres at the centromere to the centrioles Homologous Chromosomes are aligned at the centre plane of the cell Homologous chromosomes separate and each of them become a distinct chromosome Spindle fibres holding the chromosomes shorten and pull the daughter chromosomes towards the centrioles Spindle fibres break down Each set of chromosomes unwinds and uncondenses Nuclear membrane reforms Now there are 2 haploid daughter cells Not part of meiosis, cleavage forms in cell and deepens until cell splits into 2 Disintegration of nuclear membrane Asters form around centrioles and the pair of centrioles move to opposite poles of the cell Spindle fibres extend from centrioles Chromatins condense and DNA replicates, forming X-shaped chromosomes and they migrate towards centre of cell Chromosomes are attached by spindle fibres at the centromere to the centrioles Chromosomes are aligned at the centre plane of the cell Chromosomes separate into sister chromatids Spindle fibres holding the chromosomes shorten and pull the sister chromatids towards the centrioles Spindle fibres break down Each set of chromosomes unwinds and uncondenses Nuclear membrane reforms Now there are 4 haploid daughter cells Not part of meiosis, cleavage forms in cell and deepens until cell splits into 2 (Total of 4)

Meiosis produces haploid gametes 

  

Meiosis produces haploid gametes  When haploid male gametes fuses with haploid female gametes, the diploid number of chromosomes is maintained Meiosis results in genetic variation  Variation occurs due to crossing over and independent assortment Independent assortment of chromosomes means that one chromosome from each pair can combine wither either chromosome of other pair Variations increases the chances for the species to survive changes in the environment

Differences between mitosis and meiosis Mitosis Daughter cell contain the same number of chromosomes as the parent cell Pairing of homologous chromosomes does not occur No crossing over Daughter cells are genetically identical to the parent cell 2 daughter cells produced from one parent cell Involves only 1 nuclear division Occurs in normal body cells during growth or repair of body parts

`

Meiosis Daughter cells contain half the number of chromosomes as the parent cell Pairing of homologous chromosomes occurs at prophase I Crossing over may occur Daughter cells are not genetically identical to the parent cell 4 daughter cells produced from one parent cell Involves 2 nuclear division Occurs in the gonads during gamete formation

Chapter 17 Reproduction in plants Reproduction  





Reproduction is the process of producing new organisms to ensure the continuity of a species 2 types of reproduction  Sexual  Asexual Asexual reproduction is the process resulting in the production of genetically identical offspring from one parent, without the fusion of gametes  A cell divides to produce 2 identical daughter cells by mitosis  Daughter cells have the same type and amount of genes as the parent cell  Offspring are called clones Sexual reproduction is the process involving the fusion of 2 gametes to form the zygote. It produces genetically dissimilar offspring  Gametes are formed when a cell divides to produce 4 daughter cells through meiosis  Each daughter cell has half the number of chromosomes as the parent  Male gamete fuses with female gamete in a process called fertilisation to form a zygote  Zygote has same number of chromosomes as the parent cell

Parts of a flower



Petal 

`

Brightly colored to attract insects for pollination

  

 Provides a landing platform for insects  All the petals together make up the corolla Receptacle  The enlarged end of the flower stalk that bears parts of the flower Pedicel  Flower stalk Stamen  The male part of the flower  All the stamens together make up the andromecium (plural androecia)  Stamen consists of anther and filament  Filament  holds the anther in a suitable position to disperse pollen grains  Anther  produces pollen grains, each made up of 2 lobes, each containing 2 pollen sac  anther contains a vascular bundle made up of a phloem and xylem  Pollen grains

  

`

Carpel   

Pollen grains have a haploid set of chromosomes Each pollen grain has 2 nuclei, the generative nucleus and the pollen tube nucleus (a.k.a vegetative nucleus)

Carpel is the female part of the flower All the carpels together make up the pistil or gynoecium (plural gynoecia) Carpel consists of ovary, style, and one or more stigmas  Stigma  Stigma is a swollen structure that receives pollen grains  Mature stigma secretes sugary fluid to stimulate the germination of pollen grains  Style  Connects the stigma to the ovary  Holds the stigma in a suitable position to trap pollen grains  Ovary Contains ovules needed for fertilisation Combines with pollen grains to form a zygote

   

Contains one or more ovules Ovule contains ovum and the definitive nucleus Ovum has a haploid set of chromosomes Ovule is attached to the placenta by a stalk called the funicle

Pollination 



`

Pollination is the transfer of pollen grains from the anther to the stigma  Important to help bring together male and female gametes to enable fertilisation to take place  Pollination can be brought about by insects or wind  There are 2 types of pollination  Self pollination  Cross pollination Self pollination is the transfer of pollen grains from the anther to the stigma of the same flower or a different flower on the same plant  Flowers are bisexual with anthers and stigmas maturing at the same time  Stigma is situated directly below the anther  Certain flowers in bisexual plants never open (cleistogamous) and only self pollination can happen  Advantages of self-pollination  Beneficial qualities are passed down from the parent plant to the offspring  Only one parent is required  Less pollen and energy is wasted  Not dependent on external factors for pollination  More likely to take place successfully since stigma are closer to anthers  Disadvantages  Offspring produced are genetically similar to parents, causing fewer varieties of offspring

Probability of harmful recessive alleles being expressed in offspring is higher compared to cross-pollination Cross-pollination involves the transfer of pollen grains to the flower of another plant of the same species  Dioecious flowers only bear either male or female flowers, thus unable to self-pollinate  In bisexual plants, cross-pollination occurs when  Anther and stigma mature at different times  Stigmas of plants are situated a distance away from the anthers  Advantages of cross-pollination  More varieties of offspring are produced which leads to greater genetic variation  Increased probability of offspring being heterozygous  Seeds produced are capable of surviving longer before germination  Probability of harmful recessive alleles being expressed in offspring is lower as compared to cross pollination  Offspring can inherit beneficial qualities from both parents  Disadvantages of cross pollination  2 different plants of the same species required  Dependent on external factors for pollination  More energy and pollen are wasted  Less likely to successfully occur due to self pollination 



Comparison between insect-pollinated and wind-pollinated flowers Insect-pollinated flower Presence of sweet nectar to attract insects Large and sticky pollen in order for the pollen to be caught on the insect Brightly colored flowers with large petals to attract insects Stamen is usually stiff and pointing upwards

Wind-pollinated flower Nectar is absent as insects are not needed for pollination Small and light pollen in order for pollen to be carried far away by the wind Small petals in order not to obstruct the wind Stamen is usually pendulous and dangling from the sides of the flower

Fertilisation     

`

When a pollen grain lands on the tip of the stigma, a pollen tube grows from it Enzymes released by pollen grain digests a pathway to the ovule for the male gametes to travel in Once the male gametes reach the ovule, one of them fuses with the ovum to form the zygote The zygote undergoes cell division and development to form the embryo of a seed Many pollen tubes can grow simultaneously inside the stigma

Chapter 18 Reproduction in humans

Sperm urethra

`

Organ/gland Testis Scrotum

Sperm duct/vas deferens Prostate gland Urethra Penis

Organ Ovary

Oviduct/ fallopian tube Uterus Cervix Vagina

Menstrual cycle

`

Function Produces sperms and testosterone which is the primary male sex hormone Contains and protects the testes. Regulates temperature by bringing testes closer or further from the body Transports sperms to the urethra Produces a fluid that activates sperm cells and provides them with energy Common duct for sperms and urine Male erectile organ to release sperms into the vagina during sexual intercourse

Function Releases developed ovum and produces oestrogen and progesterone, which are the female sex hormones Site of fertilisation and brings ovum to uterus Site of implantation of the embryo for the development into a fetus Dilates during childbirth Female sexual organ where sperms are deposited during sexual intercourse

     

Menstrual cycle lasts between 23 – 35 days and is on average 28 days long Controlled by female sex hormones (progesterone and oestrogen) which prepare the uterus for implantation of a fertilised ovum Progesterone and oestrogen are both produced primarily by the ovaries Each menstrual cycle is defined to start at the onset of menstruation During menstruation, inner lining of uterus us shed and discharged from the body via the cervix and vagina Roughly in the middle of each cycle (day 14-15) is an event called ovulation, where a developed ovum is released by the ovary into the oviduct. Where fertilisation will take place if sperms are present

Fertilisation Amniotic sac

`

Amniotic fluid Umbilical cord

     

Occurs in the oviduct where the sperm (male gamete) and ovum (female gamete) fuse together, forming a zygote Zygote will divide rapidly to form a ball of cells Zygote will be transported to the uterus by contraction of the oviduct and sweeping of the cilia on the inner wall of the oviduct When the embryo reaches the uterus, it implants itself onto the lining of the uterus and develops into a foetus At the same time, a portion of the cells from the embryo develops into the placenta which remains attached to the uterus as the foetus develops When pregnancy occurs, menstruation is inhibited by the presence of high levels of progesterone

Amniotic sac and amniotic fluid    

The amniotic sac is a membrane that forms during fetal development Contains the amniotic fluid in which the foetus is suspended and attached to the uterus via the umbilical cord Amniotic fluid protects the foetus from external shock and allows the foetus to move freely inside the uterus During childbirth, the event whereby the amniotic sac ruptures is known as ‘water breaking’ and the amniotic fluid which is released helps lubricate the vagina

Part Placenta

`

Function  Allows diffusion of food substances and Amniotic fluid oxygen from the mother’s blood to the Umbilical cord foetus’ blood  Allows diffusion of wastes and carbon dioxide from the fetus’ blood to the mother’s blood  Allows transfer of antibodies and



Umbilical cord

   

hormones from the mother to the foetus Prevents mixing of blood of the mother and the foetus which might result in agglutination Attaches the fetus to the uterus at its navel (belly button) Contains 2 umbilical arteries and 1 umbilical vein Umbilical vein carries oxygenated and nutrient rich blood from the placenta to the foetus Umbilical arteries carry deoxygenated and nutrient-depleted blood from the foetus to the placenta

Human immunodeficiency virus (HIV)    

A virus that causes acquired immune deficiency syndrome (AIDS) by attacking the white blood cells and destroying the immune system Most frequently transmitted through unprotected sexual intercourse with an infected partner or sharing of contaminated needles An infected mother could pass the virus to her child during pregnancy Prevention methods include abstinence from sexual contact with multiple partners, using condoms and avoiding sharing of needles

Chapter 19 Heredity Basic knowledge for heredity 

`

Chromosome

    









`

A chromosome is a rod-like structure visible in the nucleus during cell division. It is made up of the molecule deoxyribonucleic acid (DNA) Chromosomes are condensed chromatin threads DNA carries the hereditary information for making organisms Each chromosome may carry many genes along its length

Gene 

Alleles 

A gene is a unit of inheritance, born on a particular locus (position) of a chromosome. It is a small segment of DNA in a chromosome that controls a particular characteristic or protein in an organism

Alleles are different forms of the same gene. They occupy the same relative positions on a pair of homologous chromosomes  E.g. the gene of the height of peas has 2 alleles: short and tall. Letters are usually used to represent alleles. Capital for dominant allele (T), lower case letter for recessive allele (t) Homologous chromosomes  Exists in pairs. One chromosome in the pair comes from the male parent and the other from the female parent  They are similar in shape and size (except sex chromosomes)  Exactly the same order or sequence of gene loci. Alleles in those gene loci may not be the same Phenotype  Refers to the physical trait which is expressed  Phenotype of an organism is the result of its genes and the effects of its environment  Tallness in pea plants is a phenotype Genotype  Genotype is the genetic makeup (pairs of alleles) of an organism, that is, the combination of genes in an organism  An organism is homozygous for a trait if 2 identical alleles controlling the trait are identical  E.g. TT or tt  An organism is heterozygous for a trait if the alleles controlling thhe trait are different  E.g. Tt  Dominant allele  A dominant allele expresses itself and gives the same phenotype in both homozygous and heterozygous  E.g. tall plants have TT and Tt genotype  Recessive allele  A recessive allele only expresses itself in homozygous condition. Does not represent itself in heterozygous conditions  E.g. pea plants are only short when the genotype is tt

Genetic diagrams

Phenotypic ratio 

Tolerant : N-tolerant 1 : 1 Where T is the allele for tolerant and t the allele for n-tolerant

Punnett square

Co-dominance  

Co-dominance results when the 2 alleles controlling a trait both express themselves in an organism E.g. Crossing a homozygous red bull and a homozygous white bull results in the offspring having both red and white fur. Both the allele for red and white hairs express themselves.

Sex determination     

`

Humans cells have 22 pairs of homologous chromosomes and 1 pair of sex chromosomes labeled X or Y Females have 2 X chromosomes, and are thus homozygous Males have 1 X and 1 Y chromosome, and are thus heterozygous Since females have only X chromosomes, the gametes (ova) produced will also only contain an X chromosome each Since males have both X and Y chromosomes, the gametes (sperms) produced can have either an X or Y chromosome

Multiple alleles  

Multiple alleles is a term used for a gene that exists in more than 2 alleles E.g. The occurrence of blood groups in humans Blood group A B AB O

Genotype IAIA or IAIO IBIB or IBIO IAIB IOIO

Discontinuous and continuous variations  





`

Variations are differences in traits between individuals of the same species There are 2 types of variations  Continuous variations  Discontinuous variations Continuous variations  Differences between individuals are gradual  E.g. height and weight  Such traits are usually controlled by many genes and influenced by the environment, such as nutrition and exercise Discontinuous variations  Are those where differences between individuals are distinct  E.g. blood group and double/single eyelids  Such traits are usually controlled by a single gene

Mutation   

Mutation is a sudden random change in the structure of a gene or in the chromosome number, usually due to a replication error which remains unrepaired. Diversity in a species is due to mutation Gene mutation produces variations between individuals as it results in new alleles or genes  E.g Albinism, a recessive gene mutation (only occurs in homozygous recessive)  Characterised by the absence of pigments in the skin, hair and eyes.  An albino individual has a reddish-white skin and white hair  Iris appears red due to lack of pigment and the presence of blood vessels below the iris  Albinos are very sensitive to sunlight and are sun burnt easily  Sickle-cell anaemia, a gene mutation

   

 `

Chromosomal

Mutation results in a change in the structure of gene controlling haemoglobin The mutated gene produces haemoglobin S (HbS), instead of haemoglobin A (HbA) HbS clumps together due to the change in its 3-D shape, making the cell sickle-shaped Normally, such a harmful allele would have been eliminated from the population as the affected individual would die before reproducing. However this disease is common in West Africa where malaria is prevalent  Individuals who are heterozygous for the sickle-cell allele suffer less from the attack of malaria because a small percentage of their red blood cells are sickle-shaped, thus more resistant to malaria  Individuals who are homozygous have shorter life spans due to sickle-cell anaemia  Hence, heterozygous individuals have a better chance of survival because they do not fully contract malaria or sickle-cell anaemia. Thus, the sickle-cell allele persists in the population mutation







E.g. down’s syndrome  The individual has 47 chromosomes instead of the normal 46 chromosomes humans have. There is an extra copy of chromosome 21 Mutagenic agents  Mutagens increase rate of mutations  Some chemicals if present in certain concentrations, are mutagenic  E.g. Tar, formaldehyde (in cigarette smoke), and lysergic acid diethylamide (LSD) Mutation and selection  Some mutations disrupt the normal functions of a cell  However some mutations are beneficial  E.g. a mutation may allow an organism to avoid predators because of better camouflage

Selection 



Evolution via natural selection  Due to variations, some individuals in a population are bound to be more suited to the environment than others  The individuals that are better suited to the environment they live in will have a higher chance of being able to reproduce and pass down their genes to their offspring  Over time the proportion of individuals in the population with the genetic advantage increases  These individuals are said to be selected by nature and the whole process is called natural selection  Natural selection is the driving force behind evolution Artificial selection  A process whereby man selects individuals from a population of organisms to propagate because they have desirable qualities  E.g. a farmer may keep the seeds of crops that bear better quality fruits and plant them so that his future batch of crops have a better chance of producing good fruits  This method is increasingly being replaced by newer and more efficient biotechnological methods such as gene cloning  However, such methods reduce the genetic diversity of the population of organisms, and in an event of sudden environmental change, the population might not be able to adapt and survive.

Natural selection Results from gene mutation Slow process

`

Artificial selection Results from manipulation by humans Faster process

Chapter 20 Molecular genetics DNA (Deoxyribonucleic acid)        

A molecule that carries genetic information A small segment of DNA carries a gene that stores information used to make polypeptides (multiple nucleotides make a gene) DNA molecule made up of 2 anti-parallel polynucleotide strands (strands running in opposite directions) Bases on one strand forms bonds with the bases on other strands according to the rule of base pairing The 2 anti-parallel strands of the DNA molecule coil to form a double-helix structure Each DNA molecule contains 2 strands twisted around each other to form a double helix A molecule of DNA is wrapped around proteins to form a single chromatin thread During cell division, chromatin threads coil tightly into structures called chromosomes inside the cell nucleus

Polynucleoti de

Basic units of DNA (nucleotide) 

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DNA is made up of nucleotides. Each nucleotide is made up of:  A sugar called deoxyribose, which is a pentose sugar  A phosphate group

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 A nitrogen-containing base The sugar and phosphate groups form the sides of the ladder Nitrogenous bases point towards the centre and form the rungs of the ladder There are 4 types of nitrogen-containing bases  Adenine (A) bonds with Thymine (T)  Guanine (G) bonds with Cytosine (C)  A and T, G and C, are complementary bases. Complementary bases are joined by hydrogen bonds

Genes      

Genes are basic units of inheritance in a living organism A gene is a sequence of nucleotides. The sequence of nucleotides controls the formations of polypeptides, which can be used to make proteins Since there are 4 different nucleotides (each with a different base), for a gene made up of n nucleotides, there are 4n different combinations 3 nucleotides in a gene form a codon and each codon codes for 1 amino acid Genetic code states which amino acid each codon forms Codon TAC TAT CAT GAG

Amino acid coded for Methionine (M) Alanine (A) Lysine (K) Glutamic acid

DNA function    

DNA is used to carry the genetic code, which is used to synthesise specific polypeptides Within DNA molecule, there are specific regions called genes, whereby information encoded is used to manufacture polypeptides Polypeptides are not directly made from DNA. Information on DNA molecule is first transcribed into a messenger molecule called mRNA, which is then translated into polypeptides The sequence of nucleotides within the genes is very specific and any changes within the gene could result in genetic diseases such as sickle-cell anaemia

Genetic engineering 

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Genetic engineering is a technique used to transfer genes from one organism to another. Individual genes may be cut off from the cells of one organism and inserted into the cells of another organism of the same or different species. The transferred gene can express itself in the recipient organism The basic structure of the genetic code is very similar in almost all organisms In all organisms, DNA is made up of the 4 nucleotides (ATGC) arranged into genes which make polypeptides

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Hence genes can be transferred between organisms and this process is part of genetic engineering By transferring genes or changing the genetic code in controlled ways, it will be responsible for an organism such as bacterium to produce different polypeptides and proteins This is called recombinant DNA technology

Transferring the human insulin gene into bacteria 1. Isolate the insulin gene. Cut gene using a restriction enzyme. This cuts the restriction site at the 2 ends of the gene to produce ‘sticky ends’. 2. Obtain plasmid from a bacterium. Cut plasmid with same restriction enzyme 3. Insert gene into plasmid. The human insulin gene will bind to the plasmid by complementary base pairing between their ‘sticky ends’. Add the enzyme DNA ligase to seal the human insulin gene to the plasmid. This plasmid which contains 2 different organisms is called recombinant plasmid 4. Mix the recombinant plasmid with E.coli bacterium. Apply temporary heat or electric shock to open up the pores in the cell surface membrane of the bacterium for the plasmid to enter 5. This transgenic bacterium will use the new gene to make insulin. Such bacteria can be isolated and grown for mass production of human insulin Ethical issues    

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There are many ethical issues surrounding genetic engineering Because the implications and risks associated with this field of research are not fully understood. Making changes to an organism’s DNA can result in very profound effects on the organism or its environment E.g. new proteins in GM food might cause allergies in humans that consume them, or result in deaths of useful insects such as bees.