IGCSE Edexcel Biology Revision

Life Processes: Cell Structures: -

Characteristics of Living Things:

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Movement Respiration Stimuli Homeostasi s Growth Reproductio n Excretion Nutrition

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Animal cells have a nucleus, cell membrane, cytoplasm, mitochondria Plant cells have a nucleus, cell membrane, wall, cytoplasm, chloroplasts, mitochondria, large sap vacuole nucleus stores the genetic data, Chromosomes Cell membrane allows substances to pass through Cytoplasm gives a cell it’s shape and allows substances to pass Mitochondria is the powerhouse of the cell, provides energy Chloroplasts in plant cells contains chlorophyll which provide photosynthesis Large sap vacuoles in plants help support the

plant cells Cell walls in plants provide structural support and protection Levels of Organization in an organism: o Organelles  Cells  Tissues  Organs  Organ Systems

Enzymes: -

Enzymes are biological catalysts and speed up and/or control reactions, which can be affected by temperature and pH levels Enzymes are proteins and therefore can be denatured (NOT killed!!!) On the protein, there is an active site, where the substrate attaches and is broken up The shape of the active site depends on the pH and temperature

Cellular Respiration: -

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Aerobic Respiration: o 6O2 + C6H12O6  6CO2 + 6H2O + Energy (Remember: 6, 6, 6 for balanced equation) o Oxygen + Glucose  Carbon Dioxide + Water + Energy Anaerobic Respiration: o C6H12O6  2C3H6O3 o Glucose  Lactic Acid

Movement of Substances: -

Substances can move into and out of cells by diffusion, osmosis (diffusion specific for water) and active transport and this is affected by concentration, temperature and surface area Diffusion is the net movement of particles from an area of high concentration to an area of lower concentration. o Randomly caused

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o Is passive and therefore doesn’t require energy Osmosis is a special kind of diffusion, where it only happens through a partially permeable membrane Active transport is when substances are moved against the concentration gradient (which is high to low) or through a selectively permeable membrane and it uses energy Variety of Organisms:

Major Groups: Plants, Animals, Fungi, Protoctists, Bacteria and Viruses -

Plants and humans are always multicellular o Plants carry out photosynthesis o Animals eat other living things to obtain their energy Fungi can either be unicellular or multicellular o They absorb food from other living things Protoctists are mostly microscopic and single celled Bacteria are microscopic single-celled organisms. o They are smaller than Protoctists Viruses are non-living parasites that reproduces inside other living cells o They are smaller than Bacteria Bacteria, Viruses, Protoctists and Fungi can be pathogens and cause disease

Plants: -

Photosynthesis through Carbon Dioxide and Water to make Sugar and Oxygen o Captured through the sun with their chlorophyll in their chloroplasts Chloroplasts store carbohydrates such as starch Plant cell walls are made out of cellulose

Animals: -

Doesn’t contain chlorophyll Animal cells don’t have a cell wall Most animals have a nervous system for co-ordination Glycogen, a carbohydrate, is stored in animal cells

Fungi: -

Fungi are saprophytes or parasites Some are multicellular o E.g. Mushrooms and molds Some are unicellular o E.g. yeast Fungal cell walls are made of chitin Multicellular fungi are made of mycelium, which is a network of structures called hyphae Fungi make enzymes and digest their food outside of their cells Many fungi act as decomposers

Protoctists:

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Some Protoctists make their own food via photosynthesis such as algae and others feed on other organisms Some Protoctists are tiny, but others can be very large

Bacteria: -

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Tiny, single celled Common shapes: o Spheres – singles, pairs, chains or groups o Rods – singles, chains, with or without flagella o Spirals Complex cell wall made of polysaccharides and proteins. Bacteria DO NOT have a nucleus They contain small circles of DNA called plasmids Some can photosynthesis because they contain chlorophyll Most bacteria feed on dead or living things Some bacteria have slime capsules for protection or flagella (little “tails”) for movement

Prokaryotes: -

Single celled organisms that have no nucleus Most are bacteria but also include archaea

Viruses: -

All are parasites and all natural viruses cause disease Can only reproduce inside the cells of the host Very simple and are found in multiple geometric shapes o Core of genetic material surrounded by protein coat Viruses either contain RNA or DNA

Breathing and Gas Exchange -

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The respiratory system takes air into and out of the body to supply oxygen and get rid of carbon dioxide from the body The movement of air from and to the lungs creates a steep concentration gradient for the diffusion of oxygen and carbon dioxide The complete respiratory system includes o Ribs o Intercostal Muscles (Internal and External) o Diaphragm o Trachea o Bronchi o Bronchioles o Alveoli o Pleural Membranes of the Thorax The alveoli have specific adaptions for efficient gas exchange

Structure of the Respiratory System: -

Nasal Passages – Warm, clean and adds moisture to entering air Epiglottis – Stops food entering the lungs Esophagus – Carries food to stomach Larynx – voice box Trachea – tube with “C” like cartilage rings and is lined with cells making mucus and cilia cells Left Bronchus – carries air to lungs Bronchioles – carries air to lungs Alveoli – tiny sacs which allow diffusion of oxygen and carbon dioxide Diaphragm – Sheet of domed muscle which helps with breathing Ribs – Bones that protect the lungs Internal Intercostal muscles – Pulls ribs down and in when you breathe out External Intercostal muscles – Pulls rubs up and out when you breathe in Pleural Membranes – Thin, moist membranes that form an airtight seal around the lungs Pleural Fluid – Fills the pleural cavity and acts as lube so lungs don’t stick to chest

Ventilation of the lungs: -

There is more oxygen and less carbon dioxide in the air of the lungs than in the blood The movements of the ribs and diaphragm brings changes in the volume and pressure in the chest cavity

Inhalation: -

Air enters lungs Volume of chest cavity expands and pressure in lungs is lower than outside Diaphragm contracts – diaphragm flattens External intercostal muscles contract thus pulling ribs up and out and internal intercostal muscles relax

Exhalation: -

Air is pushed out of lungs Volume of chest cavity decreases and pressure in lungs is higher than outside Diaphragm relaxes – diaphragm becomes dome shaped Internal intercostal muscles contract thus pulling the ribs down and in and the external intercostal muscles relax

Alveoli: -

Blood is pumped to the lungs Blood passes through the network of capillaries around the alveoli Carbon dioxide diffuses from the blood into the air Oxygen diffuses into the blood from the air Oxygenated blood is pumped throughout the body Gas Exchange in the Alveoli: o There are adaptions that make the alveoli good at its job  The alveoli has a large surface area for more diffusion  A rich blood supply to easily carry oxygen away and bring carbon dioxide  Also creates a constant steep concentration gradient between alveoli and blood  Short diffusion distances