Super Essential Notes to HKDSE Biology Revision

SUPER Essential Notes to HKDSE Biology Revision

Homeostasis -

Using the NORM, (normal level), set-point control mechanism. Negative Feedback Control System. To maintain constant internal environment and the extracellular fluid environment to be at the optimum condition for the enzymatic reaction. Organism can live in diversified environmental condition, independent of the external condition of the habitat. Homeostasis is an active, energy using process.

Regulation of : 1. Gaseous Content in blood 2. Thermoregulation 3. Osmoregulation 4. Glucose level in blood. 5. Hormonal level ( To be mention later in reproduction.) The general pathway for the regulation is : Stimulus  Receptor  Processing Centre  Effector  Response N.B. The effector can be Muscle and/or gland.

1. Gaseous Content in blood Stimulus : - The change ( can be decrease and increase ) of the concentration of carbon dioxide and oxygen in blood. Receptor : - Carotid and Aortic Bodies in the carotid arteries and the aorta : sensitive to the change of the oxygen concentration in blood. - Chemoreceptor in the medulla oblongata : sensitive to the change in the H+ level of the cerebrospinal fluid. Processing Centre :

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The respiratory centre of the medulla oblongata. Repeatedly, continuously and intermittently sending nerve impulse to the effector.

Effector : - Diaphragm muscle - Intercostal Muscle The Whole Process Flowchart : Increase in respiration rate  increase the CO2 level in blood, decrease the O2 level in blood  the aortic and carotid bodies is stimulated by the decrease in oxygen level, sending impulse to the respiratory centre of the medulla oblongata  the high concentration of CO2 diffuse to the CSF  the dissolving of the CO2 decrease the pH of the CSF stimulating the chemoreceptor of the medulla oblongata  sending impulse to the respiratory centre  the respiratory centre then send more INTENSE and increase the FREQUENCY of sending impulse to the diaphragm and intercostal muscle  Muscle contract more frequent

2.Thermoregulation Stimulus : - Change in external AIR temperature. - Change in internal blood temperature. Receptor : - Thermoreceptor of the skins : sensitive to external temperature ( EXTERNAL ) - Thermoregulation Centre of the Hypothalamus, sensitive to the blood temperature to the hypothalamus. ( INTERNAL ) Processing Centre : - Heat Gain Centre of the hypothalamus : To conserve heat. - Heat Loss Centre of the hypothalamus : To loss heat.

3.Osmoregualtion 3.1 Formation of the Glomerular Filtrate by : Ultrafiltration - Diameter of the Afferent Arteriole is > Diameter of the Efferent Arteriole - High Blood pressure build up in the glomerulus. - Forcing out some of the component of the plasma. - Except the plasma protein, RBC. - To the Bowman’s Capsule. - The forced out fluid pass through the blood capillary wall, and the wall of the Bowman’s Capsule, since they are VERY THIN. 3.2 Selective Reabsorption in different sites of the nephron -

In the First Convoluted Tubule : (UNCHANGE at ALL CONDITION !!! ) (i) Reabsorption of ALL glucose, amino acids,

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(ii)Reabsorption of 80% water , NaCl , other salts .

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In the Loop of Henle : (UNCHANGE at ALL CONDITION !!! ) (i) Reabsorption of water from the glomerular filtrate by the assistance of the salt gradient developed across the loop turn. ( You DO NOT have to know in detail how this part work. )

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**In the Second Convoluted Tubule and the Collecting Duct : (AFFECTED by BLOOD CONDITION !!! ) **The reabsorption mechanism of these TWO parts are affected by the hormonal control of the ADH. ( Antidiuretic Hormone ) 抗利尿激素

IMPORTANT CONCEPT !!! 3.3 Hormonal Regulation of the selective water reabsorption mechanism by ADH Stimulus : - VOLUME of the blood. - SOLUTE CONCENTRATION of the blood Receptor : - Osmoreceptor of the Hypothalamus : sensitive to the volume of blood / blood pressure and the solute concentration of the blood.

Regulatory Centre : - Water Loss Centre of the Hypothalamus : - Trigger the pituitary to RELEASE ( NOT SECRETE!!! ) LESS ADH. - Water Gain Centre of the Hypothalamus : - Trigger the pituitary to RELEASE MORE ADH . Response : - Larger blood Volume : Less ADH - Fewer blood Volume : More ADH - Higher Blood Solute Concentration : More ADH - Lower Blood Solute Concentration : Less ADH

The action of ADH : - ADH adjust the permeability of the Second Convoluted Tubule and the -

collecting duct. More the ADH, higher the permeability of water in the Second Convoluted Tubule and the collecting duct.

4. Regulation of Glucose Concentration in Blood

( Copyright reserved by the original inspiration of experienced Biology tutor Dr. Simon Chiang. )

Ecology -

The study of the interaction and relationship of organism in a defined habitat. The study of the interaction of abiotic and biotic factor in the ecosystem. Ecosystem is a stable, complex, self-sustainable system consists of biotic and abiotic factors. Individual (Single specie)  Population (More than one individual, same specie.)  Community (More than one individual, different species.)  Ecosystem ( Community and abiotic factors, e.g. sunlight, substratum etc )

For a sustainable Ecosystem : - Sunlight : Provide external source of energy. Support the whole ecosystem. To compensate for energy loss in energy channeling via trophic levels. - Producer : Photosynthesis, to convert light energy to chemical energy in form of

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biomass, to channel the biologically usable form of energy to the upper trophic level. Primary Consumer : Herbivores and heterotroph, cannot make their own food. Feed on plants. Secondary and higher consumers : Feed on herbivores. Decomposer : Saprophytic fungi and bacteria, that can secrete enzyme externally carrying out external digestion to break down dead organic matter to simple inorganic nitrogenous minerals. For the recycling of nutrients and organic matter in the ecosystem.

Ecological Pyramids 1. **Pyrimid of Productivity/Energy : The advantages of the pyramid of productivity: 

It takes account of the rate of production over a period of time.

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Two species of comparable biomass may have very different life spans. Therefore their relative biomasses is misleading, but their productivity is directly comparable.

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The relative energy chain within an ecosystem can be compared using pyramids of energy; also different ecosystems can be compared.

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There are no inverted pyramids.

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The input of solar energy can be added.

The disadvantages of the pyramid of productivity: 

The rate of biomass production of an organism is required, which involves measuring growth and reproduction through time.

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There is still the difficulty of assigning the organisms to a specific trophic level. As well as the organism in the food chains there is the problem of assigning the decomposers and detritivores to a particular trophic level.

Nitrogen Cycle