SUPER Essential Notes toHKDSE 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 blood2. Thermoregulation3. Osmoregulation4. 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 :

- 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 levelin 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 highconcentration of CO2 diffuse to the CSF the dissolving of the CO2 decrease the pHof the CSF stimulating the chemoreceptor of the medulla oblongata sendingimpulse to the respiratory centre the respiratory centre then send more INTENSEand increase the FREQUENCY of sending impulse to the diaphragm and intercostalmuscleMuscle 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 Bowmans Capsule.- The forced out fluid pass through the blood capillary wall, and the wall of the

Bowmans Capsule, since they are VERYTHIN.

3.2 Selective Reabsorption in different sites of the nephron

- In the First Convoluted Tubule : (UNCHANGE at ALLCONDITION !!! )- (i) Reabsorption of ALL glucose, amino acids,- (ii)Reabsorption of 80% water , NaCl , other salts .

- In the Loop of Henle : (UNCHANGE at ALLCONDITION !!! )- (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 indetail how this part work. )

- **In the Second Convoluted Tubule and the Collecting Duct : (AFFECTEDby BLOOD CONDITION !!! )

- **The reabsorption mechanism of these TWO parts are affected by thehormonal control of the ADH. ( Antidiuretic Hormone )

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 MOREADH .

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. SimonChiang. )

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, samespecie.) 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

biomass, to channel the biologically usable form of energy to the upper trophiclevel.

- Primary Consumer : Herbivores and heterotroph, cannot make their own food. Feedon 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 simpleinorganic nitrogenous minerals. For the recycling of nutrients and organic matter inthe 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.

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

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

There are no inverted pyramids.

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 involvesmeasuring growth and reproduction through time.

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

Nitrogen Cycle