Answers to Mid Year Biology P 2 (Section B)

Question 6
a. P : Artificial active immunity. Q : Artificial passive immunity.

b. P is immunity acquired by injection of vaccine but Q is immunity obtained by injection of antiserum.
P is injection of vaccine given before infection by antigen but Q is injection of antiserum given to patients already infected.
For P the immunity acquired is slow but Q the immunity acquired is immediate after injection.
For P the period of immunity acquired is for a long time but for Q the period of immunity acquired is temporary.
For P the body produce antibody but for Q the antibody is gained from outside.
For P, more than one injections may be needed but for Q the first injection gives the immediate effects of the immunity but a second injection may be needed.
For P the additional injection i.e. the booster dose is given so that the level of immunity reaches an effective level whereas for Q, the additional injection i.e. the booster dose is given so that the level of immunity which drops quickly after the first injection is restored.
(Can answer in table form, but in full sentences)

ci) P1 : The injection of the serum (antivenom) from snakes for victims bitten by snakes.
P2 : This will neutralize the poison of the snakes.

cii) P1 : The patient is given the anti-tetanus serum.
P2 : The antibodies of the serum will prevent the infection caused by the tetanus bacteria..
P3 : This system of defence does not last long as the patient does not produce antibodies from the body cells.
P4 : The antibodies from the serum will be destroyed and excreted.

Question 7
a)F : Leaf structure P : Explanation

F1 :The upper epidermis is one cell thick and transparent (does not contain chloroplasts)
P1 :Allow sunlight to penetrate the leaf and reach the light-trapping chloroplasts in the palisade mesophyll and spongy mesophyll cells

F2:Palisade mesophyll cells are cylindrical , tightly packed in an upright arrangement directly beneath the upper epidermis // the palisade mesophyll cells have a high density of chloroplasts.
P2: Allows the cells to receive and absorb the maximum amount of sunlight to carry out photosynthesis

F3:Spongy mesophyll cells contain chloroplasts// Irregular in shape and loosely arranged with lots of air spaces in between
P3:Allows the cells absorb the sunlight to carry out photosynthesis// allows easy diffusion of water and carbon dioxide into the cells

F4:Presence of xylem which forms continuous tubes throughout the plant
P4: Transports water and mineral salts from the roots to the leaves

F5:Presence of phloem which forms continuous tubes throughout the plant
P5: Transports organic products of photosynthesis from the leaves to all parts of the plant.

F6:Presence of stomata in the lower epidermis
P6: Allows the exchange of gases ( oxygen and carbon dioxide ) between the leaf and the atmosphere

bi) P1 : Compensation point is the light intensity.
P2 : at which the rate of carbon dioxide production during respiration is equal to the rate of carbon dioxide consumption during photosynthesis.

bii) P1 : During the night, light intensity is almost nil, green plants only carry out respiration, therefore only carbon dioxide is produced and no carbon dioxide is consumed.
P2 : At dawn, when there is light, green plants start to carry out photosynthesis.
P3 : However, because of the low light intensity, the rate of photosynthesis //the rate of carbon dioxide consumption is still much lower then the rate of respiration // the rate of carbon dioxide production.
P4 : As the light intensity increases during the day, the rate of photosynthesis increases until a point when it is equal to the rate of respiration.
P5 : At that particular light intensity, the plant is said to have reached// attained the compensation point.

biii) P1 : If a plant were to constantly remain at the compensation point, the rate of sugar ( glucose) / food production is constantly equal to the sugar / glucose/ food consumption.
P2 : As a result, there is no excess sugar/ food for growth and vital processes like reproduction.
P3 : This will cause the plant to be stunted and sterile.P4 : No oxygen will be released by the plant into the atmosphere to be used by other living organisms

Question 8
a) P1 : Depletion of the ozone layer is due to the widespread use of CFC.
P2 : It is used in aerosol, industrial solvents, electronics and Freon in air conditioners.
P3 : Ultraviolet radiation strikes a CFC molecule cause the chlorine atom to break away.
P4 : Then the chlorine atom collides with an ozone molecule and combines with an oxygen atom to form chlorine monoxide and oxygen.
P5 : Then the free atom of oxygen collides with the chlorine monoxide, the two oxygen atoms form a molecule of oxygen.
P6 : The chlorine atom is released and free to destroy more ozone molecules.
P7 : The chlorine produced re-enters the cycle
P8 : When the ozone layer becomes thinner, more ultraviolet radiation reaches the Earth

The effect of excessive ultraviolet radiation on human.
P1 : Reduction of the body’s immune system.
P2 : Skin cancer.
P3 : Cataract of the eye.

Effect on plants.
P1 : Reduction of the rate growth therefore reducing crop yields.

Effect on aquatic organism.
P1 : Death of plankton, reduce food supply to aquatic organism, fisherman’ catch is reduced.

Steps to overcome this problem
P1 : Reduce or stop using CFC or chlorine-based products.
P2 : Replace CFC with HCFC.
P3 : Use wrapping papers instead of polystyrene boxes.
P4 : Patch up the holes in the ozone layer by firing frozen ozone balls into the atmosphere.

bi) P1 : Increase in carbon dioxide concentration traps heat.
P2 : Increase in global atmospheric temperature make the atmosphere warmer / cause a rise in Earth’s temperature / global warming.
P3 : Melting of polar ice / rise in sea level.
P4 : This phenomenon is called green house effect

bii) F1 : Releases a lot of carbon dioxide in the air forms a layer of carbon dioxide in the atmosphere.
P1 : Traps heat / infra-red light / long-wave radiation.
P2: And causes global warming / green house effect / rise in atmospheric temperature.

F2 : Releases heavy smoke which results in the formation of haze / smog
P3 : Reduce light intensity for photosynthesis.
P4 : Less yield / productivity of the crop plants.
P5 :smog / haze prevents vision and results in the air accidents / difficulties during landing of aeroplanes.
P6 : Smoke will also cause health hazards / lung diseases / eye problems.
F3 :Destroys flora / fauna.
P7 : Causes substantial loss of herbs for medical purposes / timber.
P8 : Loss of habitat / gene pool / biodiversity.
P9 : Lack of water catchment area.
P10 : Loss of nutrient / expose to flash flood / landslide / soil erosion / water pollution

Question 9
ai) P1 : When a person touches a hot object, the sensory receptor at the fingers will be stimulated, triggering a nerve impulse.
P2 : The impulse is then sent to the spinal cord through the afferent neurone.
P3 : In the spinal cord, the impulse is transmitted from the afferent neurone to the interneurone and finally to the brain.
P4: The efferent neurone transmits the impulse to the effector so that the fingers can be pulled away from the hot object immediately.

aii)
-For Nervous system, message is carried in the form of nerve impulse but for endocrine system message is carried by hormones.
- For Nervous system, message is via nerve fibres but hormone is carried via the bloodstream.
- For Nervous system, speed of transmission is rapid but for endocrine system speed of transmission is slow.
-For Nervous system, area of response is limited to places with a nerve supply but for endocrine system, area of response is all over the body –one hormone may affect several target organs at the same time. (Can be in table form)

bi) P1 : The process of maintaining the balance of the physical factors of the body
P2 : like temperature, blood pressure, osmotic pressure of the cell fluids and other factors involving the pH of blood and the glucose concentration of the internal environment

bii) P1 : Information of abnormal conditions is sent to a control centre.
P2 : The effectors act to reverse the change.

biii) P1 : Insulin
P2 : and glucagon are the hormones regulating sugar in the blood.
P3 : If the blood sugar level is higher than normal, more insulin is secreted into the blood stream and transported to the liver.
P4 : In the liver, insulin stimulates the liver cells to convert excess glucose to glycogen and fats.
P5 : This causes the level of sugar to fall and return to normal.
P6 : If the blood sugar level is lower than normal, more glucagon is secreted into the bloodstream and transported to the liver.
P7 : In the liver, glucagon stimulates the liver cells to convert glycogen to glucose.
P8 : This causes the level of glucose to rise and return to normal.