Biology Paper 2 Questions and Answers - Form 3 Term 3 Opener Exams 2023

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SECTION A (40MARKS)

(ANSWER ALL QUESTIONS)

The apparatus below was used to investigate certain process that occurs in plants:-
1. Name the process that was being investigated (1mk)
2. How would you remove dissolved oxygen from the glucose before the experiment commencing? (1mk)
3. State what happens to the lime water as the experiment proceeds to the end (1mk)
4. State the role of oil film the experiment (1mk)
5. Explain what would happen if the temperature of glucose solution and yeast was raised beyond 45°C? (1mk)
6. State three economic importance of the process named in (a) above in industry? (3mks)
Two fresh potato cylinders of equal length were placed one in distilled water and the other in concentrated sucrose solution.
1. State the expected observations in term of length of the potato cylinders in (2mks)
  1. distilled water
  2. sucrose solution
2. Account for the change in length of the cylinder in:
  1. Distilled water (1mk)
  2. Sucrose solution (1mk)
3. 1. What would be the result in terms of length if a boiled potato was used? (1mk)
  2. Explain your answer in (c)(i) Above (1mk)
4. State two uses of the physiological process being demonstrated in the experiment(2m)
1. Distinguish between the terms homodont and heterodont. (1mk)
2. What is the function of carnasial teeth? (1mk)
3. A certain animal has no incisors, no canines, 6 premolars and 6 molars in its upper jaw, in the lower jaw there are 6 incisors, 2 canines,
  6 premolars and 6 molars. Write its dental formula (1mk)
4. Suggest the likely type of food eaten yby the organism (1mk)
5. The action of ptyalin stops at the stomach. Explain. (1mk)
6. State a factor that denatures enzymes. (1mk)
7. Name two features that increase the surface area of small intestines. (2mks)
1. Describe how insect pollinated flowers are adopted to pollination (5 marks)
2. Describe the role of each of the following hormones in the human menstrual cycle. (3 marks)
  1. Oestrogen
  2. Progesterone
  3. Luteinizing hormone
1. What is meant by the following terms?
  1. Protandry ( 1 mark)
  2. Self- sterility ( 1 mark)
2. The diagram below shows a stage during fertilization in plant
  1. Name the parts labeled Q, R, and S ( 3 marks)
    Q
    R
    S
  2. State two functions of the pollen tube ( 2 marks)
  3. On the diagram, label the micropyle ( 1 mark)

SECTION B (40 MARKS)

Answer question 6 (compulsory) in the spaces provided and either question 7 OR 8 in the spaces provided after question 8.

In an ecological study, a locust population and that of crows was estimated in a grassland area over a period of one year. The results were tabulated as shown below.

Months	J	F	M	A	M	J	A	S	O	N	D
No. of Adult locusts x 10²	90	20	11	25	200	625	15	10	35	192	456
Number of crows	4	2	0	1	8	22	2	1	1	5	15
Amount of rainfall	20	0	55	350	520	350	10	25	190	256	350

Draw a graph of population of locusts and crows against time (7mks)
1. State the relationship between rainfall and locust population (1mk)
2. Account for the relationship you have stated in b (i) above (2mks)
What happens on the populations of locusts and crows in the months of January to March? (2mks) Give a reason.
If the area of study was one square kilometer, state one method used to estimate the population of :- (2mks)
1. Locusts
2. Crows
1. State the trophic levels of the (2mks)
  1. Locusts
  2. Crows
2. Construct a simple complete food chain involving these organisms (1mk)
If the locust were removed from the food chain, what would be its effect? (2mks)
Define biomass (1mk)

Describe the
1. Process of inhalation in mammals. (10 mks)
2. Mechanism of opening and closing of stomata (10 mks)
Describe how fruits and seeds are suited to their mode of dispersal (20mks)

MARKING SCHEME.

SECTION A (40MARKS)

The apparatus below was used to investigate certain process that occurs in plants:-
1. Name the process that was being investigated
  Anaerobi respiration /fermentation;
2. How would you remove dissolved oxygen from the glucose before the experiment commencing? (1mk)
  Boiling the glucose to expel oxygen
3. State what happens to the lime water as the experiment proceeds to the end (1mk)
  Turns white/ becomes milky/cloody /precipitate
4. State the role of oil film the experiment (1mk)
  prevent entry of air/oxygen thus preventing aerobic respiration
5. Explain what would happen if the temperature of glucose solution and yeast was raised beyond 45°C? (1mk)
  High temperature denatures enzymes, reduces/stops respiration/stops the reaction.
  High temperature also kills the yeast cells hence stops respiration.
6. State three economic importance of the process named in (a) above in industry? (3mks)
  - Making of beer/Brewing/Ethanol/alcohol;
  - Baking industry/Raising of the dough:
  - Biogas making
  - Manufacture of organic acids
  - Dairy industry cheese/yoghurt making
Two fresh potato cylinders of equal length were placed one in distilled water and the other in concentrated sucrose solution:
1. State the expected observations in term of length of the potato cylinders in (2mks)
  1. distilled water
    Increased in length
  2. sucrose solution
    Decreased in length
2. Account for the change in length of the cylinder in:
  1. Distilled water (1mk)
    Increased in length, absorbed water through osmosis, (since cylinder cells were hypertonic/ at higher concentration) and become turgid
  2. Sucrose solution (1mk)
    Reduced in length, cylinder lost water to the hypertonic sucrose solution/become flaccid.
3. 1. What would be the result in terms of length if a boiled potato was used? (1mk)
    No change in length
  2. Explain your answer in (c)(i) Above (1mk)
    Cells are dead and cannot carry out osmosis
4. State two uses of the physiological process being demonstrated in the experiment (2mks)
  - opening and closing of stomata
  - Support in plants
  - Movement of water from cell to cell
  - Feeding in insectivorous plants
  - Absorption of water by root hairs
  - Absorption of water in the intestines
1. Distinguish between the terms homodont and heterodont. (1mk)
  Homodont-Organism has same shape,type and size of teeth
  Heterodont-Organism have different number,type,size and shapes of teeth
2. What is the function of carnasial teeth? (1mk)
  Slice flesh and crush bones
3. A certain animal has no incisors, no canines, 6 premolars and 6 molars in its upper jaw, in the lower jaw there are 6 incisors, 2 canines, 6 premolars and 6 molars. Write its dental formula (1mk)
  I=0, C =0, PM = 3, M 3=32
  
  3 1 3
4. Suggest the likely type of food eaten by the organism (1mk)
  Vegetations/grass
5. The action of ptyalin stops at the stomach. Explain. (1mk)
  Hydrochloric acid in the stomach denatures ptyalin stopping its activity
6. State a factor that denatures enzymes. (1mk)
  High temperatures above 400C.
  Extreme pH
7. Name two features that increase the surface area of small intestines. (2mks)
  - Villi
  - Microvilli
  - Highly coiling
  - Long
1. Describe how insect pollinated flowers are adopted to pollination ( 5 marks)
  - Large brightly coloured corolla / inflorescence / forests / tracts to attract insects.
  - Scented to attract insects
  - Have secreted nectar to attract that direct flowers secrete nectar to attract insects.
  - Pollen grains rough/spiky sticky surface to stick on insect’s body.
  - Special shaped corolla tube to enable the insect land.
2. Describe the role of each of the following hormones in the human menstrual cycle. (3 marks)
  1. Oestrogen
    - Repair / heal endometrium / wall of uterus, which is destroyed in menstruation.
    - Stimulates pituitary gland to produce the luteinising hormone
  2. Progesterone
    - Stimulates the thickening of the uterus,
    - increases the blood supply to the endometrium.
    - Inhibits the production of follicle stimulating hormone
  3. Luteinizing hormone
    - Responsible for maturation of the graafian follicle
    - Causes ovulation.
    - Stimulates corpus luteum to secrete progesterone
1. What is meant by the following terms?
  1. Protandry ( 1 mark)
    Stamens mature and pollen grains are shed off before the stigma matures.
  2. Self- sterility ( 1 mark)
    Pollen grains from the anthers cannot grow/germinate on the stigma of the same flower or plant.
2. The diagram below shows a stage during fertilization in plant.
  1. Name the parts labeled Q, R, and S ( 3 marks)
    Q Antipodal cells
    R Polar body / polar nucleus
    S Egg cell
  2. State two functions of the pollen tube ( 2 marks)
    - Path through which the male gametes reach the embryo sac to enhance fertilization.
    - Prevent other pollen grains from developing into pollen tubes hence no multiple fertilization of embryo sac.
3. On the diagram, label the micropyle (1 mark)

SECTION B (40 MARKS)

Answer question 6 (compulsory) in the spaces provided and either question 7 OR 8 in the spaces provided after question 8.

In an ecological study, a locust population and that of crows was estimated in a grassland area over a period of one year. The results were tabulated as shown below.

Months	J	F	M	A	M	J	A	S	O	N	D
No. of Adult locusts x 10²	90	20	11	25	200	625	15	10	35	192	456
Number of crows	4	2	0	1	8	22	2	1	1	5	15
Amount of rainfall	20	0	55	350	520	350	10	25	190	256	350

Draw a graph of population of locusts and crows against time (7mks)
- Labelling axes ……2mks
- Scale……………....1mk
- Plotting……………2mks
- Joining (smooth)….1mk
- Identifying the graph..1mk
1. State the relationship between rainfall and locust population (1mk)
  The population of locusts increase with increase in that the amount of rainfall;
2. Account for the relationship you have stated in b (i) above (2mks)
  - Increased amount of food;
  - Improve breeding conditions
What happens on the populations of locusts and crows in the months of January to March? (2mks)
Give a reason.
- The population of both decreases
- Less food availability for locusts and hence crows
If the area of study was one square kilometer, state one method used to estimate the population of :- (2mks)
1. Locusts …………….capture recapture;
2. Crows…………………… total counts
1. State the trophic levels of the (2mks)
  1. Locusts………………. primary consumers;
  2. crows………………..secondaryy consumers;
2. Construct a simple complete food chain involving these organisms (1mk)
  
  Grass → Locusts → crows
If the locust were removed from the food chain, what would be its effect? (2mks)
- Grass would increase;
- Crows would reduce
Define biomass (1mk)
Is the total dry weight of organisms at a particular trophic level;

1. Describe the process of inhalation in mammals. (10 mks)
  - External intercostals muscle contract
  - Internal intercostals muscles relax.
  - Ribs moves upward and outwards-
  - Diaphragm muscle contract flattening the diaphragm
  - Volume in thoracic cavity
  - Pressure decreases in the thoracic cavity than atmospheric pressure
  - Air rushes into the lungs.
2. Mechanism of opening and closing of stomata (10 mks)
  1. OPENING
    - During the day photosynthesis takes place and sugar is formed in guard cells
    - Osmotic pressure increases and water is drawn from neighbouring cells by Osmosis.
    - The guard cells become turgid, bulge outward causing opening of stomata
  2. CLOSING
    - During the night there is no photosynthesis and sugar is converted to starch.
    - Osmotic pressure decrease and water is lost to the neighbouring cell osmosis.
    - Guard cells become flaccid, closing the stomata.
Describe how fruits and seeds are suited to their mode of dispersal (20mks)
1. Water dispersal
  - Such seeds and fruits enclose air in them to lower their density for buoyancy;
  - They are fibrous/ spongy to lower the density for buoyancy;
  - Have impermeable seed coat or epicarp to prevent water from entering during flotation so as to avoid rotting;\
  - The seeds can remain viable while in water and only germinate while on a suitable medium;
2. Wind dispersal
  - They are light; and small; to be easily carried by wind currents due to lower density;
  - Have developed extension which create a larger surface area; so as to be kept afloat in wind currents e.g. * Parachute like structures; * Wing like structures;
3. Animal dispersal
  - Brightly colored to attract animals
  - Fleshy to attract animals;
  - Some have hook like structures to attach on animals fur
4. Self dispersal
  - They have weak lines on the fruit wall along which they burst open to release seeds, which get scattered. This occurs when temperature changes suddenly