KCSE Past Papers 2021 Biology Paper 3
QUESTIONS
1.a. You are provided with plant specimens labelled E, F, G, H, and J. Use the specimens to develop a dichotomous key that can be used to identify the plants from which they were obtained based on the following characteristics in the order they are given: (6 marks)
i. Leaf form
ii. Leaf venation
iii. Leaf colour
b. Account for the likely observation if fresh specimen E was exposed to light and tested for starch. (3 marks)
c. Explain one observable feature that adapts plants from which specimen G and H were obtained to a dry environment. (2 marks)
d. Besides leaf characteristics, state one other observable characteristic on the plant from which specimen F was obtained that enables it to be placed in its Class. (1 mark)
2. You are provided with solution M which is a food substance.
Procedure
a. Using the reagents provided, test for the food substance present in substance M and complete the table below. (12 marks)
Food
Test |
Procedure |
Observation |
Conclusion |
b. State two precautions one should observe while conducting the experiment in 2(a) (2 marks)
3. You are provided with specimen N and P which are plants of the same species grown under different conditions.
a. State two observable differences between the two specimens. (2 marks)
b.i. Name the phenomenon observed in specimen N. (1 mark)
ii. Explain how the knowledge on the phenomenon named in bi) is applied in agriculture(2 marks)
c. Account for the appearance of specimen N. (3 marks)
d. State two other environmental factors necessary for seed germination apart from light. (2 marks)
e. State two observable features on the specimens that make them be placed in the same Class. (2 mark)
Questions and Answers
KCSE Past Papers 2021 Biology Paper 3 (231/3)
1.a.i. Leaf simple ....go to 2
- Leaf compund....G
ii. Leaves/leaf network veined ....go to 3
- Leaves/leaf parallel veined...F
iii. Leaves/leaf green/non variegated ...G/H or go to 4
- Leaves/leaf non-green/ variegated ....E
iv. Leaf margin serrated.....G
- Leaf margin smooth.....H
Account for the likely observation if fresh specimen E was exposed to light and tested for starch. (3 marks)
- Green parts/ parts with chlorophyll will turn blue black (with iodine solution/iodine) due to presence of starch since photosynthesis has occurred; white parts turn to brown/retain iodine solution; due to absence of starch since photosynthesis has not occured
Explain one observable feature that adapts plants from which specimen G and H were obtained to a dry environment. (2 marks)
i. Rough/ hairy leaf surface; to reduce transpiration.Leaves fold; to reduce transpiration
ii. Shiny/ glossy leaf surface; to reduce transpiration folding of leaves; to reduce water loss
Besides leaf characteristics, state one other observable characteristic on the plant from which specimen F was obtained that enables it to be placed in its Class. (1 mark)
- Fibrous root system; Floral parts in threes/ multiples of three
2.a.
Food
Test |
Procedure |
Observation |
Conclusion |
Starch |
To
about 2ml of food |
Color
of iodine |
Starch
absent |
Vitamin
C (Absorbic |
To
about 2ml of DCPip |
DCPip
is decolorised or |
Vitamin
C present |
Lipids |
Put/rub
a drop of M |
No
translucent |
Lipids
absent |
State two precautions one should observe while conducting the experiment in 2(a) (2 marks)
- Avoid contamination of reagents/ apparatus/ avoid mixing of droppers/use clean
apparatus
- Avoid burning of filter paper/ plain paper when dripping
- Avoid spilling/ misusing of reagents/food substance
3.a.
N |
P |
i. Name the phenomenon observed in specimen N. (1 mark)
- Etiolation
Explain how the knowledge on the phenomenon named in bi) is applied in agriculture(2 marks)
- Proper spacing/thinning/pruning/pricking out/weeding/using a transparent material/polythene on a green house; to enable adequate penetration of light for the crop
c. Account for the appearance of specimen N. (3 marks)
- The specimen is weak/tall/long/thin; because they have grown in a darkness;/ absence of light/ insufficient light; in darkness there is high concentration of auxin in shoot tip that stimulate faster elongation; OR
- The specimen has small/ yellow leaves/white stem/ lack of chlorophyll; because they were grown in darkness; hence couldn't carry out photosynthesis/ synthesis of chlorophyll
d. State two other environmental factors necessary for seed germination apart from light. (2 marks)
- Oxygen
- Water/moisture
- Optimal/optimum temperature/warmth;
e. State two observable features on the specimens that make them be placed in the same Class. (2 mark)
- Tap root system Reticulate/network venation/branched venation/net-veined leaves;
- Broad leaves
- Compact petiole
- Accept presence of two cotyledon
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