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 TestProcedureObservationConclusion

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 TestProcedureObservationConclusion
StarchTo about 2ml of food
substance (in a test
tube). Add 2 drops of
iodince solution
Color of iodine
retained/ yellow
brown;
Reject; no change/ no
observable change
Accept; no color
change
Starch absent
Vitamin C (Absorbic
acid)
To about 2ml of DCPip
in a test tube. Add a
drop of the food
substance /M
DCPip is decolorised or
DCPip becomes
colorless
Vitamin C present
LipidsPut/rub a drop of M
onto the filter paper/
plain paper(allows the
drop to drip)
Hold against a source
of light
No translucent
Mark left (on the filter
paper)
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

apparatusAvoid burning of filter paper/ plain paper when drippingAvoid spilling/ misusing of reagents/food substance

3.a.

N
Yellow leaves/ white green/ yellow stem
small leaves
Long stem/tall stem/long internodes
thin stem
Weak/ fragile/feeble/frain stem
P
Green leaves/green stem
large/big leaves
Sort stem/short internodes
thick stem
strong/firm stem

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; ORThe 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)OxygenWater/moistureOptimal/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 leavesCompact petioleAccept presence of two cotyledon