KCSE Past Papers 2021 Biology Paper 3 (231/3)

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 occuredExplain 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 three2.a.
    Food Test Procedure Observation Conclusion
    Starch To about 2ml of food
    substance (in a test
    tube). Add 2 drops of
    iodince solution
    Color of iodine
    retained/ yellow
    Reject; no change/ no
    observable change
    Accept; no color
    Starch absent
    Vitamin C (Absorbic
    To about 2ml of DCPip
    in a test tube. Add a
    drop of the food
    substance /M
    DCPip is decolorised or
    DCPip becomes
    Vitamin C present
    Lipids Put/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
    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 cleanapparatus


  • Avoid burning of filter paper/ plain paper when dripping 
  • Avoid spilling/ misusing of reagents/food substance 


    Yellow leaves/ white green/ yellow stem
    small leaves
    Long stem/tall stem/long internodes
    thin stem
    Weak/ fragile/feeble/frain stem
    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) 

  • EtiolationExplain how the knowledge on the phenomenon named in bi) is applied in agriculture(2 marks)


  • Proper spacing/thinning/pruning/pricking out/weeding/using a transparentmaterial/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 weregrown 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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