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 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
  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 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 cleanapparatus

   

• Avoid burning of filter paper/ plain paper when dripping 
• Avoid 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) 

• 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