KCSE 2020 Biology Paper 3 (231/3)

K.C.S.E Biology Paper 3 Answers


Test tube contents Amount of effeverscence
1.(a) HCL + macerated specimen
N + H₂O
No/little effervescence/foam
/ frothing/bubbling;
Although there was adequate surface area exposed
(by macerating the potato)
for enzymatic action, the acidic rnedium/low pH did not
favour the working of the enzymes/ catalyze/increase
rate of enzymatic reaction/denature enzyme;
NaOH + macerated specimen
N + H₂O₂
Vigorous/rapid/ high/a lot of
/more effervescence;
Adequate surface area exposed (by macerating the potato)
for enzymatic action; favourable/suitable pH/alkaline
medium/high pH for enzymatic action;
NaOH + cube of specimen N
N + H₂O₂
Moderate/ average/medium effervescence Less/little surface area exposed for enzymatic action;

10 Marks


Procedure Observation Confirmation
1.b) Add (a drop of the) iodine
solution provided to specimen N;
Blue-black colour observed; Starch present (in specimen N); (3 marks)

13 Marks


2.a)(i) Specimen G Division : Spermatophyta/Spermaphyta;
Reason : Seed-bearing/naked seeds/green;
((2 marks)
(ii) Specimen E Kingdom : Fungi/Mycopliyta;
Reason : feed on dead matter/saprophytic/have hyphae/
Rhizoids/myce1ium/lack chlorophyll/non-green;
(2 marks)
(iii) Specimen M Division : Spermatophyta/Spermaphyta;
Reason : Presence of leaves/stems/roots;
Have chlorophyll/are green; Remains of fruit/seed/cotyledons;
(2 marks)
(iv) Specimen H Phylum : Arthropoda;
Reason : Segmented body/presence of limbs/jointed
appendages; Presence of exoskeleton/external skeleton/
bilateral symmetry;
(2 marks)

b)(i) Specimen F has its body covered with hair while the body of specimen K (crocodile) is covered with scales; Specimen F has the opposable thumb in its pentadactyl limb while the limbs of specimen K are uniform; Specimen F has marnmary glands while specimen K does not have;Specimen F is viviparous while specimen K is oviparous; (2 marks)

b(ii) Specimen M and J

• Specimen M has narrow; (leaves) with parallel veins; while specimen J has broad leaves; with net veins;

• Specimen M has fibrous root (system); while specimen J has tap root (system);

• Specimen M has a sheath while specimen J has a petiole;

Specimen J (bean) is a flowering plant, reproduces sexually; specimen E reproduces a asexually/sporulation/by spores;

3.a) Pisces;


  • Body covered with scales;
  • Streamlined body;
  • (Presence) of gills;
  • (Presence) of fins;
  • (Presence) of operculum;
  • (Presence) of lateral line:b) Adaptations


  • Streamlined body enables it to move fast in water with minimum/reduced resistance/friction;
  • Scales pointed backwards/overlapping to reduce friction during movement in water;
  • Body covered with a slimy substance/mucoid for easier movement/reduce friction;
  • Has fins for movement/swimming/balancing/propulsion in water
  • Swim bladder to vary its depth/buoyancy;
  • Inflexible head to enable/maintain forward thrust;
  • Myotomes that contract and relax alternately enabling side to side movement;c)
  • Protection of the (delicate) gills;
  • Opening/closing to let water out for ventilation/act as a valve/allow water to flow in one direction; d(i) For gaseous exchange; (1 mark)(ii)
  • Gill filaments are: • Numerous to increase the surface area for gaseous exchange;• Thin to reduce the diffusion distance/for easier/efficient/ faster diffusion of respiratory gases (in/out);

    • Are wet/moist to dissolve respiratory gases for efficient gaseous exchange;

    • Highly vascularized/numerous capillaries for transport of respiratory gases/maintain/create a steep concentration gradient;


  • Gill bar is long for attachment ofsupport the gill filaments; is bonny/rigid /hard to support the gill rakers/ gill filaments;
  • Gill rakers are sharp/pointed/rake-like to filter/trap foreign objects/protect the (delicate) gill filaments;
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