Observation

 

This question was compulsory. Question 6(a) was well answered as most candidates could state the structural features that adapt a toad to its habitat, although some of the candidates were unable to appropriately relate features to functions performed.
In 6(b) (i), Some candidates wrongly defined Irritability as ‘excessive response to environment’. (ii) Some candidates wrote ‘evolution’, ‘variation’ and ‘genotype’ as factors that bring about irritability. In 6(c), although most candidates wrote correct answers to this question, some others wrote wrong answers. In 6(d), most candidates could not describe courtship behavior in lizards. In 6(e), there was confusion between oviparity and viviparity. In 6(f), many candidates could answer this question correctly.

The expected answers are:

(a) Features that adapt tadpole to its habitat

- Presence of external/internal gills; for gaseous exchange

- Presence of operculum; for protection of the gills;

- Presence of spiracles for gaseous exchange;

- Muscular tail/fin; for steering/movement in water/swimming;;

- Horny jaw; enables tadpole to feed on water weeds/herbivorous feeding;

- The ear pit; enables the tadpole to detect the approach of enemies/food/direction of water current;

- Streamlined body; for easy movement in water;

- Long intestine; for herbivorous feeding;

- Dark colour; for camouflage;

- Cement gland; for attachment to water weeds;

- Cilia on the body; causing water current to flow over the gills;

- Shortened intestine; adapts to carnivorous mode of feeding.

Note: Structure must correspond with function to score. Structure x 1 mark; function x 1 mark. Function alone does not score; Structure alone scores.

 

(b)(i) Irritability: The ability/capacity of living things to respond/detect/perceive/interpret; to changes in external/internal stimuli/environment.< /p>

(ii) Environmental factors that bring about irritability in plants:

- Temperature;

- pH/level of acidity/alkalinity;

- changes in gravity;;

- humidity;

- pressure;

- light/sunlight;

- wind;

- water;

- touch.

(c)Tillage

Is the agricultural preparation of soil; by mechanical means/ploughing/breaking up/ loosening of soil surface; for cultivation of crops.

(ii) Effects of tillage on the ecosystem

- leads to compaction of the soil;

- exposes and kills soil organisms;

- controls/reduces weeds;

- leaching of soluble nutrients;

- increases soil organic matter;

- mixes humus into the soil;

- improves soil aeration/soil loosening;

- encourages erosion of top soil/surface;

- increases capillarity of water/penetration of water

 

(d)Description of courtship behaviour in lizards

- The courtship behaviour displayed is territoriality;

- Each territory is dominated by a dominant male, several females and youngs;

- A sexually mature male is brightly coloured and large;

- The female and young are less colourful and smaller;

- The dominant male defends the territory;

- Courtship starts when a male displays its full colour in front of a female;

- The female responds by arching its back;

- Raising its tail vertically;

- Or runs away/escapes;

- Mating may take place when caught.

 

(e) Explanation of terms

(i) Oviparity
Is a reproductive method in which the female parent lays its egg; which may be fertilised internally/externally; into the external environment where they hatch.

(ii) Viviparity
Is a reproductive method in which fertilised eggs develop in the mother’s body; the embryos obtain their nutrients directly from the parents in addition to that present in the eggs; through the placenta; offspring is born alive.

 

(f) Roles of Rhizobium in the nitrogen cycle

- forms symbiotic relationship with roots of leguminous plants;

- absorbs atmospheric nitrogen in the soil;

- to build up nitrates;

which the roots absorb to form proteins.