This was not a very popular question and most of the candidates avoided it. The candidates seemed to be thrown of balance by the term primary. The few candidates who attempted the question performed poorly. Most of them could not define primary growth as the irreversible increase in the length of the plant brought about by cell division in apical meristems.
They could not correctly state the importance of primary growth to the plants, describe growth in a named insect or draw the growth curves of an insect and annual herbaccous plant. Expected answers include:
Primary growth
This is an irreversible increase in the length of a stem/root/embryonic tissue;
brought about by cell division in the apical meristems.
Importance of primary growth to plants
- allows the leaves to reach adequate sunlight for photosynthesis;
- raises/lifts flowers to heights for wind/insect pollination;
- raises fruits seeds high to be dispersed effectively.
- allow roots to reach new water sources;
- to grow deep to give a firm anchorage to the plants
(b) Growth in Insect
In cockroach/termite/any named insect; Growth takes place after moulting/ecdysis; during moulting/ecdysis, the exoskeleton splits; longitudinally along the dorsal line; the larva/nymph/crawls out; and it is covered with a soft new exoskeleton; The nymph/larva rapidly grows in size; The new exoskeleton thickens; and gradually hardens. slowing down the rate of growth in the larva; the growth finally stops; until the next moulting ecdysis take place.
Growth Curve of an insect Growth curve of an annual herbaceous plant
