This was the most popular question, though it was not generally well treated by most candidates. Many candidates could define respiration but could not associate structural features with their functions and describe the process of gaseous exchange in plants. In place of ‘stomata’ some candidates wrote ‘lenticel’
Many candidates confused biochemical processes taking place in cells to produce energy with inhalation and exhalation. Candidates could not also give corresponding answers in the differences between the aerobic and anaerobic respiration.
Expected answers are:
1(a) (ii) Adaptation of respiratory surfaces in mammals
- thin walled/permeable; for easy diffusion of gases;
- large surface area; to enhance/allow maximum diffusion of gases;
- moist surface area; for gases to dissolve;
- well supplied with blood vessels/highly vascularised; for easy transport/circulation of gases .
- well ventilated surfaces; for easy access to gases.
(b) Gaseous exchange in the leaves of flowering plants
- during darkness, oxygen from the atmosphere;
- diffuses through the stomata into the air spaces;
- of the mesophyII layer of the leaf;
- it dissolves in the moist surfaces of the cells;
- and then diffuses into the mesophyII cells;
- the carbon dioxide produced from these cells diffuses out;
- through the stomata;
- during the day, oxygen diffuses out of the mesophyII of the leaf;
- to the atmosphere;
- carbon dioxide from the atmosphere;
- diffuses into the mesophyII of the cells.
(c) Differences between aerobic and anaerobic respiration
Aerobic |
Anaerobic |
- oxygen is needed/required
- water is produced as by
product
- a lot of energy is produced/38
ATPs produced
- ethanol/lactic acid not formed
as by-product
- occurs in the mitochondrion
and cytoplasm
- sugar is completely oxidised
- occurs mostly in plant and
animal cells |
oxygen is not used/required/needed;
water is not produced as by
product;
small amount of energy is
produced/ 2ATPs produced
ethanol/lactic acid formed as
by product;
occurs in the cytoplasm only;
sugar is not completely oxidised;
occurs in some bacteria/fungi ;
and muscle cells of animals. |
No table minus 1
Points must correspond to score.
Growth Curve of an insect Growth curve of an annual herbaceous plant
