Question 3
(a) State four adaptive features of aquatic plants. [8 marks]
(b) (i) What is secondary succession? [2 marks]
(ii) List three factors that bring about changes in a climax community. [3 marks]
(iii) Explain briefly succession of plants in a pond. [3 marks]
(c) List three conditions in humans that are caused by mutation. [4 marks]
Observation
Some candidates stated the features of aquatic plants without stating the function, hence losing one mark each.
A few candidates could define secondary succession, although some were defining primary succession. Many candidates could also not list factors that bring about changes in a climax community.
Many candidates could also not describe the gradual succession of plants in a pond.
A few candidates that listed conditions in humans that are caused by mutation could not spell the terms correctly. Hence, losing marks.
The expected answers are:
(a) Adaptive features of aquatic plants
- Numerous air spaces/aerenchyma; for buoyancy;
- Long petioles; to position/lift the leaf above water/for photosynthesis;
- Possession of flexible petiole; to withstand the wave of water;
- Ribbon-like leaves; to allow easy passage of water current;
- They have hairs on the surface of leaves; to prevent water from blocking stomata/repel water;
- They have a well-developed root system; to prevent being dislodged;
- Possession of stolon/bud; for vegetative reproduction.
Note: Structure and function must correspond to score;
Structure alone x1 mark
Function alone does not score.
(b) (i) Secondary succession
Is a series of changes; in an existing/disturbed habitat; leading to a stable/climax community.
(ii) Factors that bring about changes in a climax community
- Introduction of new plant/animal species/organisms;
- Change in climatic conditions;
- Destruction/disturbance by human activities;
- Natural disaster.
(iii) Succession of plants in a pond
- The initial/pioneer plants in a pond are planktons/phytoplanktons/floating macrophytes;
- which are producers;
- followed by transitional communities comprising submerged and rooted aquatic plants e.g. Elodea, Ceratophylum;
- followed by rooted hydrophytes with floating leaves e.g. Nymphae;
- finally crowded plants growing on water-logged soil;
- to support suitable climax vegetation.
(c) Conditions in humans caused by mutation
- Sickle cell anaemia;
- Down syndrome /Down’s syndrome;
- Marfan syndrome;
- Albinism;
- Colour blindness;
- Cystic fibrosis;
- Phenylketonuria;
- Tay Sachs disease;
- Haemophilia;
- Huntington’s disease.
Note: Spellings must be correct to score.