Biology Paper 2, WASSCE (PC), 2020

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.