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.