Question 8

              )   Describe the adaptations of plants to aquatic habitats giving specific
        Examples                                                                                              [10 marks]

(b)   (i)   List four characteristics of the intertidal zone                                 [ 4 marks ]
       (ii)   Explain how plants and animals in the intertidal zone are
              adapted to their habitats                                                                 [6 marks  ]

                Most candidates did not attempt this question.  Many candidates could not describe the adaptive features of plants in aquatic  habitat with examples and most could not also list the correct adaptive features of plants and animals in intertidal zone.

Expected answers include:

8(a)    Adaptations of plants to aquatic habitat

•  Aquatic plants have hairs on their surfaces; which repel water from their surface; thereby preventing blocking of the stomata; e.g. Pistia/water lettuce;
• They also have air spaces/parenchyma cells in their internal tissue; to enhance buoyancy of the plant; e.g. Nymphaea;
• Some aquatic plants e.g. Lemna; are very small in size; to enhance floating;
• Use of numerous roots, for absorption of mineral salts e.g. Salvinea;
• Some aquatic plants have long petioles; to raise leaves above water level for photosynthesis; e.g. Arrow head plant;
• The entire plant is flattened; to aid floating e.g. Lemna;
• Thin cuticle; for absorption of sunlight for photosynthesis;
• Presence of more stomata on upper surface; for diffusion of CO2  e.g. water lily/Nymphaea;
• Ribbon-shaped/finely dissected leaves; to allow free flow water current e.g. Hornwort.

 

 

                                                                                                 
     (b)(i)   Characteristics of Intertidal Zone

•  Intertidal zone is exposed to dry conditions at low tides;
• They are covered by water at high tide;
• Thus, the substratum is unstable;
• The intertidal zone receives abundant sunlight;
• The water temperature fluctuates greatly;
• Exposed to wave action.

         
  (b)(ii)    Adaptation of plant to the intertidal zone

•  They have holdfast for attachment to rocks/ substratum;
•  They posses air filled bladder for buoyancy;
•  Have leaves with flattened lamina for buoyancy;
•  Possession of dichotomous branching to allow easy flow of water over the

Plant;

• Tough/leathery thallus body/flexible stripe to withstand wave action.                                                                                      

Adaptation of Animals to intertidal zone

•  Have shells  to prevent desiccation;
• Dig holes/burrow into thin soil substratum to avoid desiccation/drying;
• Body fluid isotonic with sea water to prevent loss/gain of water;
• Possess gills for respiration;
• Strong thread/cementing materials for attachment to rocks/surfaces;
• Shell, for protection against wave action.