(a)(i) Define ecological succession. (ii) List four characteristics of ecological succession of plants. (b) Explain four factors which affect population siz...

(a)(i) Ecological succession is the gradual and orderly replacement of one community of organisms by another in a given area over a period of time, until a stable climax community is established.

(ii) Four characteristics of ecological succession of plants

• It is a gradual, orderly and progressive process.
• It begins with pioneer species and passes through several intermediate (seral) stages.
• Each stage modifies the environment, making it suitable for the next community.
• It ends in a stable, self-perpetuating climax community.

(b) Four factors which affect population size

• Natality (birth rate): a high birth rate increases population size.
• Mortality (death rate): a high death rate decreases population size.
• Immigration: movement of organisms into the area increases population size.
• Emigration: movement of organisms out of the area decreases population size. (Availability of food, predation and disease also apply.)

(c) Adaptations of tapeworm (Taenia solium) to its habitat in the human gut

• Has hooks and suckers on the scolex (head) for attachment to the gut wall so it is not washed out.
• Has a thick cuticle that resists digestion by the host's enzymes.
• Secretes anti-enzymes to protect itself from being digested.
• Has a long, flat, thin body giving a large surface area for absorbing already-digested food directly through its body wall (no gut needed).
• Is hermaphroditic and produces very many eggs, ensuring survival and spread of the species.
• Can respire anaerobically, coping with the low-oxygen conditions of the gut.