a. Classify the following biological associations under the headings in the table below: (i) Remora and shark; (ii) Lichen; (iii) Cattle and white Egret; (i...

Answer Details

(a) Classification of the biological associations:

In parasitism one partner (the parasite) benefits while the host is harmed; in mutualism both partners benefit; in commensalism one partner benefits while the other is neither helped nor harmed.

(b)(i) Three adaptive features of parasites:

• Presence of hooks and suckers for firm attachment to the host so they are not dislodged.
• A thick, resistant cuticle (and anti-enzymes) that protects them from the host's digestive juices.
• High reproductive capacity (production of very many eggs) to ensure that some offspring reach new hosts.

Other acceptable features: reduced or absent locomotory organs, reduced sense organs, and a reduced digestive system since food is absorbed already digested.

(b)(ii) Two effects of parasites on their hosts:

• They deprive the host of nutrients, causing malnutrition and weakness.
• They cause diseases and damage host tissues or organs (for example anaemia from blood loss).

(c)(i) Saprophytes are organisms that feed on dead and decaying organic matter, secreting digestive enzymes onto the material externally and absorbing the soluble digested products.

(c)(ii) Four examples of saprophytes: Mushroom, Rhizopus (bread mould), Mucor, Yeast (also Penicillium and many bacteria of decay).