Q.Compare the classes Amphibia and Reptilia under the following heads: habitat, nature of skin, type of heart, mode of fertilisation and nature of egg.

Step 1. Habitat. Amphibia leads a dual life, requiring both water (for breeding/larval stage) and land (as terrestrial adults); Reptilia is chiefly terrestrial and, unlike amphibians, is not tied to standing water for reproduction.

Step 2. Skin. Amphibian skin is smooth, moist and richly glandular, entirely without scales, and plays an active role in cutaneous respiration; reptilian skin is dry and cornified (keratinised), covered by protective scales or scutes, an adaptation that limits water loss on land.

Step 3. Heart. Both classes are typically described as having a three-chambered heart; however, Reptilia shows a notable exception in the crocodilians, which possess a fully four-chambered heart, a feature not seen anywhere in Amphibia.

Step 4. Fertilisation. Amphibian fertilisation is usually external, occurring in water; reptilian fertilisation is internal, occurring within the female's body before the egg is laid. …

Work through each of the five named heads in turn for both classes, then draw the unifying conclusion that all five diffe …

• Forgetting the crocodilian exception when stating that Reptilia has a three-chambered heart — examiners often specifically test this exception. …