Case Study
Passage with linked questions
Case Set 1
Case AnalysisPassage
A biology teacher brought live frogs to the classroom and asked students to observe their behaviour over two days. On the first day, the frogs were placed in a container with moist soil and water. Students noticed the frogs absorbing water through their skin and occasionally catching insects with their tongue. On the second day, the container was left under a bright lamp, raising the temperature significantly. The frogs became sluggish and tried to burrow into the soil. The teacher explained that frogs are cold-blooded animals that cannot regulate their internal body temperature. She further asked students to recall that frogs disappear during extreme summer and winter months in nature, sheltering in deep burrows until conditions become favourable again.
Question 1: What term is used for animals like frogs whose body temperature varies with the environment? Name the two types of seasonal dormancy observed in frogs.
- Animals whose body temperature varies with the environmental temperature are called poikilotherms or cold-blooded animals.
- The dormancy during peak summer months when frogs shelter in deep burrows is called aestivation (summer sleep).
- The dormancy during peak winter months when frogs shelter in deep burrows to protect from extreme cold is called hibernation (winter sleep).
Question 2: How do frogs obtain water, and why is this method of water intake significant for their survival?
- Frogs never drink water; instead, they absorb water directly through their moist, highly vascularised skin.
- This method of water intake is possible because the frog's skin is always maintained in a moist condition with the help of mucous glands.
- This is significant because it means the frog's survival depends entirely on a constantly moist skin environment — if the skin dries out, both water intake and cutaneous respiration are simultaneously compromised.
Question 3: During aestivation and hibernation, frogs do not use their lungs. Explain how gaseous exchange takes place during these dormant periods and why the frog's skin structure makes this possible.
- During aestivation and hibernation, frogs rely exclusively on cutaneous respiration — gaseous exchange through the skin — as their sole mode of breathing.
- Dissolved oxygen from the surrounding moist environment diffuses directly through the skin into the underlying blood capillaries, while carbon dioxide diffuses out in the reverse direction.
- This is possible because the frog's skin is thin, moist, smooth and highly vascularised; the rich network of blood capillaries just beneath the skin surface ensures efficient diffusion of gases without requiring lung activity.