Breathing and Exchange of Gases — NEET UG practice

1. Recall the definition of each respiratory volume. Respiratory volumes are the different amounts of air involved during normal and forced breathing, and each has a typical value in an adult human.

2. Tidal Volume (TV). This is the volume of air breathed in or out during normal quiet breathing.

$$TV \approx 500 \; \text{mL}$$

So, D matches II.

3. Expiratory Reserve Volume (ERV). This is the extra air that can be forcefully expired after a normal tidal expiration.

$$ERV \approx 1000\text{–}1100 \; \text{mL}$$

So, A matches III.

4. Residual Volume (RV). This is the air that always remains in the lungs even after the most forceful expiration, so the lungs never fully collapse.

$$RV \approx 1100\text{–}1200 \; \text{mL}$$

So, B matches IV.

5. Inspiratory Reserve Volume (IRV). This is the extra air that can be forcefully inspired after a normal tidal inspiration, and it is the largest of the four volumes.

$$IRV \approx 2500\text{–}3000 \; \text{mL}$$

So, C matches I.

6. Conclusion. Combining all matches:

$$A\text{-III}, \; B\text{-IV}, \; C\text{-I}, \; D\text{-II}$$

Hence, the answer is A.

1. Understand that respiratory mode depends on body organisation and habitat. Different animal groups have evolved different structures for gas exchange based on where and how they live.

2. Molluscs. Most molluscs are aquatic and possess feather-like gills, so they perform branchial respiration. So, A matches II.

3. Reptiles. Reptiles are fully terrestrial (even aquatic ones surface to breathe) and rely entirely on lungs, so they perform pulmonary respiration only. So, B matches I.

4. Adult amphibians. Adult amphibians (like frogs) use both lungs and moist skin for gas exchange, combining pulmonary and cutaneous respiration. So, C matches IV.

5. Amoeba. Amoeba is a unicellular organism with no organs at all; oxygen simply diffuses into the cell and is used directly for cellular respiration. So, D matches III.

6. Conclusion. Combining all matches:

$$A\text{-II}, \; B\text{-I}, \; C\text{-IV}, \; D\text{-III}$$

Hence, the answer is A.

1. Identify the habitat condition. The question asks specifically about respiration in water, not on land, so we must recall how frogs breathe only when submerged.

2. Recall the concept of cutaneous respiration. Frogs have thin, moist, and highly vascular (blood-vessel rich) skin, which allows dissolved oxygen present in water to diffuse directly into the blood vessels beneath the skin.

$$O_2 (\text{dissolved in water}) \xrightarrow{\text{diffusion through moist skin}} \text{blood capillaries}$$

3. Eliminate the incorrect options. The trachea and lungs are used for air-breathing organisms and are not efficient for gas exchange underwater in amphibians. The buccal cavity is used only when the frog is on land (buccopharyngeal respiration), not in water.

4. Conclusion. Since gas exchange in water happens purely through the skin (cutaneous respiration), the correct organ is the skin.

Hence, the answer is B.