AIPMT 2014 question paper with solutions

1. Check option A about retinal's role. Given that retinal is the component within all visual photopigments that actually absorbs light, this statement is correct.

2. Check option B about rod and cone photopigments. Since rods contain a single pigment (rhodopsin) while cones contain three different pigments for colour vision, this statement is correct.

3. Check option D about rhodopsin. Given that rhodopsin is indeed the purplish-red pigment found specifically in rod cells, this statement is correct.

4. Check option C about retinal's origin. Retinal is actually derived from vitamin A, not vitamin C:

$$\text{Retinal} = \text{derivative of vitamin A (not vitamin C)}$$

So this statement is incorrect.

Hence, the statement that is not correct is option C, so the answer is Option C.

1. Recall the three ways $CO_2$ is transported in blood. Carbon dioxide travels from tissues to lungs in three forms: dissolved in plasma, bound to haemoglobin as carbamino-haemoglobin, and as bicarbonate ions.

2. Understand how bicarbonate is formed. Most $CO_2$ entering the blood diffuses into red blood cells (RBCs), where it reacts with water.

$$CO_2 + H_2O \xrightarrow{\text{carbonic anhydrase}} H_2CO_3$$

3. Understand the next step of the reaction. This carbonic acid ($H_2CO_3$) is unstable and almost immediately dissociates into hydrogen ions and bicarbonate ions.

$$H_2CO_3 \rightarrow H^{+} + HCO_3^{-}$$

4. Recall the enzyme's role. The enzyme carbonic anhydrase, found exclusively inside RBCs, speeds up this reaction enormously, and also helps reverse it back to $CO_2$ and water once blood reaches the lungs (for exhalation).

5. Quantify the contribution. This bicarbonate pathway accounts for about 70% of total $CO_2$ transport (roughly 2.5 mL per 100 mL of blood), making it the dominant transport form.

6. Eliminate the incorrect options. Dissolved gas and carbamino-haemoglobin together account for the remaining, smaller portions of $CO_2$ transport, not the majority 70%.

7. Conclusion. About 70% of $CO_2$ is transported to the lungs as bicarbonate ions.

Hence, the answer is A.

1. Understand what happens to plants grown without light: when plants grow in darkness or under severely reduced light, they show an abnormal pattern of growth rather than a genetic change.

2. Identify the correct term for this abnormal growth: this condition is called etiolation, and etiolated plants characteristically show elongated (spindly), pale or white-coloured shoots, branched/thin stems, and poorly developed leaves and roots. Given this,

$$\text{Growth in darkness} \rightarrow \text{Etiolation (pale, elongated seedlings)}$$

3. Eliminate the other options: mutated implies a genetic change, which is not indicated here; embolised relates to blockage in water-conducting vessels (an air bubble/embolism), not a lighting response; defoliated means having lost leaves, which is not what is described.

Hence, the correct answer is C. Etiolated.