AIPMT 2015 question paper with solutions

1. Root pressure is a positive pressure that develops within the root xylem, pushing water upward, especially noticeable at night or in early morning when transpiration is low.

2. This pressure arises because roots actively pump mineral ions into the xylem, a process that requires the plant to spend metabolic energy (ATP) to move ions against their concentration gradient — this is called active absorption.

3. As ions accumulate inside the root xylem due to this active process, the water potential inside the xylem drops, causing water to move in from the surrounding soil by osmosis, building up pressure.

4. Passive absorption (Option A), by contrast, does not involve energy expenditure and simply follows existing water potential gradients — it does not generate root pressure on its own.

5. Increase in transpiration (Option C) actually reduces root pressure because the pulling force of transpiration dominates over the pushing force from the roots, and low osmotic potential in soil (Option D) would make water uptake harder, not easier.

6. Hence, since active absorption of ions is what generates the pressure gradient, the correct answer is B.

1. Microsporogenesis is the process of forming microspores (pollen grains), and it takes place when diploid microspore mother cells inside the anther undergo meiosis.

2. Megasporogenesis is the process of forming megaspores, and it takes place when a diploid megaspore mother cell inside the ovule undergoes meiosis.

3. Since both processes always involve meiotic division (even though they occur in different locations — the anther and the ovule respectively), the one feature common to both is that they involve meiosis.

4. Options B and C are each true for only one of the two processes, not both, so they can't describe something common to both.

5. Hence, the answer is Option A: involve meiosis.

1. Recall the concept of codominance. Codominance is a form of allelic interaction where neither allele is dominant over the other.

2. Understand what happens in the heterozygote. In a heterozygous individual carrying both alleles, both alleles express themselves fully and independently, producing a phenotype where both traits are visible simultaneously (a classic example being the AB blood group, where both A and B antigens are expressed together).

3. Eliminate the incorrect options. Option A describes linkage, not codominance. Option B describes simple (complete) dominance. Option D is not a valid description of any standard allelic interaction.

Hence, the correct answer is Option C, since codominance means both alleles are independently expressed in the heterozygote.