AIPMT 2011 Prelims question paper with solutions

1. Recall what substrate is most commonly used in distilleries to produce ethanol — it is molasses, a byproduct of sugar production.

2. To prepare it for fermentation, the molasses is diluted into a mash containing about 10–20% by weight of sugar.

3. Through the fermentation of this molasses-based mash by yeast, ethanol is produced on a commercial scale.

4. Eliminate the other options — ground gram, soyabean, and corn meal are not the most common substrates specifically used in distilleries for ethanol production.

Hence, the answer is B (Molasses).

1. Guard cells are specialized epidermal cells that surround the stomatal pore, and they have a unique feature that most other epidermal cells lack.

2. Unlike typical epidermal cells, guard cells contain chloroplasts, which allow them to carry out photosynthesis directly within these cells.

3. This ability to photosynthesize is important because it helps guard cells generate the sugars and energy needed to actively regulate ion movement (like potassium), which in turn controls the opening and closing of stomata.

4. While guard cells do also have structures like mitochondria, endoplasmic reticulum, and a cytoskeleton (as most living cells do), these are not unique to guard cells — ordinary epidermal cells possess them too, but typically lack chloroplasts.

5. Hence, since the presence of chloroplasts is the key distinguishing feature of guard cells compared to other epidermal cells, the correct answer is D.

1. Understand the sensitivity of nitrogenase - The enzyme nitrogenase, present in root nodules, converts atmospheric nitrogen ($N_2$) into ammonia but is highly sensitive to molecular oxygen and requires anaerobic conditions to function.

2. Need for oxygen regulation - Since the root nodule tissue still requires some oxygen for respiration, there must be a mechanism to keep the free oxygen concentration low specifically around nitrogenase, without eliminating oxygen entirely.

3. Role of leghaemoglobin - Leghaemoglobin acts as an oxygen scavenger/buffer — it binds oxygen and regulates (differentiates) its availability so that nitrogenase is shielded from harmful oxygen levels while the rest of the nodule cells still get enough oxygen for respiration.

4. Why other options are wrong - Leghaemoglobin does not inhibit nitrogenase (it protects it), it is not responsible for the physical differentiation of the nodule itself, and it does not control the expression of nif genes (which are responsible for coding nitrogenase and related proteins).

5. Conclusion - Hence, the function of leghaemoglobin is oxygen differentiation (regulating oxygen levels), so the answer is Option B.