AIPMT 2004 question paper with solutions

1. Define stability: this refers to how well an ecosystem resists being disturbed or damaged in the first place — a stable ecosystem is hard to disrupt.

2. Define resilience: this refers to how quickly an ecosystem can recover and return to normal after a disturbance has occurred.

3. Apply these definitions to the scenario: since the ecosystem described is "easily damaged," it must have low stability; but since it "can recover after some time," it must have high resilience.

4. Match with the correct combination: this exactly corresponds to low stability and high resilience.

Hence, the answer is B.

1. Recall the ion concentration setup at rest. Given that the resting neural membrane maintains a higher $Na^+$ concentration outside the cell and a higher $K^+$ concentration inside the cell.

2. Apply the principle of diffusion along a concentration gradient. Since diffusion always moves ions from a region of higher concentration to lower concentration if allowed to move freely:

This means sodium would diffuse into the cell.

3. Eliminate the incorrect options. Potassium would actually diffuse out (not in), and sodium would not diffuse out (since it's higher outside) — so those combinations are incorrect.

Hence, unrestricted diffusion at rest would drive $Na^+$ into the cell, so the answer is Option C.

1. First, recall Oparin's theory on the origin of life, which along with similar ideas from J.B.S. Haldane, describes the early Earth's atmosphere as a reducing atmosphere.

2. In this reducing atmosphere, hydrogen atoms — being the most abundant and reactive — combined with all the available oxygen atoms to form water, leaving essentially no free oxygen gas in the atmosphere.

3. The primitive atmosphere therefore contained gases like water vapour, methane, and hydrogen, but crucially lacked free oxygen, since oxygen accumulated later only after photosynthetic organisms evolved.

4. Hence, the answer is B. Oxygen.