Answer: (C)

Explanation: Lichens are typically the first organisms to colonize bare rock. They are therefore the pioneer species in primary succession. Many organisms require soil before they can colonize an area. Lichens that colonize bare rock secrete acids that break down the rock and start the soil-production process. Also, as lichens die, they provide some organic matter that also contributes to soil. Mosses can then colonize the thin soil; as mosses die, the soil thickens more allowing other hardy species to colonize. The process continues until a mature forest forms, sometimes centuries later. Hence, option (c) is correct.

Answer: (B)

Explanation:

• Dead Zone is an area in water body that contains little or no oxygen (or they are hypoxic) in bottom and near-bottom water. Hence, statement 1 is incorrect.
• Mostly they occur naturally but it can be caused by excessive nutrient pollution from human activities coupled with other factors. They are well-known off western coasts of North and South America, off coast of Namibia and off west coast of India in Arabian Sea. In recent times, warming of the atmosphere through climate change is predicted to lead expansion of ‘dead zones’ in the ocean. Hence, statement 2 and 3 are correct.

Answer: (A)

Explanation: Dissolved oxygen (DO) is a measure of how much oxygen is dissolved in the water – the amount of oxygen available to living aquatic organisms. The amount of dissolved oxygen in a stream or lake can tell us a lot about its water quality. Oxygen concentrations are much higher in air, which is about 21% oxygen, than in water, which is a tiny fraction of 1 percent oxygen. Dissolved oxygen levels decrease with increasing temperature and atmospheric oxygen content is far higher than dissolved oxygen levels. Ice and snow reduce the amount of sunlight reaching aquatic plants, thereby reducing photosynthesis and oxygen production. Hence, only statement 3 is correct.

Answer: (B)

Explanation: Biotope is an area that is uniform in environmental conditions and in its distribution of animal and plant life. It is often used interchangeably with the world habitat. A biotope is generally not considered to be a large-scale phenomenon. For example, a biotope might be a neighbouring park, a back garden, even potted plants or a fish tank on a porch. In other words, the biotope is not a macroscopic but a microscopic approach to preserving the ecosystem and biological diversity. Phenotype is the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment. Hence, option (b) is correct.

Answer: (C)

Explanation: Humus should be differentiated from decomposing organic matter. The latter is rough- looking material and remains of the original plant are still visible. Fully humified organic matter, on the other hand, has a uniform dark, spongy, jelly-like appearance, and is amorphous. It may remain like this for millennia or more. The process of humification can occur naturally in soil, or in the production of compost. Humus has a characteristic black or dark brown color and is organic due to an accumulation of organic carbon. The rate at which raw organic matter is converted into humus promotes (when fast) or limits (when slow) the coexistence of plants, animals, and microbes in soil. Effective humus and stable humus are further sources of nutrients to microbes, the former provides a readily available supply, and the latter acts as a longer-term storage reservoir. Hence, both statements are correct.