Answer: C

Explanation:

A keystone species is a species that has a great impact on its natural environment relative to its abundance. Keystone species play an important role in maintaining the structure of an ecological community, influencing many other organisms in the ecosystem and helping to determine the type and number of various other species in the community.

Answer: C

Explanation:

An exotic plant is one that has been introduced by humans from one region to another, either intentionally or otherwise, through human agency or accidentally. An exotic plant that has become isolated from its native ecosystem and grows on its own among the regional vegetation is considered a naturalised exotic species. Naturalised exotic species that displace native biota or threaten valuable environmental, agricultural or personal resources by the damage they cause are considered invasive.

Some of the most notorious invasive species in India include lantana, parthenium, Siam weed, Mexican devil (Ageratina adenophora) and mesquite (Prosopis juliflora). Water hyacinth (Eichhornia crassipes) has spread to many inland water bodies, while alligator weed (Alternanthera philoxeroides) has spread to both aquatic and terrestrial sites in India.

Answer: C

Explanation:

Thermoregulation is a mechanism that allows living organisms to maintain a constant internal environment. Most processes in the human body depend on temperature: metabolism, synthesis of proteins and hormones, digestion, and cognitive function. In addition, overheating or hypothermia can lead to serious illness and even death. Since small animals have a large surface area relative to their volume, they lose body heat very quickly when it is cold outside. Hence statement 1 is correct.

They then have to expend a lot of energy to produce body heat through metabolism. This is the main reason why very few animals are found in polar regions. Hence statement 2 is correct.

Answer: A

Explanation:

Red algae are able to grow at deeper depths in the ocean than green algae because of the presence of a higher amount of the pigment phycoerythrin in red algae that increases with depth. Phycoerythrin can absorb blue-green wavelengths of the visible spectrum of light and help those red algae in photosynthesis.

Answer: B

Explanation:

Water vapour is the most abundant greenhouse gas on Earth. It is responsible for about half of the Earth's greenhouse effect.