C.

sea pen and sea fan

Stinging cells are used for offence and defence. They have nematocysts, composed of capsule, shaft and thread tube. The thread tube coils around the prey or attaches to it and injects a toxin called hypnotoxin which paralyzes the victim. They are found in cnidarians- sea pen (Pennatula), sea fan (Gorgonia) etc.

D.

8.1%

The total number of species estimated is about 1.74 million. Out of these , species in India is roughly 8.1%. India with about 45000 species of plants and twice as many species of animals is one of the 12 megadiversity countries of the world.

B.

Nelumbo (lotus)

Non-native or alien species are often introduced accidently for their economic and other uses. They often become invasive ' and drive away the local species. Therefore, these species are second major cause of extinction.

Lantana camara has replaced many species in forests of Central India.

Parthenium hystero- phorus has pushed out various shrubs and herbs from open places in the plains. 

Water hyacinth Eicchornia crassipes is used in India to reduce pollution.

A.

heart

Cardiac muscle fibres are found in the wall of heart. They have dark intercalated discs at intervals. These are the specialized regions of cell membranes of two adjacent fibres. They permit the wave of muscle contraction to be transmitted from one cardiac fibre to another.

C.

Amphibians and algae

External fertilization is the fertilization that occurs outside the body of the organism. It requires an external medium such as water for its fertilization.Thus, in most aquatic organisms such as a majority of algae, fishes and amphibians, this type of fertilization occurs.