What are surface berriers?Explain the role of skin and mucus membrane as body's first line of defence.

What are molecular scissors ? Explain their role .

What role does a nucleus play in human body ?

What is speciation? Explain in brief the role of natural selection and genetic drift in this process.

What is satellite DNA in a genome ? Explain their role in DNA fingerprinting .

a] Name the parts of the human female reproductive system where i] fertilisation takes place, ii] implantation of the fertilised egg occurs. b] Explain how the embryo gets nourishment inside the mother's body. c] Write the function of following parts in human female reproductive system: i] Ovary ii] Oviduct iii] Uterus d] Describe in brief the structure and function of placenta. OR Explain the structure and important role of placenta during gestation period of woman.

A spherical conducting shell of inner radius r_(1) and outer radius r_(2) has a charge Q. (a) A charge q is placed at the centre of the shell. What is the surface charge density on the inner and outer surfaces of the shell? (b) Is the electric field inside a cavity (with no charge) zero, even if the shell is not spherical, but has any irregular shape? Explain.

What is eutrophication ? Explain its consequence on the life of plants and animals in such water bodies .