What are weeds? How can we control them?

4. What are STDs? How can we prevent sexually transmitted diseases?

What are STDs? How can we prevent STDs?

How do genes control traits?

Why do different colours get separated when a white light passes through a prism ? How can we recombine the components of white light after a prism has separated them ? Explain with the help of a figure.

A metal is found in liquid state. It is widely used in instrument for measuring blood pressure. In what form does it occur in nature ? How can we extract this metal from its ore ?

(i) What are fossils? How do we know how old the fossils are? (ii) State two differences between homologous and analogous organs.