How do variations arise in organisms? ‘‘Variation is useful for the survival of species.’’ Justify this statement with the help of an example.

1. Mention the role of the following organs of human male reproductive system:

1. Testis.
2. Scrotum.
3. Vas deferens.
4. Prostate glands.

2. What are the two roles of testosterone?

1. Explain the process of regeneration in Planaria.
2. How is regeneration different from reproduction?

Explain the meaning of sexually transmitted diseases (STDs). Give two examples of STDs each, caused due to,

1. Bacterial infection.
2. Viral infection. State in brief how the spread of such diseases may be prevented.

What changes take place in boys during the reproductive phase?

Explain why, more complex multicellular organisms cannot give rise to new organisms through regeneration.

What does HIV stand for? Is AIDS an infectious disease? List any four modes of spreading AlDS.

How are the modes for reproduction different in unicellular and multicellular organisms?

List three techniques that have been developed to prevent pregnancy. Which one of these techniques is not meant for males? How does the use of these techniques have a direct impact on the health and prosperity of a family?

Reproduction is one of the most important characteristics of living beings. Give three reasons in support of the statement.