Reproductive Health — BIOLOGY STD 12 Science — Question

Explain the mechanism of DNA replication with the help of a replication fork. What role does the enzyme DNA-ligase play in a DNA replication fork?

Embryo sacs of some apomictic species appear normal but contain diploid cells. Suggest a suitable explanation for the condition.

Match Column I with Column II.

S. No.	Column I	S. No.	Column II
A.	Cleavage	1.	Outer layer of the blastocyst that attaches to the endometrium during implantation.
B.	Implantation	2.	Mitotic divisions of the zygote in quick succession.
C.	Inner cell mass	3.	Embedding of the blastocyst in the endometrium of uterus.
D.	Trophoblast	4.	Release of secondary oocyte from the ovary.
E.		5.	Group of cells attached to one end of trophoblast that differentiate into embryo proper.

Describe the experiment that helped Louis Pasteur to dismiss the theory of spontaneous generation of life.

What are viruses parasitising bacteria called? Draw a well labelled diagram of the same.

Differentiate between geitonogamy and xenogamy in plants. Which one between the two will lead to inbreeding depression and why?

Differentiate the following and give examples:
Active and passive immunity.

When someone buys packets of cigarettes, cannot miss the statutory warning that is present on the packing which warns against smoking and says how it is injurious to health. Yet, smoking is very prevalent in our society, both among young and old. Advise the adolescents about the importance of avoiding smoking. (Mention any six points.)

Draw a labelled sketch of a mature 7-celled, 8-nucleate embryo-sac.