Science (English Medium) Class 12 - CBSE Important Questions

Coelacanth was caught in South Africa. State the significance of the discovery of Coelacanth in the evolutionary history of vertebrates.

Emasculation and bagging are the two important steps carried during artificial hybridization to obtain superior varieties of desired plants. Explain giving reasons, in which types of flowers and at what stages are the two processes carried out.

State what is apomixis. Write its significance. How can it be commercially used?

1. Nucellus
2. Antipodals
3. Synergids
4. Micropyle

Flowers which have single ovule in the ovary and are packed into inflorescence are usually pollinated by ______.

Assertion: Apomictic embryos are genetically identical to the parent plant.

Reason: Apomixis is the production of seeds without fertilization.

Trace the development of a megaspore mother cell to the formation of a mature embryo sac in a flowering plant.

The wall layer of microsporangium, which nourishes the pollen grain, is ______.

Explain the menstrual phase in a human female. State the levels of ovarian and pituitary hormones during this phase.

Describe the roles of pituitary and ovarian hormones during the menstrual cycle in a human female.

How is 'oogenesis' markedly different from 'spermatogenesis' with respect to the growth till puberty in the humans?

Draw a sectional view of human ovary and label the different follicular stages, ovum and Corpus luteum.

When and where do chorionic villi appear in humans?

Draw a diagrammatic sectional view of the female reproductive system of human and label the parts

(i) where the secondary oocytes develop

(ii) which helps in collection of ovum after ovulation

(iii) where fertilization occurs

(iv) where implantation of embryo occurs.

Explain the role of pituitary and the ovarian hormones in menstrual cycle in human females

The following is the illustration of the sequence of ovarian events (a − i) in a human female

(i) Identify the figure that illustrates ovulation and mention the stage of oogenesis it represents.

(ii) Name the ovarian hormone and the pituitary hormone that have caused the above mentioned event.

(iii) Explain the changes that occur in the uterus simultaneously in anticipation.

(iv) Write the difference between ‘c’ and ‘h’.

(v) Draw a labeled sketch of the structure of a human ovum prior to fertilization.

During the reproductive cycle of a human female, when, where and how does a placenta develop? What is the function of placenta during pregnancy and embryo development?

Describe the changes that occur in ovaries and uterus in human female during the reproductive cycle.

Explain the development of a secondary oocyte (ovum)  in a human female from the embryonic stage upto its ovulation. Name the hormones involved in this process.

Why are the human testes located outside the abdominal cavity? Name the pouch in which they are present.