Science (English Medium) इयत्ता १२ - CBSE Question Bank Solutions

In an embryo sac, the cells that degenerate after fertilisation are ______.

In a flower, if the megaspore mother cell forms megaspores without undergoing meiosis and if one of the megaspores develops into an embryo sac, its nuclei would be ______.

Name the component cells of the ‘egg apparatus’ in an embryo sac.

Draw the diagram of a mature embryo sac and show its 8-nucleate, 7-celled nature. Show the following parts: antipodals, synergids, egg, central cell, polar nuclei.

With a neat, labelled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of synergids.

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

Identify the correct statement from the following:

Why are menstrual cycles absent during pregnancy?

Mention the importance of LH surge during menstrual cycle.

A human female experiences two major changes, menarche and menopause during her life. Mention the significance of both the events.

What are the events taking place in the ovary and uterus during follicular phase of the menstrual cycle.

Given below is a flow chart showing ovarian changes during menstrual cycle. Fill in the spaces giving the name of the hormones responsible for the events shown.

What role does pituitary gonadotropins play during follicular and ovulatory phases of menstrual cycle? Explain the shifts in steroidal secretions.

In the textbook you came across “Three Mile Island and Chernobyl disasters associated with accidental leakage of radioactive wastes.” In India we had Bhopal gas tragedy. It is associated with which of the following?

Observe the figure A and B given below and answer the following questions

A	B

1. The power generation by the above two methods is non-polluting True/False.
2. List any two applications of solar energy
3. What is a photovoltaic cell?

In the figure given below, parts A and B show the level of hormones which influence the menstrual cycle. Study the figure and answer the questions that follow:

1. Name the organs which secrete the hormones represented in parts A and B.
2. State the impact of the hormones in part B on the uterus of the human female during 6 to 15 days of the menstrual cycle.

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

The graph given below shows the number of primordial follicles per ovary in women at different ages. Study the graph and answer the questions that follow.

1. What is the average age of the women at the onset of menopause?
2. At what age are maximum primordial follicles present in the ovary, according to the given graph?

Explain the monosporic development of the embryo sac in the ovule of an angiosperm.

Draw a diagram of the mature embryo sac of an angiospermic ovule and label any four parts in it.