Human Reproduction — BIOLOGY STD 12 Science — Question

Explain the process of replication of a retrovirus after it gains entry into human body.

Answer the following questions:
Explain the events that occur in a graafian follicle at the time of ovulation and thereafter.

Draw a diagram of L.S. of an anatropous ovule of an angiosperm and label the following parts

1. Nucellus
2. Integuments
3. Antipodal cells
4. Secondary nucleus.

Angiosperm flowers may be monoecious, cleistogamous or show self-incompatibility. Describe the characteristic features of each one of them and state which one of these flowers promotes inbreeding and outbreeding respectively.

Himani while watching a TV programme based on life in polar region observed that all animals in polar regions possess larger size. Also, smaller animals are not found in that region. She asked about this surprising fact to her teacher.

1. Why smaller animals (e.g. humming birds) are rarely found in polar regions?
2. What are the adaptations shown by polar animals?
3. What are the chief characteristics of polar region animals?
4. What values are shown by Himani?

Trace the events that would take place in a flower from the time the pollen grain of the same species falls on the stigma up to the completion of fertilisation.

What is endosperm and how is it formed? Describe the various types of endosperm found in angiosperms.

During the course of evolution why DNA was chosen over RNA as genetic material? Give reasons by first discussing the desired criteria in a molecule that can act as genetic material and in the light of biochemical differences between DNA and RNA.

Discuss the different barrier of innate immunity.

Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.