Category: Biology Second Paper

Pollen, anther, tube nucleus and pungamete of plants are collectively called pungametophyte. The anthers of plant stamens contain pollen mother cells. Each pollen mother cell produces four microspores or pollen grains by meiosis. Pollen is the first cell of the male gametophyte. Its nucleus divides to form two nuclei. The larger one is called the tubular nucleus and the smaller one is called the gonial nucleus. The ductal nucleus is round and the gonial nucleus is slightly curved. In this condition, the anther wall ruptures and binucleate pollen grains come out. Through pollination, it falls into the ovary of the female flower. When the pollen comes in contact with the endosperm, it gets stuck in the sticky sap and swells by absorbing the endosperm sap. Swelling causes pressure inside the pollen tube. The pressure causes the inteins to come out of the tube through the pore. It is called pollen tube. The process of pollen tube formation is called pollen emergence or germination. Cutinase enzyme degrades the cutin of the endosperm and the pollen tube enters the endosperm. The tube nucleus enters the pollen tube first and the generative nucleus later. The pollen tube enlarges and moves towards the ovary. Before the ovum reaches the pore, the germinal nucleus divides to produce two gametes or spermatozoa. The development of the pungametophyte is complete with the production of spermatozoa.

In the process of microsporogenesis, four microspores or pollen grains are produced from each pollen mother cell. Pollen is the first cell of pungametophyte. It can be round, oval, oblong or triangular. Each pollen grain is covered by a two-layered coat. The outer one is called exine and the inner one is called intein. Exine is thick, tough, uneven and composed of lignin. Its main chemical component is sporopollenin. In place of the exine are thin pore-like areas. This is called the reproductive pore (renurandhra or germpore). Pollen has 3-4 germpores (but can have up to 20). On the other hand, intein is thin, soft, smooth, elastic and made of cellulose. The cytoplasm of pollen is dense and the nucleus is in the middle of the cell. When the cell cavity is formed in the transformed state, the nucleus moves towards the periphery of the cell. Each pollen grain is 10-200 µm in diameter (according to many, 0.025-0.25 mm).
[If a pollen grain has one pore it is called monocolpate and if it has many pores it is called polycolpate]

The process by which pollen is formed is called microsporogenesis. The swollen part of the stamen head of a flower is called the anther. Anthers contain one or more archisporial cells. Each archisporial cell is large in size, the cytoplasm is dense and the nucleus is large. It produces two cells by periclinally dividing. wall cells on the outside and primary reproductive cells or sporogenous cells on the inside. Wall cells divide to form the pollen wall. The outermost layer of the wall is called the tapetum. Sporogenous cells transform into pollen mother cells either directly or by division. Each pollen mother cell divides by meiosis to form four microspores or pollen grains. The four pollen grains together are called tetrads. Most of the pollen is yellow in color. The pollinator receives nutrients from the tapetum. Plants belonging to the family Orchidaceae, Asclepiadaceae etc. have pollen grains together. Pollen sticks together in the metamorphosis to form a special structure. This is called a polynomial.
[Anthers with four anthers are dithetic anthers and this condition is called tetrasporangiate. An anther having two anthers is monothecus anther and this condition is called bisporangiate.

1. Sexual reproduction results in biological diversity.
2. Biodiversity allows organisms to easily adapt to new environments.
3. New species are created through sexual reproduction.
4. Food or grain is produced in the plant body through sexual reproduction.
5. Sexual reproduction produces seeds that protect the plant’s lineage.
6. Organisms increase the number of their species through reproduction.
7. The balance of the number of organisms in the biosphere is maintained through reproduction.

1. Sexual reproduction requires two separate reproductive cells or gametes.
2. Haploid germ cells participate in sexual reproduction.
3. Sexual reproduction results in the formation of a zygote.
4. Asexual reproduction usually takes place under unfavorable conditions in class plants.
5. The diploid state begins after sexual reproduction.
6. Crossing over occurs in sexual reproduction and new traits emerge.
7. Organisms of this genus produce gametes in the process of mitosis.
8. The process of fertilization is dependent on the mating potential of the gametes.
9. Sexual reproduction takes longer to produce offspring.

The reproduction that takes place by the union of sperm and egg is called sexual reproduction. The reproductive organs of plants are flowers. Flowers produce sperm and ovules. Sexual reproduction occurs when sperm and ovum meet. Sexual reproduction in plants is extremely diverse. A flower is a shoot specially adapted for plant reproduction.

The process by which new plants are created from the mother plant is called plant reproduction. The branch of biology that deals with plant embryogenesis, embryo development, fertilization and zygote development is called plant reproductive science. The branch of biology that deals with embryo creation and development is called embryology.
Plant reproduction is mainly of three types. Sexual reproduction, asexual reproduction and parthenogenesis.

1. Social and religious norms should be followed.
2. You should associate with a trusted partner.
3. Condom should be used during sexual intercourse.
4. Avoid taking intravenous drugs.
5. Do not reuse the same syringe.
6. Blood should be tested for virus-free before taking it.
7. Not using the same blade more than once in the salon.
8. The diseased person should be treated.
9. Sex workers should be made aware of safe sex.
10. People should be made aware.

No cure for AIDS has been discovered till date. Treatment of AIDS with drugs is called anti-retroviral therapy or ART. In the treatment of AIDS, the Food and Drug Administration-FDA (USA) recommends taking two groups of drugs together. This type of treatment is known as Highly Active Antiretroviral Therapy-HAART. The first group of drugs are Nucleoside reverse transcriptase inhibitors which delay its transmission. The second group of drugs is Protease inhibitors which block the replication of HIV. Some of the approved drugs are Fusion Inhibitors, Entry Inhibitors, Integrase Inhibitors, Pharmacokinetic Enhancers etc.

1. Antibody test, test, western blot test etc.
2. Blood T-helper cells or CD-4 cells are tested. (The normal range of CD-4 cells is 500-1,500 cells/mm3).