Category: Biology Second Paper

Inside the uterus, the nucleus of the zygote divides into two nuclei. The nucleus is located at the two poles of the cell. Nuclei of both poles divide twice in succession to form eight nuclei of four each. One nucleus from each pole moves to the center of the cell and fuses to form the secondary nucleus. Among the three upper nuclei, the large nucleus in the middle is the ovum.

Fertilization of sperm and egg occurs in the follicle. After fertilization, the ovary of the flower is stimulated. The uterus grows and changes in its various parts. As a result, the uterus grows. The wall of the uterus forms the placenta. If the ovary of each flower of an inflorescence develops into a fruit, it is called simple fruit or single fruit. Mango, jam, litchi, plum etc. are single fruits. When a single fruit is produced from a complete inflorescence, it is called a compound fruit. Composite fruits like jackfruit, pineapple etc.

The implications/importance of plant female gametophyte development in the biosphere are discussed.

1. Strygamete formation: In this process the strygametophyte develops. The main function of the female gametophyte is to produce female gametes or ovules. An ovule is produced in each female gametophyte.
2. Fertilization: The prerequisite for fertilization is the production of sperm and egg. The female gametophyte produces ovules which participate in fertilization.
3. Origin of seeds: The main source of food in the living world is seeds. Spermatozoa fuse with secondary nucleus of female gametophyte to produce seed.
4. Fertilization: In this process, the ovum unites with the sperm to form a zygote. After the zygote is formed, the ovum develops into a seed.
5. Fruit formation: After fertilization, the ovary of the flower gradually turns into a fruit.
6. Reproduction: After the union of sperm and egg, the ovule of the flower turns into a seed. Most plants on Earth reproduce by seeds. Because of this, female gametophytes play a major role in plant reproduction.
7. Formation of new species: Zygote is formed by the union of two different cells sperm and egg. It gives rise to new species with new characteristics.
8. Creation of Biodiversity: Eggs are produced in strygametophytes. A zygote is formed by the union of sperm and egg. New species are formed from the zygote. Biodiversity is created through new species.

The plant embryo, ovule, accessory nucleus, accessory cell and secondary nucleus together are called strigametophyte.

The female flower of the plant contains sporogenous cells inside the ovary. The sporogenous cell divides or develops directly into the female mother cell. The female mother cell is diploid and divides by meiosis to produce four haploid macrospores or gametes. Spore is the first cell of female gametophyte. Of the four spermatozoa, the top three are destroyed and the bottom remain viable. The nucleus of the viable zygote enlarges and divides into two nuclei in the process of mitosis. The nucleus is located at the two poles of the cell. Each nucleus is surrounded by little cytoplasm and a thin wall. At this time, the female cell turns into a sac-like organ with two poles. Nuclei of both poles divide twice in succession to form eight nuclei of four each. In this condition, one nucleus from both poles moves to the center of the cell and fuses. It is called fusion nucleus or secondary nucleus. The three upper nuclei together are called the egg apparatus. The middle of the oviduct is large

The nucleus is called the ovum and the smaller nuclei on either side are called companion nuclei or synergids. The bottom three nuclei are called antipodal cells.

There are three main parts of the embryo. These are-

1. Egg apparatus: The three cells near the oviduct of the embryo are collectively called the egg apparatus. Among them, the large cell in the middle is called ovule and the smaller cells on both sides are called companion cells.
2. Antipodal cell: The three cells on the ovule side of the embryo are collectively called antipodal cells.
3. Secondary nucleus: Two nuclei come from the two poles in the middle of the embryo. The two nuclei then fuse to form a secondary nucleus.

An embryo containing four gametes is called Tetrasporic. 7 types of tetrasporic embryos.

(i) Adoxa type: Adoxa embryo has 8 nuclei. For example, Adoxa moschatellina.

(ii) Peperomia: Peperomia is a 16-nucleate embryo sac. For example – Peperomia pellucida.

(iii) Penia type: Penia is a 16-nucleate embryo sac.

(iv) Drusa: Drusa embryo contains 16 nuclei. For example – Drusa amatista.

(v) Fritilliaria type: Fritilliaria embryo has 8 nuclei. For example, Fritilliaria imperialis.

(vi) Plumbagella: Plumbagella is an embryo sac with 8 nuclei. For example – Plumbagella micrantha.

(vii) Plumbaga type: Plumbaga is a 16 nucleated embryo sac. For example – Plumbaga zeylanica.

An embryo containing two spermatozoa is called Bisporic. Bisporic embryos are of two types.

(i) Allium type: Allium is an embryo with 8 nuclei. For example – Allium cepa.

(ii) Endymion type: Endymion is an 8-nucleate embryo sac. For example- Endymion hispanica.

An embryo containing only one zygote is called monosporic. About 75% of the plant kingdom is monosporic. In 1879, Strusberger first described the structure of the monosporic embryo of the plant Polygonum divaricatum. Monosporic embryos are of two types.

(i) Oenothera type: Oenothera is a 4-nucleate embryo sac. eg Oenothera lamarckiana.

(ii) Polygonum type: Polygonum is an 8-nucleate embryo sac. For example, Polygonum hydropiper.

The sac-like part inside the nucellus that carries the egg is called the embryo sac. Amniotic sac is of three types.
1. Monosporic: An embryo containing only one zygote is called monosporic. About 75% of the plant kingdom is monosporic. In 1879, Strusberger first described the structure of the monosporic embryo of the plant Polygonum divaricatum. Monosporic embryos are of two types.
(i) Oenothera type: Oenothera is a 4-nucleate embryo sac. eg Oenothera lamarckiana.
(ii) Polygonum type: Polygonum is an 8-nucleate embryo sac. For example, Polygonum hydropiper.
2. Bisporic: An embryo containing two spermatozoa is called Bisporic. Bisporic embryos are of two types.
(i) Allium type: Allium is an embryo with 8 nuclei. For example – Allium cepa.
(ii) Endymion type: Endymion is an 8-nucleate embryo sac. For example- Endymion hispanica.
3. Tetrasporic: An embryo containing four gametes is called Tetrasporic. 7 types of tetrasporic embryos.
(i) Adoxa type: Adoxa embryo has 8 nuclei. For example, Adoxa moschatellina.
(ii) Peperomia: Peperomia is a 16-nucleate embryo sac. For example – Peperomia pellucida.
(iii) Penia type: Penia is a 16-nucleate embryo sac.
(iv) Drusa: Drusa embryo contains 16 nuclei. For example – Drusa amatista.
(v) Fritilliaria type: Fritilliaria embryo has 8 nuclei. For example, Fritilliaria imperialis.
(vi) Plumbagella: Plumbagella is an embryo sac with 8 nuclei. For example – Plumbagella micrantha.
(vii) Plumbaga type: Plumbaga is a 16 nucleated embryo sac. For example – Plumbaga zeylanica.

A small swollen area is formed in the amara inside the ovary of the female flower. The swollen area gradually turns into an ovule. The endosperm contains 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 periclinal division. wall cells on the outside and primary reproductive cells or sporogenous cells on the inside. Wall cells divide to form the wall of the zygote. The sporogenous cell develops into the female mother cell either directly or by division. Each female mother cell divides by meiosis to produce four megaspores or gametes. Of the four spermatozoa, three are destroyed and one remains viable.

The implications/importance of plant pungametophyte development in the biosphere are discussed.
1. Pungamete formation: In this process the pungametophyte develops. The main function of pungametophyte is to produce pungametes or sperm. Two spermatozoa are produced in each pungametophyte.
2. Fertilization: The prerequisite for fertilization is the production of sperm and egg. Pungametophytes produce sperm that participate in fertilization.
3. Origin of seeds: The main source of food for the living world is seeds. The sperm produced in the pungametophyte fuse with the secondary nucleus to form the seed.
4. Fertilization: In this process, the sperm unites with the egg to form a zygote. After the zygote is formed, the flower ovule develops into a seed.
5. Fruit formation: After fertilization, the ovary of the flower gradually turns into a fruit.
6. Reproduction: After the union of sperm and egg, the ovule of the flower turns into a seed. Most plants on Earth reproduce by seeds. Because of this, pungametophytes play a major role in plant protection.
7. Formation of new species: Zygote is formed by the union of two different cells sperm and egg. It gives rise to new species with new characteristics.
8. Creation of Biodiversity: The sperm produced in the pungametophyte fertilizes the egg to form a zygote. New species are formed from the zygote. Biodiversity is created through new species.
From the above discussion, pungametophyte is a very important cell in plant life. It maintains the continuity of life by creating sperm.