Describe the process of oogenesis with a suitable diagram.

Oogenesis is the process of the formation of haploid female gametes. The initial steps in oogenesis up to the production of primary oocytes occur before birth in the female foetus. Oogenesis occurs in the outermost parts of the ovaries. It starts with a germ cell called oogonium, which undergoes mitosis to increase in number. The process of oogenesis takes place in three stages which are described below. Prenatal stage: In this stage, the primary oocyte grows while being arrested in meiosis-I. The follicular cells proliferate, forming a stratified cuboidal epithelium. Such follicular cells are called granulosa cells, which secrete glycoproteins to form zona pellucida around the primary oocyte. Antral stage: The characteristic of this stage is the presence of antrum, a central fluid-filled space formed by combining fluid-filled areas present between granulosa cells. These structures having central fluid-filled space are called secondary follicles. Every month, these secondary follicles develop under the influence of follicle-stimulating hormone and luteinizing hormone secreted from the anterior pituitary gland. Pre-Ovulatory Stage: This stage is induced by the surge of luteinizing hormone, which causes the completion of meiosis-I. In this stage, two haploid cells of unequal sizes are formed within the follicle, from which one of the daughter cells that receive less cytoplasm forms a polar body. The polar body does not participate in oogenesis. The other daughter cells are known as the secondary oocyte. The daughter cells undergo meiosis-II, in which the polar body replicates to form two polar bodies, while the secondary oocyte arrests in the metaphase stage of meiosis-II. Figure: OOGENESIS

Name chief layers of human ovum.

An ovum is a single cell released from either of the ovaries of the female reproductive organs, which is capable of developing into a new organism when fertilised with a sperm cell. It is composed of three chief layers such as corona radiata, zona pellucida, and oolemma. The corona radiata is the first layer of follicular cells present outside the zona pellucida. The zona pellucida is a glycoprotein (chemical composition) layer that surrounds the oocyte and is located between the oocyte and the follicular cells. The oolemma is the plasma membrane that surrounds the egg.

Describe the process of spermatogenesis with suitable diagrams.

Gametogenesis is the process of the formation of gametes. Oogenesis is the process of formation of female gametes inside the female gonads, ovaries and spermatogenesis refer to the formation of sperms inside the male gonads, testes. The spermatogenesis takes place in three main steps: Multiplication phase in which the undifferentiated germ cells present in the germinal epithelium of seminiferous tubules divide mitotically to form spermatogonia. The growth phase in which the spermatogonia undergo growth by the accumulation of cytoplasm and DNA. It becomes twice the size of spermatogonia and now are called primary spermatocytes. Maturation phase in which the primary spermatocytes divide by meiosis to form haploid cells. In the first meiotic division, the primary spermatocyte divide to form two haploid secondary spermatocytes followed by the second meiotic division in which each of the secondary spermatocytes divides to form a total of four spermatids. These are haploid cells form the mature spermatozoa by the process of spermiogenesis, during which the organelles of the spermatids move to the certain specific position of the cell and form the mature sperm.