During the reproductive cycle of a human female, when, where and how does a placenta develop? What is the function of placenta during pregnancy and embryo development?
During the reproductive cycle of human female, placenta develops after the implantation of zygote in the uterus.
After implantation, finger like projection called chorionic villi appear on the trophoblast. The chorionic villi are surrounded by uterine tissues and maternal blood. It is this chorionic villi and the uterine tissue which interdigitate with each other and jointly form a structural and functional unit between developing embryo and maternal body called placenta.
The functions of placenta are as follows:
1) Nutrition: It helps to transport nutrients from mother's blood to foetus for its development.
2) Respiration: It provides oxygen to the foetus and removes CO2 from the foetus.
3) Excretion: It helps in the removal of waste products from the foetus.
4) Immunity: It provides immunity to the foetus. Antibodies developed in mother's blood passes onto the foetus through the placenta.
5) Storage: It stores some fats, glycogen and iron.
6) Secretion of hormones: It secretes many hormones like oestrogen, progesterone, gonadotropin and placental lactogen that support the growth of the foetus.
How does the megaspore mother cell develop into 7-celled, 8 nucleate embryo sac in an angiosperm? Draw a labeled diagram of a mature embryo sac.
The nucleus of the functional megaspore mother cell divides mitotically to form two nuclei which move to the opposite poles, forming the 2-nucleate embryo sac. Subsequent mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages.
of the embryo sac. These mitotic divisions are strictly free nuclear in nature, that is, nuclear divisions are not followed immediately by cell wall formation. Among the eight nuclei, six are enclosed by cell walls and organised into cells, while the remaining two nuclei (called polar nuclei) are situated above the egg apparatus in a large central cell. Out of the six cells, three are grouped at the micropylar end, and constitute the egg apparatus out of which two are synergids and one egg cell. The other three cells are located at the chalazal end, and are called antipodals. All this leads to the organisation of the typical female gametophyte or embryo sac which is 8-nucleated and 7-celled.
The following is the illustration of the sequence of ovarian events (a to i) in a human female.
i) Identify the figure that illustrates ovulation and mention the stage of oogenesis it represents.
(ii) Name the ovarian hormone and the pituitary hormone that have caused the above mentioned event.
(iii) Explain the changes that occur in the uterus simultaneously in anticipation.
(iv) Write the difference between c and h.
(v) Draw a labeled sketch of the structure of a human ovum prior to fertilization.
(i) Figure 'f' illustrates ovulation. It represents the ovulatory stage of oogenesis.
(ii) The changes that cause ovulation are because of the change in level of the pituitary and ovarian hormones. The pituitary secrets two hormones called Follicle stimulating hormone (FSH) and Luteinizing hormone (LH). Estrogen is the ovarian hormone released during ovulation. The FSH and LH stimulate follicular development and secretion of estrogen from the primary follicles, the rapid secretion of LH induces graffian follicles to release and release ovum.
(iii) In anticipation of receiving the fertilised egg the primary follicles in the ovary grow to become graffian follicles and simultaneously the endometrium of the uterus regenerates and through proliferation and the blood supply is increased.
(iv) In the figure, (c) stage represents the secondary follicle and the (h) stage represents the degenerating corpus luteum.
|
Secondary follicle |
Corpus luteum |
|
1.It is found in the menstrual stage |
1.It is found in the luteal stage. |
|
2.It is Surrounded by layers of granulosa cells |
2.Layers of granulosa cells are absent |
|
3.Theca layer is present. |
3.No theca layer is present |
(a) Draw a diagrammatic sectional view of the female reproductive system of human and label the parts:
(i) where the secondary oocytes develop
(ii) which helps in collection of ovum after ovulation
(iii) where fertilization occurs
(iv) where implantation of embryo occurs.
(b) Explain the role of pituitary and the ovarian hormones in menstrual cycle in human females.(a) View of the female reproductive system of human
(b) Changes happening in ovary and uterus during menstrual cycle are caused by change in the levels of pituitary and ovarian hormones.
After menstrual phase gonadotropin i.e., Luteinising hormone (LH) and follicular stimulating hormone (FSH) are released from pituitary. Their level gradually increases during follicular phase and it stimulates development of follicles and secretion of estrogen by growing follicles.
Both LH and FSH attain peak on 13th & 14th day.
Rapid secretion LH causes ovulation on day 14.
During luteal phases Graafian follicle changes to corpus luteum which secretes Progesterone Progesterone maintains endometrium which is necessary for implantation.
(a) Name the technology that has helped scientists to propagate on a large scale the desired crops in a short duration. List the steps carried out to propagate the crops by the said technique.
(b) How are somatic hybrids obtained?
(a) Tissue culture is the technique that has helped scientists propagate the desired crops on a large scale in a short duration. The following steps are carried out to propagate crops by tissue culture:
i) Tissue culture is the process of developing a complete plant from a part of a plant. The plant part is called an explant.
ii) Explants can be grown in sterile conditions in special nutrient media to regenerate complete plants.
iii) Nutrient media contain a carbon source (such as sucrose), organic salts, vitamins, amino acids and phytohormones.
iv) Hence, propagation is achieved for a large number of plants in a short duration. This process is called micro propagation.
v) All the plants obtained by tissue culture are called somaclones since they are genetically identical to each other as well as the parent plant.
(b) Somatic hybrids are obtained by the method of somatic hybridisation. In this method, the somatic parts of two plants are hybridised. Protoplasts are isolated and fused to get a hybrid protoplast that grows further to form a new plant. For example, protoplasts of potato and tomato have been actually fused to form a pomato. But this plant is not commercially viable, as it does not have all the desired combination of characteristics for its commercial utilization
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