CBSE Class 12 Biology Human Reproduction Worksheet Set C

Long Answer Questions

Questions. (i) Draw a sectional view of seminiferous tubule of a human. Label the following cells in the seminiferous tubule:
(a) Cells that divide by mitosis to increase their number.
(b) Cells that undergo Meiosis I.
(c) Cells that undergo Meiosis II.
(d) Cells that help in the process of spermiogenesis.
(ii) Mention the role of Leydig cells.
OR
Draw a labelled sectional view of seminiferous tubule of a human male.
Answer. (i) Refer to Fig. 3.8.
(a) Cells that divide by mitosis to increase their number—Spermatogonia
(b) Cells that undergo Meiosis I—Primary spermatocytes
(c) Cells that undergo Meiosis II—Secondary spermatocytes
(d) Cells that help in the process of spermiogenesis—Sertoli cells
(ii) Role of Leydig cells: They synthesise and secrete testicular hormones called androgens.

Questions. (i) Explain the events taking place at the time of fertilisation of an ovum in a human female.
(ii) Trace the development of the zygote up to its implantation in the uterus.
(iii) Name and draw a labelled sectional view of the embryonic stage that gets implanted
Answer. (i) Fertilisation: Refer to Basic Concepts Point 5.   (Image 111)
(ii) Implantation: Refer to Basic Concepts Point 6.

Questions. (i) Draw a diagrammatic labelled sectional view of a seminiferous tubule of a human.
(ii) Describe in sequence the process of spermatogenesis in humans. 
Answer. (i)

Diagrammatic sectional view of a seminiferous tubule (enlarged)

(ii) Spermatogenesis
• The process of formation of spermatozoa (sperms) from diploid spermatogonia is called spermatogenesis. It occurs in the seminiferous tubules of the testes after attaining puberty.

• It includes the following phases:
(a) Multiplication phase: The male germ cells (spermatogonia) present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers.
(b) Growth phase: Spermatogonia grow and increase in size and form primary spermatocytes. Each spermatogonium is diploid and contains 46 chromosomes.
(c) Maturation phase or formation of spermatids: Some of the spermatogonia called primary spermatocytes periodically undergomeiosis. Aprimaryspermatocyte completes the first meiotic division (reduction division) leading to formation of two equal haploid cells called secondary spermatocytes, which have only 23 chromosomes each. The secondary spermatocytes undergo the second meiotic division to produce four equal haploid spermatids.

Questions. Draw a diagram of the microscopic structure of human sperm. Label the following parts in it and write their functions.
(i) Acrosome (ii) Nucleus (iii) Middle piece 
OR
Draw a diagram of a human sperm. Label only those parts along with their functions, that assist the sperm to reach and gain entry into the female gamete.
OR
Draw a diagram of a mature human sperm. Label any three parts and write their functions.
Ans. For diagram

(i) Acrosome: Contains hydrolytic enzymes that help in dissolving membranes of the ovum for fertilisation.
(ii) Nucleus: Carries genetic material of male.
(iii) Middle piece: Contains a number of mitochondria that provide energy for the movement of  the tail that facilitate sperm motility.

Questions. Study the figure given below:

(i) What is being depicted in the diagram?
(ii) Name ‘a’ and ‘b’ cells. What is the difference between them with reference to the number of chromosomes?
(iii) Pick out and name the motile cells.
(iv) What is ‘f’ cell? Mention its function.
(v) Name the structure of which the given diagram is a part.
Answer. (i) The seminiferous tubule is being depicted in the diagram.
(ii) a—Spermatogonium, b—Primary spermatocyte
They both are diploid and have 46 chromosomes each.
(iii) e—Spermatozoa
(iv) f—Sertoli cell. It provides nutrition to the germ cells.
(v) Seminiferous tubule.

Questions. Name the hormones influencing (i) ovulation, (ii) development of corpus luteum.
Answer. (i) Ovulation: Gonadotropins like luteinising hormone and follicular stimulating hormone, and estrogen.
(ii) Development of corpus luteum: Luteinising hormone and progesterone.

Questions. Draw the following diagrams related to human reproduction and label them.
(i) The zygote after the first cleavage division
(ii) Morula stage
(iii) Blastocyst stage (sectional view)
Answer.

Questions. (a) How is ‘oogenesis’ markedly different from ‘spermatogenesis’ with respect to the growth till puberty in the humans?
Answer. (a) Oogenesis is initiated at the embryonic stage whereas spermatogenesis begins only at puberty.

Questions. Describe the change that occur in ovaries and uterus in human female during the reproductive cycle.
Answer.

Diagrammatic presentation of various events during a menstrual cycle

Questions. Name the stage of human embryo at which it gets implanted. Explain the process of implantation.
OR
Draw a labelled diagram of a human blastocyst. How does it get implanted in the uterus?
Answer.
The human embryo gets implanted at blastocyst stage.
The trophoblast layer of the blastocyst get attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment the uterine cell divides rapidly and covers the blastocyst. As a result the blastocyst becomes embedded in the endometrium of the uterus.

Questions. Name the source of gonadotropins in human females. Explain the changes brought about in the ovary by these hormones during menstrual cycle.
OR
Describe how the changing levels of FSH, LH and progesterone during menstrual cycle induce changes in the ovary and the uterus in human female.
Answer. Gonadotropins (LH and FSH) are secreted by the anterior lobe of pituitary gland.

• Gonadotropins (LH and FSH) increase gradually during the follicular phase (proliferative phase) of menstrual cycle and stimulate follicular development as well as secretion of estrogen by the growing follicles.
• LH and FSH attain a peak level in the middle of the cycle (about 14th day) and rapid secretion of LH induces rupture of Graafian follicle followed by ovulation (release of ovum).
• LH stimulates transformation of Graafian follicle into corpus luteum.

Please click on below link to download CBSE Class 12 Biology Human Reproduction Worksheet Set C