How Do Organisms Reproduce

NCERT Exemplar Problems

Short Answer Type Questions

Part 2

Question 38. Why cannot fertilisation take place in flowers if pollination does not occur?

Answer: For fertilization to occur, it is necessary that the male gamete reaches the female gamete. This can only happen when the pollen grains are transferred to the stigma through any means of pollination. So, fertilization cannot take place in flowers if pollination does not occur.

Question 39. Is the chromosome number of zygote, embryonal cells and adult of a particular organism always constant? How is the constancy maintained in these three stages?

Answer: The answer to the first part of this question is a definite yes. Meiosis is the cell division which happens during gametogenesis, i.e. during gamete formation. This results in number of chromosomes getting halved in gametes. When fertilization happens, the number of chromosomes becomes equal to that in somatic cells. After that, mitosis takes place during rest of the stages of life. And thus, the constancy of chromosomal number is maintained in all the three stages as mentioned in this question.

Question 40. Where is the zygote located in the flower after fertilization?

Answer: After fertilization, zygote is located in the ovary.

Question 41. Reproduction is linked to stability of population of a species. Justify the statement.

Answer: Every species has to constantly struggle for its survival. Natural predators and vagaries of nature keep on removing a large section of the population of a particular species. Moreover, the natural cycle of life and death also removes a section of the population. Reproduction is a way to replenish the lost section of population. Thus, it can be said that reproduction is linked to the stability of population of a species.

Question 42. How are general growth and sexual maturation different from each other?

Answer: General growth and sexual maturation are different from each other in many senses. General growth is all about attaining physical maturity in which the organism undergoes through various stages to become an adult. Once the physical growth is complete, it lays the foundation for sexual maturity. Sexual maturity is related to preparing the body for physical and psychological responsibilities related to reproduction.

Question 43. Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system.

Answer: The path of sperm during ejaculation is as follows:

Vas deferens → Seminal Vesicle → Urethra

Glands associated with the male reproductive system and their functions are as follows:

Testis: Secretes the hormone testosterone.
Prostate gland: Makes the medium of semen alkaline
Seminal vesicle: Adds fluid content to the semen
Cowper’s gland: The secretion of this gland lubricates the urethra before ejaculation and neutralizes the acidic traces of urine in the urethra

Question 44. What changes are observed in the uterus if fertilisation does not occur?

Answer: The uterus prepares during every ovulation cycle in anticipation of a possible pregnancy. The lining of the uterus thickens so that it can give support to the developing embryo. When fertilization does not occur, this lining disintegrates because it is no longer required. The fragments of the lining are shed along with blood and the discarded egg; through the vagina. The discharge of discarded tissues is called menstrual flow and the process is called menstruation.

Question 45. What changes are observed in the uterus subsequent to implantation of young embryo?

Answer: Once the zygote is implanted in the uterine wall, several changes take place in the uterus. The uterine lining thickens so that it can give support to the growing embryo. It is richly supplied with blood so that it can provide nourishment to the embryo.

Question 46. What are the benefits of using mechanical barriers during sexual act?

Answer: Mechanical barriers during sexual act provide two benefits. The first benefit is avoidance of unwanted pregnancy and the second benefit is prevention of sexually transmitted diseases.

Question 47. In the given figure, label the parts and mention their functions

Production of egg
Site of fertilization
Site of implantation
Entry of the sperms

Answer:

Question 48. What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg?

Answer: The ratio of chromosome number between and egg and its zygote is 1 : 2. Sperm and eggs are genetically different in terms of the nature of the 23rd chromosome. The 23rd chromosome is a Y chromosome in sperm, while it is an X chromosome in egg.