NCERT Class X Science Class: Chapter –8. How Do Organisms Reproduce? – Part-7

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Question 37:

In tobacco plant, the male gametes have twenty four chromosomes.

  • What is the number of chromosomes in the female gamete?

  • What is the number of chromosomes in the zygote?

Answer:

  • Number of chromosomes in female gamete is 24

  • Number of chromosomes in zygote is 48

Question 38:

Why cannot fertilization take place in flowers if pollination does not occur?

Answer:

In a flower fertilization requires both male and female gametes. If pollination does not occur, male gamete is not available hence, fertilization cannot take place.

Question 39:

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

Answer:

Yes, the constancy is maintained because cells in all these three structures undergo only mitotic divisions.

Question 40:

Where is the zygote located in the flower after fertilization?

Answer:

Zygote is located inside the ovule which is present in the ovary.

Image Zygote

Image Zygote

Image Zygote

Question 41:

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

Answer:

In reproduction, DNA passes from one generation to the next. Copying of a DNA takes place with consistency but with minor variations. This consistency leads to stability of species.

Question 42:

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

Answer:

General growth refers to different types of developmental process in the body like increase in height, weight gain, changes in shape and size of the body but sexual maturation is specific to changes reflected at puberty like cracking of voice, new hair patterns, development of breast in female etc.

Image general growth of female

Image General Growth of Female

Image general growth of female

Question 43:

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

Answer:

Sperm comes out from testis into the vas deferens and then passes through urethra before ejaculation. The secretions of seminal vesicle and prostate glands provide nutrition to the sperms and also facilitate their transport.

Question 44:

What changes are observed in the uterus if fertilization does not occur?

Answer:

The thick and spongy lining of the uterus slowly breaks and comes out through the vagina as blood and mucus.

Question 45:

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

Answer:

The uterine wall thickens that is richly supplied with blood. A special tissue called placenta develops which connects embryo to the uterine wall that provides nutrients and oxygen to it.