Reproduction

NCERT In Text Questions

Question: 1. What is the importance of DNA copying in reproduction?

Answer: DNA copying is the basic event of reproduction because DNA contains information for inheritance of characters or traits from parents to the next generation. DNA present in the cells undergoing reproduction produces its copy so that the information for the development of characters may pass over to the next generation through dividing cells or gametes.

Question:2.Why is variation beneficial to the species but not necessary for the individual?

Answer: A species comprises a large number of individuals. Each individual may have specific type of variations of different nature. Individually, these variations may not be of much benefit to a particular organism, but when a species faces a drastically altered condition, some of its members may survive because of possessing such variations that enable it to face the new situation. In this way, variations save the species from becoming extinct and promote its survival for a longer time.

Question:4. How will an organism benefit if it reproduces through spores?

Answer: (a) It is a simpler and faster mode of reproduction.

(b) Spores being small and light, get easily dispersed through wind, water and animals. Thus dispersal of the species becomes easier.

(c)Spores bear thick resistant covering to enable them to survive even in unfavourable conditions.

Question: 5. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Answer: Certain specialized cells found in simple organisms have the potential of giving rise to new individuals when they get detached from the parent body. This process is called regeneration. Complex organisms lack such specialized cells, so when a mass of cells in complex from gets detached, it fails to grow into a new individual.

Question: 6. Why is vegetative propagation practiced for growing certain types of plants?

Answer: vegetative propagation practiced for growing certain types of plants for the following reasons:

(a)To preserve characters of the plants through successive generations.

(b)Seedless plants can be grown through vegetative reproduction.

( c) Through cutting and grafting methods, flowers and fruits can be grown in a shorter time.

(d)It is a cheaper, easier and more rapid method of plant propagation.

Question:7. Why is DNA copying is an essential part of the process of reproduction?

Answer: DNA copying is an essential part of the process of reproduction because DNA contain all the information, to be passed over to the next generation for the development of characteristics. During reproduction, new cells are formed and each one of them must receive a copy of DNA so that specific characteristics may develop in the newly formed individuals.

Question: 8. How is the process of pollination different from fertilization?

Pollination is thr process of transfer of pollen grains from the anther of a flower to the stigma of the same flower or another, where fertilization is a post- pollination phase during which fusion of male and female gametes occurs to form zygote.

Question: 9.What is the role of the seminal vesicles and the prostate gland?

Answer: The seminal vesicles in males store sperms and produces a viscous fluid which acts as a medium for sperm motility and stimulates uterine contraction to help the sperms move forward into female tract. Prostate gland secretes a milky fluid which helps in sperm mobility.

Question: 10. What arev the changes seen in girls at the time of puberty?

Answer: Following changes are seen in the girls during puberty.

Enlargement of breast, development of external genitalia, development of pubic hair, deposition of fat on buttocks, thighs and breast, widening of pelvis and beginning of menstruation.

Question: 11. How does the embryo get nourishment inside the mother?s body?

Answer: Human egg practically lacks yolk, hence it cannot provide nourishment to the embryo. After fertilization, the embryo descends into the uterus of the female. A physiological communication between foetus and the inner wall of the uterus of mother is formed, which is called placenta. Throough placenta, nourishment to the embryo is provided from mother?s blood by diffusion across the placenta.

Question: 12. If a woman is using a copper T, will it help in protecting her from sexually transmitted diseases?

Answer: Copper T is an intra uterine device to prevent unwanted pregnancy. It cannot help in protecting a woman from sexually transmitted diseases as, even after introducing copper T, seman, which is the source of transmission of STDs, comes in direct contact with vaginal fluid.

NCERT Exercise Questions and Answer

Question:1. Asexual reproduction takes place through budding in:

(a)Amoeba

(b)yeast

(c ) plasmodium

(d) Leishmania

Answer: (b) yeast

Question:2. Which of the following is not a part of the female reproductive system in human beings?

(a)Ovary

(b)uterus

(c )Vas deferens

(d)fallopian tube

Answer: (c ) Vasdeferens

Question: 3. The anther contains

(a)Sepals

(b)ovules

(c)Carpel

(d)Pollen grains

Question:4. What are the advantages of sexual reproduction over asexual reproductive?

Answer: During the process of sexual reproduction, gametes are formed which involve DNA copying mechanism, crossing over and fusion of gametes from biparental sources. Error in DNA copying mechanism and crossing over produce different forms of variations in different individuals. When the gametes of two individuals with different types of variations combine, they create a new combination of variations. Such variations not only enhance the survival chances for a species but also play an important role in evolution.

During asexual reproduction, variation are not produced; even if they appear, are very slow and occur mainly through mutation, thus are of no use in evolution and survival of species.

Question:5. What are the functions performed by the testes in human beings?

Answer: Testes are the primary sexual organs of males, which perform the following function:

(a)Sperms are fomed inside the seminiferous tubules of tastes.

(b)Leydig cells (interstitial cells) of testes produce the male sex hormone- testosterone.

Testosterone controls the normal growth of genital organs are helps in the development of secondary sexual characters of males.

Question:6. Why does menstruation occur?

The endomerium of uterus of a female becomes ready to receive foetus at an interval of every twenty ? eight days. If fertilization does not occur and an embryo is not formed, endometrium breaks down and bleeding occurs. This process is called menstruation. So, menstruation occurs as a consequence of nnonfertilisation of egg.

Question:7. Draw a labeled diagram of a longitudinal section of a flower.

Answer:

Question:8. What are the different method of contraception?

Answer: The different method of contraception are:

(a) use of condrom in males and diaphragm in females

(b) Use of loop or copper T in females.

(c) Oral contraceptive drugs taken by females.

(d) Surgical method like vasectomy in males and tubectomy in females.

Question:9. How are the males of reproduction different in unicellular and multicellular organism.

Answer: In unicellular organisms, asexual modes of reproductive like fission, fragmentation and sporulaton are the main means of producing new organisms. However some forms exhibit primitive type of sexual reproduction like conjugation in Paramecium and formation of isogametes in polystomella. In multicellular organisms, the primary source of reproduction is through sxual means, although in relatively simpler multicellular forms reproduction occurs by budding, regeneration,spore formation, and vegetative propagation.

Question:10. How does reproduction help in providing stability to populations of species?

Answer: Reproduction is the only means to ensure he continuity of an species, By reproductive, organisms produce large number of new individuals out of which several get perished and only some survive. These surviving organisms replace the naturally dying members of the population. Hence the population as a whole is not affected and remains stable.

Question:11. What are the reasons for adopting contraceptive method?

Answer: Contraceptive methods are adopted:

(a)to avoid unwanted birth.

(b) to regulate the proper spacing between pregnancies.

(c)to keep the population of a country under control.

(d)to maintain a ratio between home economy and size of the family.