NCERT Exemplar Class 10 Science Solutions

Chapter 08-How do Organisms Reproduce?-Long Answers

Long Answer Type Questions
Q.49. Why budding, fragmentation and regeneration all are considered as asexual types of reproduction? With neat diagrams explain the process of regeneration in Planaria.
Answer. Budding, fragmentation and regeneration are considered as asexual types of reproduction because none of them includes gamete formation and fertilization. All of these give rise to offspring from single parent only.
Regeneration in Planaria It exhibits regeneration i.e. ability to grow the broken body part again. If the body of Planaria is cut into any number of pieces, each piece grows into a complete organism i.e. reproduction through regeneration.
Regeneration is carried out by specialized cells which proliferate and produce large numbers of daughter cells. Different cells from the group of daughter cells then differentiate into various cell types and tissues.


Q.50. Write two points of difference between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction.
Answer.
Difference between asexual and sexual types of reproduction:


Meiosis during gamete formation introduces genetic variations via process of crossing over. Random fusion of male and female gametes during fertilization adds more genetic variations in offspring.

Q.51. Distinguish between pollination and fertilization. Mention the site and product, of fertilization in a flower. Draw a neat, labeled diagram of a pistil showing pollen tube growth and its entry into the ovule.
Answer. Distinguish between Pollination and Fertilization


The site of fertilization in flowers is ovule which in turn is present in ovary. The product of fertilization is a zygote.


Q.52. Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.
Answer. Distinguish between a Gamete and Zygote


Importance of gametes and zygote in sexual reproduction Gametes are product of meiosis and hence carry half the chromosome number as that of parent cells. This chromosome number is restored during fertilization and zygote formation. Hence, gamete and zygote are the two phases of sexually reproducing organisms that help maintain the constant chromosome number in each species.

Q.53. Draw the diagram of a flower and label the four whorls. Write the names of gamete producing organs in the flower.
Anwers. The four whorls of a flower from outside towards inside are
(i) Calyx (whorl of sepals)
(ii) Corolla (whorl of petals)
(iii) Androecium (male reproductive unit)
(iv) Gynoecium (female reproductive unit)


Anther serves as male gamete producing organ while ovary serves as female gamete producing organ in the flower.
Q.54. What is placenta? Mention its role during pregnancy.
Answer.
Followed by fertilization, placenta is developed which serve to provide nutrition and oxygen to developing embryo from the mother’s blood. It is a disc embedded in the uterine wall and contains villi on the embryo’s side of the tissue while blood spaces surrounding the villi are present on mother’s side. The embryo is connected to the placenta by umbilical cord, a tube like structure.
Placenta serves to fulfill all nutritional requirements of developing embryo by supplying food and oxygen from mother’s blood to the embryo. Waste products of developing embryo are removed by transferring them into the mother’s blood through the placenta. Functions of placenta are facilitated by villi that provide large surface areas for passage of nutrition and oxygen to embryo from mother through blood.
Q.55. What are various ways to avoid pregnancy? Elaborate any one method.
Answer. Methods to avoid undesired pregnancy are called contraceptive methods. It includes
(i) Mechanical barrier that prevent arrival of sperm to the egg, e.g., condom.
(ii) Chemical Drugs or contraceptive pills – Small dosage of female hormones that prevent released of egg.
(iii) Loop or copper-T- physical devices to prevent pregnancy.
(iv)Surgical method- permanent contraception by vasectomy and tubectomy.
Surgical methods: Vasectomy refers to surgical method in which vasa deferentia in human males are cut and sealed to prevent pregnancy by making seminal fluid devoid of sperms. Tubectomy refers to surgical process in which oviducts in human females are cut and sealed to prevent pregnancy by inhibiting released of egg.
Q.56. How does fertilization take place? Fertilization occurs once in a month. Comment.
Answer. Fusion of male gamete sperm and female gamete egg in fallopian tube (oviduct) is called as fertilization. The process starts with introduction of sperms, produced in testes of male, into the vagina of the woman through penis during copulation or mating. Highly active and mobile sperms pass from cervix through the uterus into the oviducts. Ovulation, in female, releases ovum in oviduct. Irrespective of release of millions of sperms into the vagina at one time, only one sperm fuses with the ovum in the oviduct to form a zygote i.e. fertilization.
Ovulation is release of ovum from ovary into oviduct and takes place only once in a month i.e. 14th day of menstrual cycle. Hence, fertilization can occur only once in a month.
Q.57. Reproduction is essentially a phenomenon that is not for survival of an individual but for the stability of a species. Justify.
Answer. Each species faces many forces that reduce the number of individuals constantly. Some of them are namely struggle for survival, competition for natural resources, predation, natural cycle of ageing and death, any natural calamity etc. All these natural forces reduce the number of individuals per species.
Reproduction is the process of production of own kind. It includes production of offspring having both similarities and variations among themselves and from parents. Further, the process of DNA replication and its inheritance to offspring ensure production of own kind only. Therefore, reproduction not only restore the number of individuals removed from the species by above mentioned natural forces but also maintain heredity of genetic characters and introduction of variations, as needed for continuity and stability of a species. Without it, all of the existing species will diminish soon and life will come to an end.
Q.58. Describe sexually transmitted diseases and mention the ways to prevent them.
Answer.Sexually Transmitted Diseases are the infectious diseases that are transmitted during unprotected sexual intercourse from infected partner. Example: bacterial infections like gonorrhoea and syphilis, and viral infections like warts and HIV-AIDS. STD caused by bacteria infection (e.g., chlamydia, gonorrhea, and syphilis) are treatable with antibiotics. To prevent STDs, the following precautions can be taken.
(i) Practices involving protected sexual intercourse reduce the risk in STD.
(ii) Avoid multiple sex partners and maintain personal hygiene.