Class 10 Science

How Do Organisms Reproduce

NCERT Exemplar Problems

Long Answer Type Questions

Question: 49. Why are budding, fragmentation and regeneration all 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 gamete formation does not happen during these modes of reproduction and a single parent carries out the process of reproduction.

When the body of planaria is cut off into several part, each part regenerates its complementary part to develop into a new individual.

The following figure shows regeneration in planaria:

Regeneration in Planaria

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: Two points of difference between asexual and sexual reproduction are as follows:

  1. A single parent is involved in asexual reproduction, while two parents are involved in sexual reproduction.
  2. Meiosis does not happen in asexual reproduction, while meiosis happens in sexual reproduction during gamete formation.

Reason of variations in offspring produced by sexual reproduction: Two sets of genes are contributed by different parents, which bring different sets of characters in the offspring.

Q: 51. Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.

Answer: Difference between pollination and fertilization: Transfer of pollen grains from anther to stigma is called pollination. On the other hand, fusion of male and female gametes is called fertilization. Pollination is a physical process in which movement of pollen grains are attained by certain physical factors. Fertilization is a biological process. Ovary is the site of fertilization and embryo is the product of fertilization.

The following figure shows fertilization in plant:

Fertilisation in Flower

Q: 52. Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.

Answer: Gamete is formed as a result of meiosis in gametogenetic cells. Zygote is formed after fusion two different kinds of gametes. Different types of gametes are formed by different parents. Zygote is formed in the female reproductive part only.

Role of gamete in sexual reproduction: Gamete formation results in halving of number of chromosomes which is necessary to maintain the number of chromosomes in an organism which reproduces sexually.

Role of zygote in sexual reproduction: Zygote formation makes the number of chromosome equal to the somatic cells. Further, it is the zygote which undergoes mitosis to develop into an embryo and subsequently into a new individual.

Q: 53. Draw the diagram of a flower and label the four whorls. Write the names of gamete producing organs in the flower.

Answer: The gamete producing organs in the flower are: anther and ovary.

Four Whorls of Flower

Q: 54. What is placenta? Mention its role during pregnancy?

Answer: It is a issue which is attached with the embryo and the uterine wall. It is a disc-like structure which is embedded in the uterine wall. On the embryo’s side of the tissue lie the villi and on the mother’s side lie blood spaces. The blood spaces surround the villi. The placenta works as a channel between the mother and the embryo. Nutrients and oxygen are supplied to the embryo through this. Additionally, excretory products from the embryo are removed through the placenta.

Q: 55. What are various ways to avoid pregnancy? Elaborate any one method.

Answer: There are various methods to avoid pregnancy. The physical barrier methods prevent the entry of sperm into the uterus. The hormonal pills prevent transfer of egg to the uterus. Copper-T is a method which prevents entry of sperms in the fallopian tube and thus prevents fertilization. Surgical methods are permanent methods to stop the chances of pregnancy.

Copper-T: Copper-T is in the shape of ‘T’ and is made of copper. Copper is known to have contraceptive properties. Moreover, copper-T makes a barrier in the at the opening of the fallopian tubes in the uterus and thus prevents sperms from entering the fallopian tubes to prevent fertilization.

Question: 56. How does fertilisation take place? Fertilisation occurs once in a month. Comment.

Answer: During the ovulation cycle; one egg is released by either of the ovaries. The egg reaches the fallopian tube. The sperm enters the vagina during mating. From there, it enters the uterus through cervix and reaches fallopian tube. Numerous sperms reach the fallopian tube but only one sperm is required for fertilization.

Since only one egg is released in a single ovulation cycle and ovulation cycle happens once in a month, so fertilization occurs once in a month.

Question: 57. Describe sexually transmitted diseases and mention the ways to prevent them.

Answer: A disease which can be transmitted through sexual contact is called sexually transmitted disease or STD. Lack of hygiene is usually a major factor in providing conditions for spread of STDs. But unprotected sex with multiple and unknown partners is the biggest reason for the spread of STDs. Some of the ways to prevent STDs are as follows: