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NCERT Class 10 Science How do Organisms Reproduce?: Exercise Solutions

Step-by-step working for every question of End-of-chapter exercises in NCERT's Class 10 Science book, chapter “How do Organisms Reproduce?”, written by Shishya. Each question is in our own short words; open the NCERT chapter for the exact wording and figures.

1. Exercises Q1

   Budding is the mode of asexual reproduction in (a) Amoeba (b) yeast (c) Plasmodium (d) Leishmania.

   1. Budding is a type of asexual reproduction where a small outgrowth, called a bud, forms on the parent body.
   2. This bud grows in size and eventually detaches to become a new, independent organism.
   3. Among the given options, yeast is a unicellular fungus that reproduces asexually through budding.
   4. Amoeba reproduces by binary fission, while Plasmodium and Leishmania reproduce by multiple fission or other methods, not budding.

   Answer: (b) yeast

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2. Exercises Q2

   Which is not part of the human female reproductive system: (a) ovary (b) uterus (c) vas deferens (d) fallopian tube?

   1. The ovary is a female organ that produces eggs and hormones.
   2. The uterus is the female organ where the embryo develops.
   3. The fallopian tube is the female duct where fertilization usually occurs.
   4. The vas deferens is a male duct that carries sperm from the testes to the urethra.
   5. Therefore, the vas deferens is not part of the human female reproductive system.

   Answer: (c) vas deferens

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3. Exercises Q3

   The anther contains (a) sepals (b) ovules (c) pistil (d) pollen grains.

   1. The anther is the male reproductive part of a flower that produces gametes.
   2. Inside the anther, microspores develop into mature male gametes.
   3. These male gametes are enclosed within pollen grains.
   4. Therefore, the anther contains pollen grains.

   Answer: (d) pollen grains

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4. Exercises Q4

   What are the advantages of sexual reproduction over asexual reproduction?

   1. Sexual reproduction involves the fusion of gametes from two parents, which introduces genetic variation in the offspring.
   2. This genetic variation allows the population to adapt to changing environmental conditions more effectively.
   3. Offspring produced through sexual reproduction are generally better equipped to survive in diverse or unpredictable habitats.
   4. Asexual reproduction produces genetically identical clones, which can be a disadvantage if the environment changes or if a disease targets that specific genetic makeup.
   5. Therefore, sexual reproduction increases the chances of survival and evolution for the species over time.

   Answer: Sexual reproduction provides genetic variation, leading to better adaptation and survival in changing environments compared to asexual reproduction.

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5. Exercises Q5

   What do the testes do in human beings?

   1. The testes are the primary male reproductive organs located in the scrotum.
   2. They produce millions of sperm cells every month through the process of spermatogenesis.
   3. They also secrete the male sex hormone testosterone.
   4. Testosterone is responsible for the development of male secondary sexual characteristics during puberty.
   5. It also maintains the production of sperm throughout adult life.

   Answer: The testes produce sperm cells and secrete the hormone testosterone.

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6. Exercises Q6

   Why does menstruation occur?

   1. Every month the ovary releases an egg, and the lining of the uterus thickens and gets a rich blood supply to nourish an embryo if the egg is fertilised.
   2. If the egg is not fertilised, this thick lining is not needed.
   3. So the lining slowly breaks down.
   4. The broken-down lining, along with blood and mucus, is shed through the vagina.
   5. This monthly shedding of the uterine lining is called menstruation.

   Answer: Menstruation occurs when the egg is not fertilised: the thickened, blood-rich lining of the uterus is not needed, so it breaks down and comes out through the vagina as blood and mucus, about once a month.

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7. Exercises Q7

   Describe a labelled longitudinal section of a flower.

   1. Draw a vertical cut through the centre of a flower to show its internal structure.
   2. Label the outermost whorl of sepals as the Calyx, which protects the flower bud.
   3. Label the next whorl of coloured petals as the Corolla, which attracts pollinators.
   4. Label the stamens, which consist of a filament and an anther that produces pollen.
   5. Label the pistil or carpel, which is the female reproductive part of the flower.
   6. Label the stigma at the top of the pistil, which receives pollen grains.
   7. Label the style, the tube connecting the stigma to the ovary.
   8. Label the ovary at the base of the pistil, which contains the ovules.
   9. Label the ovules inside the ovary, which develop into seeds after fertilization.

   Answer: A labelled longitudinal section of a flower shows the calyx, corolla, stamens (filament and anther), and pistil (stigma, style, ovary, and ovules).

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8. Exercises Q8

   What are the different methods of contraception?

   1. Contraceptive methods are techniques used to prevent pregnancy by stopping the meeting of sperm and egg or preventing implantation.
   2. Barrier methods like condoms and diaphragms physically block the passage of sperm into the female reproductive tract.
   3. Hormonal methods such as oral pills, injections, and implants use synthetic hormones to suppress ovulation or alter the uterine lining.
   4. Intrauterine devices (IUDs) are inserted into the uterus to prevent implantation of the fertilized egg and may release copper or hormones.
   5. Surgical methods like vasectomy in males and tubectomy in females permanently cut or block the tubes that carry gametes.

   Answer: Barrier (mechanical) methods such as condoms; hormonal methods such as oral pills that change the hormone balance so eggs are not released; devices such as the copper-T placed in the uterus; and surgical methods (vasectomy in males, tubectomy in females) that block the tubes carrying sperm or eggs.

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9. Exercises Q9

   How do modes of reproduction differ in unicellular and multicellular organisms?

   1. Unicellular organisms reproduce by simple cell division where one cell splits into two new cells.
   2. Multicellular organisms reproduce through complex processes involving specialized reproductive organs.
   3. In unicellular organisms, the entire body participates in reproduction as there is no division of labor.
   4. In multicellular organisms, only specific cells or organs are dedicated to the reproductive function.
   5. Unicellular reproduction is generally faster and simpler, often occurring through binary fission or budding.
   6. Multicellular reproduction involves growth, development, and often the fusion of gametes from two parents.
   7. Thus, the main difference lies in the complexity of the process and the involvement of specialized structures.

   Answer: Unicellular organisms reproduce by simple cell division, while multicellular organisms use complex processes involving specialized organs and often gamete fusion.

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10. Exercises Q10

    How does reproduction help keep populations of a species stable?

    1. Reproduction creates new individuals that replace those that die or leave the population.
    2. It maintains the genetic continuity of the species by passing on hereditary material.
    3. By balancing the number of births against deaths, it prevents the population from declining to zero.
    4. This process ensures the species continues to exist and its population size remains relatively constant over time.

    Answer: Reproduction helps keep populations stable by replacing lost individuals and maintaining the species' genetic line, preventing extinction.

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11. Exercises Q11

    What could be the reasons for using contraceptive methods?

    1. Contraceptive methods are used to prevent pregnancy by stopping the meeting of sperm and egg.
    2. They help in controlling the birth rate and spacing between children.
    3. They allow couples to plan their family size according to their needs and resources.
    4. They can also help in preventing certain sexually transmitted diseases if barrier methods are used.

    Answer: Contraceptive methods are used to prevent pregnancy, control birth rate, space children, and plan family size.

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