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NCERT Exemplar · Class 10 Science How do Organisms Reproduce?

58 questions · 58 still being checked

Short Answer Questions 38–48 (part 5 of 6)

  1. Exercise 38

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

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    NCERT’s answer
    In a flower fertilisation requires both male and female gametes. If pollination does not occur, male gamete is not available hence fertilisation cannot take place.
    Fertilisation needs a male gamete to reach the egg cell inside the ovule. Pollen grains germinate only after landing on the stigma, growing a pollen tube through the style down to the micropyle. Without pollination no pollen tube forms, so the male gametes never reach the ovule.Answer: No pollen tube forms without pollination, so the male gamete cannot reach the egg and fertilisation fails.

  2. Exercise 39

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

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    NCERT’s answer
    Yes, the constancy is maintained because cells in all these three structures undergo only mitotic divisions.
    Yes. Fertilisation restores \(\displaystyle 2n\); after that every division is mitosis, so each daughter cell gets the full set. \[n + n \xrightarrow{\text{fertilisation}} 2n_{\text{zygote}} \xrightarrow{\text{mitosis}} 2n_{\text{embryonal cells}} \xrightarrow{\text{mitosis}} 2n_{\text{adult}} \] DNA is copied once before each mitosis, which then splits it equally.Answer: Yes, \(\displaystyle 2n\) stays constant in zygote, embryonal cells and adult because they arise only by mitosis.

  3. Exercise 40

    Where is the zygote located in the flower after fertilization?

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    NCERT’s answer
    Zygote is located inside the ovule which is present in the ovary.
    The zygote lies inside the ovule, in the embryo sac at the micropylar end, within the ovary.Answer: Inside the ovule (in the embryo sac), enclosed in the ovary.

  4. Exercise 41

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

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    NCERT’s 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.
    Reproduction passes copied DNA to the next generation. \[\text{consistent DNA copying} \Rightarrow \text{same body design} \Rightarrow \text{niche still suited} \Rightarrow \text{stable population} \] Only minor variations arise, so offspring keep the design that fits the species' niche.Answer: Consistent DNA copying preserves the body design suited to the niche, so the population stays stable.

  5. Exercise 42

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

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    NCERT’s 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.
    General growth is the increase in height, weight, shape and size of the whole body, in both sexes.Sexual maturation begins at puberty:\[\text{gonads mature} \Rightarrow \text{sex hormones}\uparrow \Rightarrow \text{reproductive organs and secondary sexual characters develop} \]Answer: Growth enlarges the whole body; sexual maturation makes the body capable of reproduction.

  6. Exercise 43

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

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    NCERT’s answer
    Sperm comes out from testis into the vas deferens and then passes through urethra before ejaculation. The secretions of seminal vesicle and prostrate glands provide nutrition to the sperms and also facilitate their transport.
    \[\text{testis} \rightarrow \text{epididymis} \rightarrow \text{vas deferens} \rightarrow \text{ejaculatory duct} \rightarrow \text{urethra} \rightarrow \text{outside} \]Sperm formed in the testis mature and are stored in the epididymis, then pass along the vas deferens. Seminal vesicles add a fructose-rich fluid that nourishes and activates sperm; the prostate gland adds an alkaline fluid that neutralises acidity and raises motility — together with sperm these fluids form semen, expelled through the urethra.Answer: \(\displaystyle \text{testis} \to \text{epididymis} \to \text{vas deferens} \to \text{urethra}\); seminal vesicle nourishes sperm, prostate neutralises acidity — both aid motility.

  7. Exercise 44

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

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    NCERT’s answer
    The thick and spongy lining of the uterus slowly breaks and comes out through the vagina as blood and mucus.
    If fertilisation fails, the corpus luteum degenerates and progesterone falls. The thickened, vascular endometrium built to receive an embryo is no longer supported, so it breaks down and is shed with the unfertilised egg as blood and mucus — menstruation, recurring about every $\displaystyle 28$ days.Answer: The endometrium breaks down and sheds as menstrual blood/mucus (~$\displaystyle 28$-day cycle) once progesterone support is withdrawn.

  8. Exercise 45

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

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    NCERT’s 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.
    After implantation, the endometrium thickens further and turns highly vascular to nourish the embryo. A placenta forms from embryonic and uterine tissue — the site of oxygen, nutrient and waste exchange between mother and foetus — while the uterine wall enlarges and its muscles thicken to accommodate the growing foetus.Answer: Endometrium thickens/vascularises, a placenta forms for maternal–foetal exchange, and the uterine wall enlarges and thickens as pregnancy proceeds.

  9. Exercise 46

    What are the benefits of using mechanical barriers during sexual act?

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    NCERT’s answer
    Mechanical barriers like condom prevents the sperms from reaching the egg. Thus it is an effective method to avoid pregnancy. It also prevents transmission of infections during sexual act.
    \[\text{mechanical barrier} \Rightarrow \text{sperm cannot reach the egg} \Rightarrow \text{no fertilisation, no pregnancy} \]Condoms also block exchange of body fluids, so they protect against sexually transmitted infections.Answer: They prevent pregnancy by keeping sperm away from the egg, and condoms also protect against sexually transmitted infections.

  10. Exercise 47

    In the given Figure 8.3\displaystyle 8.3 label the parts and mention their functions
    (a)
    Production of egg
    (b)
    Site of fertilisation
    (c)
    Site of implantation
    (d)
    Entry of the sperms
    NCERT_Question_Class10_Science_Exemplar_Ch8_Q47

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    NCERT’s answer
    (a)
    Ovary (production of egg)
    (b)
    Oviduct (site of fertilisation)
    (c)
    Uterus (site of implantation)
    (d)
    Vagina (entry of the sperms)
    NCERT_Solution_Class10_Science_Exemplar_Ch8_Q47_ncert
    (a)
    Ovary — paired organs beside the uterus; produce eggs and secrete oestrogen/progesterone.
    (b)
    Fallopian tube (oviduct) — links ovary to uterus; site of fertilisation.
    (c)
    Uterus — central chamber with vascular lining; site of implantation.
    (d)
    Vagina — canal opening to the exterior; entry point for sperms.
    Answer: (a) Ovary (b) Fallopian tube (c) Uterus (d) Vagina.

  11. Exercise 48

    What would be the ratio of chromosome number between an egg and its zygote? How is the sperm genetically different from the egg?

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    NCERT’s answer
    The ratio is $\displaystyle 1$ : 2. Sperms contain either X or Y chromosome whereas an egg will always have an X chromosome.
    \[\text{egg (haploid)}: n = 23, \qquad \text{zygote (diploid)}: 2n = 46 \] \[n : 2n = 23 : 46 = 1 : 2 \] \[\text{sperm}: 22 + X \ \text{or}\ 22 + Y, \qquad \text{egg}: 22 + X \]A sperm carries either X or Y; an egg always carries X.Answer: Egg : zygote = $\displaystyle 1$ : $\displaystyle 2$; a sperm carries X or Y, an egg always carries X.