Solution of How do organisms Reproduce (Page No - 1 69- Biology by Lakhmir Singh, Class 10 | Extra Documents, Videos & Tests for Class 10 PDF Download

Question 26:
(a) What are gametes ?
(b) In which sort of reproduction are gametes involved ?
(c) What is formed when two gametes fuse ?
(d) What is this act of fusion called ?
Solution :
(a) The cells involved in sexual reproduction are called gametes. (b) Sexual reproduction. (c) Zygote is formed when two gametes fuse. (d) Fertilisation.

Question 27:
(a) Write the names of (a) male sex hormone, and (b) female sex hormones.
(b) What name is given to the fusion of sperm and ovum ?
(c) Name the tissue through which the foetus gets all the requirements from the mother’s body.
Solution :
(a)
(i) Testosterone.
(ii) Oestrogen and Progesterone.
(b) Fertilisation.
(c) Placenta.

Question 28:
(a) Draw a neat sketch of the stamen of a flower. Mark in it filament and anther.
(b) Draw a neat sketch of the carpel of a flower. Mark in it stigma, style and ovary.
(c) What is made in (i) anther, and (ii) ovary, of a flower ?
Solution :
(a)

Stamen: Male reproductive organ of a plant

(b)

Carpel: Female reproductive organ of a plant 

(Carpel is also called Pistil)

(c)
(i)Male gametes(insides pollen).
(ii) Female gametes (inside ovum).

Question 29:
(a) Explain the terms ‘self pollination’ and ‘cross-pollination’ ?
(b) How do the insects help in cross-pollination ?
(c) How is the process of pollination different from fertilization ?
Solution :
(a)
(i) Self pollination ? When the pollen grains from the anther of a flower are transferred to the stigma of the same flower (or another flower on the same plant), it is called self pollination.
(ii) When the pollen grains from the anther of a flower on one plant are transferred to the stigma of a flower on another similar plant, it is called cross pollination.
(b) When an insect sits on the flower of a plant for sucking nectar, then the pollen grains from the anther of this flower sticks to its body. And when this insect sits on another flower of another similar plant, then the pollen grains sticking to its body are transferred to the stigma of this second flower. In this way, the insect transfers the pollen grains from the anther of flower in one plant to the stigma of flower in another plant and causes cross pollination.
(c)

Question 30:
(a) Explain the term ‘fertilisation’.
(b) Give some examples of different modes of fertilisation in nature ?
(c) What type of fertilisation takes place in (i) fish, and (ii) birds ?
Solution :
(a) The fusion of male and female gamete to form zygote during sexual reproduction is called fertilisation.
(b) Internal and external fertilisation.
(c)
(i) External fertilisation.
(ii) Internal fertilisation.

Question 31:
(a) What are the male and female gonads in human beings ? Mention their functions.
(b) State the advantages of sexual reproduction over asexual reproduction.
Solution :
(a) In males, the gonads are testes. The function of testes is to make sex cells called sperms and to make sex hormone called testosterone. In females, the gonads are ovaries. The function of the ovaries is to make mature female sex cell called ova or egg and also to make female sex hormones called oestrogen and progesterone.
(b) Advantages of sexual reproduction over asexual reproduction:
(i) Sexual reproduction combines DNA from two individuals (male and female) due to which the offspring has lot of variations. On the other hand, in asexual reproduction, only the DNA of one individual is copied due to which the variations in the offspring are extremely small.
(ii)Due to lot of variations, sexual reproduction allows species to change to more advanced forms from one generation to the next and speed up evolution whereas asexual reproduction does not allow a species to change much from one generation to the next and hence, evolution becomes very slow.

Question 32:
Describe the various steps involved in the sexual reproduction in animals. Draw labelled diagrams to show the fertilisation of an ovum (or egg) by a sperm to form a zygote.
Solution :
The sexual reproduction in animals takes place in the following steps:
(i) The male parent produces male gamete called sperms. The sperm is a small cell with a long tail (flagellum) for movement.
(ii) The female parent produces female gamete called ova which is much bigger cell than the sperm, having a lot of cytoplasm.
(iii) The sperm enters into the ovum and fuses with it to form a new cell called zygote and this process is called fertilisation.
(iv) The zygote then divides again and again to form a large number of cells and ultimately the zygote grows and develops to form a baby.

Fertilisation of an ovum (or egg) by a sperm to form a zygote

Question 33:
Why does menstruation occur ? Describe the menstrual cycle in human females (or women).
Solution :
(a) Since the ovary of female release one egg every month, therefore, the uterus also prepares every month to receive a fertilised egg. The inner lining of the uterus becomes soft and thick with lots of blood capillaries in it. This preparation is necessary as in case the egg is fertilised by the sperm, it helps to keep the egg and nourish it. If however, the egg is not fertilised, then the thick lining of the uterus is not required and the uterus lining breaks down and comes out through the vagina in the form of blood and mucous. This is called menstruation.
(b) Menstruation cycle in females:
(i) When a girl reaches puberty at the age of 10 ? 12 years, the sex hormones released it her blood cause some of the ova in the ovaries to become mature.
(ii) Usually one mature egg is released from the ovary into the oviduct once every 28 days. This is called ovulation.
(iii) Before ovulation, the inner lining of the uterus becomes thick and spongy, and full of blood capillaries, and prepares itself to receive the fertilised egg.
(iv) If the ovum does not get fertilised, then the thick and soft inner lining of the uterus is no longer needed and hence it breaks and the dead ovum comes out from vagina in the form of bleeding called menstruation.
(v) Menstruation usually occurs 14 days after ovulation and usually lasts for 3 to 5 days.
(vi) After menstruation is over, the inner lining of the uterus starts building up again so that it becomes ready to receive the next ovum in case it gets fertilised.
(vii) If the ovum does not get fertilised even now, then the menstruation takes place again and this cycle goes on repeating.

Question 34:
(a) Write the various steps involved in the sexual reproduction in plants.
(b) Name two plants which reproduce by sexual reproduction method and two plants which reproduce by asexual reproduction methods.
Solution :
(a) The sexual reproduction in plants takes place in the following steps:
(i) The male organ of flower called ‘stamen’ makes the male gametes of the flower. These male gametes are present in pollen grains.
(ii) The female organ of a flower called ‘carpel’ makes the female gametes present in the ovules and are called ova or egg.
(iii) The male gametes present in the pollen grains fertilises the female gametes or egg cells present in the ovules.
(iv) The fertilised egg cells grow within ovules and become seeds.
(v) The seeds produce new plants on germination.
(b) Sexual reproduction: Wheat plant and sunflower plant; Asexual reproduction: Ferns and mosses.

Question 35:
(a) What type of plants reproduce by sexual reproduction method ?
(b) What is a seed ? What are the parts of a seed ? Explain with the help of a labelled diagram.
Solution :
(a) Flowering plants.
(b) A seed is the reproductive unit of a plant (which can be used to grow a new plant). Plumule, radical and cotyledon are the parts of seed.

Question 36:
(a) What is puberty ? Who attains puberty at an earlier age in human beings : male or female (boy or girl) ?
(b) Mention two functions each of (i) human testes, and (ii) human ovaries.
Solution :
(a) The age at which the sex hormones begin to be produced and the boy and girl become sexually mature (able to reproduce) is called puberty. Females attain puberty at an age of 10-12 years.
(b)
(i) The function of testes is to make sex cells called sperms and to make sex hormone called testosterone.
(ii) The function of the ovaries is to make mature female sex cell called ova or egg and also to make female sex hormones called oestrogen and progesterone.

Question 37:
(a) What is gestation period ? How much is the gestation period in humans ?
(b) Name one method of contraception which also protects against sexually transmitted diseases.
(c) Name one sexually transmitted disease for which no definite cure has been found so far. What is the causative organism of this disease ?
Solution :
(a) The time period from the fertilisation up to the birth of a baby is called gestation. The average gestation period in humans is about 9 months (about 38 weeks).
(b) Condoms.
(c) AIDS has no cure. Its causative organism is HIV (human Immunodeficiency Virus).

Question 38:
What are the three types of methods used for birth control (or regulating child birth) ? Give one example of each type.
Solution :
(a) Barrier method – Condom.
(b) Chemical method – Oral pills.
(c) Surgical method – Vasectomy.

Question 39:
(a) What is the name of surgical method of birth control in human males in which the sperm ducts are cut and ligated (tied) at both ends ?
(b) What is the name of surgical method of birth control in human females in which the oviducts are cut and ligated (tied) at both ends ?
(c) Name the contraceptive device used by the human males which acts as a sheath over the male organ and traps the sperms in it.
(d) Name the contraceptive device used by human females which is put over the cervix.
Solution :
(a) Vasectomy.
(b) Tubectomy.
(c) Condom.
(d) Diaphragm.