Lakhmir Singh & Manjit Kaur: How do Organisms Reproduce?, Solutions- 3 | Science Class 10 PDF Download

Page No - 168

Question 1:
Where are a plant’s sex organs located ?
Solution :
In flowers.

Question 2:
What is the function of a flower ?
Solution :
The function of a flower is to make male and female gametes and to ensure that fertilisation will take place to make new seeds for the reproduction of plant.

Question 3:
What are the reproductive organs in a flower ?
Solution :
Stamen and carpel.

Question 4:
What is the name of :
(a) male part of a flower ?
(b) female part of a flower ?
Solution :
(i) Stamen.
(ii) Carpel.

Question 5:
What is the name of female organ of a flower (other than carpel) ?
Solution :
Pistil.

Question 6:
What is the other name of sex cells ?
Solution :
Gametes.

Question 7:
What is the name of sex cells (other than gametes) ?
Solution :
Germ cells.

Question 8:
Name the male and female gametes in animals.
Solution :
The male gamete in animals is sperm and the female gamete is ovum (egg).

Question 9:
Where is the male gamete formed :
(i) in humans ?
(ii) in flowering plants ?
Solution :
(i) Testes.
(ii) Anther.

Question 10:
Where is the female gamete formed :
(i) in humans ?
(ii) in flowering plants ?
Solution :
(i) Ovary.
(ii) Ovary.

Question 11:
Name two animals which undergo external fertilisation and two animals which undergo internal fertilisation ?
Solution :
(i) External fertilisation: Frog and fish
(ii) Internal fertilisation: Dogs and cows.

Question 12:
Define sexual reproduction.
Solution :
The reproduction which takes place by the combination of special reproductive cells called ‘sex cells’ is called sexual reproduction.

Question 13:
Do all organisms give birth to individuals like humans ?
Solution :
No. All organisms do not give birth to individuals like humans.

Question 14:
Write the full forms of the following as they occur in biology :
(i) STD (ii) AIDS (iii) HIV
Solution :
(i) STD – Sexually Transmitted Diseases. (ii) AIDS – Acquired Immune Deficiency Syndrome. (iii) HIV – Human Immunodeficiency virus.

Question 15:
What is the causative organism for the following diseases ?
(i) Gonorrhoea (ii) Syphilis (iii) AIDS
Solution :
(i) Bacteria.
(ii) Bacteria.
(iii) Virus.

Question 16:
What are the organs in humans which produce the gametes ?
Solution :
Testes in males and ovaries in females.

Question 17:
(a) What are the male sex cells in humans called ?
(b) Name the organ which produces male sex cells.
Solution :
(a) Sperms.
(b) Testes.

Question 18:
(a) What are the female sex cells in humans called ?
(b) Name the organ which produces female sex cells.
Solution :
(a) Eggs.
(b) Ovaries.

Question 19:
Which part of the human body :
(a) produces sperms ?
(b) produces ova ?
(c) passes Sperms from a man to a woman ?
Solution :
(a) Testes.
(b) Ovaries.
(c) Penis.

Question 20:
(a) What do the testes in a man produce ?
(b) What do the ovaries in a woman produce ?
Solution :
(a) Sperms.
(b) Ova (eggs).

Question 21:
(a) Where in the human body does an ovum get fertilised ?
(b) Where does a fertilised ovum develop into a baby in the human body ?
Solution :
(a) Oviduct (fallopian tube).
(b) Uterus (womb).

Question 22:
Name the liquid that contains sperms
Solution :
Semen.

Question 23:
What is the name of the process in which thickened uterus lining alongwith blood vessels is removed from the body of a human female through vaginal bleeding
Solution :
Menstruation.

Question 24:
(a) For how much time does menstruation last in human females (or women) ?
(b) What is the frequency of menstrua] cycle in human females (or women) ?
Solution :
(a) 3 to 5 days.
(b) Once every 28 days.

Question 25:
Fill in the following blanks with suitable words :
(a) Pollen grains contain………… gametes of a plant.
(b) Ovules contain………… gametes of a plant.
(c) The ovary of a flower becomes………… after fertilisation.
(d) The ovule becomes a……. after fertilisation.
(e) Flowering plants reproduce by…………. method of reproduction.
(f) The female organ of reproduction in the flower is the………………
(g) The male organ of reproduction in the flower is the……………….
(h) The name of the structure in the flower in which the male gamete is formed is…………
(i) The………. at the base of the carpel contains egg cells.
(j) The term used to refer to the transfer of pollen from the stamen of one flower to the carpel of another
flower of the same species is………….
(k) The cells involved in sexual reproduction are called……………
(l) Fusion of gametes gives rise to a single cell called …………..
(m) The process of fusion of gametes is called…………
(n) A multicellular animal starts its life from a……….. through sexual reproduction.
(o) The union of a sperm nucleus with an egg nucleus is known as…………… and results in a……………. egg.
(p) The menstrual cycle is controlled by……………..
Solution :
(a) Male.
(b) Female.
(c) Fruit.
(d) Seed.
(e) Sexual.
(f) Carpel.
(g) Stamen.
(h) Anther.
(i) Ovary.
(j) Cross pollination.
(k) Gametes.
(l) Zygote.
(m) Fertilisation.
(n) Single cell (zygote).
(o) Fertilisation; fertilised.
(p) Hormones.

Page No - 169

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.