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Class 10 LAKHMIR SINGH AND MANJIT KAUR Solutions Biology Chapter 3 - How do Organisms Reproduce?

How do Organisms Reproduce? Exercise 141

Solution 1


Solution 2

(a) Sexual reproduction.
(b) Asexual reproduction.

Solution 3


Solution 4

Ferns and mosses.

Solution 5

(a) Sexual reproduction.
(b) Asexual reproduction.

Solution 6

Sexual method.

Solution 7

(a) Dogs and cows.        
(b) Amoeba and Hydra.

Solution 8

Bread mould (Rhizopus fungus).

Solution 9

Binary fission; Asexual method.

Solution 10

(a) Bryophyllum and money plant.    
(b) Bryophyllum and Begonia

Solution 11


Solution 12

(a) Budding and regeneration.        
(b) Multiple fission.

Solution 13


(i) Fragmentation.          

(ii) Binary fission.

Solution 14

(a) Cutting.
(b) Grafting.

Solution 15


Solution 16


Solution 17

Hibiscus and Bougainvillea.

Solution 18

Rose and grapes.

Solution 19

The different methods of asexual reproduction are:
(i) Fission
(ii) Budding.
(iii) Spore formation.
(iv) Regeneration.
(v) Fragmentation.
(vi) Vegetative propagation.

Solution 20

Because all these methods involves a single parent for the production of a new organism, without the involvement of gametes.

Solution 21

(a) Reproduction.

(b) Multiple; Binary.

(c) Cutting.

(d) Tubers.

(e) Layering.

Solution 22


Asexual Reproduction Sexual Reproduction
(i) The offspring arises from a single parent.

(ii) The production of new organism does not involve gametes.

Example:- Amoeba, Yeast.
(i) The offspring arises from two parents of different sexes.

(ii) The production of new organisms involves the use of gametes.

Example:- Fish, Frogs, etc.

(b) (i) Sexual Method: Cats, Humans, birds.

(ii) Asexual method: Amoeba, Hydra.

Solution 25

(a) The process of growing many plants from one plant by man-made methods is called artificial propagation of plants.

(b) The methods used for artificial propagation of plants are:

(i) Cutting (ii) Layering and (iii) Grafting

(c) (i) Rose grows by means of cutting. (ii) Jasmine grows by layering







How do Organisms Reproduce? Exercise 142

Solution 34

(a) Theproduction of new organisms from the existing organisms of the same species is known as reproduction.

(b) The two methods of reproduction in living organisms are asexual reproduction and sexual reproduction.

(c) Amoeba reproduces by binary fission by dividing its body into two parts. When the amoeba cell reaches its maximum size, the nucleus of amoeba lengthens and divides into two parts. After that the cytoplasm of amoeba divides into two parts, one part around each nucleus. In this way one parent amoeba divides to form two smaller amoebae.

(d) Binary fission.

(e) Paramecium and Leishmania.

Solution 35


Fission Fragmentation
(i) It is a process in which an organism splits to form two or more new organisms.

(ii) Fission occurs in unicellular organisms.

Example : Amoeba.
(i) It is a process in which the body breaks up into two or more pieces on maturing, each of which subsequently grows to form a complete new organism.

(ii) It takes place in multicellular organisms.

Example : Spirogyra.

(b) Amoeba reproduces by fission and spirogyra reproduces by fragmentation.

(c) Multiple fission is a process in which a parent organism splits to form many new organisms at the same time. Plasmodium reproduces by multiple fission.

(d) Hydra reproduces by budding. In hydra, first a small outgrowth called bud is formed on the side of its body by repeated mitotic divisions of its cells. This bud then grows gradually to form a small hydra by developing a mouth and tentacles. The tiny new hydra detaches itself from the parent body and develops into a separate organism.

(e) Yeast.

Solution 26

Layering - In this method, a branch of the plant is pulled towards the ground and the part of it is covered with moist soil leaving the tip of the branch exposed above the ground. After some time, new roots develop from the part of the branch buried in the soil. The branch is then cut off from the parent plant. The part of the plant which has developed roots grows to become a new plant. The layering method is used for the propagation of plants like Jasmine, Strawberry, Raspberry, Lemon and Guava.

Solution 27

(a) Fission means the splitting of an organism into two new organisms.


Binary Fission Multiple Fission
(i) In binary fission, the parent organism splits to form two new organisms.

(ii) It occurs during normal conditions.
(i) In multiple fission, the parent organisms splits to form many new organisms.

(ii)It takes place during unfavorable conditions.

(c) Amoeba reproduces by binary fission and Plasmodium reproduces by multiple fission.

(d) Both the above mentioned organisms are animals.

Solution 28

(a) Yes, because it leads to the formation two daughter cells.
(b) The new organisms produced by one parent through asexual reproduction (which are genetically identical to the parent) are called clones. The offspring's formed by asexual reproduction exhibit remarkably similarity because the replication of DNA in the cells is done by certain biochemical reactions which synthesise more of genetic material. When the DNA already present in the nucleus of the parent cell is replicated by making more DNA at the time of asexual reproduction then slight variations come in the two copies formed. Due to this the two DNA molecules formed will be similar but not identical.

Solution 29

(a) Water does not provide any energy to the yeast cells. So, yeast cells fail to multiply in water due to inadequate energy in its cells. Sugar provides energy to them to carry out reproduction by multiplying rapidly.
(b) Moisture is necessary for the growth of bread mould. The moist slice of bread provides both moisture and nutrients due to which bread mould grows profusely. On the other hand, the dry slice of bread provides nutrients but no moisture. So, in the absence of moisture, bread mould does not grow on the dry slice of bread.

Solution 30

(a) A tuber is the thickened, underground stem (or root) of a plant which is swollen with stored food. Stem tuber: Potato; Root tuber: Sweet potato.

(b) Buds.

(c) Potatoes.

Solution 31

(a) Vegetative propagation is an asexual method of reproduction in which new plants are obtained from the parts of old plants (like stems, roots and leaves) without the help of any reproductive organs.
(b) Buds.
(c) The fields have dry stems of the old grass plants all over them. These dry stems have buds which are in the inactive state. By getting rainwater, the buds present on the dry grass stems get activated and grow to produce new grass plants.

Solution 32

(a) Bryophyllum can be reproduced by vegetative propagation by using either a piece of its stem or leaves. The leaves of a Bryophyllum plant have special buds in their margins which may get detached from the leaves, fall to the ground and then grow to produce a new plant.

(b) Money plant can be grown by vegetative propagation by using a piece of its stem which has at least one leaf on it. One end of the stem is dipped in water and after a few days new roots appear at the point where the leaf was attached. This piece of stem grows gradually into a new money plant.

Solution 33

(i) - (j)

(ii) - (g)

(iii) - (f)

(iv) - (k)

(v) - (b)

(vi) - (h)

(vii) - (a)

(viii) - (d)

(ix) - (c)

(x) - (e)

(xi) - (i)

(xii) - (i)

How do Organisms Reproduce? Exercise 143

Solution 36

(a) Spore formation; asexual reproduction.

(b) Yeast is tiny, unicellular non green plant which reproduces by budding.
In yeast, first a bud appears on the outside of the cell wall. The nucleus of the parent yeast cell divides into two parts and one part of the nucleus moves into the bud. Ultimately, the bud separates off from the parent yeast cell and forms a new yeast cell.

(c) Hydra; Budding.

(d) Sponge and corals.

Solution 37

(a) Grafting - It is a method in which the cut stems of two different plants (one with roots and other without roots) are joined together in such a way that the stems join and grow as a single plant.

(b) The cut stem of a plant having roots is called stock and the cut stem of the other plant without roots is called scion.

(c) In grafting, two plants are chosen which are used as scion and stock. First the stem is removed from the plant chosen to be made scion by giving a slanting cut. The scion is placed over the stock and is fitted together by binding tightly by a piece of cloth or plastic sheet. The cut soon heals and the stock and scion of two plants grow together to become one plant.

(d) Banana and pineapple.

(e) Advantages of grafting method:

(i) It enables us to combine the most desirable characteristics of the two plants in its flowers and fruits.

(ii) It can be used to produce varieties of seedless fruits.


Cutting Grafting
(i) A small part of the plant which is removed by making a cut with a sharp knife is called cutting.

(ii) The new plant formed is exactly similar to the parent plant.
(i) It is a method in which the cut stems of two different plants (one with roots and other without roots) are joined together in such a way that the stems join and grow as a single plant.

(ii) The new plant produced has the characteristics of both the parent plants.

Solution 38

(a) The production of new plants from a small piece of plant tissue (or cells) removed from the growing tips of a plant in a suitable growth medium is called tissue culture.

(b) Orchids, dahlia, carnation, chrysanthemum.


(i) The chromosomes in the nucleus of a cell contains information for the inheritance of features from the parents to the next generation in the form of DNA molecules so the characteristics of a parent organism are transmitted to their offsprings.

(ii) When the DNA already present in the nucleus of a parent cell is copied by making more of DNA by certain biochemical reactions, then slight variations come in the two copies formed. Thus, variations are produced in the offspring's during reproduction which form the basis of evolution.

Example: Offspring's produced by asexual reproduction have slight variations from their parents.

(d) The process of reproduction introduces some variations in the individual organisms of a species which enables them to survive even in adverse environmental conditions such as excessive heat or cold, etc. In this way, the introduction of variations during reproduction provides stability to the populations of various species.

(e) Variation is useful for the survival of species even in adverse environmental conditions. This happens as follows: There may be some drastic changes like excessive heat or cold etc in the habitat of a species of organisms. If all the organisms of a population living in that habitat are exactly identical, then there is a danger that all of them may die and no one would survive under these conditions. This will eliminate the species from that habitat completely however, if some variations are present in some individual organisms to tolerate these drastic changes then there is a chance for them to survive and flourish even in adverse environment.

Example: Certain bacteria living in temperate water - If the temperature of water increases too much due to global warming most of them will not be able to tolerate excessive heat and would die however, if there are bacteria with variation then there is a chance for them to survive.

Solution 39

(a) A small part of the plant which is removed by making a cut with a sharp knife is called cutting.

(b) While making a cutting, care should be taken to see that there are some buds on it.

(c) In this method, a cutting of the parent plant having some buds on it is taken and its lower part is buried in the moist soil. After few days, the cutting develops roots and shoot, and grows into a new plant which is exactly similar to the parent plant.

(d) Rose and Bougainvillea

How do Organisms Reproduce? Exercise 168

Solution 1

In flowers.

Solution 2

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.

Solution 3

Stamen and carpel.

Solution 4

(i) Stamen.

(ii) Carpel.

Solution 5


Solution 6


Solution 7

Germ cells.

Solution 8

The male gamete in animals is sperm and the female gamete is ovum (egg).

Solution 9

(i) Testes.
(ii) Anther.

Solution 10

(i) Ovary.
(ii) Ovary.

Solution 11

(i) External fertilisation: Frog and fish
(ii) Internal fertilisation: Dogs and cows.

Solution 12

The reproduction which takes place by the combination of special reproductive cells called 'sex cells' is called sexual reproduction.

Solution 13

No. All organisms do not give birth to individuals like humans.

Solution 14

(i) STD - Sexually Transmitted Diseases.

(ii) AIDS - Acquired Immune Deficiency Syndrome.

(iii) HIV - Human Immunodeficiency virus.

Solution 15

(i) Bacteria.

(ii) Bacteria.

(iii) Virus.

Solution 16

Testes in males and ovaries in females.

Solution 17

(a) Sperms.
(b) Testes.

Solution 18

(a) Eggs.

(b) Ovaries.

Solution 19

(a) Testes.
(b) Ovaries.
(c) Penis.

Solution 20

(a) Sperms.
(b) Ova (eggs).

Solution 21

(a) Oviduct (fallopian tube).
(b) Uterus (womb).

Solution 22


Solution 23


Solution 24

(a) 3 to 5 days.
(b) Once every 28 days.

Solution 25

(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.

How do Organisms Reproduce? Exercise 169

Solution 36

(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.


(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.

Solution 37

(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).

Solution 38

(a) Barrier method - Condom.

(b) Chemical method - Oral pills.

(c) Surgical method - Vasectomy.

Solution 39

(a) Vasectomy.

(b) Tubectomy.

(c) Condom.

(d) Diaphragm.

Solution 26

(a) The cells involved in sexual reproduction are called gametes.

(b) Sexual reproduction.

(c) Zygote is formed when two gametes fuse.

(d) Fertilisation.

Solution 27

(a) (i) Testosterone. (ii) Oestrogen and Progesterone.

(b) Fertilisation.

(c) Placenta.

Solution 28



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

Solution 30

(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.

Solution 31

(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.

Solution 32

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.

Solution 34

(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.

Solution 35

(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.

How do Organisms Reproduce? Exercise 170

Solution 54

(a) The flowers which contain only one sex organ, either stamens or carpels are called unisexual flowers like Papaya and watermelon plants. The flowers which contain both the sex organs i.e. both the stamen and the carpel are called bisexual flowers like Hibiscus and Mustard plant.

(b) The transfer of pollen grains from the anther of a stamen to the stigma of a carpel is called pollination. It takes place when pollen grains are carried from the anther to the stigma of the flower.

(c) When a pollen grain falls on the stigma of the carpel, it bursts open and grows into a pollen tube downwards through the style towards the female gamete in the ovary. A male gamete moves down the pollen tube and enters the ovule in the ovary. The tip of the pollen tube bursts open and male gamete comes out of the pollen tube which combines with the nucleus of the female gamete present in the ovule to form a fertilised egg called zygote.

(d) The fertilised egg divides several times to form an embryo within the ovule which develops a tough coat around it and is gradually converted into a seed. The ovary of the flower develops and becomes a fruit with seeds inside it.

Solution 55


(b) (i) Corolla (ii) Calyx.
(c) (i) Stamen is the male reproductive organ of the plant.
(ii) Carpel is the female reproductive organ of the plant.
(d) Pistil.
(e) Pollen grains.

Solution 40

(a) (i) Vasectomy (ii) Tubectomy.
(b) (i) Condom (ii) Diaphragm.

Solution 41

(a) The prevention of pregnancy in women (by preventing fertilisation) is called contraception. There are 3 methods of contraception: (i) Barrier method (ii) Chemical method (iii) Surgical method.

(b) (i) Vasectomy - In males, a small portion of the sperm duct (Vasdeferens) is removed by surgical operation and both the cut ends are ligated properly. This prevents the sperms from coming out.

(ii) Tubectomy - In females, a small portion of the oviducts is removed by surgical operation and the cut ends are ligated. This prevents the ovum from entering into the oviducts. (c) No.

Solution 42

(a) The diseases which are spread by sexual contact with an infected person are called Sexually Transmitted Diseases.

Example: Aids, Syphilis.

(b) IUCD (Copper - T).

Solution 43

(a) (i) The oral pills contain hormones which stop the ovaries from releasing ovum into the oviduct.

(ii) The vaginal pills contain the chemicals called spermicides which kill the sperm.

(b) Copper- T is effective in preventing pregnancy. It is placed inside the uterus and it prevents the flow of sperms in the uterus.

(c) AIDS.

Solution 44

(a) (i) Vasectomy (ii) Tubectomy.
(b) (i) Cotyledons (ii) Radicle (iii) Plumule.

Solution 45

The offsprings and parents of organisms reproducing sexually have same number of chromosomes due to reduction division (meiosis) during gamete formation which reduces the number of chromosomes into half in both male and female gametes. During fertilisation when male and female gametes fuse the original numbers of chromosomes as in parents is restored in the offspring. 

Solution 46

(a) 24.

(b) 48.

Solution 47

(a) 1:2.


Gamete Zygote
Gamete represents the sex cell or germ cell in sexual reproduction and it is of two types: Male gametes (Sperm) and Female gamete (Eee). It is the product of fertilization in which a male and a female gamete fuse with each other.

Solution 48

(a) Fertilisation in humans can occur only once in a month because ovulation takes place once every month i.e. an egg is released once every month by ovary.

(b) (i) Uterus. (ii) Vagina.

Solution 49

A - Oviduct (Fallopian tube); B - Ovary; C - Uterus (Womb);

D - Vagina.

(a) Part D - (Vagina).

(b) Part B - (Ovary).

(c) Part A - Oviduct.

(d) Part C - Uterus.

Solution 50

The testes are situated in the scrotal sac outside the main body cavity because the formation of sperms requires a lower temperature than the normal body temperature. Its disadvantage of being outside the main body cavity is that it is more prone to injury.

Solution 51

(a) Ovaries in female; Both make gametes.

(b) Oviducts in females; Both transport gametes.

(c) Vagina in female; Both are copulatory organs.

Solution 52

AIDS damages the body's immune system so that the body becomes weak and cannot protect itself against infection thus the virus does not kill the humans directly.

Solution 53

(a) Placenta.

(b) About 9 months.

(c) Cervix.

How do Organisms Reproduce? Exercise 171

Solution 57

(a) The changes observed in girls during puberty are: Hair grows under armpits and pubic region. Mammary glands develop and breasts become enlarged. The hips broaden and extra fat is deposited in various parts of the body like hips and thighs. Fallopian tubes, uterus and vagina enlarge. Ovaries start to release eggs and menstruation starts. Feelings and sexual drives associated with adulthood begin to develop.

(b) Ovaries.

(c) Working of human female reproductive system: The human female reproductive system consists of:

(i) Ovaries - These are the primary reproductive organs in women. They are oval shaped organs which are inside the abdominal cavity of a woman near the kidneys and produces mature female sex cells called ova or eggs. They also produce female sex hormones called Oestrogen and Progesterone. Each ovary is composed of several thousand follicles which mature to form ripe eggs at puberty.

(b) Oviduct - These are paired tubes which have funnel shaped openings that cover the ovaries. The ovum released by an ovary goes into the oviduct through its funnel shaped opening. The fertilisation of egg by a sperm takes place in it. It is also known as fallopian tube.

(c) Uterus - It is a bag like organ in which the fertilised egg develops into a baby. It is connected through a narrow opening called cervix to another tube called vagina. It is commonly called womb.

(d) Vagina - It is a tubular structure. It receives the penis for putting sperms into the women's body. It is also called birth canal because it is the passage through which the baby is born.

Solution 58

(a) The release of an ovum from an ovary is called ovulation. In human females, the ovaries start releasing ovum once every 28 days from the age of puberty.

(b) Oviducts.

(c) Fertilisation is possible if mating takes place during the middle of menstrual cycle because in a normal healthy girl the ovulation takes place on the 14th day of the beginning of menstrual cycle of 28 days.

(d) The embedding of embryo in the thick lining of the uterus is called implantation.

(e) Placenta - Placenta is a disc like special tissue which develops between the uterus wall and the embryo after implantation. Its function is the exchange of nutrients, oxygen and waste products between the embryo and the mother.

(f) Umbilical cord.

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