Home » Lakhmir Singh Class 10 Biology » Lakhmir Singh Class X Biology Chapter 6 – How do Organisms Reproduce

Lakhmir Singh Class X Biology Chapter 6 – How do Organisms Reproduce


Exercise : Solution of Questions on page Number : 141


Answer: 1
The process of reproduction ensures that a plant or animal species does not disappear from Earth.


Answer: 2
(a) Sexual reproduction
(b) Asexual reproduction


Answer: 3
True. Bread moulds are fungi. Bread moulds reproduce by spores that can be considered as their seeds.
Note: According to Whittaker’s system of classification, bread mould is placed in a different kingdom named fungi and not in the kingdom plantae. However, if we compare bread mould with plants then we can compare their spores with seeds of plants.


Answer: 4
Bryophyllum and potato can reproduce asexually through vegetative reproduction.


Answer: 5
(a) Sexual reproduction involves gametes.
(b) Asexual reproduction does not involve gametes.


Answer: 6
Human beings reproduce sexually.


Answer: 7
(a) Two animals which reproduce sexually are cow and lion.
(b) Two animals which reproduce asexually are Planaria and Hydra.


Answer: 8
Fungi reproduce through spore formation; for e.g., bread moulds.


Answer: 9
Paramecium reproduces by the method of fission. It is a method of asexual reproduction.


Answer: 10
(a) Grass and money plant can be grown from their broken stems.
(b) Bryophyllum and Begonia can be grown from their leaves.


Answer: 11
Yeast reproduces by the method of budding.


Answer: 12
(a) Hydra reproduces by regeneration and budding.
(b) Plasmodium reproduces by multiple fission.


Answer: 13
(i) Spirogyra reproduces by fragmentation.
(ii) Leishmania reproduces by binary fission.


Answer: 14
(a) Rose plant is artificially propagated through the method of cutting.
(b) Apple tree is artificially propagated through the method of grafting.


Answer: 15
Layering is the artificial propagation method used for producing jasmine plants.


Answer: 16
Strawberry plants are propagated by layering.


Answer: 17
Jasmine and strawberry plants are propagated by layering.


Answer: 18
Rose and grapes plants are propagated by the cutting method.


Answer: 19

The different methods of asexual reproduction are:

  • Fission
  • Budding
  • Spore formation
  • Regeneration
  • Fragmentation, and
  • Vegetative reproduction

Answer: 20
Budding, fragmentation and regeneration are considered to be the different types of asexual reproduction, as these methods need only one parent and no gamete formation.


Answer: 21
(a) The process of reproduction ensures continuity of life on Earth.
(b) Plasmodium reproduces by the process of multiple fission, whereas Paramecium reproduces by the process of binary fission.
(c) Rose plants and sugarcane are usually propagated by the cutting method.
(d) Vegetative reproduction of a potato plant is done by using its tuber.
(e) Strawberry plants are propagated by the natural layering method.


Answer: 22
(a)

Sexual Reproduction  Asexual Reproduction
 Requires two parents  Requires only one parent
 Gamete is formed  Gamete formation not required

(b) Amoeba and Hydra reproduce asexually.
Cats, humans and birds reproduce sexually.


Answer: 23
(a) Regeneration is the process in which an organism can produce new organisms from their damaged or lost body parts. Hydra and Planaria can regenerate fully from their lost body parts.
(b) In complex multicellular organisms, the specialised cells form tissues, tissues form organs and organs coordinate to form a system. Due to this high degree of specialisation, multicellular organisms cannot reproduce by regeneration.


Answer: 24
The process in which new plants are grown from the old parts of another plant like roots, shoots and leaves, without involving any reproductive organ, is termed as vegetative propagation. For example, guava trees can be propagated using their roots, and Bryophyllum can be propagated by using its leaves.
The advantages of vegetative propagation are as follows:

  • The plants cultivated are genetically identical to their parents.
  • Plants can be cultivated faster as compared to growing them from their seeds.

Answer: 25
(a) Artificial propagation refers to the man-made method of obtaining several plants from one plant.
(b) Three common methods of artificial propagation are cutting, layering and grafting.
(c) Rose is grown by the cutting method, and apple is grown by the grafting method.


Exercise : Solution of Questions on page Number : 142


Answer: 26

In the layering method, one of the branches of a plant is pulled down into the ground and covered with moist soil in such a way that the tip of the branch remains above the surface. After a few days, new roots start growing from the part buried in the soil. This part of the branch is then separated from the parent plant to let it develop into a new plant.
Plants which can be propagated by the layering method are jasmine, lemon, guava, strawberry, raspberry, etc.


Answer: 27
(a) Fission is the process of asexual reproduction in which a unicellular organism divides to form two daughter cells.
(b) In binary fission, the parental cell divides into two daughter cells. In multiple fission, the parent organism keeps on dividing for innumerable times giving rise to many offsprings.
(c) Amoeba reproduces by binary fission and Plasmodium by multiple fission.
(d) Organisms named above are protozoa; thus, they are animal-like.


Answer: 28
(a) In unicellular organisms, cell division can be considered as reproduction, as it produces two independent daughter cells identical to their parent. This process is termed as fission.
(b) Genetically identical organisms are called clones. Asexual reproduction involves only one parent; therefore, the resulting offspring will not only have same genes but will also be similar to each other.


Answer: 29
(a) Since yeast is a non-green plant, it cannot make its own food. Thus, they don’t get the energy to reproduce. However, in a sugar solution it grows well, as sugar acts as a good source of energy.
(b) A moist slice of a bread provides all the favourable conditions needed by the spores of the bread mould to germinate. This is the reason why bread mould cannot grow profusely on a dry slice of a bread.


Answer: 30
(a) The thickened and swollen stem or root of a plant that stores food and is present underground is called a tuber. For example, potato is a stem tuber and sweet potato is a root tuber.
(b) The bud or eye is the organ of propagation present in a tuber.
(c) Potato is propagated through its tuber.


Answer: 31
(a) Vegetative propagation is the process of growing new plants from the parts of an old plant without involving any reproductive organ.
(b) This something is any of the plant parts like roots, stems or leaves.
(c) After it rains, the inactive buds in the dried shoots of a grass plant, lying all over the ground, become active and give rise to new plants. This is the reason why green grass plants start growing on dry fields on their own after a spell of shower.


Answer: 32
(a) In Bryophyllum, the buds are present on the leaf margins. These buds have the potential of vegetative reproduction. When these buds get detached from the leaves and fall on ground, they grow into new plants. In cases where the buds don’t detach from the leaves, plantlets start forming over the later.

(b) Money plant can be grown by the vegetative propagation of its stem. Cut a piece from its stem, comprising at least one leaf, and dip it into water. After a few days, roots will grow from the point of attachment of the leaf, and the stem will start developing into a new plant.


Answer: 33

ColumnI                                       Column II
(i) Plasmodium                    (j) Multiple fission
(ii) Spirogyra                       (g) Fragmentation
(iii) Jasmine                         (f) Layering
(iv) Apple tree                     (k) Grafting
(v) Bryophyllum                  (b) Leaves
(vi) Potatoes                         (h) Tubers
(vii) Rhizopus                      (a) Spore formation
(viii) Hydra                          (d) Budding
(ix) Planaria                          (c) Regeneration
(x) Leishmania                      (e) Binary fission
(xi) Sugar cane                      (i) Cutting
(xii) Rose                               (i) Cutting


Answer: 34
(a) Reproduction is the process of producing new organisms from the existing ones.
(b) Two general methods of reproduction are asexual and sexual.
(c) The cell of an Amoeba after attaining its maximum size starts dividing. The nucleus of the cell divides first, followed by the cytoplasm. Thus, a single cell divides into two identical cells.

(d) Amoeba reproduces by binary fission.
(e) Leishmania and Paramecium reproduce by this method of binary fission.


Answer: 35
(a)

                Fission                 Fragmentation
Fission occurs in unicellular organisms. Fragmentation occurs in multicellular organisms.

(b) Amoeba reproduces by binary fission and Spirogyra reproduces by fragmentation.
(c) In multiple fission, the parent cell repeatedly divides to form innumerable organisms at the same time. Plasmodium reproduces by this method.
(d) Hydra reproduces by the method of budding. A small outgrowth called bud is formed on one side of its body by repetitive mitotic division. This bud gradually grows into a full hydra, developing its mouth and tentacles. The new Hydra detaches itself from its parent and start living as a separate organism.

(e) Yeast reproduces by the same method as Hydra, i.e. budding.


Exercise : Solution of Questions on page Number : 143


Answer: 36
(a) The bread mould reproduces by spore formation. It is an asexual mode of reproduction.
(b) Yeast is a non-green plant (fungus). It reproduces by budding. In yeast, a bud first appears outside its cell wall. Immediately the parent nucleus divides itself into two in such a way that one of its parts moves into the bud. Then the bud detaches itself from the parent cell to form a new yeast cell.
Figure: Reproduction in yeast

(c) Hydra reproduces by the same method as yeast, i.e. budding.
(d) Sponges and corals are the two marine animals that reproduce by the same method as yeast; however, they form colonies.


Answer: 37
(a) Grafting is a method of artificial propagation in which the stem of two plants are cut, one with and the other without roots. These stems are then joined together to form a single plant.
(b) The lower portion of the graft, i.e. the stem with roots is termed as a stock. The upper portion of the graft, i.e. the stem without roots is termed as a scion.
(c) In grafting, two plants of the desired traits are chosen. First the plant that is chosen as a scion is cut in slantingly, then the stock is also cut in the same manner. After that, the scion is placed over the stock and tightly fitted together. Either they are tied by a piece of cloth or covered using a polythene sheet.

(d) Apple and orange trees are propagated by the method of grafting.
(e) The first advantage of this method of propagation is that plants with desired characteristics are obtained. Also, with this method, young stems can be made to flower and bear fruits quickly.
(f) In the cutting method, only one plant is involved, and the new plant is identical to its parent. Whereas in grafting, two plants are involved, and the new plant is completely different from its parents.


Answer: 38
(a) Tissue culture is the process of propagating new plants from a small piece of a plant’s tissue that is obtained from the growing tip of that plant in a suitable growth medium.
(b) Orchids, Dahlia, carnation and Chrysanthemum are propagated by the method of tissue culture.
(c) DNA copying refers to the replication of DNA at the time of cell division. It plays a very important role in giving rise to slight variations in offsprings in comparison to the parents particularly in asexual reproduction where only single parent is involved.
Example: When a cell divides, the DNA of the cell gets replicated first so that the daughter cells get equal amount of DNA from the parent. DNA replication occurs through biochemical process which is not accurate. Hence, variations are introduced in the DNA during replication. When the cell divides, the daughter cells acquire a slightly different DNA to that of the parent. Therefore, the DNA of the daughter cell is similar to that of the parent but not identical.
(d) Reproduction ensures that new offsprings are produced continuously to replace the dying individuals of the population. Thus, it ensures continuity of life and provides stability to the population.
(e) Variation during reproduction ensures that a species can survive and flourish even in adverse conditions. Thus, it is beneficial to the species but not necessary for the individual.


Answer: 39
(a) Cutting is a method of vegetative propagation of plants. It is a means of asexual reproduction.
(b) Proper care should be taken while cutting a stem, for this purpose, so as to ensure that the stem has a few buds on it.
(c) In the cutting method, a part of the stem comprising buds on it is cut from the plant using a sharp knife. This stem is then buried in a suitable medium. After some days, the stem develops roots and starts growing into a new plant.

(d) Rose and sugarcane are propagated by the cutting method.


Answer: 40
(c) a method of producing genetically identical offsprings
Asexual reproduction involves only one parent; therefore, the offsprings are genetically identical.


Answer: 41
(b) Plasmodium
It reproduces by multiple fission.


Answer: 42
(c) malaria
Plasmodium reproduces by multiple fission and causes malaria.


Answer: 43

(d) Leishmania
Leishmania is the protozoan that has flagellum at its one end.


Answer: 44
(b) (i), (iii) and (iv)
Banana, yeast and Amoeba reproduce asexually. Banana reproduces by vegetative propagation, yeast propagates by the method of budding and Amoeba propagates by binary fission.


Answer: 45
(d) Planaria
It reproduces by regeneration.


Answer: 46
(c) Leishmania
It is a protozoan which causes kala-azar.


Answer: 47
(d) continue the species forever
Reproduction provides the means of producing new offsprings, so that a species can continue surviving on earth forever.


Answer: 48
(d) Yeast
Yeast is the unicellular organism which reproduces by budding.


Answer: 49
(d) Hydra
Hydra is a multicellular organism. It reproduces by budding.


Exercise : Solution of Questions on page Number : 144


Answer: 50
(d) (i) and (iv)
The offsprings formed by the method of asexual reproduction have greater similarity among themselves. This is because asexual reproduction involves only one parent and does not require gametes.


Answer: 51
(c) Budding
Hydra is a simple multicellular animal that has tentacles and lives in freshwater. It reproduces by budding.


Answer: 52
(c) Yeast fungus
Yeast reproduces by budding.


Answer: 53
(a) (i) and (iii)
The factors responsible for the rapid spreading of bread mould on slices of bread are the presence of a large number spores in air and the presence of moisture and nutrients in bread that act as food for the fungi.


Answer: 54
(a) Fern
Fern is a non-flowering plant which reproduces by forming spores.


Answer: 55
(d) (ii) and (iv)
Yeast, Hydra, corals and sponges reproduce by budding.


Answer: 56
(d) they reproduce asexually
Amoeba, yeast and bacterium are unicellular organism that reproduce asexually.


Answer: 57
(c) Planaria
It reproduces by regeneration.


Answer: 58
(d) Yeast
Yeast is a fungus and is considered as a non green plant. It reproduces by budding.


Answer: 59
(c) Hydra
It is a multicellular organism that reproduces by budding.


Answer: 60
(b) breaking up of filaments into smaller bits
In Spirogyra, reproduction takes place by fragmentation that involves breaking down the filaments into smaller bits.


Answer: 61
(d) multiple fission
The ability of a cell to divide itself into several cells during reproduction is called multiple fission.


Answer: 62
(d) hyphae
Hyphae are the fine thread-like structures of the fungi that are spread on the whole surface of a slice of bread.


Answer: 63
(b) stems, roots and leaves
Plants can reproduce through their stems (like grass), roots (like guava) and leaves (like Bryophyllum).


Answer: 64
(d) Hydra and Planaria
Hydra and Planaria reproduce through regeneration. They can regenerate fully from their cut body parts.


Answer: 65
(c) Corals and sponges
In corals and sponges, the buds remain attached to their parents permanently, and form colonies.


Answer: 66
(c) fungi
Fungi reproduce asexually through the formation of spores.


Exercise : Solution of Questions on page Number : 145


Answer: 67
(d) Spirogyra
It reproduces by the method of fragmentation in which the filament is broken down into small pieces.


Answer: 68
(c) seas anemone and Spirogyra
They reproduce asexually by the method of fragmentation.


Answer: 69
(b) two daughters
In binary fission, a single-celled organism divides into two daughter cells that are identical to their parent.


Answer: 70
(c) scion
Scion is the upper part of the graft, which does not have roots.


Answer: 71
(a) stock
Stock is the lower part of the graft, which is fixed to the ground and has roots.


Answer: 72
(d) malaria parasite
Plasmodium, which causes malaria, reproduces by ​multiple fission.


Answer: 73
(c) Leishmania
Leishmania, which has a flagellum or whip-like structure at one end, reproduces by binary fission.


Answer: 74
(d) Hydra
Hydra is a tiny animal that has tentacles on one end, and reproduces by the method of budding.


Answer: 75
(c) Hydra
Hydra can reproduce by the method of budding similar to yeast, and also by regeneration as in the case of Planaria.


Answer: 76
(c) grafting
Stock and scion are the two parts of a graft.


Answer: 77
(c) clones
The genetically identical offsprings formed by asexual reproduction are called clones.


Answer: 78
(a) micropropagation
Micropropagation is a tissue culture method of asexual reproduction in plants, which forms callus.


Answer: 79
(d) P, Q, R and S
In Planaria, each body piece can regenerate into a full, new organism.


Answer: 80
(a) The organism A is Leishmania, B is Plasmodium, C is Amoeba and D is Paramecium.
(b) One body feature of organism A is that it has a whip-like structure called flagellum at one end.
(c) Female Anopheles mosquito carries the organism B and transmits it from one person to another.
(d) (i) Organism A reproduces by binary fission.
(ii) Organism B reproduces by multiple fission.
(e) Organisms C and D are found in ponds.


Answer: 81
(a) The organism X is yeast and organism Y is Hydra.
(b) The process by which the organism X converts sugar into alcohol is fermentation.
(c) Organism X is a fungus; hence, it belongs to the category of non-green plants.
(d) Organism Y is a multicellular organism and comprises tentacles at one end.
(e) Organism X is unicellular, and the organism Y is multicellular.


Exercise : Solution of Questions on page Number : 146


Answer: 82
(a) The common name of the organism is bread mould, and its scientific name is Rhizopus.
(b) Spores of fungus are present in the air in their inactive form. When these spores get the favourable condition like a moist bread, they germinate and grow into new organisms.
(c) The fine, thread-like projections on the surface of the bread are known as hyphae.
(d) The knob-like structures are sporangium, which contain the spores.
(e) This method of reproduction is known as spore formation.
(f) Mucor fungus reproduces by the method of spore formation.
(g) Ferns and mosses are two non-flowering plants which reproduce by this method.


Answer: 83
(a) The shapeless lump of mass X is known as callus.
(b) This method of producing new plants is known as tissue culture.
(c) The jelly is called agar.
(d) The chemicals used to stimulate the growth of plant cells and fasten the development of roots and shoots are called plant hormones.
(e) Orchids and dahlia are two flowering plants that are propagated by this method.
(f) The main advantage of this technique is that it is extremely fast, and the plantlets are obtained in a few weeks. Secondly, this method produces disease-free plantlets.
(g) The other name of this technique is micropropagation.


Answer: 84
(a) This method of propagating plants or trees is known as grafting.
(b) The segregated stem of tree X is termed as stock.
(c) The segregated stem of tree Y that is devoid of roots is termed as scion.
(d) The layer Z is called the cambium layer.
(e) The cambium layer of both the stems should be joined, as they are responsible for the growth of a new tree.
(f) Four trees which are propagated by this method are apple, pineapple, orange and grapes.
(g) The main advantage of cultivating plants in this method is that the graft will have the most desirable features of both the parts, i.e. the stock and the scion.


Answer: 85
(a) This method of propagating plant is known as cutting.
(b) While removing a small part of the shoot from the parent plant using a knife, one has to be careful about the fact that the shoot has some buds on it.
(c) Sugarcane and banana are those two plants which are propagated by this method, and are consumed as food.
(d) Using this method, many new plants can be produced from one plant. This is one of the advantages of this method.
(e) This is an asexual method of reproduction, as it involves only one parent and no gamete formation.
(f) The genetically identical plants produced by this method are called clones.


Answer: 86
(a) This method of propagating plants is known as layering.
(b) To get propagated by this method, a plant should have soft horizontal branches.
(c) Jasmine and China rose are the two plants that are propagated by this method for their flowers.
(d) Guava and lemon are the two plants that are propagated by this method for their fruits.
(e) Strawberry gets propagated naturally by this method by forming runners.


Exercise : Solution of Questions on page Number : 147


Answer: 87
(a) The worm X is Planaria.
(b) The organism Y which posses the same characteristic as of X is Hydra.
(c) The process in which a complete organism is formed from a lost body part of its parent is regeneration.
(d) X and Y are multicellular organisms.
(e) A dog cannot be produced from a lost body part like its tail, as this animal has a high degree of organisation in its body.


Answer: 88
(a) Tuber is the general name of those underground stems like X.
(b) Potato is an example of X.
(c) The points Y present on X are known as buds.
(d) No, it is not necessary to plant the entire stem X in the ground. This stem has many buds (Y) on it that form the vegetative organ of reproduction.
(e) This method of reproduction is termed as vegetative propagation.
(f) The main advantage of this method is that it is comparatively faster to growing plants from seeds.


Answer: 89
(a) The alga X is likely to be Spirogyra.
(b) The alga is green in colour.
(c) This mode of forming new alga from the breaking-up of the parent alga is termed as fragmentation.
(d) The splitting of Amoeba is termed as fission, which occurs only in unicellular organisms. The splitting of alga is termed as fragmentation, which occurs only in multicellular organisms.
(e) Sea anemone reproduces in the same way as the alga X.


Answer: 90
(a) The plant X is Bryophyllum.
(b) The entities, Y, present on the leaves of X are known as buds.
(c) Other than X, Begonia can also be reproduced by its leaves.
(d) Money plant can be propagated from its broken stem similar to plant X.
(e) Buds are present in the dry stems of the old grass lying in the fields. These buds get activated after a spell of shower, and start producing new grasses.


Exercise : Solution of Questions on page Number : 168


Answer: 1
A plant’s sex organs are located in its flower.


Answer: 2
The function of a flower is to carry out sexual reproduction in plants through the formation of male and female gametes. Flowers ensure that the gametes fertilise to form seeds that further help in reproducing plants.


Answer: 3
Stamen and carpel are the reproductive organs of a flower.


Answer: 4
(a) The male part of a flower is called stamen.
(b) The female part of a flower is called carpel.


Answer: 5
Pistil is the other name of the female organ of a flower.


Answer: 6
The other name of sex cells is gametes.


Answer: 7
The male sex cells are called sperms and the female reproductive cells are called eggs.


Answer: 8
The male gametes are called sperms and the female gametes are called ovum or eggs.


Answer: 9
(i) In humans, the male gametes are formed in the testes.
(ii) In flowering plants, the male gametes are formed in the anther of the stamen.


Answer: 10
(i) In humans, the female gametes form in the ovaries.
(ii) In flowering plants, the female gametes form in the ovary of the pistil.


Answer: 11
Fish and frog undergo external fertilisation.
Human and lion undergo internal fertilisation.


Answer: 12
The method of reproduction in which the male sex cell fuses with the female reproductive cell is termed as sexual reproduction.


Answer: 13
No, all organisms don’t give birth to humans. For example, a hen lays eggs.


Answer: 14
(i) STD: Sexually Transmitted Diseases
(ii) AIDS: Acquired Immunodeficiency Syndrome
(iii) HIV: Human Immunodeficiency Virus


Answer: 15
(i) Gonorrhoea is caused by bacteria.
(ii) Syphilis is caused by bacteria.
(iii) AIDS is caused by virus.


Answer: 16
In males, testes produce male gametes called sperms; and in females, ovary produces female gametes called eggs.


Answer: 17
(a) The male sex cells in humans are called sperms.
(b) Testes produce male sex cells.


Answer: 18
(a) The female sex cells in humans are called ova or eggs.
(b) Ovary produces the female sex cells.


Answer: 19
(a) Testes produce sperms in the human body.
(b) Ovary produces ova.
(c) The penis passes the sperms from a man to a woman.


Answer: 20
(a) The testes of a man produce male gametes called sperms.
(b) The ovary of a woman produces female gametes called eggs or ova.


Answer: 21
(a) The ovum gets fertilised in the oviduct of a female body.
(b) In the uterus, a fertilised ovum develops into a baby.


Answer: 22
The seminal fluid or semen contains sperms.


Answer: 23
Menstruation is the periodic process in which the thickened uterus lining, along with blood vessels, is removed from the body of a female through vaginal bleeding.


Answer: 24
(a) The menstruation cycle lasts for 3-5 days in a female.
(b) The frequency of the menstrual cycle is once after every 28 days.


Answer: 25
(a) Pollen grains contain male gametes of a plant.
(b) Ovules contain female gametes of a plant.
(c) The ovary of a flower becomes a fruit after fertilisation.
(d) The ovule becomes a seed after fertilisation.
(e) Flowering plants reproduce by the sexual method of reproduction.
(f) The female reproductive organ of a flower is carpel.
(g) The male sex organ of a flower is stamen.
(h) The structure of a flower in which the male gamete is formed is pollen.
(i) The ovary 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 pollination.
(k) The cells involved in sexual reproduction are called gametes.
(l) Fusion of gametes gives rise to a single cell called zygote.
(m) The process of fusion of gametes is called fertilisation.
(n) A multicellular animal starts its life from a zygote in sexual reproduction.
(o) The union of a sperm nucleus with an egg nucleus is known as fertilisation and it results in a diploid egg.
(p) The menstrual cycle is controlled by hormones.


Exercise : Solution of Questions on page Number : 169


Answer: 26
(a) The sex cells or reproductive cells are called gametes.
(b) Gametes are involved in sexual reproduction.
(c) Two gametes fuse to form a zygote.
(d) The act of fusion of gametes is called fertilisation.


Answer: 27
(a) (a) Testosterone is the male sex hormone.
(b) Oestrogen is the female sex hormone.
(b) The fusion of sperm and ovum is termed as fertilisation.
(c) A foetus gets all its requirement from the mother’s body through the tissue called placenta.


Answer: 28
(a) Stamen of a flower

(b) Carpel of the flower

(c) (i) Male gametes called pollen grains are produced in the anther.
(ii) Female gametes called eggs are produced in the ovary.


Answer: 29
(a) In self pollination, pollens from the anther are transferred to the stigma of the same flower or another flower of the same plant.
In cross pollination, pollens from the anther of one flower are transferred to the stigma of the another flower of another plant but of the same species.
(b) When an insect sits on a flower, the pollens from the anther stick to their wings. The same insect when sits on another flower, the pollens from its wings stick to the stigma of that flower thereby affecting pollination.
(c) Pollination is the transfer of male gametes onto the female gametes, while fertilisation is the fusion of these two gametes.


Answer: 30
(a) Fertilisation is the fusion or union of male and female gametes to form a zygote.
(b) There are two modes of fertilisation, i.e., external fertilisation as seen in case of fishes and frogs, and internal fertilisation that happens in humans, dogs, etc.
(c) (i) In fish, external fertilisation takes place.
(ii) In birds, internal fertilisation takes place.


Answer: 31
(a) The male gonads are the testes and they produce sperms. The female gonad is the ovary and it produces eggs or ova.
(b) In sexual reproduction, there is a variation in the offsprings produced, which is impossible in case of asexual reproduction, as in the latter process, offsprings produced are identical to their parent.


Answer: 32
The various steps involved in the sexual reproduction in animals are as follows:
Male gametes called sperms are produced by the male parent.
Female gametes called eggs are produced by the female parent.
The sperm fuses with the egg to form zygote. This process is termed as fertilisation.
The zygote divides repeatedly to form a large number of cells. Ultimately it grows and develops into a baby.


Answer: 33
Menstruation occurs due to the rupture or removal of the inner, thick and soft lining of the uterus when fertilisation does not take place.
The menstrual cycle of a female is as follows:
After a female attains puberty, every month one of the ova of the ovary matures and gets released once in every 28 days by the process of ovulation.
The lining of the uterus becomes thick and spongy before ovulation in order to receive the fertilised egg. If the egg is not fertilised, this lining of the uterus breaks and comes out of the vagina in the form of blood known as menstrual flow.
This occurs on the 14th day of ovulation and lasts for 3-5 days.
After this flow stops, the uterus starts preparing itself again for the fertilised egg. If it does not receive the fertilised egg, the same set of events are repeated.


Answer: 34
(a) The various steps involved in the sexual reproduction in plants are as follows:
Male and female gametes are formed in the anther and the ovule respectively.
Male gametes fertilise female gametes present in the ovules.
The fertilised eggs grow and develop into seeds.
These seeds germinate under favourable conditions to form plants.
(b) Sexual reproduction takes place in mango and rose plants. Ferns and mosses propagate by asexual reproduction.


Answer: 35
(a) The plants with flowers i.e. flowering plants, reproduce by sexual reproduction.
(b) Seed is the reproductive unit of a plant. The various parts of a seed are plumule, radicle and cotyledon.


Answer: 36
(a) Puberty is the age at which males and females attain sexual maturity. In human beings, females attain puberty earlier than males.
(b) (i) Testes produce male gametes (sperms) and the hormone testosterone, responsible for secondary sexual changes in males.
(ii) Ovaries produce female gametes (ova or egg) and the hormone oestrogen, responsible for secondary sexual changes in females.


Answer: 37
(a) The period of pregnancy is called the gestation period. It is of 9 months in humans.
(b) A barrier method of contraception (e.g., condom) also protects us from sexually transmitted diseases.
(c) AIDS is a sexually transmitted disease for which no definite cure has been found so far. HIV is the causative organism of this disease.


Answer: 38
The three types of methods used for birth control are:
Barrier method, e.g., condom
Chemical method, e.g., oral pills
Surgical method, e.g., vasectomy


Answer: 39
(a) The surgical method of birth control in human males in which the sperm ducts are cut and ligated (tied) at both ends is called vasectomy.
(b) The surgical method of birth control in human females in which the oviducts are cut and ligated (tied) at both ends is called tubectomy.
(c) The contraceptive device used by human males which acts as a sheath over the male organ and traps the sperms in it is called a condom.
(d) The contraceptive device used by human females which is put over the cervix is known as copper T.


Exercise : Solution of Questions on page Number : 170


Answer: 40
(a) (i) The surgical method of birth control for men is called vasectomy in which a small portion of the vas deferens is cut and their ends are sealed to prevent sperms from coming out.
(ii) The surgical method of birth control for women is called tubectomy in which a portion of oviducts are cut and their ends are ligated to prevent the release of eggs.
(b) The two devices used in the barrier method of birth control are condoms and diaphragms.


Answer: 41
(a) Contraception is defined as the prevention of pregnancy in females by preventing fertilisation. The barrier method, chemical method and surgical method are some of the methods of contraception.
(b) (i) The surgical method of birth control for men is called vasectomy, in which a small portion of the vas deferens is cut and their ends are sealed to prevent sperms from coming out.
(ii) The surgical method of birth control for women is called tubectomy, in which a portion of the oviducts are cut and their ends are ligated to prevent the release of eggs.
(c) No, using copper-T will not protect a woman from sexually transmitted diseases (STDs).


Answer: 42
(a) The disease which is caused by sexual contact with an infected person is termed as a sexually transmitted disease. Examples: AIDS and syphilis.
(b) IUCD such as copper-T prevents fertilised egg from being implanted into the uterus.


Answer: 43
(a) (i) Oral pills have hormones that stop the ovaries from releasing ovum.
(ii) Vaginal pills have spermicides which kill the sperms.
(b) Copper-T prevents the implantation of fertilised egg in the uterus and, thus, prevents pregnancy.

(c) AIDS is caused by HIV.


Answer: 44
(a) The surgical method for birth control (or preventing pregnancy) which is carried out (i) in men is known as vasectomy and (ii) in women is known as tubectomy.
(b) The part of the seed which (i) contains stored food is called cotyledon, (ii) grows into roots is called radicle and (iii) grows into shoot is called plumule.


Answer: 45
Gametes of sexually-reproducing animals have half the number of chromosomes as that of the parents. Thus, during fertilisation, when two gametes i.e. male and female gametes, fuse, the offspring produced will have the same amount of DNA or the same number of chromosomes as that of the parent.


Answer: 46
(i) The number of chromosomes in a female gamete is equal to the number of chromosomes in a male gamete, i.e., 24.
(ii) The zygote is formed by the fusion of a male and a female gamete. Therefore, the number of chromosomes in a zygote is twice as many as that of a gamete, i.e., 48.


Answer: 47
(a) The ratio of chromosome numbers between an egg and its zygote is 1 : 2. The number of chromosomes in a zygote is two times the number of chromosomes in an egg.
(b)

        Gamete          Zygote
A gamete is a sex cell and is of two types: male and female. A zygote is formed by the fusion of a male and a female gamete.
It has 24 chromosomes. It has 48 chromosomes.

Answer: 48
(a) A human female produces one egg a month through the process of ovulation therefore, fertilisation can occur once in a month.
(b) The scientific name of (i) womb is uterus and (ii) birth canal is vagina.


Answer: 49
Part A is the oviduct; B is the ovary; C is the uterus and D is the vagina.
(a) Sperms enter through the vagina (D).
(b) The ovary (B) releases the eggs.
(c) Fertilisation takes place in the oviduct (A).
(d) The foetus develops in the uterus (C).


Answer: 50
The formation of sperm requires a temperature lower than that of the body. Therefore, the testes are situated in the scrotal sac outside the main body cavity providing them a lower temperature.
Their position outside the main body cavity makes the testes prone to injury.


Answer: 51
(a) The ovary. Both make gametes.
(b) The fallopian tubes. Both act as ducts for carrying and transporting gametes.
(c) The Vagina. The penis discharge sperms and the vagina receives it.


Answer: 52
HIV affects the immune system of a person who has AIDS. This weakens the body making it unable to fight any infection. Therefore, people who die from AIDS are not killed by the virus itself but by other infections.


Answer: 53
(a) The placenta is the life support system of a foetus.
(b) A human baby takes 9 months to develop before birth.
(c) The cervix is the narrow opening between the uterus and the vagina.


Answer: 54
(a) Unisexual flowers have only one kind of sex organ, either stamen or pistil, e.g., flowers of papaya and water melon. Bisexual flowers have both stamen and pistil, e.g., flowers of Hibiscus and mustard.
(b) Pollination is the transfer of pollen grains from the stamen to the stigma of the pistil. Pollination occurs when pollen grains are carried from the anther to the stigma by insects, birds, wind or water.
(c) Fertilisation occurs after pollen grains fall on the stigma. Upon falling on the stigma, the pollen grains burst and grow a pollen tube taht passes downwards from the style to the ovary containing the ovule. The male gamete present in the pollen moves downward through the pollen tube and reaches the ovule. This gamete fuses with the egg to form a zygote. This process is known as fertilisation.

(d) After fertilisation, the eggs in the ovule grow and develop into seeds. The ovule develops a thick coating and forms the seed, whereas the ovary develops into a fruit that contains the seed.


Answer: 55
(a) A flower

(b) (i) The corolla
(ii) The calyx
(c) (i) Stamen is the male reproductive organ in a flower.
(ii) Carpel is the female reproductive organ in a flower.
(d) The other name of carpel is pistil.
(e) The yellow powdery substance present in the anther of a flower are pollen grains.


Exercise : Solution of Questions on page Number : 171


Answer: 56
(a) Boys at puberty develop hair in their armpits, chest, face and around the pubic region. They become muscular and their voices crack. Penis and testes become large. The testes begins producing sperms.
(b) Testes produce sperms in human males.
(c) Testes are the primary reproductive organs of human males. They are located in the scrotum outside the body. They produce sperms, which engage into a coiled tube called epididymis and get stored there. Sperms are then carried away through the vas deferens, which joins the urethra. On way to the urethra, sperms also receive secretions from the seminal vesicles and the prostrate gland. The urethra carries sperms to the penis, which opens outside the body.

(d) The seminal vesicles and the prostrate gland produce seminal fluid, which then gets mixed with sperms to form semen.


Answer: 57
(a) Girls at puberty develop hair in their armpits and around the pubic region. The mammary glands develop and become large. The hips get broadened and extra fat gets deposited on various parts of the body. The ovaries start releasing eggs; the vagina enlarges and menstruation starts.
(b) Ovaries in humans produce ova, which are also known as egg cells.
(c) Ovaries are the primary reproductive organs in females, which produce ovum or egg. Above the ovary lies the oviducts, or fallopian tubes, which are connected to the uterus. The eggs move into the oviduct from the ovaries, where it gets fertilised by a sperm. The fertilised ovum develops into a baby in the uterus. The uterus is connected to the vagina by the cervix. The vagina opens outside the body and receives sperms.

(d) In humans, fertilisation is internal. Sperms are introduced in the vagina by the penis during copulation. The sperms move up through the cervix, enter the uterus and pass into the oviducts. In the oviducts, the egg gets fertilised by one of the sperms. Zygote is formed by the fusion of a sperm and an egg. This zygote divides multiple times to form a hollow ball of the cells called embryo.


Answer: 58
(a) Ovulation is the release of an ovum from the ovary. It happens once in 28 days in human females.
(b) Fertilisation takes place in fallopian tubes, or oviducts, in human females.
(c) Fertilisation is possible if mating takes place during the middle of the menstrual cycle because at that time, ovulation occurs and the egg is released.
(d) Implantation is the embedding of the embryo in the thick lining of the uterus.
(e) Placenta is a disc-like tissue that develops between the uterus wall and the embryo. It helps the embryo in meeting its requirements from the mother.
(f) The umbilical cord connects the embryo with the placenta in the mother’s body.


Answer: 59
(d) pollen grains
An anther contains male gametes called pollen grains.


Answer: 60
(c) vas deferens
The vas deferens is a part of the male reproductive system in humans.


Answer: 61
(b) Oviduct
The oviduct is a part of the female reproductive system in humans.


Answer: 62
(b) Hepatitis
Hepatitis is not a sexually transmitted disease.


Answer: 63
(c) Condom
Condom acts as a physical barrier during intercourse and protects a person from acquiring any sexually transmitted disease.


Answer: 64
(b) Tubectomy
The surgical method of birth control in females is termed as tubectomy.


Answer: 65
(b) Vasectomy
Vasectomy is a surgical method of contraception that stops the sperms from reaching the ovum and thus, prevents pregnancy.


Answer: 66
(a) a zygote
A zygote is formed by the fertilisation of the egg and a sperm cell.


Answer: 67
(b) conveys nutrients and wastes to and from the embryo, respectively.
The exchange of nutrients, oxygen and waste products between the embryo and the mother’s body takes place through the umbilical cord.


Answer: 68
(c) Gonorrhoea
Gonorrhoea is caused by bacteria, which spreads through sexual contact.


Answer: 69
(d) a virus
AIDS is caused by HIV.


Exercise : Solution of Questions on page Number : 172


Answer: 70
(c) production of a large number of gametes is unnecessary.
In internal fertilisation, there is no need for the production of a large number of gametes as it provides a safe environment.


Answer: 71
(d) Y makes sperms and V makes seminal fluid
Y represents the testes that produce sperms and V represents the prostrate gland that produces seminal fluid.


Answer: 72
(c) anther and ovary
The anther produces pollen grains which are male gametes and the ovary produces ovules which are female gametes.


Answer: 73
(c) pollination, fertilisation, embryo, seed
The pollens are transferred to the stigma by pollination, the gametes then fuse and under go fertilisation to form the zygote which develops into an embryo and, then, into a seed.


Answer: 74
(d) genes
Genes carry the genetic information and are responsible for the transmission of characteristics from parents to offspring.


Answer: 75
(c) both similarities and variations with parents
Offsprings produced by sexual reproduction show similarities as well as variations with parents.


Answer: 76
b) halving of chromosomes during gamete formation
The gametes have half the number of chromosomes. After their fusion, the zygote thus formed has a full set of chromosomes. Therefore, the numbers of chromosomes in parents and offsprings of a particular species remain constant.


Answer: 77
(b) pollen grains on upper surface of stigma and ovule.
Pollen grains land on the surface of the stigma. Hence, the pollen tube is formed so that the pollens can reach the ovules present in the ovary.


Answer: 78
(d) (ii) and (iv)
Plants have sexual reproductive organs such as stamen and pistil. A fruit is formed after fertilisation in plants.


Answer: 79
(a) testis → vas deferens → urethra
Sperms are produced in the testis and then carried away by the vas deferens to the urethra.


Answer: 80
(b) formation of sperms
The testes lie outside the body in the scrotum because sperm production requires low temperature, which is provided by the scrotum.


Answer: 81
(d) (iii) and (iv)
The development of the placenta and the secretion of oestrogen is done by human female body organs.


Exercise : Solution of Questions on page Number : 173


Answer: 82
(c) cracking of voice
Cracking of voice in males is brought about by the male hormone testosterone, which is produced after sexual maturation.


Answer: 83
(d) menstruation
When a female starts to menstruate, it indicates that she is sexually mature and can start her reproductive life.


Answer: 84
(c) genetic material comes from two parents of the same species
The sexual reproduction involves two parents of the same species. Thus, both of them contribute to the genetic material of the offspring and bring about the variations.


Answer: 85
(c) Ovary
The ovary of a flower has ovules and the ovary of a human female has eggs.


Answer: 86
(b) (ii), (iii) and (iv)
Unisexual flowers have either male or female sexual organ. Therefore, they cannot self-pollinate and, thus, show cross pollination. The ovary of the female organ develops into a fruit after fertilisation, therefore flowers having stamens cannot produce fruits.


Answer: 87
(c) (i), (ii) and (iii)
Sexual reproduction in flowers requires two types of gametes, namely pollen grains and ovules. The fusion of the gametes results in the formation of the zygote. This process is termed as fertilisation.


Answer: 88
(b) fertilisation
Fertilisation is the fusion of two gametes in a sexual reproduction. It produces genetically different offsprings and does not lead to the formation of clones.


Answer: 89
(c) plumule, cotyledon and radicle
A represents the plumule which forms the shoot. B represents the cotyledon and C represents the radicle which forms the roots.


Answer: 90
(a) gametes, zygote, embryo, seed
Gametes of flowers fuse to form a zygote. This zygote develops into an embryo that later forms the seed.


Answer: 91
(d) radicle
The radicle of a seed forms the root after germination.


Answer: 92
(d) anther and testes
In flowers, the anther produces pollen grains. In humans, the testes produces sperms.


Answer: 93
(a) 2 : 1
The number of chromosomes in a human sperm is half the number of chromosomes in a zygote, i.e., their ratio is 2 : 1.


Answer: 94
(b) 14
A germ cell has 14 pairs of chromosomes i.e. half the number of chromosomes present in the normal body cell of an organism.


Answer: 95
(a) A represents the carpel. The carpel is composed of the stigma, style and ovary.
(b) The ovary contains gametes in the form of ovules.
(c) B represents the stamen. The swollen tip of the stamen is the anther.
(d) The anther has pollen grains.
(e) The stamen (B) is a male part and the carpel (A) is a female part.


Exercise : Solution of Questions on page Number : 174


Answer: 96
(a) A represents pollen grains. The process of transferring pollen grains from one flower to another flower of the similar plant by insects is known as cross pollination.
(b) B represents the pollen tube.
(c) C is the male gamete which moves down through the pollen tube (B).
(d) D is the female gamete (or egg). The structure E represents the ovule.
(e) F is the zygote.


Answer: 97
(a) The process is termed as (i) menstruation scientifically and (ii) periods in everyday language.
(b) The approximate age for a girl to undergo her first period is between 10 and 12 years. A human female usually attains puberty or sexual maturity at this stage.
(c) This process is repeated after every 28 days and usually lasts for 3 to 5 days.
(d) The onset of this process signifies sexual maturity in human females.
(e) During pregnancy, this process stops temporarily but starts again eventually.
(f) At the age of about 45–50, this process stops permanently.


Answer: 98
(a) (i) The organ A is the ovary and (ii) the gamete B is an egg.
(b) The tube-like structure C is the oviduct or the fallopian tube.
(c) (i) D represents the testes and (ii) the gamete E represents sperm.
(d) The duct F is the sperm duct or the vas deferens.
(e) (i) The cell G is the zygote, (ii) the ball of cells H is the embryo and (iii) the organ I is the uterus.
(f) (i) X represents female and (ii) Y represents male.


Answer: 99
(a) The fertilised egg cell E is also called the zygote.
(b) The tissue T is the placenta.
(c) The string-like structure S is the umbilical cord.
(d) Oxygen and nutrients pass from the mother’s blood to the embryo and carbon dioxide passes from the embryo to the mother’s blood through the placenta (T).
(e) When a baby is born, the umbilical cord is still attached to the baby. It is cut and tied to separate the baby from the mother.


Answer: 100
(a) A represents immature follicles.
(b) B represents the process of ovulation.
(c) The time period x is 28 days.
(d) The event C is pregnancy.
(e) The time period y is the gestation period, i.e., 9 months.
(f) D represents the process of menstruation.
(g) The chemical substance E is the hormone oestrogen.


Exercise : Solution of Questions on page Number : 175


Answer: 101
(a) A represents the vas deferens.
(b) B represents sperms.
(c) C represents the testes.
(d) The cell D is the egg or ova.
(e) The surgical method of birth control available to males is called vasectomy.


Answer: 102
(a) The structure P is the oviduct.
(b) The cell Q are the eggs or ovum.
(c) The organ R is oviduct.
(d) The reproductive cell S is sperm.
(e) The surgical method of birth control available to females is tubectomy.


Answer: 103
(a) The device X is condom.
(b) Y represents sperms.
(c) The device Z is copper-T.
(d) The general name of these methods of birth control is called barrier method or IUCD (Intrauterine Contraceptive Device).
(e) Using condoms (X) during sexual intercourse can protect a person from sexually transmitted disease.


Answer: 104
(a) The pills A contain hormones.
(b) The common name of pills A is oral pills.
(c) The pills B contain spermicides.
(d) The common name of pills B is vaginal pills.
(e) The general name of these methods of birth control is called chemical method.


Answer: 105
(a) The name of the device Y is copper-T or IUCD.
(b) The organ Y is the uterus.(c) This method cannot protect a woman from acquiring STDs.


Answer: 106
(a) A is gonorrhoea and C is syphilis.
(b) B is AIDS.
(c) The virus D is Human Immunodeficiency Virus (HIV).
(d) A, B and C can be caused by sexual contact with an infected person.
(e) AIDS (B) does not have a definite cure as yet.


Exercise : Solution of Questions on page Number : 176


Answer: 107
A is the ovum.
B is sperm.
C is the zygote.
D is the uterus.
E is the embryo.
F is the foetus.
The person X is a female and Y is a male.


Answer: 108
In humans, fertilisation is internal. The zygote divides and forms the embryo which is implanted in the uterus. This embryo receives all the nutrients and care from the mother’s body and develops into an adult.
In frogs, fertilisation is external and the zygote is formed outside the body. Thus, it forms a larva instead of developing directly into an adult.


Answer: 109
The ovary of a flower develops into a fruit after fertilisation. The ovary is a part of the carpel. Thus, in spite of the young stamens being removed artificially, the flower produces fruits.


Answer: 110
(a) The process of fertilisation is similar in plants and humans as both involve male and female gametes and show internal fertilisation.
(b)

Fertilisation in plants Fertilisation in animals
External agents are required for pollination. External agents are not required.
The seed is formed after fertilisation. The human baby is formed after fertilisation.

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