Science Ncert Exemplar Solutions for Class 10 Science Chapter 8 How Do Organisms Reproduce are provided here with simple step-by-step explanations. These solutions for How Do Organisms Reproduce are extremely popular among Class 10 students for Science How Do Organisms Reproduce Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Science Ncert Exemplar Book of Class 10 Science Chapter 8 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Science Ncert Exemplar Solutions. All Science Ncert Exemplar Solutions for class Class 10 Science are prepared by experts and are 100% accurate.

Page No 65:

Question 1:

In the list of organisms given below, those that reproduce by the asexual method are

(i) banana (ii) dog
(iii) yeast (iv) Amoeba

(a) (ii) and (iv)
(b) (i), (iii) and (iv)
(c) (i) and (iv)
(d) (ii), (iii) and (iv)

Answer:

From the given list of organisms, banana, yeast and Amoeba reproduce through asexual methods.

Hence, the correct answer is option (b).

Page No 65:

Question 2:

In a flower, the parts that produce male and female gametes (germ cells) are
(a) stamen and anther
(b) filament and stigma
(c) anther and ovary
(d) stamen and style

Answer:

In a flower, male gametes are carried in pollen grains which are produced in anther and female gamete or egg is produced inside ovules which are produced in the ovary.

Hence, the correct answer is option (c).

Page No 65:

Question 3:

Which of the following is the correct sequence of events of sexual reproduction in a flower?
(a) pollination, fertilisation, seedling, embryo
(b) seedling, embryo, fertilisation, pollination
(c) pollination, fertilisation, embryo, seedling
(d) embryo, seedling, pollination, fertilisation

Answer:

During sexual reproduction, first pollination, that is, transfer of pollen grains from the anther to the stigma occurs. After transfer, pollen grain germinates on the stigma to form pollen tube which carries male gametes to the egg present inside the ovule for fertilisation. After fertilisation, zygote forms which develops into an embryo and ovule develops into a seed. On seed germination, embryo develops into a seedling under appropriate conditions. 

Hence, the correct answer is option (c).

Page No 65:

Question 4:

Offspring formed by asexual method of reproduction have greater similarity among themselves because
(i) asexual reproduction involves only one parent
(ii) asexual reproduction does not involve gametes
(iii) asexual reproduction occurs before sexual reproduction
(iv) asexual reproduction occurs after sexual reproduction

(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)

Answer:

In asexual reproduction, offspring develop from a single parent without fusion of gametes. So, asexually produced offspring resemble to each other.

Hence, the correct answer is option (a).



Page No 66:

Question 5:

Characters transmitted from parents to offspring are present in
(a) cytoplasm
(b) ribosome
(c) Golgi bodies
(d) genes

Answer:

The chromosomes in the nucleus of a cell contain information for inheritance of characters from parents to next generation in the segments of DNA called genes.

Hence, the correct answer is option (d).

Page No 66:

Question 6:

Characters that are transmitted from parents to offspring during reproduction show
(a) only similarities with parents
(b) only variations with parents
(c) both similarities and variations with parents
(d) neither similarities nor variations

Answer:

During reproduction, a cell creates copies of DNA using chemical reactions. These copies are not identical due to variations result during the process of copying of DNA. So, the characters transmitted from parents to offspring show similarity as well as variations with parents.

Hence, the correct answer is option (c).

Page No 66:

Question 7:

A feature of reproduction that is common to Amoeba, Spirogyra and Yeast is that
(a) they reproduce asexually
(b) they are all unicellular
(c) they reproduce only sexually
(d) they are all multi-cellular

Answer:

Amoeba reproduces through binary fission, Spirogyra through fragmentation and yeast through budding. Binary fission, fragmentation and budding are the methods of asexual reproduction.

Hence, the correct answer is option (a).

Page No 66:

Question 8:

In Spirogyra, asexual reproduction takes place by
(a) breaking up of filaments into smaller bits
(b) division of a cell into two cells
(c) division of a cell into many cells
(d) formation of young cells from older cells.

Answer:

Spirogyra is an multicellular alga with filamentous body. It reproduces asexually through fragmentation in which its filament breaks up into smaller pieces, each of which grows into a new individual.

Hence, the correct answer is option (a).

Page No 66:

Question 9:

The ability of a cell to divide into several cells during reproduction in Plasmodium is called
(a) budding
(b) reduction division
(c) binary fission
(d) multiple fission

Answer:

The nucleus of the malaria parasite, Plasmodium, divides repeatedly to form a number of nuclei. Each nucleus gets surrounded by small amount of cytoplasm leading to the formation of many daughter cells. This process of reproduction is called multiple fission.

Hence, the correct answer is option (d).

Page No 66:

Question 10:

The correct sequence of reproductive stages seen in flowering plants is
(a) gametes, zygote, embryo, seedling
(b) zygote, gametes, embryo, seedling
(c) seedling, embryo, zygote, gametes
(d) gametes, embryo, zygote, seedling

Answer:

During sexual reproduction in flowering plants, male and female gametes produced in the male and female reproductive parts of the flower, respectively fuse to form the zygote. This zygote then develops into embryo inside the seed. The embryo gives rise to a seedling on seed germination.

Hence, the correct answer is option (a).

Page No 66:

Question 11:

The number of chromosomes in parents and off-springs of a particular species remains constant due to
(a) doubling of chromosomes after zygote formation
(b) halving of chromosomes during gamete formation
(c) doubling of chromosomes after gamete formation
(d) halving of chromosomes after gamete formation

Answer:

In sexually reproducing organisms, gametes are formed through meiosis so that they contain half the number of chromosomes and DNA. The original number of chromosomes and DNA are re-established when gametes from two individuals combine.

Hence, the correct answer is option (b).



Page No 67:

Question 12:

In Rhizopus, tubular thread-like structures bearing sporangia at their tips are called
(a) filaments
(b) hyphae
(c) rhizoids
(d) roots

Answer:

In Rhizopus, spores containing blob-like structures or sporangia are borne at the tips of tubular, thread-like structures called hyphae.

Hence, the correct answer is option (b).

Page No 67:

Question 13:

Vegetative propagation refers to formation of new plants from
(a) stem, roots and flowers
(b) stem, roots and leaves
(c) stem, flowers and fruits
(d) stem, leaves and flowers

Answer:

Vegetative propagation is a form of asexual reproduction in plants in which new plants arise from vegetative parts such as stem, roots and leaves.

Hence, the correct answer is option (b).

Page No 67:

Question 14:

Factors responsible for the rapid spread of bread mould on slices of bread are
(i) large number of spores
(ii) availability of moisture and nutrients in bread
(iii) presence of tubular branched hyphae
(iv) formation of round shaped sporangia

(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (ii)
(d) (iii) and (iv)

Answer:

Bread mould is a saprophyte which lives on dead and decaying plant material and obtain its nutrition. It reproduces asexually through production of thick-walled spores. These spores germinate to form hyphae on coming in contact with moist surface. So, the factors responsible for the rapid spread of bread mould on slices of bread are large number of spores and availability of moisture and nutrients in bread.

Hence, the correct answer is option (c).

Page No 67:

Question 15:

Length of pollen tube depends on the distance between
(a) pollen grain and upper surface of stigma
(b) pollen grain on upper surface of stigma and ovule
(c) pollen grain in anther and upper surface of stigma
(d) upper surface of stigma and lower part of style

Answer:

Once a pollen grain reaches on the stigma of the pistil, it germinates to form a pollen tube which grows down the style to reach the ovule present inside the ovary. So, the length of the pollen tube depends on the distance between the pollen grain on the upper surface of the stigma and the ovule.

Hence, the correct answer is option (b).

Page No 67:

Question 16:

Which of the following statements are true for flowers?
(i) Flowers are always bisexual
(ii) They are the sexual reproductive organs
(iii) They are produced in all groups of plants
(iv) After fertilisation they give rise to fruits

(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (ii) and (iv)

Answer:

Flowers are the reproductive parts of a group of plants called angiosperms. Flowers are either unisexual or bisexual. After fertilisation, ovary of the gynoecium develops into a fruit.
Out of given four statements, statement (ii) and (iv) are true.

Hence, the correct answer is option (d).

Page No 67:

Question 17:

Which among the following statements are true for unisexual flowers?
(i) They possess both stamen and pistil
(ii) They possess either stamen or pistil
(iii) They exhibit cross pollination
(iv) Unisexual flowers possessing only stamens cannot produce fruits

(a) (i) and (iv)
(b) (ii), (iii) and (iv)
(c) (iii) and (iv)
(d) (i), (iii) and (iv)

Answer:

Flowers which possess either stamens or pistil are called unisexual flowers. These flowers are borne either on the same or different flowers thus, pollen grains need to be transferred from one flower to another through agents like wind, water or animals, that is, cross pollination occurs. Since fruits develop from the ovary of the pistil, unisexual flowers with stamens only cannot bear fruits.
Out of the given four statements, (ii), (iii) and (iv) are true for unisexual flowers.

Hence, the correct answer is option (b).



Page No 68:

Question 18:

Which among the following statements are true for sexual reproduction in flowering plants?
(i) It requires two types of gametes
(ii) Fertilisation is a compulsory event
(iii) It always results in formation of zygote
(iv) Offspring formed are clones

(a) (i) and (iv)
(b) (i), (ii) and (iv)
(c) (i), (ii) and (iii)
(d) (i), (ii) and (iv)

Answer:

During sexual reproduction in flowering plants, male and female gametes fuse, that is, fertilisation occurs. This results in the formation of zygote. So, out of the given four statements, (i), (ii) and (iii) are true.

Hence, the correct answer is option (c).

Page No 68:

Question 19:

In Figure 8.1, the parts A, B and C are sequentially

(a) cotyledon, plumule and radicle
(b) plumule, radicle and cotyledon
(c) plumule, cotyledon and radicle
(d) radicle, cotyledon and plumule

Answer:

The given figure shows the details of a seed. The parts labelled as A, B and C are Plumule, Cotyledon and Radicle, respectively.

Hence, the correct answer is option (c).

Page No 68:

Question 20:

Offspring formed as a result of sexual reproduction exhibit more variations because
(a) sexual reproduction is a lengthy process
(b) genetic material comes from two parents of the same species
(c) genetic material comes from two parents of different species
(d) genetic material comes from many parents

Answer:

During sexual reproduction, gametes produced through meiosis from two different individuals of the same species fuse to form a new individual. These gametes have genetic material or DNA copies with variations. Fusion of gametes combines their DNAs with variations. So, the resulting offspring  has new combinations of variants.

Hence, the correct answer is option (b).

Page No 68:

Question 21:

Reproduction is essential for living organisms in order to
(a) keep the individual organism alive
(b) fulfill their energy requirement
(c) maintain growth
(d) continue the species generation after generation

Answer:

No living organism lives forever. The species would disappear with the death of an organism. So, living organisms produce new organisms similar or identical to themselves through the process called reproduction so as to continue their species generation-after-generation.

Hence, the correct answer is option (d).

Page No 68:

Question 22:

During adolescence, several changes occur in the human body. Mark one change associated with sexual maturation in boys
(a) loss of milk teeth
(b) increase in height
(c) cracking of voice
(d) weight gain

Answer:

During adolescence, boys begin to have new thick hair growth on the face and their voices begin to crack. Further, the penis occasionally begins to become enlarged and erect, either in daydreams or at night.

Hence, the correct answer is option (c).

Page No 68:

Question 23:

In human females, an event that reflects onset of reproductive phase is
(a) growth of body
(b) changes in hair pattern
(c) change in voice
(d) menstruation

Answer:

With the onset of reproductive phase, uterine lining of human females becomes thick and spongy to nourish the embryo if fertilisation had taken place. In the absence of fertilisation, this lining is not needed any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes place roughly every month and is known as menstruation.

Hence, the correct answer is option (d).



Page No 69:

Question 24:

In human males, the testes lie in the scrotum, because it helps in the
(a) process of mating
(b) formation of sperm
(c) easy transfer of gametes
(d) all the above

Answer:

In human males, sperm formation requires a temperature lower than the normal body temperature. So, testes are located outside the abdominal cavity in scrotum.
Hence, the correct answer is option (b).

Page No 69:

Question 25:

Which among the following is not the function of testes at puberty?
(i) formation of germ cells
(ii) secretion of testosterone
(iii) development of placenta
(iv) secretion of estrogen

(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)

Answer:

Testes are the male reproductive parts in humans. These are responsible for the formation of male gametes and secretion of hormone, testosterone. Thus, statements (iii) and (iv) are not the function of testes at puberty.

Hence, the correct answer is option (c). 

Page No 69:

Question 26:

The correct sequence of organs in the male reproductive system for transport of sperms is
(a) testis → vasdeferens → urethra
(b) testis → ureter → urethra
(c) testis → urethra → ureter
(d) testis → vasdeferens → ureter

Answer:

In human males, male gametes or sperms are formed in the testes. After formation, the sperms formed are delivered through the vas deferens which unites with a tube coming from the urinary bladder called urethra.

Hence, the correct answer is option (a).

Page No 69:

Question 27:

Which among the following diseases is not sexually transmitted?
(a) Syphilis
(b) Hepatitis
(c) HIV - AIDS
(d) Gonorrhoea

Answer:

Among the given diseases, hepatitis is a viral disease which spreads on consumption of food or water contaminated with fecal matter.

Hence, the correct answer is option (b).

Page No 69:

Question 28:

In a bisexual flower inspite of the young stamens being removed artificially, the flower produces fruit. Provide a suitable explanation for the above situation.

Answer:

A bisexual flower possesses both the male reproductive parts, stamens and female reproductive part, pistil. If the stamens are removed, pistil is present in the flower. On cross pollination followed by successful fertilisation, the ovary of the pistil would have developed into a fruit. 

Page No 69:

Question 29:

Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.

Answer:

Reproduction is a process through which living organisms produce new individuals. In case of unicellular organisms like Amoeba, a single cell divides to form two new daughter cells. Hence, cell division can be considered as a type of reproduction in unicellular organisms.

Page No 69:

Question 30:

What is a clone? Why do offsprings formed by asexual reproduction exhibit remarkable similarity?

Answer:

Clone is an organism produced through asexual reproduction and resembles its parent. Offspring produced through asexual reproduction receive exact copy of DNA from their single parent. So, they exhibit remarkable similarity.

Page No 69:

Question 31:

Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes?

Answer:

Sexually reproducing organisms produce gametes through meiosis as a result they receive only half the number of chromosomes and half the amount of DNA as compared to the nonreproductive body cells.When these gametes from two individuals combine during sexual reproduction to form a new individual, the original number of chromosomes and the DNA content in the new generation are restored. 

Page No 69:

Question 32:

Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.

Answer:

An organism requires energy to perform various life processes such as nutrition, respiration, etc. so as to sustain its life and also to reproduce. Since water lacks source of energy, colonies of yeast fail to multiply in it whereas sugar solution provides source of energy, colonies of yeast multiply in it.  



Page No 70:

Question 33:

Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?

Answer:

Bread mould reproduces asexually through production of thick-walled spores. These spores require moisture to germinate to form hyphae and nutrients to grow profusely. Both conditions (moisture and nutrients) required for profuse growth of bread mould are provided on moist slice of bread whereas dry slice of bread provides only nutrients not the moisture. 

Page No 70:

Question 34:

Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.

Answer:

Two reasons for the appearance of variations among the progeny formed by sexual reproduction are:

  • Two parents, each with different set of characters take part in sexual reproduction.
  • Gametes from two different individuals possess different combinations of genes which are combined in the zygote.

Page No 70:

Question 35:

Would a Planaria cut vertically into two halves regenerate into two individuals? Complete Figure 8.2 D and E by indicating the regenerated regions.

Answer:

Yes, a Planaria would regenerate into two individuals if cut vertically into two halves. 

The regenerated regions in D and E are shown by shaded parts below.

Page No 70:

Question 36:

From the internet, gather information about the chromosome numbers of five animals and five plants. Correlate the number with the size of organism and answer the following questions.
(a) Do larger organisms have more number of chromosomes/cells?
(b) Can organism with fewer chromosomes reproduce more easily than organisms with more number of chromosomes?
(c) More the number of chromosomes/cells greater is the DNA content. Justify.

Answer:

Chromosome number of animals

  Animal Chromosome Number
1. Rat 21
2. Elephant 56
3. Giraffe 30
4. Cat 38
5. Horse 64

Chromosome number of plants
 
  Plants Chromosome Number
1. Maize 20
2. Onion 16
3. Rice 12
4. Wheat 42
5. Mango 40

(a) There is no correlation between the size of an organisms with the number of chromosomes present in the cells of its body. So, larger organisms do not have more number of chromosomes per cell. 
(b) Process of reproduction follows a common pattern and is not dependent on the number of chromosomes in an organism. So, the organisms with fewer number of chromosomes need not reproduce more easily than the organisms with more number of chromosomes.
(c) Each chromosome is made up of DNA and protein. So, if a cell has more number of chromosomes, it will possess the greater DNA content.
 

Page No 70:

Question 37:

In tobacco plant, the male gametes have twenty four chromosomes.
What is the number of chromosomes in the female gamete?
What is the number of chromosomes in the zygote?

Answer:

Male and female gametes are produced through meiosis and have the same number of chromosomes. So, the number of chromosomes in the female gamete of a tobacco plant will be 24. Since a zygote is formed by the fusion of male and female gametes, it would contain the double the number of chromosomes that male or female gametes. So, the number of chromosomes in the zygote of a tobacco plant will be 48.

Page No 70:

Question 38:

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

Answer:

In flowering plants, male gametes are produced in the pollen grains inside the anther. Pollination brings the pollen grains having male gametes from the anther to the stigma where they germinate to carry the male gametes to the female gamete or egg present in the ovule for fertilisation. So, it pollination does not occur, fertilisation will also not take place.

Page No 70:

Question 39:

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

Answer:

Mitosis is a cell division which results in the formation of two daughter cells from a cell with the same number of chromosomes. Zygote undergoes mitotic divisions to develop into an embryo which in turn, also undergoes mitotic divisions to become an adult. So, the constancy of chromosomes is maintained in these three stages.

Page No 70:

Question 40:

Where is the zygote located in the flower after fertilization?

Answer:

In flowering plants, female gamete or egg is produced inside the ovule of the ovary. Since after fertilisation egg becomes a zygote, it is also located inside the ovule of the ovary.

Page No 70:

Question 41:

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

Answer:

During reproduction, DNA is passed from one generation to another so DNA is copied with consistency but with minor variations. This helps the maintenance of body design features that allow the organism to use a particular niche where it lives. Reproduction is therefore, linked to the stability of populations of species.

Page No 70:

Question 42:

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

Answer:

General growth refers to the developmental changes by which the body becomes larger. Examples of general growth are increase in height, increase in weight, change in shape and size of the body. On the contrast, sexual maturation refers to specific changes that occur at puberty like cracking of voice, new hair patterns, development of breast in females, development of beard and moustaches in males, etc.

Page No 70:

Question 43:

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

Answer:

Sperms, after their formation in the testes, comes out into the vas deferens and then pass through urethra before ejaculation. The glands associated with human male reproductive system are seminal vesicle and prostrate glands. These glands add their secretions which provide nutrition to the sperms and also facilitate their transport.



Page No 71:

Question 44:

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

Answer:

If fertilisation does not occur, the thicken and spongy lining of uterus slowly breaks and comes out through the vagina as blood and mucous.

Page No 71:

Question 45:

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

Answer:

Subsequent to implantation of young embryo, the lining of uterus becomes thick and is richly supplied with blood to nourish the growing embryo. A disc-shaped placenta becomes embedded in the uterine wall to provide nutrition and oxygen to the embryo.

Page No 71:

Question 46:

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

Answer:

Mechanical barriers such as condoms prevent the sperms from reaching the egg. Their benefits are as follows:

  • They prevent contraception or pregnancy.
  • They prevent the transmission of sexually transmitted diseases.

Page No 71:

Question 47:

In the given Figure 8.3 label the parts and mention their functions

(a) Production of egg
(b) Site of fertilisation
(c) Site of implantation
(d) Entry of the sperms

Answer:

(a) Production of egg - Ovary
(b) Site of fertilisation - Fallopian tube or oviduct
(c) Site of implantation - Uterus
(d) Entry of the sperms - Vagina

Page No 71:

Question 48:

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

Answer:

The egg is produced through meiosis so it contains half the number of chromosomes than a zygote. So, the ratio of chromosome number between an egg and zygote is 1:2. Humans males have two types of sex chromosomes - X and Y whereas human females have two X chromosomes. So, the sperms contain either X or Y chromosome whereas eggs contain only X chromosome leading to genetic difference between them.

Page No 71:

Question 49:

Why are budding, fragmentation and regeneration all considered as asexual types of reproduction? With neat diagrams explain the process of regeneration in Planaria.

Answer:

Asexual reproduction is a type of reproduction in which new organisms are formed from a single parent. In budding, new organism is formed as a bud from the single parent cell. On the contrast, in fragmentation, parent body breaks down into a smaller pieces, each of which grows into a new organism. And, in regeneration, an individual is cut into many pieces, each piece grows into a new individual. Since all these three modes of reproduction, single parent is involved so these are considered as types of asexual reproduction.

Regeneration in Planaria

Planaria can be cut into a number of pieces and each piece grows into a complete organism. This is known as regeneration. In the diagram below, the body of the Planaria is cut horizontally into three pieces and each piece regenerates into a new organism.

Page No 71:

Question 50:

Write two points of difference between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction.

Answer:

Differences between asexual and sexual reproduction
 

Asexual Reproduction Sexual Reproduction
It involves only one parent.  It generally involves two parents of opposite sex.
It generally does not involve production of gametes. It involves the formation of gametes.
There is no fertilisation and formation of zygote. Fertilisation occurs and results in the formation of zygote.
Asexually produced offspring resemble to each other and their parents. Sexually produced offspring show some variations from their parents.

Gametes involved in sexual reproduction possess some variations due to inaccuracy in DNA copying mechanisms. When male and female gametes fuse, their variations combine thus creating new combinations of variations in the offspring. Thus, offspring formed by sexual reproduction possess variations.

Page No 71:

Question 51:

Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower.
Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.

Answer:

Pollination is the process of transfer of pollen grains from the anther to the stigma of the pistil. Fertilisation is the process of fusion of male and female gametes resulting in the formation of zygote.
The site of fertilisation in the flower is the ovule and the product of fertilisation is the zygote.

Page No 71:

Question 52:

Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.

Answer:

Differences between a gamete and a zygote

 
Gamete Zygote
It is formed through meiosis. It is formed from the fusion of male and female gametes.
It is the sex or germ cell that takes part in fertilisation. It is the product of fertilisation.
The gametes are of two types -male and female gametes, each possessing characters of their parents.  It possesses characters of both the parents.
It is the last cell of its generation. It develops into an embryo which grows into a new individual so, zygote is the first cell of the new generation.

Role of gamete in sexual reproduction - Gamete is the sex or germ cell specialised to take part in sexual reproduction. Fusion of a male gamete with a female gamete produces a zygote.

Role of zygote in sexual reproduction - Zygote develops into an embryo that later forms the new individual.

Page No 71:

Question 53:

Draw the diagram of a flower and label the four whorls. Write the names of gamete producing organs in the flower.

Answer:


                     A flower and its whorls 
The male gamete producing organs in the flower is stamen (anther) and the female gamete producing organ is pistil (ovule of the ovary).



Page No 72:

Question 54:

What is placenta? Mention its role during pregnancy?

Answer:

Placenta is a special disc-like organ embedded in uterine wall. It is an intimate connection between the embryo and the uterine wall. It contains blood spaces on the mother's side and thousands of villi (small projections) on the foetal side that provide a large surface area for the exchange of nutrients and oxygen between the mother and the foetus. 

Role of placenta during pregnancy:

The exchange of materials between the blood of mother and foetus takes place through placenta. It provides nutrition to the foetus. It also serves as the respiratory (by allowing exchange of oxygen and carbon dioxide) and excretory organs (by allowing excretion of waste material of foetus into mother's blood) of the foetus.

Page No 72:

Question 55:

What are various ways to avoid pregnancy? Elaborate any one method.

Answer:

The various ways to avoid pregnancy are:

  • Mechanical barriers
  • Drugs
  • Contraceptive devices
  • Surgical methods
Mechanical barriers: This method of contraception prevent the meeting of the sperms with egg. The most common mechanical barrier is condoms. The condom acts as mechanical barrier between an egg and a sperm and prevents fertilization. It is particularly useful because it not only prevents pregnancy but also the spread of sexually transmitted diseases.

Drugs: The production of gametes, fertilization, and implantation of the fertilized egg are all processes that are controlled by hormones. Chemical drugs that alter the hormonal balance of the female body can prevent release of egg and fertilization. These drugs are available in the form of pills that can be taken orally. 

Contraceptive devices: Devices such as loop or copper-T are also drug-based contraceptive methods. They are placed inside the uterus to prevent fertilization.

Surgical methods: Surgery can block the release of sperm or the egg. They are safe methods in the long run if performed by competent medical professionals.

Page No 72:

Question 56:

How does fertilisation take place? Fertilisation occurs once in a month. Comment.

Answer:

During sexual intercourse, sperms are released in the vaginal passage from where they travel upwards through uterus and reach the oviduct or fallopian tube. If an egg released from the ovary is present in one of the fallopian tubes, a sperm fuses with it resulting in fertilisation. 
Since one egg is produced every month by one of the ovaries, fertilisation occurs once in a month.

Page No 72:

Question 57:

Reproduction is essentially a phenomenon that is not for survival of an individual but for the stability of a species. Justify.

Answer:

Organisms need energy for their growth and survive. They obtain the required energy from life processes such as nutrition and respiration. Reproduction is a process through which living organisms produce new organisms of their own kind. Thus, this process requires lots of energy rather than providing energy. So, reproduction is not essential for survival.
Also, during reproduction, genetic material is transferred from one generation to another through DNA copying. DNA is copied with high constancy and considerable variations and these variations help the species to adjust and survive in the constantly changing environment. Thus, reproduction is essential for the stability of the species.

Page No 72:

Question 58:

Describe sexually transmitted diseases and mention the ways to prevent them.

Answer:

Sexually transmitted diseases are the diseases which are transmitted through sexual contact. These diseases are caused by bacteria e.g., gonorrhoea and syphilis and viruses e.g., AIDS and warts.
The ways to prevent transmission of these diseases are:

  • Use of mechanical barriers such as condom for the penis during sex
  • Avoid sex with unknown partners/multiple partners



View NCERT Solutions for all chapters of Class 10