NCERT Exemplar Class 10 Science Chapter 8 How do Organisms Reproduce?
In this article you will get CBSE Class 10 Science chapter 8, Control How do Organisms Reproduce: NCERT Exemplar Problems and Solutions
NCERT Exemplar Class 10 Science Chapter 8 How do Organisms Reproduce?
Multiple Choice Questions (MCQs)
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. (b)
Explanation: Among the given options, Amoeba (binary fission), Yeast (budding) and banana (vegetative propagule) reproduce by asexual reproduction whereas dogs reproduce by sexual method.
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. (c)
Explanation: Anther produce pollen through microsporogenesis and ovary produce egg cell by megasporogenesis.
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, fertilization
Answer. (c)
Explanation: In pollination, pollen grains transfer from stamen to stigma after which fertilization takes place during which germ cells fuse together to form zygote which in turn leads to embryo formation. Fertilized ovule becomes seed and seeds germinate to produce Seedling.
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. (a)
Explanation: Asexual reproduction does not involve gamete formation and fertilization.
Question. 5 Characters transmitted from parents to offspring are present in
(a) Cytoplasm
(b) Ribosome
(c) Golgi bodies
(d) Genes
Answer. (d)
Explanation: Genes are the stretch of DNA and determine genetic characters.
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. (c)
Explanation: Meiosis during gamete formation and fertilization produce variations while DNA replication ensures similarities.
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 multicellular
Answer. (a)
Explanation: All of them reproduce asexually.
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. (a)
Explanation: Fragmentation is type of asexual reproduction in animals wherein parental body is broken down into pieces and each of these pieces develops into an individual animal.
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. (d)
Explanation: Multiple fission is repeated division of organism to produce many daughter cells simultaneously.
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. (a)
Explanation: Gamete formation is followed by pollination and fertilization to produce zygote which in turn leads to embryo formation. Fertilized ovule become seed and seeds germinate to produce Seedling.
Question. 11 The number of chromosomes in parents and offsprings 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. (b)
Explanation: Meiosis reduces the chromosome number to half which is then restored by fertilization.
Question. 12 In Rhizopus, tubular thread-like structures bearing sporangia at their tips are called
(a) Filaments
(b) Hyphae
(c) Rhizoids
(d) Roots
Answer. (b)
Explanation: Thin branched filaments of fungi are called as hyphae.
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. (b)
Explanation: Flowers are the organs of sexual reproduction in plants.
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. (c)
Explanation: Bread mold prefers damp and warm substratum with ample supply of nutrients on which its air-borne spores land and germinate to produce mycelium.
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. (b)
Explanation: Pollen tube carries male gametes to ovule and hence, is long equal to the distance between stigma and ovary.
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 fertilization they give rise to fruits
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (ii) and (iv)
Answer. (d)
Explanation: Flowers are the sexual reproductive organs of a plant and a fertilized flower give rise to fruit.
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. (b)
Explanation: Unisexual flowers have either male or female reproductive organs and are cross pollinated ones. A fertilized flower gives rise to fruit.
Question. 18 Which among the following statements are true for sexual reproduction in flowering plants?
(i) It requires two types of gametes.
(ii) Fertilization 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 (iv)
(d) (i), (ii) and (iii)
Answer. (d)
Explanation: Sexual reproduction involves fertilization of male and female gamete to produce zygote having genetic variations.
Question. 19 In figure 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. (c)
Explanation: Plumule ‘A’ give rise to shoots, cotyledon ‘B’ serves to store food and radicle ‘C’ grows into roots.
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. (b)
Explanation: Sexual reproduction produces genetic variations by meiosis during gamete formation and fertilization of male and female gametes.
Question. 21 Reproduction is essential for living organisms to order to
(a) Keep the individual organism alive
(b) Fulfill their energy requirement
(c) Maintain growth
(d) Continue the species generation after generation
Answer. (d)
Explanation: Reproduction serves to continue the species which would otherwise extinct due to struggle for survival and natural/accidental death of individuals.
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. (c)
Explanation: Cracking of voice is one of the secondary sexual characters of human males.
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. (d)
Explanation: Development of female secondary sexual characters marks onset of puberty and initiation of menstrual cycle reflects onset of reproductive phase.
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 of these
Answer. (b)
Explanation: Scrotum provides lower temperature needed for sperm formation.
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. (c)
Explanation: Development of placenta and secretion of estrogen are female reproductive functions.
Question. 26 The correct sequence of organs in the male reproductive system for transport of sperms is
(a) Testis → vas deferens → urethra
(b) Testis → ureter → urethra
(c) Testis → urethra → ureter
(d) Testis → vas deferens → ureter
Answer. (a)
Explanation: Vas deferens delivers sperms from testes to urethra coming from the urinary bladder.
Question. 27 Which among the following diseases is not sexually transmitted?
(a) Syphillis
(b) Hepatitis
(c) HIV-AIDS
(d) Gonorrhoea
Answer. (b)
Explanation: Hepatitis is water borne viral disease.
Short Answer Type Questions
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 has both male and female reproductive organs. Removal of young stamens to avoid self pollination does not rule out the possibility of cross pollination. Transfer of pollen grains from the anther of another flower to the stigma of emasculated flower causes cross-pollination and fertilized flower forms fruits.
Question. 29 Can you consider cell division as a type of reproduction in unicellular organism? Give one reason.
Answer.
Unicellular organisms reproduce by asexual reproduction which is simple division of parent cell into two daughter cells. Now, these two daughter cells grow into mature organism. Hence, cell division can be considered as mode of reproduction in single celled organisms. Eg: Amoeba.
Question. 30 What is a clone? Why do offspring formed by asexual reproduction exhibit remarkable similarity?
Answer.
Clones are the group of cells or individuals produced by asexual reproduction. Since asexual reproduction does not involve gamete formation by meiosis and fertilization of male and female gametes, the offspring are genetically similar to the single parent. Meiosis and fertilization are the two main sources of genetic variations in sexually reproducing plants.
Question. 31 Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes?
Answer.
Sexual reproduction includes gamete formation through meiosis and fertilization. Meiosis reduces the number of chromosomes to half in male and female gametes. This reduced chromosome number is then restored to normal during fertilization of male and female gametes. This is how; constant chromosome number is maintained in sexually reproducing organisms.
Question. 32 Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this.
Answer.
Water does not serve as source of all required nutrients necessary for growth and reproduction of yeast cells. On the other hand, sugar solution serve as source of organic compounds and cellular respiration of these compounds release energy needed for reproduction. That’s why yeast colonies do not multiply in water but do so in sugar solution.
Question. 33 Why does bread mould grow profusely on a moist slice of bread rather than on a dry slice of bread?
Answer.
Wet dump substratum with supply of nutrients is favored by Rhizopus for spore germination. Spores remain dormant till they come in contact with moist surface. Hence spores of bread mold germinate on moist bread serving as source of moisture and nutrients.
On the other hand, dry bread does not provide moisture needed for spore germination and growth of hyphae.
Question. 34 Give two reasons for the appearance of variations among the progeny formed by sexual reproduction.
Answer.
Production of genetic variation during sexual reproduction is result of:
(1) Meiosis during gamete formation; crossing over and independent assortment of genes produce genetic variations.
(2) Random fusion of genetically diverse gametes male and female gametes further aid in genetic diversity of offspring.
Question. 35 Would a Planaria cut vertically into two halves regenerate into two individuals? Complete the given figure D and E by indicating the regenerated regions.
Answer.
Planaria exhibits regeneration. If its body is cut into two vertical halves, each piece of the body of Planaria grows into a complete individual.
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.
Number of chromosomes in somatic cells of some animals and plants
| Animals | Number of Chromosomes |
| CatLionDogElephantKingfisher | 38387858132 |
| Plants | |
| PotatoOatsWheatMangoRice | 4842424024 |
(a) No, there is no correlation between size of organism and its chromosome number. Even smaller organisms may have more chromosomes than the larger ones.
(b) No, process of reproduction is independent of the chromosome number and depends on a environmental factors like nutrients availability, water source, suitable mate etc.
(c) Yes, Genes are the stretch of DNA. Genes are linearly arranged on chromosomes. Hence, more the number of chromosomes, greater is the amount of DNA.
Question. 37 In tobacco plant, the mate 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 of a species have same number of chromosomes. Hence, number of chromosome in the female gamete of tobacco plants is 24. Zygote is formed by fusion of male and female gamete, it will have 48 chromosomes.
Question. 38 Why cannot fertilization take place in flowers if pollination does not occur?
Answer.
Pollination is transfer of pollen from one flower to the stigma of same/other flower of same or another plant. It takes place after gamete formation. Only after arrival of pollen grains on stigma and entry of pollen tube into ovary, male gamete can fuse with female gamete (ovum). Hence, pollination is prerequisite for fertilization.
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.
Yes, zygote, embryonic cell and adult of a particularorganism always constant have constant chromosome number.
Sexual reproduction includes gamete formation through meiosis and fertilization. Meiosis reduces the number of chromosomes to half in male and female gametes. This reduced chromosome number is then restored to normal during fertilization of male and female gametes. This is how; constant chromosome number is maintained in sexually reproducing organisms. Growth and development of zygote into embryonic cell and then into adult one takes place by mitosis (equatorial cell division) which produce the daughter cells carrying same chromosome number as that of parent cell.
Question. 40 Where is the zygote located in the flower after fertilization?
Ans. Pollination is transfer of pollen from one flower to the stigma of same/other flower of same or another plant. It takes place after gamete formation. Only after arrival of pollen grains on stigma and entry of pollen tube (carrying the male gametes) into ovary, male gamete can fuse with female gamete (ovum). Ovum is present in ovule and ovule is present in ovary.
Therefore, the zygote is present inside the ovule.
Question. 41 Reproduction is linked to stability of population of a species. Justify the statement.
Answer.
Each species faces many forces that reduce the number of individuals constantly. Some of them are namely struggle for survival, competition for natural resources, predation, natural cycle of ageing and death, any natural calamity etc. All these natural forces reduce the number of individuals per species.
Reproduction is the process of production of own kind. It includes production of offspring having both similarities and variations among themselves and from parents. Further, the process of DNA replication and its inheritance to offspring ensure production of own kind only. Therefore, reproduction not only restore the number of individuals removed from the species by above mentioned natural forces but also maintain heredity of genetic characters and introduction of variations, as needed for continuity of a species.
Question. 42 How are general growth and sexual maturation different from each other?
Answer.
General growth includes increase in height, weight gain, changes in shape and size of the body. Also called as somatic phase, the reproductive organs are less active during somatic growth.
Sexual maturation is a cumulative process that includes all the changes needed to prepare the body for sexual reproduction. It ensures onset of puberty and reproductive phase of an individual.
Question. 43 Trace the path of sperm during ejaculation and mention the gland and their functions associated with the male reproductive system.
Answer.
Path of sperm during ejaculation is Testis -> vas deferens à urethra.
Glands associated with male reproductive system are
(a) Testis Secrete the androgens (testosterone).
(b) Prostate gland serves to provide the force needed for ejaculation. It secretes thin, milky alkaline fluid that adjusts the pH of seminal fluid and serves in motility of sperms.
(c) Cowper glands Their secretion lubricates the end of penis during sexual intercourse and may contain few sperms.
(d) Seminal vesicle adds alkaline pH (to counteract acidic pH of vagina), fructose (a nutrient), mucus and coagulating and local acting enzymes.
Question. 44 What changes are observed in the uterus if fertilization does not occur?
Answer.
If fertilization does not occur, thickened endometrium (inner lining of uterus) is disintegrated and sloughed off during menstruation phase (day1-5). Endometrium is needed to support implantation and nutrition of embryo only under pregnancy and is otherwise disintegrated as it does not have any function in non pregnant woman.
Question. 45 What changes are observed in the uterus subsequent to implantation of young embryo?
Answer.
The uterine lining is thickened every month support the growing embryo. Followed by fertilization, placenta is developed which serve to provide nutrition and oxygen to developing embryo from the mother’s blood. It isa disc embedded in the uterine wall and contains villi on the embryo’s side of the tissue while blood spaces surrounding the villi are present on mother’s side. Waste products of developing embryo are removed by transferring them into the mother’s blood through the placenta.
Question. 46 What are the benefits of using mechanical barriers during sexual act?
Answer.
(i) It serves a barrier to prevent arrival of sperm to egg and thus avoids unwanted pregnancy.
(ii) It also protects a person from sexually transmitted diseases.
Question. 47 In the given figure label the parts and mention their functions
(a) Production of egg
(b) Site of fertilization
(c) Site of implantation
(d) Entry of the sperms
Answer.
(a) Ovary (production of egg)
(b) Oviduct (site of fertilization)
(c) Uterus (site of implantation)
(d) Vagina (passage for entry of the sperms)
Question. 48 What would be the ratio of chromosome number between an egg andzygote? How is the sperm genetically different from the egg?
Answer.
The ratio of chromosome number between egg and its zygote is 1 : 2. Egg is product of meiosis and hence contains half the chromosome number of its parent cell. Zygote is product of fertilization of male and female gamete and therefore, contains double the chromosome number of egg cell.
Sperms and eggs differ from each other in type of sex chromosome. The sperm contain either X or Y-chromosome whereas an egg will always have an X-chromosome.
Long Answer Type Questions
Question. 49 Why budding, fragmentation and regeneration all are considered as asexual types of reproduction? With neat diagrams explain the process of regeneration in Planaria.
Answer. Budding, fragmentation and regeneration are considered as asexual types of reproduction because none of them includes gamete formation and fertilization. All of these give rise to offspring from single parent only.
Regeneration in Planaria It exhibits regeneration i.e. ability to grow the broken body part again. If the body of Planaria is cut into any number of pieces, each piece grows into a complete organism i.e. reproduction through regeneration.
Regeneration is carried out by specialized cells which proliferate and produce large numbers of daughter cells. Different cells from the group of daughter cells then differentiate into various cell types and tissues.
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.
Difference between asexual and sexual types of reproduction:
| S. No. | Asexual Reproduction | Sexual Reproduction |
| 1. | Here only one parent is required. | It involves two parents. |
| 2. | The process of gametogenesis does not occur. | It starts with production of gametes through gametogenesis. |
| 3. | No fertilization and zygote formation takes place here. | Gamete formation is followed by fusion of male and female gametes (fertilization) leading to zygote formation. |
| 4. | It includes only mitosis. Offspring are genetically identical clones. | Meiosis occurs at the time of gamete formation. Meiosis and fertilization produce genetic variations in offspring. |
Meiosis during gamete formation introduces genetic variations via process of crossing over. Random fusion of male and female gametes during fertilization adds more genetic variations in offspring.
Question. 51 Distinguish between pollination and fertilization. Mention the site and product, of fertilization in a flower. Draw a neat, labeled diagram of a pistil showing pollen tube growth and its entry into the ovule.
Answer.
Distinguish between Pollination and Fertilization
| S. No. | Pollination | Fertilization |
| 1. | It is the transfer of pollen grains from anther of one flower to the stigma same /other flower of same plant or on stigma of different plant of same species. | It is the fusion of male and female gametes. |
| 2. | It is a physical Process. | It is a biological process. |
The site of fertilization in flowers is ovule which in turn is present in ovary. The product of fertilization is a zygote.
Question. 52 Distinguish between a gamete and zygote. Explain their roles in sexual reproduction.
Answer.
Distinguish between a Gamete and Zygote
| S. No. | Gamete | Zygote |
| 1. | The germ cells that are fused during sexual reproduction are called gametes, e.g., sperm (male) and Ova (female). | It is product of fusion of male gamete and female gamete during sexual reproduction. |
| 2. | Gametes are unfertilized reproductive cells. | Zygote is fertilized egg or fertilized Ovum. |
| 3. | Being the product of meiosis, gamete are always haploid cells | Since zygote is product of fusion of haploid male and female gamete, it is a diploid structure. |
Importance of gametes and zygote in sexual reproduction Gametes are product of meiosis and hence carry half the chromosome number as that of parent cells. This chromosome number is restored during fertilization and zygote formation. Hence, gamete and zygote are the two phases of sexually reproducing organisms that help maintain the constant chromosome number in each species.
Question. 53 Draw the diagram of a flower and label the four whorls. Write the names of gamete producing organs in the flower.
Anwers.
The four whorls of a flower from outside towards inside are
(i) Calyx (whorl of sepals)
(ii) Corolla (whorl of petals)
(iii) Androecium (male reproductive unit)
(iv) Gynoecium (female reproductive unit)
Anther serves as male gamete producing organ while ovary serves as female gamete producing organ in the flower.
Question. 54 What is placenta? Mention its role during pregnancy.
Answer.
Followed by fertilization, placenta is developed which serve to provide nutrition and oxygen to developing embryo from the mother’s blood. It isa disc embedded in the uterine wall and contains villi on the embryo’s side of the tissue while blood spaces surrounding the villi are present on mother’s side. The embryo is connected to the placenta by umbilical cord, a tube like structure.
Placenta serves to fulfill all nutritional requirements of developing embryo by supplying food and oxygen from mother’s blood to the embryo. Waste products of developing embryo are removed by transferring them into the mother’s blood through the placenta. Functions of placenta are facilitated by villi that provide large surface areas for passage of nutrition and oxygen to embryo from mother through blood.
Question. 55 What are various ways to avoid pregnancy? Elaborate any one method.
Answer.
Methods to avoid undesired pregnancy are called contraceptive methods.It includes
(i) Mechanical barrier that prevent arrival of sperm to the egg, e.g., condom.
(ii) Chemical Drugs or contraceptive pills – Small dosage of female hormones that prevent released of egg.
(iii) Loop or copper-T- physical devices to prevent pregnancy.
(iv)Surgical method- permanent contraception by vasectomy and tubectomy.
Surgical methods: Vasectomy refers to surgical method in which vasa deferentia in human males are cut and sealed to prevent pregnancy by making seminal fluid devoid of sperms. Tubectomy refers to surgical process in which oviducts in human females are cut and sealed to prevent pregnancy by inhibiting released of egg.
Question. 56 How does fertilization take place? Fertilization occurs once in a month. Comment.
Answer.
Fusion of male gamete sperm and female gamete egg in fallopian tube (oviduct) is called as fertilization. The process starts with introduction of sperms, produced in testes of male, into the vagina of the woman through penis during copulation or mating. Highly active and mobile sperms pass from cervix through the uterus into the oviducts. Ovulation, in female, releases ovum in oviduct. Irrespective of release of millions of sperms into the vagina at one time, only one sperm fuses with the ovum in the oviduct to form a zygote i.e. fertilization.
Ovulation is release of ovum from ovary into oviduct and takes place only once in a month i.e. 14th day of menstrual cycle. Hence, fertilization can occur only once in a month.
Question. 57 Reproduction is essentially a phenomenon that is not for survival of an individual but for the stability of a species. Justify.
Answer.
Each species faces many forces that reduce the number of individuals constantly. Some of them are namely struggle for survival, competition for natural resources, predation, natural cycle of ageing and death, any natural calamity etc. All these natural forces reduce the number of individuals per species.
Reproduction is the process of production of own kind. It includes production of offspring having both similarities and variations among themselves and from parents. Further, the process of DNA replication and its inheritance to offspring ensure production of own kind only. Therefore, reproduction not only restore the number of individuals removed from the species by above mentioned natural forces but also maintain heredity of genetic characters and introduction of variations, as needed for continuity and stability of a species. Without it, all of the existing species will diminish soon and life will come to an end.
Question. 58 Describe sexually transmitted diseases and mention the ways to prevent them.
Answer.
Sexually Transmitted Diseases are the infectious diseases that are transmitted during unprotected sexual intercourse from infected partner. Example: bacterial infections like gonorrhoea and syphilis, and viral infections like warts and HIV-AIDS. STD caused by bacteria infection (e.g., chlamydia, gonorrhea, and syphilis) are treatable with antibiotics. To prevent STDs, the following precautions can be taken.
(i) Practices involving protected sexual intercourse reduce the risk in STD.
(ii) Avoid multiple sex partners and maintain personal hygiene.