CBSE Class 10 Science How Do Organisms Reproduce

1. Advantages of VegetativePropagation

It allows quicker and easy propagation/exact copy of the parent/ seedless plant propagation.

2. Disadvantages of Vegetative Propagation

Vegetative propagation doesn‟t favour much variation and evolution of new species.

3. Regeneration is the ability of an organism to regenerate the lost part.(eg:arm regeneration in star fishes).Sometimes,an organism can be made from its fragmented body parts.e.g. Planaria.

4. Flower is the reproductive part of the plant .A complete flower has four whorls-sepals, petals, stamens and carpels.

5. Unisexual flowers and bisexual flowers

Unisexual flowers                                           Bisexual flowers

Have either stamen or carpel                           Have both stamen and carpel    

e.g.Water melon, papaya                                e.g. hibiscus, rose

6. Pollination: Transfer of pollen grains from anther lobe to the stigma of the flower.

                                        Pollination

Self pollination                                           Cross pollination

7. Post pollination changes in plants Growth of pollen tube/motion of male gametes towards the ovule/ fertilisation

8. Fertilised ovule develops in to seed and ovary develops into fruit

9. Unisexual and bisexual organisms

10. The fusion of male and female gamete is called fertilisation.

12. On reaching puberty,one egg is produced every month by one of the ovaries.The release of egg by the ovaryiscalled ovulation, which takes place at 12-16 th day of menstrual cycle.During that time ,if sexual contact takes place,sperm fuses with the egg producing zygote which get implanted in the uterus at 32 cell stage.

13. It is through placenta glucose and oxygen are given to the developing embryo and waste materials are removed from embryo and given to the mothers blood.

14. Common birth control measures (a) Physicalbarriermethodslikecondoms and vaginal diaphragm/chemical methods like oral or vaginal pills/ surgical methods like tubectomy in females and vasectomy in males/IUCD e.g. Copper T

15. STD are sexually transmitted diseases spread through sexual contact with the infected Person.Common bacterial STDs are syphilis and gonorrhea..AIDS (Acquired ImmunoDeficiency Syndrome) and warts are examples of viral STDs

CBSE Class 10 Science Chapter 8 How Do Organisms Reproduce MCQs

Question. If there is no formation of egg cell during the development of ovule, then after fertilisation which of the following structure will not develop?
(a) Embryo
(b) Endosperm
(c) Seed
(d) Fruit 
Answer. A

Question. Which of the following statements are incorrect about puberty?
(i) Body shows starting of sexual maturity at this stage.
(ii) The rate of general body growth begins to proceed faster as the reproductive tissues begin to mature.
(iii) Changes taking place in the body parts are different in boys and girls.
(iv) All the changes during puberty takes place very fast.
(a) (iii) and (iv)
(b) (ii) and (iv)
(c) (i), (ii) and (iii)
(d) (i), (ii), (iii) and (iv)
Answer. D

Question. Which of the following match is correct?
(a) Cotyledon – Food store
(b) Plumule _ Future shoot
(c) Radicle – Future root
(d) All of these
Answer. B

Question. Select the incorrect statement regarding seeds.
(a) Seeds have tough seed coat that protects them from external environment.
(b) Cotyledons store food.
(c) Plumule develops into the root system.
(d) Seeds contain the future plant called embryo.
Answer. D

Question. Which of the following is not a surgical method of birth control?
(i) Copper-T         (ii) Tubectomy
(iii) Vasectomy   (iv) Using condoms
(a) (i) and (iv)
(b) Only (iv)
(c) (ii), (iii) and (iv)
(d) (i), (ii) and (iii)
Answer. A

Question. IUCD is for
(a) vegetative propagation
(b) contraception
(c) increasing fertility
(d) avoiding miscarriage.
Answer. B

Question. Which of the following diseases is transmitted sexually?
(a) Sleeping sickness
(b) Jaundice
(c) Elephantiasis
(d) Syphilis
Answer. D

CBSE Class 10 Science Chapter 8 How Do Organisms Reproduce Very Short Answer Type Questions

Question. What is the function of pollen grains in flowers?
Answer. Pollen grains produce male gametes which fertilise the egg cell present in the ovule.

Question. What changes occur in the flower after fertilisation?
Answer. After fertilisation, the flower withers. The sepals and the petals dry up, the ovary converts into fruit, the ovule forms the seed and the zygote forms the embryo which is enclosed in the seed.

Question. Mention any one limitation of vegetative propagation.
Answer. One limitation of vegetative propagation is that it does not show genetic variation.

Question. Why is fertilisation in flowering plants not possible without pollination?
Answer. Pollination allows pollen grains to reach carpel which contains the egg. Thus, fertilisation which involves fusion of male and female germ cells can occur only after pollination.

Question. Name the parts in human body where sperms and eggs are produced.
Answer. Sperms are produced in testes (males) and eggs are produced in ovary (female).

Question. Why copper - T cannot protect a woman from sexually transmitted diseases?
Answer. Copper-T is an intrauterine device which acts as contraceptive but does not provide protection against sexually transmitted diseases as it does not provide any barrier against mixing of body fluids from two individuals.

Question. Name the type of reproduction which
(a) involves gametes
(b) Does not involve gametes.
Answer. (a) Sexual reproduction
(b) Asexual reproduction.

Question. Define puberty.
Answer. It is the beginning of development for sexual maturity which occurs at the age of 10-14 years in girls and 13—15 years in boys. Fully formed primary sex organs start secreting hormones for slow development of secondary sex organs and secondary sex characters.

Question. Newly formed DNA copies may not be identical at times. Give one reason.
Answer. Error in DNA copying due to incorporation of wrong nucleotide.

Question. Name two simple organisms having the ability of regeneration.
Answer. Hydra, Planaria.

Question. What are those organisms called which bear both the sex organs in the same individual? Give one example of such organism.
Answer. Bisexual or hermaphrodite, eg. Mustard, Hydra.

Question. How is the process of binary fission in Amoeba different from that of Leishmania?
Answer. In Amoeba, binary fission can occur in any plane. In Leishmania the plane of division is vertical.

CBSE Class 10 Science Chapter 8 How Do Organisms Reproduce Short Answer Type Questions

Question. Why is variation so important?
Answer. Variation is so important because
(i) Populations of organisms normally live and interact with definite kinds of ecological niches. If there is an alteration in the ecological conditions of such places, the population of organisms will get damaged and may be wiped out. The variants of the organisms, however, may have better chances of survival. The surviving individuals may reproduce and develop a kind of population which is suited to the changed niche.
(ii) It makes some individuals better fitted in the struggle of existence.
(iii) It helps the individuals to adapt themselves according to the changing environment.
(iv) It allows breeders to improve races of useful plants and animals for increase resistance, better yield, quicker growth and lesser input.
(v) Preadaptation caused by the presence of neutral variations are extremely useful for survival against sudden changes in environment e.g., resistance against a new pesticide or antibiotic.
(vi) It constitutes raw material for evolution.
(vii) It gives each organism a distinct individuality.

Question. “Multicellular organisms cannot divide cell by cell”. List two reasons to justify this statement.
Answer. 1. In multicellular organisms, cell by cell division is a method of growth and not a method of multiplication as in unicellular organisms.
2. Multicellular organisms have developed complex and specialised reproductive structures which are not possible in single celled organisms.

Question. (a) Name the organ which helps in providing nutrition to embryo. Where is it located?
(b) What causes the delivery of child from mother’s uterus?
Answer. ( a) Placenta is the organ which provides nourishment to the embryo. It is formed jointly by embryo and uterus. Placenta is located in the uterus of the mother.
(b) Foetal ejection reflex is produced in response to signals from fully formed foetus and its supporting placenta.

Question. (a) Write the advantage of sexual reproduction over asexual reproduction.
(b) Name the male and female parts of a flower.
Answer. (a) Advantage of Sexual Reproduction. Sexual reproduction introduces variations and maintains the vigour and vitality of the individuals.
(b) Male—Stamens.
Female—Carpels.

Question. (a) Differentiate between unisexual and bisexual flowers.
(b) Which of the following plants produce unisexual flowers: Watermelon, Hibiscus, Mustard, Papaya?
Answer. ( a) Unisexual flowers are those flowers which possess only one type of reproductive organs, either stamens or carpels. Bisexual flowers are those flowers which have both the types of reproductive organs, i.e., stamens and carpels.
(b) Watermelon, Papaya.

Question. (a) List two events during binary fission in Amoeba.
(b) In which two of the following organisms, regeneration takes place: Lion, Planaria, Hydra, Lotus.
Answer. (a) 1. Elongation of nucleus followed by division into two.
2. Cleavage of cytoplasm in between the two daughter nuclei to form two daughter cells.
(b) Regeneration. Planaria, Hydra.

Question. (a) Name the process by which pollen grains are transferred from anther to stigma. Mention any one external agent which performs this process in some flowers. .
(b) Differentiate between its two types. Give one example of each.
Answer. (a)
1. Pollination
2. Air/Insects.
(b) Two types, self pollination and cross pollination. Self pollination is transfer of pollen grains from the anther to the stigma of the same flower (e.g., Commeliria, Wheat) while cross pollination is transfer of pollen grains from the anther of one flower to the stigma of another flower of the same species (e.g., Salvia).

Question. List the modes of pollination and define each of them.
Answer. Pollination is of two types, self pollination and cross pollination.
Self Pollination. It is the transfer of pollen grains from the anther to the stigma of the same flower, e.g., Commelina, Wheat.
Cross Pollination. It is the transfer of pollen grains from the anther to the stigma of another flower of the same species, e.g., Salvia.

Question. (a) Name the structure in human male reproductive system that delivers the sperms from the testes to the urethra.
(b) Name the structure in human female reproductive system which delivers the egg from the ovary to the uterus.
Answer. (a) Vas deferens
(b) Fallopian tube.

Question. (a) Differentiate between reproduction and regeneration.
(b) Name any two organisms which grow by regeneration.
Answer. (a) Reproduction is the formation of new individuals by the grown up organisms with the help of propagules or germ cells. Regeneration is growth of injured parts of the individuals for repair and replacement of lost parts.
(b) Planaria and Hydra can grow by regeneration.

Question. (a) Which organ is responsible for implantation of zygote?
(b) State the function of fallopian tubes.
Answer. (a) Zygote (in the form of blastocyst) gets implanted in uterus with the help of villi.
(b) i. Fallopian Tubes,
ii. Conduct ovum from ovary to uterus,
iii. Fertilization occurs inside fallopian tube.

Question. What is pollination? How does it take place?
Answer. Pollination is the transfer of pollen grains from an anther to a stigma. Pollination between anther to the stigma of the same flower is called self pollination. It occurs through contact between the two.
Pollination between anther of one flower and stigma of another flower is cross pollination. It requires an external agency which may be abiotic (wind, water) or biotic (insects, birds, bats, worms, etc.).

Question. Name and explain in brief the four different methods of contraception.
Answer. Contraception literally means prevention of pregnancy.
Different methods for the prevention of pregnancy are as follow:
(i) Barrier methods in which a mechanical barrier such as condom, cervical cap or diaphragm is used for preventing the entry of sperms in the female genital tract or vagina. Thus, sperms and egg do not meet and fertilisation is prevented from taking place.
(ii) Chemical methods of contraception are those in which release of eggs from the ovary can be prevented by the intake of pills by the female. The oral pills are hormonal preparations and are also termed as oral contraceptives.
(iii) Intra-Uterine Contraceptive Devices (IUCDs) are placed in the uterus to prevent pregnancy. These devices are very effective and popularly used by females. Copper-T and Lippes Loop are examples of IUCDs. These devices are placed in the uterus by skilled personnel.
(iv) Surgical method : Contraception can also be brought about by surgically removing or tying a part of vas deferens (vasectomy) in the male and removing or tying a part of fallopian tube (tubectomy) in the female. Surgery should be performed by well trained doctors under sterile conditions.

Question. List two functions each of the following parts of human female reproductive system.
(a) Ovaries (b) Fallopian tubes (c) Uterus
Answer. (a) Ovaries : (i) It produces ovum.
(ii) It secretes female sex hormone.
(b) Fallopian tubes : (i) It conveys the ovum from the ovary to the uterus.
(ii) It acts as site for fertilisation.
(c) Uterus : (i) It nourishes the fertilised ovum which develops into the fetus.
(ii) It holds the fetus till the baby is mature enough for birth.

Question. What happens when the egg is not fertilised in human females? 
Answer. One egg is produced every month by one of the ovaries.
The uterus prepares itself every month to receive and nurture the growing embryo. The lining thickens and is richly supplied with blood to nourish the growing embryo. If the egg is not fertilised, this lining is not needed any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucus. This cycle takes place roughly every month and is known as menstruation. It usually lasts for about two to eight days.

Question. What does HIV stands for? Is AIDS an infectious disease? List any four modes of spreading AIDS.
Answer. HIV stands for Human Immunodeficiency Virus.
Yes, AIDS is an infectious disease. It is transmitted sexually or through exposure to contaminated blood.
Four modes of spreading AIDS are :
(i) Unprotected sex with an infected partner
(ii) Use of contaminated needle and syringes
(iii) Use of contaminated razors for shaving
(iv) Transfusion of infected blood or blood products.

Question. What is vegetative propagation? How does vegetative propagation take place in potato?
Answer. Vegetative propagation is the process of formation of the plant from vegetative propagules or units, such as stem, root, leaf, buds, etc. Tuber of potato is the swollen underground stem and bears number of nodes or eyes. Each eye bears one or many buds. New plants are produced from the buds on the eyes of the stem tuber.

Question. (a) Why has Government of India prohibited prenatal sex determination by law? State its benefits in the long run.
(b) Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections caused due to unsafe sex.
Answer. (a)Prenatal sex determination was banned in India in 1994. This was done to prevent sex selective abortion. It is being used to kill the normal female fetus. This killing of the unborn girl child is called female feticide which is reducing the number of girls drastically in some societies of our country. Due to reckless female feticide, male–female sex ratio is declining at an alarming rate. Its benefit in the long run is that the female-male ratio could be maintained for a healthy society.
(b) Bacterial diseases due to unsafe sex are gonorrhoea, syphilis.
Viral diseases due to unsafe sex are AIDS, genital herpes.

Question. (a) List few disadvantages of vegetative propagation?
(b) What is placenta? Explain its functions in humans.
Answer. (a) Some disadvantages of vegetative propagation are:
(i) Plants produced by this technique possess less vigour.
(ii) They are more prone to diseases.
(iii) They show no genetic variations.
(b) Placenta is a specialised tissue between fetus and uterine wall of mother. It develops finger-like processes called villi, which grows into tissue of the uterus.
Functions of placenta are listed below :
(i) Provides nutrition
(ii) Helps in the exchange of gases such as oxygen and carbon dioxide
(iii) Helps in the excretion, that is the removal of nitrogenous waste material from the fetal blood to that of the mother.
(iv) It secretes hormones such as estrogen and progesterone.
(v) Placenta provides protection by partitioning the blood of the fetus and the mother. Thus, unwanted materials such as germs cannot contaminate the blood of the fetus.
(vi) Acts as a storage of glycogen. This glycogen gets converted to glucose and fulfils the energy requirement of the fetus.

Question. Reproduction is linked to stability of population of a species. Justify the statement.
Answer. Reproduction is the only means to ensure the continuity of a species. During reproduction, DNA passes from one generation to the next. Copying of DNA takes place with consistency but with minor variations. This consistency leads to stability of species. Hence, reproduction is linked to stability of a species population. By reproduction, organisms produce large number of new individuals of their own kind out of which several get perished and only some survive. These surviving organisms replace the naturally dying members of the population. Hence, the population as a whole is not affected and remains stable.

Question. Differentiate between natural and artificial vegetative propagation in plants.
Answer. Differences between natural and artificial propagation in plants are as follows:

Question. Suppose there is no meiosis and the gametes are formed by mitotic divisions. What kind of situation do you expect under such circumstances?
Answer. Normally the two haploid gametes fuse to form one diploid zygote. The zygote develops into a mature organism. At maturity, the organism develops sex organs and gametes are formed from diploid cells by meiosis resulting in the formation of haploid gametes. This process continues generation after generation. Now if there is no meiosis at the time of gamete formation the gametes formed as a result of mitosis will be diploid. The two diploid gametes will fuse to form a 4n zygote which develops in tetraploid organism. Again this 4n organism will develop 4n gametes which fuse to form 8n zygote. The number of chromosomes will continue to double after each generation and a time will come when there will be only DNA on earth.

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