CBSE Class 10 Science How Do Organisms Reproduce Notes Set A

Class-X

Chapter 8: How do organisms reproduce?

Points to remember

Key learnings:

1) Reproduction is the biological process by which new individuals of the same kind are produced.

2) Reproduction is not essential for the survival of an organism, but is vital for the survival of a species.

3) Reproduction produces identical copies of the body design.

4) DNA is the informational macromolecule of our body. It provides information for protein synthesis.

5) During cellular reproduction, DNA duplication occurs followed by creation of an additional cellular apparatus.

6) The process of DNA copying is not accurate, resulting in variations arising during reproduction, which is the basis for evolution.

7) Variations may or may not be beneficial for the individual, but help in the survival of the species during adverse conditions.

8) Depending on their body design, the modes of reproduction differ in different organisms.

9) Reproduction is broadly divided into asexual and sexual reproduction.

10) Fission, fragmentation, regeneration, budding, vegetative propagation and spore formation are various modes of asexual reproduction.

11) Fission occurs in unicellular organisms like bacteria and protozoa through simple cell division. Depending on the number of individuals formed, fission may be binary or multiple fission.

12) On maturation, certain multi-cellular organisms (with simple body makeup) break up into smaller fragments, each of which develops into new individual. This reproductive method is called fragmentation.

13) Simple reproductive methods cannot occur in higher multi- cellular organisms, since they have a complex and carefully organized body structure.

14) In complex multi-cellular organism, reproduction is brought about by a single, specialized cell type that is capable of proliferating and forming all other cell types of the body.

15) Regeneration is found in many completely differentiated simple organisms, like Hydra and Planaria. If such an organism is split into several parts, most of the parts will develop into complete organisms.

16) Regeneration involves specialized totipotent cells which proliferate and differentiate to form the complete body.

17) Certain organisms like Hydra produce buds on their body surface, which mature into new individuals and separate from parent body.

18) Vegetative propagation is used by many plants, especially those incapable of producing seeds. Here, new plants are produced from roots, stems or leaves of parent plant. This reproductive method is widely used by plant breeders.

19) Spore formation is an asexual mode of reproduction found in certain multicellular organisms like Rhizopus. The thick walled spores have the capacity to develop into new individuals

20) Sexual reproduction requires both male and female sexes to produce the offspring.

21) Sexual reproduction creates large number of novel variations.

22) In comparison to the non-reproductive body cells, the germ cells contain only half the chromosome number.

23) The male gamete is smaller and motile whereas the female gamete is larger and stores food.

24) When the offspring is produced by the union of the male and female gametes, its specific chromosome number and DNA content is re-established.

25) In angiosperms, flower is the reproductive organ of the plant.

26) Stamen, the male reproductive part of flower, is made up of anther and filament. Carpel is the female reproductive part and is composed of stigma, style and ovary.

27) The pollen grain is present in the anther whereas the egg cell is enclosed in the ovary. .

28) Pollination and fertilization are two essential events in reproduction of angiosperms.

29) Pollination is the transfer of pollen grains from anther to stigma. It may be either self-pollination or cross-pollination.

30) Pollen tube carries the male gamete from stigma to the female gamete in ovary.

31) Fertilization of male and female gametes produces the zygote, which then forms the embryo.

32) Following fertilization, the ovule develops into seed whereas the ovary forms the fruit. On germination, the seed develops into a seedling.

33) In humans, reproduction occurs sexually.

34) Puberty is the time when the juvenile body of a person starts sexual maturation.

35) Before puberty, the body resources are used mainly to grow and develop the organism to its adult size. Once this is achieved, puberty sets in.

36) Some changes occurring during puberty are common to boys and girls, whereas other changes are specific to boys and girls.

37) Changes such as appearance of pimples on face, growth of thick hair in armpits and genital areas occur in both boys and girls.

38) Increase in breast size, darkening of nipples and occurrence of menstruation are puberty associated changes in girls. In boys, facial hair growth, cracking of voices and occasional enlargement of penis occur during puberty.

39) Changes associated with puberty are slow and gradual and does not occur uniformly in everyone.

40) The changes taking place during puberty, signals the occurrence of sexual maturation in an individual to other members of the same population.

41) In humans, the male reproductive system is composed of testes, vas deferens, seminal vesicles, prostate gland, urethra and penis.

42) Testis is situated outside the abdominal cavity. It produces sperms and secretes testosterone.

43) Sperm shows a small head containing the genetic material and a long tail, which helps in motility.

44) Vas deferens and urethra are the thin tubes through which sperms are transported from testes to outside. The sperms are nourished in the seminal fluid.

45) The female reproductive system is made up of ovaries, fallopian tubes, uterus, cervix and vagina.

46) Ovaries are responsible for production of ova/egg as well as for secreting the hormones, estrogen and progesterone.

47) On reaching puberty, ovulation occurs once a month in females, wherein one immature egg present in any one of the ovaries becomes mature and is released. This egg is carried by the fallopian tube.

48) Sperms which are introduced into the vagina of females during intercourse, may encounter the egg on reaching the fallopian tube, resulting in fertilization.

49) The zygote gets implanted in the uterus and develops into the embryo.

50) The placenta provides nourishment and oxygen to the embryo and removes the waste generated by the embryo.

51) Gestation period is nine months in humans after which the child is born due to uterine contractions.

52) In case fertilization does not occur, the released egg along with the thickened lining of the uterus is shed out through the vagina in a process called menstruation.

53) Engaging in unprotected sexual intercourse can cause pregnancy as well as spreading of sexually transmitted diseases like gonorrhea, syphilis and AIDS. 

54) Condoms help to control the spread of sexually transmitted diseases.

55) Unwanted pregnancies can be avoided through several contraceptive methods.

56) Mechanical barrier methods prevent sperm from reaching the egg. E.g. – condom.

57) Oral contraceptive pills alter the hormonal balance, thereby preventing the egg from being released.

58) Surgical blocking of vas deferens in male or fallopian tube in female can also prevent pregnancy.

59) Abortions remove unwanted pregnancies, but this method is being misused to carry out female foeticide.

60) Birth control methods are essential to keep the human population in check and thereby improve the standard of living for everyone.
 

Top definitions
 

1) Reproduction - The biological process by which new individuals of the same parental kind are produced.

2) Variation – The differences found among individuals of a group or species, caused either by genetic differences or by the effect of environment on genes.

3) Asexual reproduction – Reproduction in which new generations are created from a single individual.

4) Fission – A type of asexual reproduction in which the unicellular parent organism divides into two or more parts, each developing into genetically identical individuals.

5) Binary fission – Fission in which the parent cell divides to form two similar daughter cells.

6) Multiple fission – Fission in which the parent cell divides to produce more than two daughter cells.

7) Fragmentation – The reproductive method in which certain multi- cellular organisms, on maturation, break up into smaller fragments, each of which develops into new individual.

8) Budding – The reproductive method in which an organism produces an outgrowth on its body surface, which then matures and develops into a new individual.

9) Vegetative propagation – The reproductive method in which new plants are produced asexually from roots, stems or leaves of the parent plant.

10) Spore - A small, usually single-celled reproductive body produced by certain fungi, bacteria, algae, and nonflowering plants, which is highly resistant to desiccation and heat and is capable of growing into a new organism.

11) Sexual reproduction - Mode of reproduction in which new individuals are produced by fusion of a male and a female gamete.

12) Pollination – Transfer of pollen grains from the anther to the stigma.

13) Self-pollination – Transfer of pollen grains from the anther to the stigma of the same flower.

14) Cross-pollination – Transfer of pollen grains from the anther of one flower to the stigma of another flower.

15) Fertilization – Fusion of male and female gametes to form zygote, which eventually develops into an embryo.

16) Germination – The process in which a seed develops into a seedling under appropriate conditions.

17) Puberty - The period during adolescence when a child's body becomes sexually mature and develops into adult form.

18) Sperm – The male reproductive cell or gamete produced in the testes.

19) Ova – The female reproductive cell or gamete produced in the ovary. 

20) Ovulation – The periodic release of an ovum from the ovary.

21) Menstruation - The monthly discharge of blood and shed mucous lining of the uterus through the vagina of non-pregnant women from puberty to menopause.

22) Contraception – The prevention of conception by the use of birth control devices or pills or surgery.

Top diagrams

Asexual reproduction: The process of producing offsprings which involves a single parent without the formation of gametes is called asexual reproduction.

Spore: A spore is a single-celled or multi-celled reproductive structure which gets separated from its parent and under favourable conditions gives rise to new individual.

Seed: A seed is the reproductive unit of a plant from which a new plant grows.

Vegetative propagation: It is mainly seen in plants and is an asexual mode of reproduction where a new plant grows from different parts of plant like roots, stem, leaves etc., rather than from a seed.

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

Pollination: The process of transfer of pollen grains from anthers of stamens to the stigma of carpel within the same flower or different flower of same plant or to any other flowers of
different plants but of same species is called pollination.

Double fertilisation: The process by which a male gamete fuses with an egg to form zygote and the second male gamete unites with two polar nuclei to form endosperm is called double fertilisation.

Primary sex organs: They are the gonads i.e., testes and ovaries which produce gametes and secrete sex hormones.

Gametes: The special cells involved in sexual reproduction to produce the offsprings are called gametes or sex cells.

Puberty: The age at which sex hormones are produced, reproductive organs become matured and have the capacity to give rise to new individual and there is development of secondary sexual characters in both males and females.

Fertilisation: The process of fusion of male and female gametes to produce the zygote is called fertilisation.

Gestation period: It is the time from fertilisation till the birth of the new born.

Parturition: The delivery of full term baby from the uterus of mother after the end of gestation period is called parturition.

Important Questions for NCERT Class 10 Science How Do Organisms Reproduce

Question. A sexual reproduction in plants which produces seed without fertilization is known as :
(A) Parthenogenesis
(B) Sporulation
(C) Apomixis
(D) Vegetative reproduction
Answer : C

Question. Which one of the following is a character of self-pollinated flower ?
(A) Flowers are large and showy.
(B) Petals remain closed and do not open
(C) Stigma and another mature at different time.
(D) Pollens are produced in a very large quantities.
Answer : B

Question. In human female, immature eggs are for the first time seen in ovary
(A) at puberty
(B) before birth, at the fetus stage
(C) during the first menstrual cycle
(D) after the first year birth.
Answer : B

Question. Period of complete development of foetus starting with implantation till the birth of young one called as
(A) Gestation period
(B) Parturition
(C) Pregnancy
(D) both (A) and (C)
Answer : D

Question. The following figure shows which process

(A) Vegetative reproduction
(B) Multiple fission
(C) Regeneration
(D) Budding
Answer : C

Question. Double fertilization is a unique feature of :
(A) Bryophytes
(B) Angiosperm
(C) Algae
(D) Gymnosperm
Answer : B

Question. In seed plants, the non-motile gametes are carried to female gamete by :
(A) Air
(B) Pollen tube
(C) Water
(D) Insects
Answer : B

Question. Menopause is the stage in female when
(A) Menstruation starts
(B) Puberty
(C) Reproduction capacity arrested
(D) Ovaries enlarges
Answer : C

Question. The vegetative reproduction in Bryophyllum takes place through which organ ?
(A) Root
(B) Stem
(C) Leaf
(D) Seed
Answer : C

Question. A pollen tube, produced from the pollen grain, contains .. male gametes
(A) One
(B) Two
(C) Seven
(D) Eight
Answer : B

Question. Growth of pollen tubes towards ovule for ‘fertilization is due to ....
(A) Thigmotropism
(B) Phototropism
(C) Chemotropism
(D) Hydrotropism
Answer : C

Question. If you want to produce plants like orange, grape, rose for commercial purpose, which method do you choose.?
(A) Cutting
(B) Grafting
(C) Tissue culture
(D) Layering
Answer : A

Question. In the following diagram, ABC are :

(A) Cotyledon, Plumule, Radicle
(B) Plumule, Redicle, Cotyledon
(C) Radicle, Cotyledon, Plumule
(D) Plumule, Cotyledon, Radicle
Answer : D

Question. Which is the common method of artificial reproduction in plants ?
(A) Cutting
(B) Layering
(C) Grafting
(D) All of them
Answer : D

Question. The production of plants through tissue culture is known as :
(A) Parthenocarpy
(B) Polyembryony
(C) Fragmentation
(D) Micropropagation
Answer : D

Question. Seed is modification of
(A) ovary
(B) ovule
(C) thalamus
(D) all of these.
Answer : B

Question. Human egg and sperm are similar in that :
1. About the same number are produced per month.
2. Both have the same degree of motility.
3. The have the same number of chromosomes.
4. They are about the same size.
Choose the right option
(A) 1 and 2
(B) 3 and 4
(C) Only 3
(D) All the above
Answer : C

Question. Select the correct statement in the following and choose the correct option :
i. Double fertilization occurs in flowering plants.
ii. After maturation ovary change into seed
iii. Zygote develops into embryo
iv. Pollen grains form in stigma
(A) i and iv
(B) i, ii, and iii
(C) i and iii
(D) All of the above
Answer : C

Question. Grafting in monocot plants is not possible because they have :
(A) Parallel venation
(B) Have only one cotyledon
(C) Have cambium
(D) Have scattered vascular bundles
Answer : D

Fill in the blanks.

Question. All plants produced by vegetative propagation are ...... similar.
Answer : genetically

Question. Sperm formation requires ...... temperature than the normal body temperature.
Answer : lower

Question. The spores of Rhizopus are covered by ...... that protect them until they come into contact with moist surface.
Answer : thick walls

Question. Mechanical barriers do not allow ...... between sperm and egg.
Answer : fusion

Question. The terminal part of carpel is called ...... .
Answer : stigma

Question. Placenta is embedded in the ...... wall.
Answer : uterine

Question. Both vasectomy and tubectomy ensure that ...... will not take place.
Answer : fertilization

Question. Pollen grains are produced in ...... .
Answer : stamen

Question. The egg is carried from the ovary to the womb through ...... .
Answer : Fallopian tube

Question. The embryo is connected to the ...... by ...... .
Answer : placenta, umbilical cord

Question. Small fragments of ...... filament grow into new individuals.
Answer : Spirogyra

Question. Pollen tube reaches the ovary through ...... .
Answer : style

Question. The embedding of embryo in the wall of the uterus is called ...... .
Answer : implantation

Write Yes/No.

Question. Do DNA from two different individuals combine during sexual reproduction?
Answer : Yes

Question. Does the ovule develop into seed beforefertiliza tion?
Answer : No

Question. Can we say that grafting is not useful for agriculture?
Answer : No

Question. Is fruit formed from ovary?
Answer : Yes

Question. Is variation unimportant for the survival of species over time?
Answer : No

Question. Is the period during adolescence called puberty?
Answer : Yes

Question. Does Spirogyra reproduce by any other means than fragmentation?
Answer : No

Question. Do testes secret testosteron?
Answer : Yes

Very-Short-Answer Questions

Question. Give two exampleswhere self-pollination takes place.
Answer : Self-pollination takes place in pea and Hibiscus.

Question. Give two examples where spore formation is the common mode of reproduction.
Answer : Rhizopus(bread mould) and Mucor reproduce by spore formation.

Question. Why are petals brightly coloured?
Answer : Brightly coloured petals attract insects and so help in pollination.

Question. When does embryo germinate?
Answer : The embryo germinates when it finds favourable environmental condition.

Question. Where are sperms produced?
Answer : Sperms are produced in the testes.

Question. Where is ovary located in a plant?
Answer : Ovary in a plant is located at the base of carpel in gynoecium.

Question. What is the importance of tubectomy?
Answer : Tubectomy prevents the passage of ova down the Fallopian tube, thus ensuring fertilization does not happen.

Question. Where do pollen grains germinate?
Answer : Pollen grains germinate on the stigma.

Question. Give an example where multiple fission is found.
Answer : Multiple fission is found in Chlorella.

Question. What is the reproductive organ of a male flower?
Answer : Androecium

Short Answer Type Questions

Question. What is the importance of DNA copying in reproduction?
                                        OR
Why is DNA copying an essential part of the process of reproduction?
Answer : Reproduction involves producing same kind of species from parents. The genetic information is passed to the offspring by DNA present in each cell. This DNA, which is replicated (copied) is responsible for the resemblance of parents with offsprings with same traits. New traits are passed on due to difference in copying, new variations may occur and new species may evolve.

Question. (a) What is the location of following: (i) DNA in a cell,
(ii) Gene (b) Expand DNA.
Answer : (a) (i) DNA is found in nucleus of cell, (ii) Genes are located on the chromosomes.
(b) Deoxyribonucleic acid.

Question. (a) (i) Write full form of DNA.
(ii) State the role of DNA in the cell nucleus.
(iii) What will be the effect if the information of the DNA is changed?
(b) Explain the importance of DNA copying in reproduction.
Answer : (a) (i) Deoxy Ribonucleic Acid
(ii) It helps in synthesis of protein and transfer of genetic characteristics.
(iii) Proteins will be changed.
(b) Body designs are similar due to DNA copying.
DNA cell nucleus carry information for synthesis of protein.
If DNA copying will not take place then body design will change.

Question. When a cell reproduces, what happens to its DNA?
Answer : During the process of reproduction, transmission of DNA from parents to offspring takes place. Before reproduction, DNA is replicated, which means two copies of DNA are produced. When the cell divides into two, these two copies are distributed equally between the two daughter cells so that similar amount and type of DNA is transferred from the parent cell to the daughter cells. It maintains the consistency in the amount and type of DNA in the living organism of a particular species.

Question. How does reproduction help in providing stability to the populations of species?
Answer : It is because reproduction is a process by which species increase their population. If the rate of birth is more than death, the size of population will increase and will be more stable.

Question. Reproduction is one of the most important characteristics of living beings. Give three reasons in support of the statement.
Answer : Reproduction is an energy consuming process which is not essential for the survival of an individual.
But it is the most important characteristic of all living beings, because of the following reasons:
(i) Reproduction helps in increasing the number of members of a population.
(ii) By replacing the dead members with the new ones, it minimises the risk of extinction of a species.
(iii) It brings about variations in species, thus leading to their evolution.

Question. Why is variation beneficial to the species but not necessary for the individual?
Answer : If environmental conditions undergo drastic change, some member of a species having variations of tolerating changed temperature may be able to survive, e.g. suppose population of bacteria is living in temperate water. If temperature of water increases due to global warming, most of the bacteria will die. However, if few variants are resistant to heat, then they would survive and grow further. Thus variation is useful for the survival of species over time, but it is not necessary for the individual

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