CBSE Class 10 Science How Do Organisms Reproduce

1. Advantages of VegetativePropagation

These CBSE Class 10 Science notes on Chapter 8, How Do Organisms Reproduce, cover asexual reproduction in plants and animals (fission, fragmentation, regeneration, budding, spore formation and vegetative propagation), sexual reproduction in flowering plants, pollination and fertilisation, the human reproductive system, reproduction and birth control measures, and sexually transmitted diseases. A question bank with answers for the chapter is included at the end.

Chapter 8: How Do Organisms Reproduce

Reproduction: Concept Map

Asexual reproduction in plants:
1. Vegetative propagation, e.g. rose
2. Spore formation, e.g. fungi
3. Fragmentation, e.g. Spirogyra

Asexual reproduction in animals:
1. Budding, e.g. Hydra
2. Regeneration, e.g. Planaria
3. Fission: binary fission, e.g. Amoeba; multiple fission, e.g. Plasmodium

Sexual reproduction:
1. In plants: stamen (male part) produces pollen, which forms the male gamete; carpel (female part) has the ovary, which contains the female gamete. Fusion of the gametes forms the zygote, which develops into an embryo.
2. In animals: testis produces sperm (male gamete) and ovary produces egg (female gamete). Fusion of the sperm and egg forms the zygote, which develops into an embryo.

Reproduction: Overview Flow Chart

• Reproduction
  • Asexual Reproduction
    • Fission
      • Binary Fission
        • Division in any plane, e.g. Amoeba
        • Division in single plane, e.g. Leishmania
      • Multiple Fission
    • Fragmentation
    • Regeneration
    • Budding
    • Vegetative Reproduction
      • Cutting
      • Grafting
      • Layering
    • Spore Formation
  • Sexual Reproduction
    • In Plants
      • Male Reproductive Part / Stamen
      • Female Reproductive Part / Carpel
      • Pollination
        • Self Pollination
        • Cross Pollination
      • Fertilization
      • Post Fertilization Changes
        • Zygote \(\rightarrow\) Embryo
        • Ovary wall \(\rightarrow\) Fruit
        • Ovule \(\rightarrow\) Seed
  • Human Reproductive System
    • Male: Testes, Scrotum, Vas deferens, Seminal vesicles, Prostate gland, Urethra
    • Female: Ovary, Oviduct / Fallopian tube, Uterus, Cervix, Vagina
    • Birth Control Measures
      • Barrier method, e.g. Condoms, Diaphragm
      • Chemical method, e.g. hormonal pills, Copper-T / Loop
      • Surgical method, e.g. Male: Vasectomy; Female: Tubectomy

Asexual Reproduction

Fission: the parent cell divides into two or more new cells.
Binary fission: division in any plane, e.g. Amoeba. Division in a single plane is also seen, e.g. Leishmania.
Multiple fission: the parent divides into many daughter cells at once, e.g. Plasmodium.
Fragmentation: the body breaks into pieces, and each piece grows into a new organism, e.g. Spirogyra.
Regeneration: the ability of an organism to regenerate a lost part, e.g. arm regeneration in starfish. Sometimes a whole organism can be made from its fragmented body parts, e.g. Planaria.
Budding: a new individual develops as a bud from the parent body, e.g. Hydra.
Spore formation: spores are produced in sporangia and grow into new individuals, e.g. fungi such as Rhizopus.
Vegetative propagation: new plants grow from vegetative parts such as roots, stems and leaves, e.g. rose. Bryophyllum produces buds on the leaves. Methods of vegetative propagation include cutting, grafting and layering.

Advantages of vegetative propagation:
1. It allows quick and easy propagation.
2. It produces an exact copy of the parent.
3. It is the only method for propagating seedless plants.

Disadvantages of vegetative propagation:
Vegetative propagation does not favour much variation, so it does not help in the evolution of new species.

Sexual Reproduction in Flowering Plants

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

Unisexual and bisexual flowers:

Pollination: the transfer of pollen grains from the anther lobe to the stigma of the flower.
Self pollination: transfer of pollen from the anther to the stigma of the same flower or another flower on the same plant.
Cross pollination: transfer of pollen from the anther of one plant to the stigma of a flower on a different plant of the same species.

Post-pollination changes in plants: growth of the pollen tube, movement of the male gametes towards the ovule, and fertilisation.

Fertilisation: the fusion of the male and female gametes.

After fertilisation, the fertilised ovule develops into a seed, and the ovary develops into a fruit.

Unisexual and Bisexual Organisms

Unisexual organisms: have only male or only female reproductive organs, e.g. human beings, cats, dogs.
Bisexual organisms (hermaphrodites): have both male and female reproductive organs, e.g. flatworms, earthworms, leeches.

Human Reproductive System

Parts and functions:

Male reproductive system: testes, scrotum, vas deferens, seminal vesicles, prostate gland, urethra.
Female reproductive system: ovary, oviduct (fallopian tube), uterus, cervix, vagina.

Menstrual Cycle, Ovulation and Pregnancy

On reaching puberty, one egg is produced every month by one of the ovaries. The release of the egg by the ovary is called ovulation, and it takes place on the 12th to 16th day of the menstrual cycle. If sexual contact takes place during this time, the sperm fuses with the egg to form a zygote. The zygote gets implanted in the uterus at the 32-cell stage.

Through the placenta, glucose and oxygen are supplied to the developing embryo, and waste materials are removed from the embryo and passed into the mother's blood.

Birth Control Measures

Barrier methods: condoms and the vaginal diaphragm, which prevent the sperm from reaching the egg.
Chemical methods: oral or vaginal pills (hormonal pills).
Intrauterine devices (IUCD): Copper-T or loop.
Surgical methods: vasectomy in males and tubectomy in females.

Sexually Transmitted Diseases (STDs)

STDs are diseases spread through sexual contact with an infected person. Common bacterial STDs are syphilis and gonorrhoea. AIDS (Acquired Immuno Deficiency Syndrome) and warts are examples of viral STDs.

Important Diagrams

[Figure 8.1: Binary fission in Amoeba. An Amoeba is shown dividing in stages into two daughter Amoebae.]
[Figure 8.2: Multiple fission in Plasmodium. The Plasmodium cell is shown with many small daughter cells formed inside its outer covering.]
[Figure 8.3: Regeneration in Planaria. A Planaria is shown cut into pieces, and each piece regrows into a complete worm.]
[Figure 8.5: Leaf of Bryophyllum with buds. Small plantlets (buds) are seen along the edges of the leaf.]
[Figure 8.6: Spore formation in Rhizopus. Sporangia on the tips of the fungal hyphae release spores into the air.]
[Figure 8.7: Longitudinal section of a flower. Labels: stigma, style, ovary, ovules, anther, filament (together forming the stamen), petal, sepal and pistil.]
[Figure 8.8: Germination of pollen on the stigma. Labels: pollen grain, stigma, pollen tube, male germ-cell, ovary and female germ-cell.]
[Figure 8.9: Germination of a seed. Labels: plumule (future shoot), cotyledon (food store) and radicle (future root).]
[Figure 8.10: Human male reproductive system. Labels: seminal vesicle, ureter, bladder, prostate gland, penis, urethra, vas deferens, testis and scrotum.]
[Figure 8.11: Human female reproductive system. Labels: oviduct (fallopian tube), ovary, uterus, cervix and vagina.]

Crossword

Across
1. Plasmodium reproduces by this method.
4. Male reproductive part of a flower.
5. Also called 'future shoot'.
6. Female reproductive part of a flower.
7. A contraceptive that creates a mechanical barrier.
9. An organism that reproduces by budding and regeneration.
11. The leaves of this plant produce buds for reproduction. (Answer printed in the grid: BRYOPHYLLUM)

Down
2. Embryo gets rid of waste through.
3. A STD.
8. The lower flask-shaped part of the carpel.
10. I am the blueprint of life.

Crossword grid (as printed, with the given answer to 11 Across):

Question Bank

Very short answer questions (1 mark)

1. Name the plant in which vegetative propagation takes place by leaves. [1 Mark]

Answer: Bryophyllum.

Teacher's Note:
a) Bryophyllum forms plantlets along the edges of its leaves.

2. Write scientific term for the following: [1 Mark]

a) Release of ovum from ovary.
b) Onset of menstrual cycle in a female.

Answer:
a) Ovulation
b) Menarche

Teacher's Note:
a) Ovulation takes place around the middle of the menstrual cycle.
b) Menarche is the first menstrual period, which marks the start of puberty in girls.

3. Where does fertilization takes place in human female? [1 Mark]

Answer: Oviduct (fallopian tube).

Teacher's Note:
a) The egg is fertilised in the upper part of the oviduct.

Short answer questions (2 marks)

1. What is the importance of DNA copying in reproduction? [2 Marks]

Answer:
1. DNA copying is essential for transferring genetic material from one generation to the next.
2. The copies also allow the offspring to inherit the characteristics of the parents.

Teacher's Note:
a) Without DNA copying, the cell cannot pass on its genetic instructions after division.
b) Small variations that appear during copying also lead to variation among the offspring.

2. How is pollination different from fertilization? [2 Marks]

Answer:
1. Pollination is the transfer of pollen grains from the anther lobe to the stigma of the flower.
2. Fertilisation is the fusion of the male and female gametes to form the zygote.

Teacher's Note:
a) Pollination happens before fertilisation and does not involve any fusion of cells.
b) Pollen grains must grow a pollen tube before fertilisation can take place.

3. What is the role of seminal vesicles and the prostate gland? [2 Marks]

Answer: The seminal vesicles and the prostate gland provide nutrition and mobility to the sperms.

Teacher's Note:
a) The fluid from these glands mixes with sperms to form semen.
b) This fluid helps the sperms to move and survive.

Short answer questions (3 marks)

1. What are the advantages of vegetative propagation? [3 Marks]

Answer:
1. It is a quick, easy and economical method of propagation.
2. It produces exact copies of the parent plant.
3. It is the only method for propagating seedless plants.

Teacher's Note:
a) Farmers use vegetative propagation for crops that rarely produce viable seeds.
b) Because all the plants are identical, vegetative propagation gives little variation.

2. How does the embryo get nourishment inside the mother's body? [3 Marks]

Answer:
1. The embryo gets nutrition and oxygen from the mother's blood through the placenta.
2. The placenta also removes the waste materials of the embryo and passes them into the mother's blood.
3. The embryo is connected to the placenta by the umbilical cord.

Teacher's Note:
a) The placenta is attached to the wall of the uterus.
b) The blood of the mother and the embryo do not mix directly.

3. (a) What is AIDS? (b) Name the causative organism? (c) List the important modes of transmission of the disease. [3 Marks]

Answer:
a) Acquired Immuno Deficiency Syndrome.
b) HIV (Human Immunodeficiency Virus).
c) Modes of transmission:
i) Sexual contact
ii) Through infected blood transfusion
iii) Contaminated syringes
iv) Infected mother to child

Teacher's Note:
a) HIV attacks the immune system, so the body cannot fight infections.
b) AIDS is caused by a virus, not by bacteria.
c) AIDS is not spread by casual contact such as touching or sharing food.

4. What are the different methods of contraception? [3 Marks]

Answer:
a) Barrier method: condoms used by males, or the vaginal diaphragm used by females.
b) Chemical method: oral pills or vaginal pills used by females.
c) Surgical method: vasectomy in males and tubectomy in females.

Teacher's Note:
a) Barrier methods stop the sperm from reaching the egg.
b) Chemical methods work mainly by preventing ovulation.
c) Surgical methods are permanent and should be chosen after proper counselling.

5. Sankalp is a student of class 10, who is very much neglected by his relatives. The reason for their behavior was death of his parents after suffering from a disease called AIDS. He is well taken care of by his teachers and class mates. (VBQ) [3 Marks]

a) What values were shown by his teachers and classmates?
b) Will the disease called AIDS spread by sitting close to each other or by hand shaking with each other?
c) List two ways of transmission of the disease.

Answer:
a) Caring and knowledge of biology.
b) No, AIDS will not spread by sitting close to each other or by hand shaking.
c) i) Sexual contact
ii) Infected blood

Teacher's Note:
a) AIDS does not spread through hand shaking or sitting close to a person, so the student can be safely included in class.
b) AIDS spreads only through body fluids such as blood and semen, not through casual contact.

Long answer questions (5 marks)

1. Explain the process of fertilization in plants with the help of neat labeled diagram. [5 Marks]

[Figure: Germination of pollen on the stigma, as in Figure 8.8. Label the pollen grain, stigma, pollen tube, male germ-cell, ovary, ovule and female germ-cell. Diagram to be added.]

Answer:
1. A pollen grain lands on the stigma after pollination.
2. The pollen grain absorbs sugar from the stigma and grows a pollen tube through the style towards the ovary.
3. The pollen tube carries the male gametes (male germ-cells) down to the ovule inside the ovary.
4. The male gametes move through the pollen tube towards the ovule.
5. The male gamete fuses with the female gamete (egg cell) inside the ovule. This fusion is fertilisation, and it forms the zygote.

Teacher's Note:
a) The pollen tube is the path by which the male gamete reaches the ovule.
b) After fertilisation, the ovule develops into a seed and the ovary develops into a fruit.
c) The labelled diagram should show the pollen tube reaching the ovule.
d) Fertilisation in plants is called double fertilisation in some textbooks, because a second male gamete fuses with the polar nuclei.

10. Describe the different methods of asexual reproduction seen in animals with the help of neat labelled diagrams. [5 Marks]

Answer:
1. Fission: the parent divides into two (binary fission, as in Amoeba) or many (multiple fission, as in Plasmodium) daughter cells.
2. Regeneration: the lost part of the body is regrown, and in Planaria a whole new worm can grow from a fragmented piece.
3. Budding: a new individual develops as an outgrowth or bud on the parent body and separates after growing, as in Hydra.
4. Labelled diagrams: Fig 8.1 (binary fission in Amoeba), Fig 8.2 (multiple fission in Plasmodium), Fig 8.3 (regeneration in Planaria), Fig 8.4 (budding in Hydra).

Teacher's Note:
a) Binary fission divides the cell into two equal parts, while multiple fission produces many daughter cells.
b) Regeneration and budding are both forms of asexual reproduction, but budding needs a separate bud to form first.
c) Asexual reproduction produces offspring identical to the parent.
d) Draw each diagram with clear labels and a short caption.

Have either stamen or carpel                           Have both stamen and carpel    

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

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

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

Question. Which of the following can not regenerates with the help of layering ?
(A) Jasmine
(B) Rose
(C) Mango
(D) Cactus
Answer : D

Question. Development of egg without fertilization is
(A) parthenocarpy
(B) polyembryony
(C) parthenogenesis
(D) adventive embryony
Answer : C

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. Scion is a term in relation to
(A) layering
(B) cutting
(C) grafting
(D) micropropagation
Answer : C

Question. Anemophily is pollination by
(A) air
(B) water
(C) insects
(D) animal
Answer : A

Question. Pollination between different flowers of same plant is called
(A) autogamy
(B) geitonogamy
(C) allogamy
(D) xenogamy
Answer : B

Question. Double fertilization is
(A) fusion of two male gametes with egg
(B) fusion of one male gamete with egg and the other male gamete with the polar bodies
(C) both are correct
(D) both are incorrect
Answer : B

Question. Which one of the following is propagated by means of cuttings ?
(A) Sugarcane
(B) Coffee
(C) Citrus
(D) All of these
Answer : D

Question. The zygote is formed by the fusion of-
(A) male gametes
(B) male & female gametes
(C) female gametes
(D) spores & gametes
Answer : B

Question. The genetic information is stored in -
(A) DNA
(B) RNA
(C) Ribosome
(D) ER
Answer : A

Question. Graffian follicles are found in
(A) testis of mammals
(B) ovary of frog
(C) ovary of cockroach
(D) ovary of mammals
Answer : D

Question. Progesterone is secreted by
(A) corpus luteum
(B) thyroid
(C) thymus
(D) testis
Answer : A

Question. The structure meant for the nourishment of developing embryo in case of plants is -
(A) pollen tube
(B) endosperm
(C) both A & B are correct
(D) none of these
Answer : B

Question. Site of fertilization in mammals is
(A) ovary
(B) uterus
(C) vagina
(D) fallopian tube
Answer : D

Question. The process of reproduction which involves only a single parent to form an individual
(A) sexual reproduction
(B) asexual reproduction
(C) none of these
(D) Both A & B are correct
Answer : B

Question. Which is not a method of asexual reproduction-
(A) Micropropagation
(B) Budding
(C) Sowing
(D) Layering
Answer : C

Question. Acrosome is formed by
(A) mitochondria
(B) centrioles
(C) golgi bodies
(D) ribosomes
Answer : C

Question. Each female flower consists of
(A) ovary
(B) stigma
(C) ovary, style and stigma
(D) thalamus
Answer : C

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. 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. Loss of reproductive capacity in women after age of 45 years is
(A) menstruation
(B) ageing
(C) menopause
(D) menarche
Answer : C

Question. Acrosome aids the sperm to
(A) penetrate vitelline membrane of ovum
(B) find ovum
(C) swim
(D) higher activity
Answer : A

Question. In mammals, the testes lies in scrotal sacs due to
(A) presence of urinary bladder
(B) presence of rectum
(C) long vas–deferens
(D) requirement of low temperature for sperm formation
Answer : D

Question. Testes descend into scrotum in mammals for
(A) Spermatogenesis
(B) Development of visceral organs
(C) Fertilization
(D) Development of sex organs
Answer : A

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. Release of oocytes from ovary is
(A) gestation
(B) ovulation
(C) parturition
(D) implantation
Answer : B

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

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.

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. (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.

Please click the link below to download CBSE Class 10 Science-How Do Organisms Reproduce.