How do Organisms Reproduce? — Class 10 Science
Science · Chapter 7
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Chapter summary
Key ideas & terms
- Asexual reproduction
- Reproduction from a single parent without gamete fusion.
- Pollination
- Transfer of pollen from anther to stigma in flowers.
- Fertilisation
- Fusion of male and female gametes to form a zygote.
- Variation
- Differences among offspring that aid adaptation and survival.
Extra questions & answers
Why is variation beneficial to a species but not always to the individual?
Variation helps the species survive environmental changes over time, even though a particular variation may not benefit every individual.
What is vegetative propagation? Give one advantage.
Growing new plants from vegetative parts (root, stem, leaf); it preserves desirable traits and produces flowering/fruiting faster.
Why is reproduction important for a species?
It ensures the continuity of a species from one generation to the next and passes on variations that help the species survive and adapt.
Name and define any three methods of asexual reproduction.
Fission (a parent splits into two or more, e.g. Amoeba), budding (a new organism grows as a bud, e.g. Hydra) and fragmentation (the body breaks into pieces that grow into new organisms, e.g. Spirogyra).
What is vegetative propagation, and what is one advantage?
Growing new plants from vegetative parts such as roots, stems or leaves; it preserves the desirable features of the parent and produces flowers and fruits earlier.
What are pollination and fertilisation in flowering plants?
Pollination is the transfer of pollen from the anther to the stigma; fertilisation is the fusion of the male gamete from the pollen with the egg in the ovule to form a zygote.
Name the male and female reproductive parts of a flower.
The stamen (anther and filament) is the male part, and the carpel/pistil (stigma, style and ovary) is the female part.
What changes occur in humans at puberty?
The reproductive organs mature and secondary sexual characters appear, such as growth of hair, changes in voice and body, preparing the body for reproduction.
What are some methods of contraception?
Barrier methods (condoms), oral contraceptive pills, intra-uterine devices (IUDs), and surgical methods; some also help prevent sexually transmitted infections.
Why is variation important in sexual reproduction?
Sexual reproduction mixes the genes of two parents, producing variations that help a population adapt and survive in changing environments.
QUESTIONS
1. What is the importance of DNA copying in reproduction?
DNA copying transfers the hereditary information and basic body design of the parent to the offspring. Small inaccuracies during copying also create variations, which may help the species survive changing environmental conditions.
2. Why is variation beneficial to the species but not necessarily for the individual?
Variation increases the chance that some members of a species will survive when environmental conditions change. However, a particular variation may be neutral, harmful or even fatal to the individual that possesses it, so it is not necessarily beneficial to every individual.
QUESTIONS
1. How does binary fission differ from multiple fission?
In binary fission, one parent cell divides to form two daughter cells, as in Amoeba and Leishmania. In multiple fission, one parent cell divides to form many daughter cells at the same time, as in Plasmodium.
2. How will an organism be benefited if it reproduces through spores?
Spores are produced in large numbers and can spread to new places. Their thick protective walls help them survive unfavourable conditions, and they germinate when suitable moisture and other conditions become available.
3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Complex organisms have specialised cells organised into tissues, organs and organ systems in definite positions. A separated body part usually lacks the complete organisation and specialised cells needed to form an entire organism, so regeneration cannot normally serve as their method of reproduction.
4. Why is vegetative propagation practised for growing some types of plants?
Vegetative propagation is used because it produces genetically similar plants that retain the desirable characteristics of the parent. Such plants often flower and bear fruit earlier, and the method also allows the multiplication of plants such as banana, orange, rose and jasmine that may not produce viable seeds.
5. Why is DNA copying an essential part of the process of reproduction?
DNA contains the hereditary information required for building and maintaining an organism. Copying it ensures that this information is passed to the new cells or offspring, while small copying variations provide differences that support the long-term survival and evolution of the species.
QUESTIONS
1. How is the process of pollination different from fertilisation?
Pollination is the transfer of pollen grains from the anther to the stigma of a flower. Fertilisation is the fusion of the male germ-cell from the pollen with the female gamete in the ovule, producing a zygote.
2. What is the role of the seminal vesicles and the prostate gland?
The seminal vesicles and prostate gland add secretions to the sperms. These secretions form a fluid that nourishes the sperms and makes their transport and movement easier.
3. What are the changes seen in girls at the time of puberty?
At puberty, girls experience enlargement of the breasts, darkening of the nipples, growth of hair in the armpits and genital region, increased activity of oil glands that may cause pimples, maturation of the reproductive organs and the beginning of menstruation.
4. How does the embryo get nourishment inside the mother’s body?
The embryo receives nourishment through the placenta, a specialised tissue embedded in the uterine wall. Its villi provide a large surface area through which glucose and oxygen pass from the mother’s blood to the embryo, while wastes from the embryo pass into the mother’s blood for removal.
5. If a woman is using a copper -T, will it help in protecting her from sexually transmitted diseases?
No. A copper-T helps prevent pregnancy by acting inside the uterus, but it does not prevent the exchange of body fluids or contact through which sexually transmitted diseases spread. A condom provides protection against many such infections to some extent.
EXERCISES
1. Asexual reproduction takes place through budding in
(a) Amoeba.
(b) Yeast.
(c) Plasmodium.
(d) Leishmania.
(b) Yeast.
2. Which of the following is not a part of the female reproductive system in human beings?
(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Fallopian tube
(c) Vas deferens
3. The anther contains
(a) sepals.
(b) ovules.
(c) pistil.
(d) pollen grains.
(d) pollen grains.
4. What are the advantages of sexual reproduction over asexual reproduction?
Sexual reproduction combines genetic material from two individuals and produces greater variation among offspring than asexual reproduction. These variations improve the ability of a species to adapt to environmental changes and provide material for evolution.
5. What are the functions performed by the testis in human beings?
The testes produce male germ-cells called sperms. They also secrete the hormone testosterone, which supports sperm formation and brings about male secondary sexual characteristics during puberty.
6. Why does menstruation occur?
Every month the uterus develops a thick, blood-rich lining to receive and nourish a possible embryo. If the released egg is not fertilised, this lining is no longer needed, so it breaks down and leaves the body through the vagina as blood and mucus. This process is menstruation.
7. Draw a labelled diagram of the longitudinal section of a flower.
The diagram should show a longitudinally cut flower with the following labels: stigma at the top of the pistil, style below it, ovary at the swollen base containing ovules, stamens consisting of anthers and filaments around the pistil, and the surrounding petals and sepals.
8. What are the different methods of contraception?
Contraceptive methods include barrier methods such as condoms; hormonal methods such as oral pills that prevent the release of eggs; intrauterine devices such as the loop or copper-T; and surgical methods such as blocking the vas deferens in males or the fallopian tubes in females.
9. How are the modes for reproduction different in unicellular and
multicellular organisms?
In unicellular organisms, the division of the single cell itself creates new individuals, as in binary or multiple fission. Multicellular organisms have specialised tissues and organs, so they use methods such as budding, fragmentation, vegetative propagation, spore formation or sexual reproduction involving specialised reproductive cells and organs.
10. How does reproduction help in providing stability to populations of species?
Reproduction continuously replaces individuals that die and maintains the population of a species. Accurate DNA copying preserves the basic body design suited to the species’ environment, while variations produced during reproduction help some individuals survive environmental changes, supporting the species over time.
11. What could be the reasons for adopting contraceptive methods?
Contraceptive methods may be adopted to prevent unwanted pregnancies, space or limit the number of children, protect the physical and mental health of the parents, plan a family according to available resources and, in the case of condoms, reduce the risk of many sexually transmitted infections.