Chapter 8 — How do Organisms Reproduce
Welcome to HSLC Guru! This English-medium study guide for Class 10 Science Chapter 8 — How do Organisms Reproduce — has been carefully prepared for ASSEB students. It explains why reproduction is essential for the continuity of species, the major modes of asexual and sexual reproduction in plants and animals, and the structure and functioning of human reproductive systems. The notes include a clear summary, complete textbook question answers, additional MCQs, fill in the blanks, true/false questions and a handy glossary, all aligned with the ASSEB syllabus.
Summary
Importance of Reproduction: Reproduction is the biological process by which living organisms produce offspring of their own kind. Although reproduction is not essential for the survival of an individual, it is absolutely essential for the continuity of a species on Earth. Reproduction also creates variations through DNA copying, and these variations form the raw material for evolution and help populations adapt to changing environmental conditions. Without reproduction, life as we know it would gradually disappear from the planet.
Asexual Modes of Reproduction: In asexual reproduction, a single parent produces offspring that are genetically identical to it. The main modes include — (i) Fission, which can be binary fission as in Amoeba and Leishmania or multiple fission as in Plasmodium; (ii) Budding, seen in Hydra and yeast where a small bud grows out of the parent body and detaches; (iii) Fragmentation, common in Spirogyra where the body breaks into pieces and each piece grows into a new individual; (iv) Regeneration, in which simple animals like Planaria regrow from cut pieces; (v) Vegetative propagation in plants through roots, stems, leaves (e.g., Bryophyllum) or by artificial methods like cutting, layering and grafting; and (vi) Spore formation, as in Rhizopus, where asexual spores germinate to form new mycelium.
Sexual Reproduction in Flowering Plants: A typical flower has four whorls — sepals (green protective structures), petals (colourful, attract pollinators), stamens (male reproductive part with anther and filament producing pollen) and pistil/carpel (female reproductive part with stigma, style and ovary containing ovules). Pollination is the transfer of pollen from anther to stigma; it may be self-pollination or cross-pollination, carried out by wind, water or insects. After pollination, the pollen grain germinates, the male gamete fuses with the egg cell inside the ovule and fertilisation takes place. The fertilised ovule develops into a seed and the ovary into a fruit.
Sexual Reproduction in Humans and Reproductive Health: The male reproductive system consists of testes (produce sperms and testosterone), vas deferens, seminal vesicles, prostate gland and penis. The female reproductive system includes ovaries (produce eggs and female hormones), fallopian tubes, uterus and vagina. Puberty marks sexual maturity, characterised by secondary sexual characters. The menstrual cycle of about 28 days prepares the uterus for pregnancy; if fertilisation does not occur, the uterine lining is shed as menstruation. After fertilisation in the fallopian tube, the zygote implants in the uterus and a placenta develops to supply nutrients and oxygen to the embryo. Reproductive health includes prevention of sexually transmitted diseases (like gonorrhoea, syphilis, HIV/AIDS) and use of contraceptive methods such as barrier methods (condoms), oral pills, IUDs and surgical methods.
Textbook Questions and Answers
Very Short Answer Questions (1 Mark)
Q1. What is reproduction?
Answer: Reproduction is the biological process by which living organisms produce new individuals of their own kind, ensuring the continuity of the species.
Q2. Name the organism that reproduces by binary fission.
Answer: Amoeba reproduces by binary fission.
Q3. Name the organism that shows multiple fission.
Answer: Plasmodium, the malarial parasite, reproduces by multiple fission.
Q4. Which part of the flower develops into a fruit?
Answer: The ovary of the flower develops into a fruit after fertilisation.
Q5. What is pollination?
Answer: Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a pistil.
Q6. Where does fertilisation occur in human females?
Answer: Fertilisation in human females occurs in the fallopian tube (oviduct).
Q7. Name the male reproductive hormone.
Answer: The male reproductive hormone is testosterone, secreted by the testes.
Q8. What is the function of the placenta?
Answer: The placenta supplies oxygen and nutrients from the mother to the developing embryo and removes its waste products.
Q9. Give one example of a plant that shows vegetative propagation through leaves.
Answer: Bryophyllum reproduces vegetatively through buds present on the margins of its leaves.
Q10. What is meant by puberty?
Answer: Puberty is the stage in human life when the reproductive organs become functional and secondary sexual characters develop.
Short Answer Questions (2-3 Marks)
Q1. Differentiate between asexual and sexual reproduction.
Answer: In asexual reproduction, a single parent produces offspring that are genetically identical to itself; gametes are not involved. In sexual reproduction, two parents (male and female) are involved, gametes are produced and fuse during fertilisation, and the offspring show variations due to genetic recombination.
Q2. Describe budding in Hydra.
Answer: In Hydra, certain cells of the body undergo repeated cell division to form a small outgrowth called a bud. The bud gradually grows, develops a mouth and tentacles, and finally separates from the parent body to live as an independent organism.
Q3. What is vegetative propagation? Mention any two advantages.
Answer: Vegetative propagation is the production of new plants from vegetative parts like roots, stems and leaves without involving seeds. Advantages — (i) plants produced are genetically identical to the parent, preserving desirable characters; (ii) it is a faster method, and plants like banana and rose that do not produce viable seeds can be propagated easily.
Q4. Explain double fertilisation in flowering plants briefly.
Answer: In flowering plants, two male gametes are released by a pollen tube into the embryo sac. One male gamete fuses with the egg to form a zygote (syngamy), and the other fuses with two polar nuclei to form the endosperm (triple fusion). Since fertilisation takes place twice, it is called double fertilisation.
Q5. What changes are seen in girls during puberty?
Answer: At puberty in girls, breasts develop, hair grows in the armpits and pubic region, the menstrual cycle begins, the hips broaden, and the voice becomes slightly higher. Internally, the ovaries start releasing mature eggs and the uterus prepares for possible pregnancy.
Q6. Why does menstruation occur?
Answer: Each month, the uterus prepares a thick lining rich in blood vessels to receive a fertilised egg. If fertilisation does not take place, this lining is no longer needed and is shed along with the unfertilised egg as blood and tissue. This shedding is called menstruation and lasts for about 3-5 days.
Long Answer Questions (5-6 Marks)
Q1. Describe the various modes of asexual reproduction with examples.
Answer: The major modes of asexual reproduction are — (i) Binary fission: the parent cell divides into two equal daughter cells, e.g., Amoeba, Leishmania (where division occurs along a definite plane). (ii) Multiple fission: the nucleus divides repeatedly to form many daughter nuclei, each surrounded by cytoplasm, releasing many daughter cells, e.g., Plasmodium. (iii) Budding: a small outgrowth (bud) from the parent grows and detaches as a new individual, e.g., Hydra and yeast. (iv) Fragmentation: the body breaks into two or more fragments, each developing into a complete organism, e.g., Spirogyra. (v) Regeneration: a piece cut from the body grows into a complete organism by repeated cell division, e.g., Planaria. (vi) Spore formation: special reproductive structures called spores germinate under favourable conditions, e.g., Rhizopus. (vii) Vegetative propagation: new plants develop from vegetative parts such as stem (potato), root (sweet potato) or leaf (Bryophyllum).
Q2. Draw a labelled diagram of a typical flower and describe the parts.
Answer: A typical flower has four whorls arranged on the thalamus — (i) Calyx made of green sepals that protect the flower bud. (ii) Corolla made of brightly coloured petals that attract insects for pollination. (iii) Androecium, the male whorl, made of stamens; each stamen has a filament and an anther where pollen grains containing male gametes are produced. (iv) Gynoecium or pistil, the female whorl, consisting of stigma (sticky tip), style (slender stalk) and ovary (basal swollen part containing ovules). The ovule contains the egg cell. After pollination and fertilisation, the ovule becomes a seed and the ovary becomes a fruit.
Q3. Describe the human male reproductive system with the functions of its parts.
Answer: The human male reproductive system consists of — (i) Testes: a pair of oval organs lying outside the abdomen in the scrotum to maintain a temperature about 2-3°C lower than body temperature; they produce sperms and the male hormone testosterone. (ii) Vas deferens: long tubes that carry sperms from the testes to the urethra. (iii) Seminal vesicles and prostate gland: secrete a fluid that nourishes sperms and forms semen. (iv) Urethra: a common passage in the penis for urine and semen. (v) Penis: the male copulatory organ that delivers sperms into the female body. Testosterone also brings about secondary sexual characters at puberty.
Q4. Describe the human female reproductive system and the menstrual cycle.
Answer: The female reproductive system has — (i) Ovaries: a pair of organs that produce eggs and female hormones (oestrogen and progesterone). (ii) Fallopian tubes (oviducts): where fertilisation takes place. (iii) Uterus: a muscular pear-shaped organ where the embryo develops. (iv) Vagina: the passage that connects the uterus to the outside and receives sperms. The menstrual cycle is a monthly cycle of about 28 days. An egg is released from the ovary (ovulation) around day 14. The uterus develops a thick lining to receive a fertilised egg. If fertilisation does not occur, the lining and unfertilised egg are shed as menstrual flow over 3-5 days.
Q5. What is contraception? Discuss the main methods of contraception.
Answer: Contraception means the prevention of unwanted pregnancy by using methods that block fertilisation or implantation. The main methods are — (i) Barrier methods: physical devices like condoms and diaphragms prevent sperms from meeting the egg; condoms also help in preventing STDs. (ii) Chemical methods: oral pills containing hormones change hormonal balance and prevent ovulation. (iii) Mechanical methods: intra-uterine devices (IUDs) like the copper-T are placed in the uterus to prevent implantation. (iv) Surgical methods: vasectomy in males (cutting and tying vas deferens) and tubectomy in females (cutting and tying fallopian tubes) provide a permanent solution. Contraception is essential for population control and maintaining reproductive health.
Additional Practice Questions
Multiple Choice Questions (MCQ)
Q1. Which of the following organisms reproduces by budding?
(a) Amoeba (b) Hydra (c) Planaria (d) Spirogyra
Answer: (b) Hydra.
Q2. The male gamete in flowering plants is present in —
(a) anther (b) stigma (c) ovary (d) ovule
Answer: (a) anther.
Q3. Spirogyra reproduces asexually by —
(a) binary fission (b) budding (c) fragmentation (d) regeneration
Answer: (c) fragmentation.
Q4. The female part of a flower is called —
(a) stamen (b) sepal (c) petal (d) pistil
Answer: (d) pistil.
Q5. Fertilisation in humans takes place in the —
(a) ovary (b) uterus (c) fallopian tube (d) vagina
Answer: (c) fallopian tube.
Q6. The structure that supplies food and oxygen to a developing embryo is —
(a) uterus (b) placenta (c) ovary (d) vagina
Answer: (b) placenta.
Q7. Which of the following is a sexually transmitted disease?
(a) Cholera (b) Tuberculosis (c) AIDS (d) Malaria
Answer: (c) AIDS.
Q8. Copper-T is used for —
(a) treatment of cancer (b) preventing pregnancy (c) curing AIDS (d) increasing fertility
Answer: (b) preventing pregnancy.
Q9. Multiple fission is observed in —
(a) Amoeba (b) Plasmodium (c) Yeast (d) Hydra
Answer: (b) Plasmodium.
Q10. The average length of human menstrual cycle is —
(a) 14 days (b) 21 days (c) 28 days (d) 35 days
Answer: (c) 28 days.
Fill in the Blanks
Q1. Reproduction by means of spores is called __________.
Answer: spore formation.
Q2. The male reproductive part of a flower is __________.
Answer: stamen.
Q3. The fusion of male and female gametes is called __________.
Answer: fertilisation.
Q4. __________ is the male sex hormone in humans.
Answer: Testosterone.
Q5. The shedding of the uterine lining each month is called __________.
Answer: menstruation.
True or False
Q1. Reproduction is necessary for the survival of an individual organism.
Answer: False. It is not necessary for the survival of an individual but is essential for the continuity of the species.
Q2. Bryophyllum reproduces vegetatively through its leaves.
Answer: True.
Q3. The ovary of a flower develops into a seed.
Answer: False. The ovary develops into a fruit, while the ovule develops into a seed.
Q4. AIDS is caused by a bacterium.
Answer: False. AIDS is caused by the HIV virus.
Q5. The placenta connects the embryo with the mother.
Answer: True.
Glossary
| Term | Meaning |
|---|---|
| Reproduction | Process by which living organisms produce new individuals of their own kind. |
| Asexual Reproduction | Reproduction involving a single parent without the formation of gametes. |
| Sexual Reproduction | Reproduction involving fusion of male and female gametes from two parents. |
| Binary Fission | Division of a parent cell into two equal daughter cells, e.g., Amoeba. |
| Multiple Fission | Division of a parent cell into many daughter cells, e.g., Plasmodium. |
| Budding | Asexual reproduction in which a new organism develops as a small bud on the parent. |
| Fragmentation | Breaking of the body into pieces, each developing into a new individual. |
| Regeneration | Ability of an organism to grow back lost or cut parts into a complete body. |
| Vegetative Propagation | Production of new plants from vegetative parts like roots, stems and leaves. |
| Spore Formation | Asexual reproduction by means of microscopic reproductive units called spores. |
| Pollination | Transfer of pollen grains from anther to stigma. |
| Fertilisation | Fusion of male and female gametes to form a zygote. |
| Zygote | The cell formed by the fusion of male and female gametes. |
| Puberty | Stage when reproductive organs become functional and secondary sexual characters appear. |
| Menstruation | Monthly shedding of the uterine lining when fertilisation does not occur. |
| Placenta | Disc-like structure that supplies nutrition and oxygen from mother to embryo. |
| Contraception | Methods used to prevent unwanted pregnancy. |
| STDs | Sexually transmitted diseases such as gonorrhoea, syphilis and AIDS. |
This completes the HSLC Guru study notes for Class 10 Science Chapter 8 — How do Organisms Reproduce, prepared as per the ASSEB syllabus. Revise the summary, practise the textbook and additional questions, and use the glossary for quick revision before your examination.