1. Introduction to Reproduction
All living organisms grow, and one of the most important features of living things is their ability to reproduce – to produce new individuals of their own kind.
Reproduction is the biological process by which living organisms produce new individuals of their own species.
Importance of Reproduction
- Continuity of species: Reproduction ensures that a species continues to exist on Earth over generations.
- Population replacement: It maintains the number of individuals of a species when older ones grow old or die.
- Basis of variation: Reproduction (especially sexual reproduction) introduces variations that may respond to natural selection and lead to evolution.
- Multicellular organisms: Reproduction helps organisms make copies of their body design for the next generation.
Reproduction vs Growth
| Reproduction | Growth |
|---|---|
| Process of producing new individuals of a species | Increase in size, mass or number of cells of an organism |
| Ensures continuity of the species | Helps an organism mature and carry out life processes |
| Occurs only in living organisms | Occurs in living organisms (increase in non-living things is called increase in size, not growth) |
| Result: a new individual is formed | Result: the same individual becomes larger or more mature |
DNA Copying and Reproduction
Before reproduction, the cell copies its DNA (deoxyribonucleic acid), which carries the information for building the body and its traits. DNA copying is not completely perfect, so small differences can arise during the copying process.
- Why offspring resemble parents: The offspring inherit nearly the same DNA (and therefore similar characteristics) as the parents.
- Why offspring are not identical: Small inaccuracies during DNA copying, and mixing of genetic material during sexual reproduction, create minor differences (variations).
Reproduction is closely linked to DNA copying: it passes information from parent to offspring, and slight copying variations are the basis of variation in a population.
2. Asexual Reproduction
Asexual reproduction is the mode of reproduction that involves only a single parent and produces offspring that are genetically similar to the parent.
Main Characteristics
- Only one parent is involved.
- No fusion of male and female gametes occurs.
- The offspring are usually genetically identical (clones) to the parent (except for small DNA copying variations).
- It is generally fast and does not require special reproductive organs.
Advantages and Limitations
| Advantages | Limitations |
|---|---|
| Rapid reproduction and increase in numbers | Offspring are genetically almost identical, so little variation |
| Only one parent needed; no partner required | If the environment changes, all individuals may be affected similarly |
| No energy spent on gamete formation or mating | Less ability to adapt to new or changing conditions compared to sexual reproduction |
Methods of Asexual Reproduction
1. Fission
Fission is a type of asexual reproduction in which a unicellular organism splits into two or more new individuals.
- Binary fission: The parent cell divides into two equal halves producing two daughter cells, e.g. Amoeba (splits at any plane), Bacteria. In organisms like Leishmania fission occurs in a definite orientation (lengthwise).
- Multiple fission: The nucleus divides many times and each nucleus forms a new individual, e.g. Plasmodium (malaria parasite).
2. Fragmentation
Fragmentation is a form of asexual reproduction in which the body of a multicellular organism breaks into two or more fragments, and each fragment grows into a complete new organism.
Example: Spirogyra (a filamentous green alga). When a filament breaks, each fragment grows into a new filament.
3. Regeneration
Regeneration is the ability of an organism to regrow lost parts of its body to form a complete new organism.
Example: Planaria and Hydra. When a Planaria is cut into pieces, each piece can grow into a complete new Planaria. This happens because the body has specialised (actively dividing) cells that can differentiate to form various tissues and organs.
Regeneration is different from fragmentation: in fragmentation, the parent breaks naturally; in regeneration, specialised cells regrow lost body parts.
4. Budding
Budding is a mode of asexual reproduction in which a small outgrowth (bud) develops on the parent body, grows, and eventually separates to form a new individual.
Example: Hydra and Yeast. In Hydra, a bud arises from the parent body; it develops tentacles and mouth, and later detaches as a new individual. In Yeast, a bud forms and may either separate or remain attached forming a small chain.
5. Vegetative Propagation
Vegetative propagation is a method of asexual reproduction in plants in which new plants grow from vegetative parts such as roots, stems, leaves and buds.
Natural Vegetative Propagation
- Roots: Sweet potato and dahlia grow from roots.
- Stems: Potato (tuber), ginger (rhizome), onion, garlic, sugarcane (grow from the nodes of stems).
- Leaves: Bryophyllum forms small plantlets on the edges of its leaves; each can grow into a new plant.
Artificial Vegetative Propagation
- Cutting: A stem piece (with buds) is placed in soil; roots arise and a new plant grows, e.g. rose, sugarcane, money plant.
- Layering: A branch is bent and pressed into the soil with a part buried; roots develop at the buried portion, e.g. jasmine.
- Grafting: A stem (scion) of one plant is joined with the rooted part (stock) of another so they grow together, e.g. mango, apple.
- Tissue culture: Small pieces of a plant (or cells) are grown on a nutrient medium in a laboratory to produce many new plants, e.g. orchids, banana.
Advantages of Vegetative Propagation
- Reproduction is faster than growing from seeds.
- Plants produced are genetically similar to the parent, so desirable traits are preserved.
- It is useful for plants that do not produce viable seeds.
- Some cultivated plants flower and fruit earlier than plants grown from seeds.
Binary Fission vs Multiple Fission
| Binary Fission | Multiple Fission |
|---|---|
| Parent cell divides into two daughter cells | Parent cell divides into many daughter cells |
| Nucleus divides only once | Nucleus divides many times repeatedly |
| Examples: Amoeba, Bacteria, Leishmania | Examples: Plasmodium |
| Usually faster | Usually takes more time (many nuclei form) |
3. Sexual Reproduction
Sexual reproduction is the mode of reproduction in which two parents produce male and female gametes, which fuse to form a zygote that develops into a new individual.
A gamete is a specialised reproductive cell. The male gamete (sperm in animals, pollen/male gamete in plants) fuses with the female gamete (ovum/egg), and this fusion is called fertilisation. The cell formed after fusion is the zygote.
Male gamete + Female gamete → Zygote
Why Sexual Reproduction Creates Greater Variation
- Genetic material from two different parents combines, so the offspring mix traits of both parents.
- The process of gamete formation shuffles the hereditary material, producing new combinations.
- DNA copying during gamete formation also introduces minor changes.
- Result: offspring differ from each other and from parents, increasing variation in the population.
Importance of Sexual Reproduction
- Provides diversity in traits, which helps species survive changes in the environment.
- Combines characteristics of two parents, which may improve the offspring.
- Forms the raw material (variation) on which natural selection can act over generations.
Asexual vs Sexual Reproduction
| Asexual Reproduction | Sexual Reproduction |
|---|---|
| One parent involved | Two parents (male and female) usually involved |
| No gamete formation | Gametes are formed |
| No fusion of gametes (no fertilisation) | Gametes fuse (fertilisation) to form a zygote |
| Offspring genetically almost identical to parent | Offspring show variation from both parents |
| Fast; large numbers produced quickly | Slower; fewer offspring produced |
| Examples: fission, budding, fragmentation, vegetative propagation | Examples: flowering plants, most animals including humans |
4. Sexual Reproduction in Flowering Plants
The flower is the reproductive part of a plant. A typical flower consists of four whorls: sepals (calyx), petals (corolla), stamens (androecium) and the carpel/pistil (gynoecium).
Parts of a Flower
| Part | Whorl | Main Function |
|---|---|---|
| Sepals | Outermost | Protect the flower bud |
| Petals | Inner to sepals | Attract insects for pollination; usually brightly coloured |
| Stamen (male part) – Anther + Filament | Androecium | Anther produces pollen grains (contain male gametes); filament holds the anther |
| Carpel/Pistil (female part) – Stigma + Style + Ovary | Gynoecium | Stigma receives pollen; style connects stigma to ovary; ovary contains ovules holding the female gamete (egg) |
| Ovule | Inside ovary | Bears the female gamete; after fertilisation develops into the seed |
Male and Female Reproductive Parts
- Male part (stamen): Anther contains pollen grains, which carry the male gametes (male germ cells).
- Female part (carpel/pistil): The ovary contains ovules, each of which has an egg (female gamete). The stigma receives pollen grains.
Pollination
Pollination is the transfer of pollen grains from the anther of a flower to the stigma of a flower.
- Self-pollination: Pollen is transferred from the anther to the stigma of the same flower (or another flower of the same plant).
- Cross-pollination: Pollen is transferred from the anther to the stigma of a flower on a different plant of the same species.
Agents of Pollination
- Insects: Brightly coloured, fragrant petals attract insects, which carry pollen from one flower to another.
- Wind: Small, light, dry pollen grains are carried by wind (e.g. maize, grasses).
- Other agents: Birds, water and animals also pollinate some flowers.
Self-Pollination vs Cross-Pollination
| Self-Pollination | Cross-Pollination |
|---|---|
| Pollen transfers within the same flower/plant | Pollen transfers between flowers of different plants |
| One parent plant involved | Two parent plants involved |
| Produces less variation | Produces more variation in offspring |
| Does not require an external agent | Usually requires insects, wind or other agents |
| Example: pea | Example: maize, most insect-pollinated flowers |
5. Fertilisation in Flowering Plants
Fertilisation is the fusion of the male gamete and the female gamete to form a zygote. In flowering plants it happens in the following steps:
Steps of Fertilisation
- Pollen lands on the stigma during pollination.
- The pollen grain germinates and a pollen tube grows out of it.
- The pollen tube grows down through the style towards the ovary.
- The pollen tube enters the ovule through a tiny opening.
- The male gamete moves down the pollen tube and fuses with the female gamete (egg) inside the ovule.
- A zygote is formed, which develops into an embryo.
Pollen tube carries the male gamete to the ovule, where fertilisation forms the zygote.
After Fertilisation
- Zygote: The fertilised egg; it divides to form the embryo.
- Embryo: The young developing plant inside the seed.
- Ovule → Seed: The ovule develops into a seed (seed contains the embryo and stored food).
- Ovary → Fruit: The ovary develops into the fruit (fruit protects the seeds and helps in their dispersal).
Ovule → Seed | Ovary → Fruit | Zygote → Embryo
6. Human Reproductive System
Humans reproduce sexually. The male produces sperm (male gametes) and the female produces ova (female gametes). Their reproductive systems are adapted to produce these gametes, bring them together for fertilisation, and support the development of the new individual in the mother.
A. Male Reproductive System
| Organ | Main Function |
|---|---|
| Testes | Produce sperm (male gametes) and the hormone testosterone; present in a pair, outside the abdominal cavity |
| Scrotum | A pouch that holds the testes outside the body to keep them at the right temperature for sperm production |
| Vas deferens | Tube that carries sperm from the testes to the urethra |
| Seminal vesicles and Prostate gland | Add their secretions to the sperm to form a fluid called semen, which provides nutrition and transport for the sperm |
| Urethra | Tube through which semen (and urine) is passed out |
| Penis | External organ that releases semen into the female reproductive tract (transfer of sperm) |
B. Female Reproductive System
| Organ | Main Function |
|---|---|
| Ovaries | Produce ova (female gametes) and the female hormones oestrogen and progesterone; present in a pair |
| Fallopian tubes (Oviducts) | Carry the ovum from the ovary towards the uterus; fertilisation (fusion of sperm and ovum) takes place here |
| Uterus | Muscular organ where implantation of the embryo and development of the foetus take place |
| Cervix | Lower narrow part of the uterus, opening into the vagina |
| Vagina | Muscular tube that receives the male gamete (sperm) during mating and acts as the birth canal during childbirth |
Male vs Female Reproductive System
| Feature | Male | Female |
|---|---|---|
| Gamete produced | Sperm | Ovum (egg) |
| Reproductive organ (pair) | Testes | Ovaries |
| Passage of gamete | Vas deferens → urethra | Fallopian tube |
| Where offspring develops | – | Uterus |
| Main hormone | Testosterone | Oestrogen, progesterone |
7. Puberty and Adolescence
Puberty is the stage of life when the reproductive organs become functionally mature and the body begins to develop the ability to reproduce.
Adolescence is the period of transition from childhood to adulthood, during which many physical and emotional changes occur.
Physical Changes During Puberty
- Increase in height and body growth (a sudden growth spurt).
- Changes in voice (deepening of voice in boys).
- Development of secondary sexual characteristics (facial/body hair in boys; breast development, broadening of hips in girls).
- Maturation of the reproductive organs.
- In girls, the onset of menstruation (menarche).
Role of Reproductive Hormones
- In males: Testosterone (from testes) brings about the male changes during puberty.
- In females: Oestrogen (from ovaries) brings about the female changes and regulates the menstrual cycle.
These hormones are controlled by the pituitary gland, which starts secreting increased amounts of follicle-stimulating and luteinising hormones at puberty.
8. Human Reproduction
Fertilisation, Implantation and Development
- Sperm and ovum: During sexual intercourse, sperms enter the female reproductive tract and swim towards the fallopian tube.
- Fertilisation: A sperm fuses with an ovum in the fallopian tube to form a zygote.
- Zygote division: The zygote divides repeatedly as it moves towards the uterus.
- Implantation: The developing ball of cells attaches (implants) to the wall of the uterus.
- Embryo: After implantation the developing structure is called an embryo.
- Foetus: After about 8 weeks of development, the embryo is called a foetus (organs have started forming).
- Placenta: A disc-like structure embedded in the uterine wall; it supplies oxygen and nutrients from the mother to the foetus through the umbilical cord and removes waste.
- Birth: After about 9 months (about 38–42 weeks), the fully developed baby is born through the vagina (birth canal).
Sperm + Ovum → Fertilisation → Zygote → Embryo → Implantation → Foetus → Birth
The Role of the Placenta
- Plays the role of a lung: supplies oxygen to and removes carbon dioxide from the foetus.
- Plays the role of a digestive system: transfers digested nutrients from the mother’s blood to the foetus.
- Plays the role of an excretory organ: removes nitrogenous waste from the foetus into the mother’s blood.
Large amounts of hormones are secreted by the mother during pregnancy, which prepare the breast tissue for producing milk after the baby is born.
9. Menstrual Cycle
Menstruation (periods) is the shedding of the uterine lining (along with blood) through the vagina, which occurs when fertilisation has not happened.
- The menstrual cycle repeats roughly every 28–30 days in females of reproductive age.
- During the cycle, the ovary releases one mature ovum around the middle of the cycle. This release is called ovulation.
- The uterine lining (endometrium) thickens to prepare for a possible pregnancy.
What Happens When Fertilisation Does NOT Occur
- The thickened uterine lining is not needed to support a pregnancy.
- The lining breaks down and is discharged through the vagina as blood and tissue.
- This discharge is called menstruation, and it lasts for about a few days (typically 3–5).
What Happens When Fertilisation Occurs
- The zygote is formed and gets implanted in the uterine lining.
- The thickened lining is retained to support the developing embryo.
- Menstruation is stopped, which is why a missed period can indicate pregnancy.
- Hormones (oestrogen and progesterone) regulate this thickening and shedding of the lining.
| Ovulation | Menstruation |
|---|---|
| Release of a mature ovum from an ovary | Shedding of the uterine lining with blood |
| Occurs around the middle of the cycle (~day 14 in a 28-day cycle) | Occurs if fertilisation does not take place |
| Ovum leaves the ovary into the fallopian tube | Tissue and blood leave the body through the vagina |
10. Reproductive Health
Reproductive health is the state of complete physical, mental and social well-being related to the reproductive system, and not merely the absence of disease.
Why Reproductive Health is Important
- Helps prevent the spread of sexually transmitted infections.
- Ensures safe and responsible reproductive practices.
- Supports family planning and personal well-being.
- Maintaining personal hygiene reduces the risk of reproductive infections.
Personal Hygiene and Safe Practices
- Maintain cleanliness of the body (especially during puberty and menstruation).
- Seek proper medical guidance and regular health check-ups.
- Practice responsible, safe behaviour and mutual commitment between partners.
Sexually Transmitted Infections (STIs)
- Infections transmitted through sexual contact, e.g. gonorrhoea, syphilis, HIV (Human Immunodeficiency Virus)/AIDS (Acquired Immunodeficiency Syndrome).
- HIV damages the body’s immune system and can lead to AIDS.
- Prevention: safe sexual practices, awareness, faithfulness to a single partner, avoiding risky behaviour, and seeking medical help early.
There is no cure for AIDS today. It can only be prevented. Early and correct medical guidance is essential for any infection of the reproductive system.
Contraception
Contraception refers to methods that prevent pregnancy. Contraceptives also help in family planning and can reduce the spread of STIs.
| Method | How it works | Examples |
|---|---|---|
| Barrier methods | Physically block the meeting of sperm and ovum | Condoms (also prevent STIs), diaphragm |
| Oral contraceptive pills | Hormones prevent ovulation or change the uterine lining | Birth control pills (only under proper guidance) |
| IUCD (Intra Uterine Contraceptive Device) | A device placed in the uterus that prevents implantation | Copper-T |
| Surgical methods | Block or cut the tubes carrying gametes so fertilisation cannot occur | Vasectomy (male), tubectomy (female) |
11. Importance of Variation
Variation is the difference in characteristics shown by individuals of the same species or between parent and offspring.
Why Variations Occur
- DNA copying errors: DNA copying during cell division is not always perfect, so small changes appear.
- Sexual reproduction: Mixing of genetic material from two parents produces new combinations of traits.
Role of Variation in Survival
- In a changing environment, some variants may be better suited to survive and reproduce.
- If a disease or climate change affects one type, other variants may survive, keeping the population alive.
- Variation is the raw material for natural selection and evolution.
Inherited vs Non-inherited Variation
| Inherited Variation | Non-inherited Variation |
|---|---|
| Passed from parents to offspring through genes/DNA | Acquired during an individual’s lifetime; not passed to offspring |
| Can be inherited by the next generation | Cannot be inherited by the next generation |
| Example: eye colour, height | Example: scars, changes due to exercise |
Why Sexual Reproduction Contributes More to Variation
- Genetic material of two parents combines, so offspring get a mixture of traits.
- Gamete formation shuffles the arrangement of hereditary material.
- Each individual produced is different from others, increasing diversity in the population.
12. Important Definitions
The biological process by which organisms produce new individuals of their own species.
Reproduction involving a single parent, with no fusion of gametes, producing genetically similar offspring.
Reproduction involving two parents and the fusion of male and female gametes to form a zygote.
A form of asexual reproduction in which a unicellular organism splits into two (binary) or many (multiple) daughter cells.
Asexually reproducing multicellular organisms breaking into fragments, each growing into a new individual, e.g. Spirogyra.
Asexual reproduction in which lost body parts are regrown by specialised cells to form complete organisms, e.g. Planaria.
Asexual reproduction in which a small outgrowth (bud) on the parent develops into a new individual that later detaches, e.g. Hydra.
Asexual reproduction in plants from vegetative parts (roots, stems, leaves) rather than seeds.
The transfer of pollen grains from the anther to the stigma of a flower.
The fusion of a male gamete with a female gamete to form a zygote.
A specialised reproductive cell (sperm in males, ovum in females) that takes part in fertilisation.
The single cell formed by the fusion of male and female gametes; the first cell of a new individual.
The early developing organism formed after the zygote begins to divide.
The developing baby in the uterus after about eight weeks, when organs have begun to form.
The attachment of the developing embryo to the wall of the uterus.
The discharge of blood and the uterine lining through the vagina when fertilisation has not occurred.
The release of a mature ovum from the ovary during the menstrual cycle.
Complete physical, mental and social well-being related to the reproductive system.
Methods used to prevent pregnancy, also helpful in family planning.
An infection transmitted through sexual contact, such as gonorrhoea, syphilis or HIV/AIDS.
13. Solved Examples
Basic Questions
Define reproduction and state its main types.
Show Answer
Answer: Reproduction is the biological process by which organisms produce new individuals of their own species. Its two main types are asexual reproduction (single parent, no gamete fusion) and sexual reproduction (two parents, fusion of gametes).
Why is DNA copying an essential part of reproduction?
Show Answer
Answer: DNA copying (replication) passes the hereditary material from the parent to offspring, ensuring that the new individual has the characteristic features of the species. Mild inaccuracies in copying also bring about variation, which is important for evolution.
Name the female reproductive organ of a flower and state its parts.
Show Answer
Answer: The female reproductive organ of a flower is the carpel (pistil). It has three parts: stigma (receives pollen), style (connects stigma to ovary) and ovary (contains ovules with the egg).
Define pollination and name the agents that help in pollination.
Show Answer
Answer: Pollination is the transfer of pollen grains from the anther to the stigma of a flower. Agents that help in pollination: insects, wind, birds and water.
What happens in a female body when the ovum is not fertilised?
Show Answer
Answer: When the ovum is not fertilised, the thickened uterine lining is not needed to support a pregnancy. It breaks down and is discharged along with blood through the vagina. This is called menstruation.
Moderate Questions
Distinguish between binary fission and multiple fission with suitable examples.
Show Answer
Answer: In binary fission, one parent cell divides into two daughter cells (nucleus divides first) and each grows into a new organism – e.g. Amoeba, Bacteria. In multiple fission, the nucleus divides repeatedly to form many nuclei, each becoming a new organism – e.g. Plasmodium.
How is regeneration different from fragmentation? Give one example of each.
Show Answer
Answer: In fragmentation, a multicellular organism simply breaks into pieces, and each mature piece grows into a new individual – e.g. Spirogyra. In regeneration, specialised cells of a cut body part grow to form a complete organism – e.g. regeneration of a whole Planaria from a cut part.
Why is variation important for the survival of a species?
Show Answer
Answer: Variation gives some individuals traits better suited to the environment. When conditions change (e.g. a new disease or climate change), these better-suited variants survive and reproduce, keeping the species alive. Variation is thus the raw material for natural selection.
Draw a neat flow chart showing the path of a sperm in the male reproductive system after its production in the testes.
Show Answer
Answer: Testes (sperm produced) → vas deferens → urethra → penis (semen passed out). Seminal vesicles and the prostate gland add their secretions to form semen.
What is the role of the placenta in human reproduction?
Show Answer
Answer: The placenta is a disc-like structure embedded in the uterine wall. It supplies oxygen and digested nutrients to the foetus, removes its waste products, and lets the mother’s blood exchange gases and materials with the foetus through the umbilical cord.
Mention the changes that occur in boys and girls during puberty.
Show Answer
Answer: Common changes: rapid increase in height, change in body shape. In boys: deepening of voice, growth of facial/body hair, maturation of testes (due to testosterone). In girls: breast development, broadening of hips, onset of menstruation (due to oestrogen).
How do hormones control the changes during puberty?
Show Answer
Answer: At puberty the pituitary gland secretes increased amounts of follicle-stimulating and luteinising hormones. These activate the testes to release testosterone and the ovaries to release oestrogen, which bring about the physical and reproductive changes of puberty.
Application Questions
A gardener is asked to quickly grow many identical rose plants from a single plant. Which method should the gardener use and why?
Show Answer
Answer: The gardener should use vegetative propagation (e.g. by cuttings). It produces many genetically identical plants quickly, does not need seeds, and preserves the desirable traits of the parent plant.
Maize produces very light pollen grains and the flowers do not have brightly coloured petals. What is the likely agent of pollination and why?
Show Answer
Answer: Wind. Light pollen can be carried far by air currents, and plants pollinated by wind need not attract insects, so they lack showy petals.
Why is reproduction by budding potentially harmful if it happens in the wrong body part?
Show Answer
Answer: The technique of budding (used in grafting, yeast etc.) is natural in simple organisms. However, uncontrolled cell division in a human body part is a sign of development of a tumour (cancer); such rapid multiplication of cells is harmful, not helpful, in complex organisms.
A couple uses only oral contraceptive pills. Which stage of reproduction do the pills mainly affect, and what precaution should they take?
Show Answer
Answer: Oral contraceptive pills work by preventing ovulation (release of the ovum) or by changing the uterine lining so that implantation does not occur. Precaution: contraceptives should be taken only under proper medical guidance as they affect the hormonal balance.
In a potato, small buds (eyes) are used to grow new plants. Identify the type of reproduction and state the advantage.
Show Answer
Answer: Vegetative propagation. The advantage is that all plants produced are genetically identical to the parent (uniform crop), and the method is fast and reliable without requiring seeds.
Competency Questions
Two students grew Spirogyra in two trays. In tray A they kept the filament whole, and in tray B they broke it into many small pieces. Predict what will be observed in each tray after one week, giving the reason.
Show Answer
Answer: Tray B will show many new Spirogyra filaments, while tray A will show only one (the original filament growing). Reason: Spirogyra reproduces by fragmentation – each piece can grow into a complete new filament.
A scientist removed the anthers of a pea flower before pollen was released. Would the flower still form seeds? Justify.
Show Answer
Answer: No seeds would form because pollination and fertilisation cannot take place – the anther produces the pollen that carries the male gamete. Without male gametes, the ovule cannot be fertilised, so no seed develops.
Study the table and identify the plant reproduced by a method other than seeds:
| Plant | Method |
|---|---|
| Banyan | Seed |
| Sugarcane | Vegetative propagation by stem |
| Maize | Seed |
| Mango | Seed |
Explain how this method differs from reproduction by seeds.
Show Answer
Answer: Sugarcane. It reproduces by vegetative propagation where new plants arise from the stem instead of a seed. Unlike seed reproduction (which involves fertilisation and variation), vegetative propagation produces genetically identical offspring quickly without gamete fusion.
In a human female, fertilisation failed in a particular cycle even though the ovum was released. Trace the sequence of events in her uterus over the next few days.
Show Answer
Answer: The ovum was released at ovulation but not fertilised. The thickened uterine lining is not required to support a pregnancy, so it breaks down and is discharged through the vagina as menstruation (periods), marking the start of the next menstrual cycle.
Case-Based Questions
A laboratory observes Amoeba and Plasmodium dividing under the microscope. In Amoeba, the cell splits into two equal halves, while in Plasmodium many cells are produced at once, each of which can cause infection.
(a) Name the two kinds of reproduction described here.
(b) Which one of them is faster in producing numbers, and why?
Show Answer
Answer: (a) Amoeba shows binary fission and Plasmodium shows multiple fission. (b) Multiple fission is faster in producing numbers because the nucleus divides repeatedly into many nuclei at one time, producing several daughter organisms from a single parent.
An apple farmer found that apples from a tree grown from a seed were not identical to the parent tree, while apples from a tree grown from a cutting of a good tree were identical.
(a) Why were the seed-grown trees different?
(b) Identify the method used for the cutting-grown tree.
Show Answer
Answer: (a) Seed-grown trees come from sexual reproduction: fertilisation combines traits of two parents, producing variation, so they are not identical. (b) Vegetative propagation (artificial, by stem cutting) – offspring are genetically identical to the parent.
A health survey reported that the use of condoms among young adults reduced both unplanned pregnancies and the spread of certain infections.
(a) Name the infections whose spread is reduced.
(b) Why does a condom prevent both?
Show Answer
Answer: (a) Sexually transmitted infections such as gonorrhoea, syphilis and HIV/AIDS. (b) A condom is a barrier method – it prevents the sperm from meeting the ovum (preventing pregnancy) and blocks the transfer of infectious agents between partners (preventing STIs).
During a school talk, a student asked why the uterus wall thickens every month but the mother-to-be needs a tender womb only when pregnant.
(a) Why does the uterine lining thicken each month?
(b) What happens to this lining (i) if fertilisation occurs, and (ii) if it does not?
Show Answer
Answer: (a) The uterine lining thickens to prepare a soft, nourishing bed for the embryo in case fertilisation occurs. (b) (i) If fertilisation occurs, the embryo implants into the thickened lining and the lining is retained to support its development. (ii) If fertilisation does not occur, the lining breaks down and is shed with blood as menstruation.
14. Application-Based Learning
A farmer wants to grow a large number of identical banana plants quickly without seeds. Which method should be chosen? Give one reason.
Show Answer
Answer: Vegetative propagation (using suckers/stems). Reason: it produces many genetically identical plants quickly and preserves the desirable traits of the parent plant.
Why are angiosperm flowers that depend on insects usually brightly coloured and fragrant?
Show Answer
Answer: Bright colours and fragrance attract insects. When an insect visits a flower to collect nectar, it carries pollen grains from that flower to another, helping in cross-pollination.
In yeast, a small bulb-like outgrowth appears, grows and finally detaches. Name the process and the organism in which it is also seen in a similar form.
Show Answer
Answer: The process is budding. It is also seen in Hydra (a small bud forms on the parent body, grows and detaches).
A patient with a wound is advised to keep the wound clean and covered. Relate this to the growth of disease-causing cells in the body.
Show Answer
Answer: A wound can get infected, which may cause uncontrolled multiplication of harmful cells (tumour formation in the wrong place) or infection. Keeping it clean prevents infection and any cell growth that could harm the body.
Why is it important to plant saplings from a single good mango tree using vegetative propagation instead of growing seeds?
Show Answer
Answer: Vegetative propagation ensures the new plants are genetically identical to the good parent tree and preserves its superior fruit quality. Seeds produce variable offspring due to fertilisation.
Explain why sexually transmitted infections can be a danger to unborn babies even though the infection starts in the mother.
Show Answer
Answer: Some STIs, e.g. HIV, can pass across the placenta through the mother’s blood to the developing foetus, infecting the baby before birth. Hence STIs are dangerous not only to the individual but also to the unborn child.
Suggest one reason why a gardener prunes (cuts) the tip of a rose plant.
Show Answer
Answer: Pruning removes the growing tip and encourages the growth of many side branches. Some plants respond by developing several buds or new shoots, which may be used for vegetative propagation or to make the plant bushy.
Riya noticed that her periods stopped for two months. Give the most likely biological reason and one more reason why this could happen.
Show Answer
Answer: The most likely reason is that fertilisation occurred, so the uterine lining is retained to support the embryo and menstruation stops (pregnancy). Other reasons: hormonal imbalance, stress or illness – all of which can affect the menstrual cycle.
15. Competency-Based Questions
Sita planted a rose cutting and a mango seed on the same day. After a year the rose plant flowered, but the mango plant was still a young sapling. Explain the difference observed.
Show Answer
Answer: The rose cutting reproduces by vegetative propagation using stored food of the parent stem, so it grows and flowers faster. The mango sapling came from a seed, which requires germination and then slow growth through the seedling phase before it flowers.
In an experiment, two Planaria were cut into two pieces each. All four pieces grew into complete Planaria. (a) Name the phenomenon. (b) State its significance in nature.
Show Answer
Answer: (a) Regeneration. (b) Significance: it allows damaged or broken organisms to repair and also acts as a mode of asexual reproduction, enabling an organism to produce more individuals from cut parts.
Student A says variation in offspring arises only because of mutations. Student B says variation also arises because of sexual reproduction. Who is correct? Justify.
Show Answer
Answer: Student B is correct. In sexual reproduction the genetic material of two parents combines, producing new combinations of traits. Mutations (DNA copying inaccuracies) are only one cause; sexual reproduction itself produces variation in every generation.
A flower has its ovary deep inside the calyx so that wind cannot easily carry its pollen. Identify the likely agent of pollination and give one reason.
Show Answer
Answer: Likely insects. Deep-hidden ovaries and nectaries attract insects that crawl inside the flower. Wind is ruled out because the pollen would not be exposed to air currents.
Two patients visit a doctor. Patient X was advised a surgical method of contraception and patient Y a barrier method. Name a suitable method for each and give one reason for the choice.
Show Answer
Answer: Patient X: vasectomy/tubectomy – a permanent surgical method that blocks gamete transport. Patient Y: condom – a barrier method that prevents both pregnancy and sexually transmitted infections.
Fertilisation occurred in the fallopian tube of a woman, but the embryo failed to implant in the uterus. Predict the most likely consequence.
Show Answer
Answer: Since the embryo is not implanted, it cannot receive nourishment and is lost along with the uterine lining during the next menstruation. Pregnancy does not continue, and the cycle repeats.
16. Case-Based Learning
Mohan planted two plants – one from a potato tuber and one from an onion seed. The potato plant produced many similar tubers, while the onion plant produced onions of different sizes.
(a) Which plant showed asexual reproduction?
(b) Why were the onion plants variable?
(c) State one advantage of the potato method.
Show Answer
Answer: (a) The potato plant – by vegetative propagation through the buds (eyes) of the tuber. (b) Onion plants came from seeds (sexual reproduction), so fertilisation produced variation. (c) The potato method produces many genetically identical plants quickly without seeds.
In a nature trail, students found a Spirogyra filament in a pond, a Planaria under a stone, and Hydra attached to a leaf. All three can reproduce without two parents.
(a) Name the asexual method of each.
(b) Which of them forms a complete new organism even from a cut piece?
Show Answer
Answer: (a) Spirogyra – fragmentation; Planaria – regeneration; Hydra – budding. (b) Planaria, because its specialized cells can regenerate a complete organism from a cut fragment.
A pollen grain from a flower landed on the stigma of a flower belonging to a different plant.
(a) Name this type of pollination.
(b) Which agents could have brought the pollen here?
(c) Which part of the ovule receives the male gamete?
Show Answer
Answer: (a) Cross-pollination. (b) Insects, wind, birds or water. (c) The female gamete (egg) inside the ovule receives the male gamete carried down the pollen tube.
An ultrasound scan of a pregnant woman showed a developing baby at about 20 weeks, with a disc-like structure attached to the uterine wall and a tube connecting it to the baby.
(a) Name the disc-like structure and the connecting tube.
(b) State two functions of the disc-like structure.
Show Answer
Answer: (a) The disc-like structure is the placenta; the connecting tube is the umbilical cord. (b) The placenta supplies oxygen and digested nutrients to the foetus, and removes carbon dioxide and nitrogenous waste from it.
A school health talk explained that a couple choosing contraception need not risk their health, provided the method is chosen carefully.
(a) Name two barrier methods of contraception.
(b) Why is the IUCD (Copper-T) not a barrier method?
Show Answer
Answer: (a) Condom and diaphragm. (b) The IUCD is placed inside the uterus and works mainly by preventing implantation of the embryo, not by physically blocking the meeting of sperm and ovum; hence it is not a barrier method.
17. Self-Practice Questions
- Define reproduction. Why is it important for a species?
- Name the two main types of reproduction on the basis of the number of parents involved.
- In which type of reproduction is the offspring genetically most similar to the parent?
- Give one example each of unicellular organisms reproducing by binary fission and multiple fission.
- What is the role of DNA copying in reproduction?
- Name the organism that reproduces by fragmentation.
- Why is regeneration not the same as reproduction in all organisms?
- In which organism do buds appear on the parent body and later detach to form a new individual?
- Define vegetative propagation and give two artificial methods of it.
- Name the male and female reproductive parts of a flower.
- Name the four whorls of a flower in order from outside to inside.
- What is pollination? Name two agents of pollination.
- Distinguish between self-pollination and cross-pollination.
- What is a pollen tube? What role does it play in fertilisation?
- After fertilisation, what do the ovule and the ovary of a flower develop into?
- Name the male and female gametes in human beings.
- Where are sperm and testosterone produced in the male reproductive system?
- Where does fertilisation take place in the female reproductive system?
- What is the function of the uterus?
- Where is the ovum released at ovulation?
- What is implantation?
- After how many weeks is the developing embryo called a foetus?
- State the main functions of the placenta.
- Name the hormones responsible for the changes of puberty in males and females.
- What happens to the uterine lining when fertilisation does not occur?
- Define menstruation and state its approximate duration in days.
- Name two sexually transmitted infections.
- Why must contraceptives be chosen only under proper medical guidance?
- Name one barrier method of contraception and one surgical method of contraception.
- Why does sexual reproduction produce more variation than asexual reproduction?
Answer Key
| Q.No. | Answer |
|---|---|
| 1 | Production of new individuals of the same species; ensures continuation of the species and introduces variation. |
| 2 | Asexual reproduction (one parent) and sexual reproduction (two parents). |
| 3 | Asexual reproduction. |
| 4 | Binary fission: Amoeba / Bacteria; multiple fission: Plasmodium. |
| 5 | Passes hereditary material to offspring and, through copying errors, produces variation. |
| 6 | Spirogyra. |
| 7 | Regeneration forms a whole organism from a cut part of an organism; reproduction normally produces new individuals irrespective of cutting. |
| 8 | Hydra (also yeast by budding). |
| 9 | Production of new plants from vegetative parts (roots/stems/leaves); artificial methods: cutting, layering, grafting. |
| 10 | Male: stamen (anther + filament); female: carpel/pistil (stigma + style + ovary). |
| 11 | Sepals, petals, stamens, carpels. |
| 12 | Transfer of pollen from anther to stigma; agents: insects, wind (also birds, water). |
| 13 | Self-pollination: within same flower/plant, less variation; cross-pollination: between plants, more variation, needs an agent. |
| 14 | A tube that grows from a pollen grain through the style to the ovule; it carries the male gamete to fuse with the egg. |
| 15 | Ovule → seed; ovary → fruit. |
| 16 | Male: sperm; female: ovum (egg). |
| 17 | Testes. |
| 18 | Fallopian tube (oviduct). |
| 19 | It is the site of implantation and development of the embryo/foetus. |
| 20 | Into the fallopian tube from the ovary (around the middle of the cycle). |
| 21 | Attachment of the developing embryo to the wall of the uterus. |
| 22 | About 8 weeks after fertilisation. |
| 23 | Supplies oxygen and nutrients to the foetus; removes waste; exchanges gases between mother and foetus. |
| 24 | Male: testosterone; female: oestrogen. |
| 25 | It breaks down and is shed with blood as menstruation. |
| 26 | Discharge of blood and uterine lining through the vagina when the ovum is not fertilised; about 3–5 days. |
| 27 | Gonorrhoea, syphilis, HIV/AIDS (any two). |
| 28 | They affect hormonal balance and must be suited to each individual to avoid health risks. |
| 29 | Barrier: condom (also diaphragm); surgical: vasectomy / tubectomy. |
| 30 | Genetic material of two parents combines and gamete formation shuffles traits, creating new combinations in every generation. |
18. Common Mistakes to Avoid
| Mistake | Correction |
|---|---|
| Saying "fertilisation happens in the uterus" | Fertilisation occurs in the fallopian tube; the uterus is the site of implantation and development. |
| Confusing fragmentation with regeneration | Fragmentation is simply breaking into pieces (Spirogyra); regeneration involves specialised cells regrowing a complete organism (Planaria). |
| Writing sperm is produced in the penis | Sperm is produced in the testes; the penis only transfers semen. |
| Thinking the fruit comes from the ovule | The ovule becomes the seed; the ovary becomes the fruit. |
| Stating germination and regeneration are same | Germination is the growth of a seed into a seedling; regeneration is the regrowth of a whole organism from a body part. |
| Writing HIV = AIDS | HIV is the virus that can cause AIDS (Acquired Immuno Deficiency Syndrome); infection may not always mean full AIDS. |
| Calling the stigma the female gamete | The stigma is only the receiving surface; the female gamete (egg) lies inside the ovule in the ovary. |
19. Board Exam Tips
- Draw well-labelled diagrams of: binary fission (Amoeba), budding (Hydra), flower, pollen tube fertilisation, and the male and female reproductive systems.
- Learn the pathway tables: asexual methods, flower parts, contraception methods, and male vs female systems.
- For definition questions, start with the exact term, e.g. "Asexual reproduction is …" and then add one supporting example.
- When distinguishing, present the two concepts point by point in a table for full marks.
- For 2-mark "why" questions, always give the reason plus one example (e.g. why variation matters).
- Revise PYQs: reproduction, fertilisation in flowers, and human reproductive system are repeatedly asked in CBSE board exams.
- Use proper biological terms (gamete, zygote, implantation, placenta) rather than everyday language.
20. Quick Revision
- Reproduction: formation of new individuals of a species; key to continuity of life.
- Asexual reproduction: single parent, no gametes, fast, little variation – fission, fragmentation, regeneration, budding, vegetative propagation.
- Sexual reproduction: two parents, gametes fuse at fertilisation to form a zygote, more variation.
- Flower: sepals, petals, stamens (anther + filament), carpels (stigma + style + ovary with ovules).
- Pollination: anther → stigma (self vs cross; agents: insects, wind).
- Fertilisation in plants: pollen tube carries male gamete to ovule; ovule → seed, ovary → fruit.
- In humans: sperms (testes) + ovum (ovary) → fertilisation in fallopian tube → zygote → implantation → embryo → foetus (~8 weeks) → birth.
- Placenta: nourishment, gas exchange and waste removal for the foetus.
- Puberty changes are controlled by testosterone (male) and oestrogen (female).
- Menstrual cycle ~28–30 days; menstruation occurs when the ovum is not fertilised.
- Reproductive health: hygiene + safe practices; STIs like gonorrhoea, syphilis, HIV/AIDS; contraception (barrier, pills, IUCD, surgical).
- Variation due to DNA copying and sexual reproduction; raw material for evolution.