Reproduction, Growth & Adolescence
Reproduction, Growth & Adolescence
Modes of Reproduction – Sexual, Asexual and Vegetative
Reproduction is the process by which living organisms produce new individuals of their own kind. It ensures continuity of species on the Earth.
| Mode of reproduction | Basic idea | Seen in | Exam-focus point |
|---|---|---|---|
| Asexual reproduction | Single parent; no formation or fusion of gametes; offspring are genetically identical to parent. | Many plants, bacteria, fungi, simple animals. | Very fast; useful in stable environment; produces clones. |
| Vegetative reproduction | Asexual reproduction using vegetative parts of plant – root, stem, leaf. | Potato, sugarcane, Bryophyllum, onion, jasmine etc. | Important in agriculture and horticulture for uniform quality plants. |
| Sexual reproduction | Two parents; involves formation and fusion of male and female gametes. | Most plants and animals, including humans. | Offspring show variation; better adaptation to changing environment. |
Asexual reproduction – common types (school level)
| Type | Description | Examples |
|---|---|---|
| Binary fission | Parent cell divides into two equal daughter cells. | Amoeba, Paramecium, many bacteria. |
| Budding | Small outgrowth (bud) develops on parent, later detaches. | Yeast, Hydra. |
| Fragmentation | Body breaks into pieces; each piece grows into new individual. | Some algae like Spirogyra. |
| Spore formation | Special spores are produced and spread by air; each spore grows into new plant. | Rhizopus (bread mould), many fungi, ferns. |
Vegetative propagation in plants (natural and artificial)
| Mode | Part used | Example crops (India context) |
|---|---|---|
| By roots | Modified roots grow into new plants. | Sweet potato, dahlia. |
| By stems | Tubers, runners, rhizomes, bulbs. | Potato, ginger, onion, garlic, banana, sugarcane, grasses. |
| By leaves | Leaf buds or notches. | Bryophyllum leaves with plantlets at leaf margins. |
| Cutting | Short piece of stem with nodes is planted. | Rose, hibiscus, grapes, many garden plants. |
| Layering | Branch is bent down and covered with soil; roots form at covered part. | Jasmine, grape, some ornamental shrubs. |
| Grafting | Stem of one plant (scion) fixed on rooted plant (stock). | Mango, citrus, guava, apple – to get improved varieties. |
Memory Line: “Asexual = one parent, identical; sexual = two parents, varied.” – Asexual is quick and uniform; sexual is slower but produces variation.
Exam Tip: If the question mentions no gamete, one parent, fast multiplication, same characters → answer is asexual/vegetative. If it mentions gametes, fertilisation, variation → answer is sexual reproduction.
Sexual Reproduction in Plants and Seed Dispersal
Flowering plants reproduce sexually using flowers as reproductive organs.
Structure of a typical flower (school level)
| Whorl | Parts | Main function |
|---|---|---|
| Calyx | Sepals | Protect flower in bud stage. |
| Corolla | Petals | Attract insects for pollination. |
| Androecium (male) | Stamens = anther + filament | Anther produces pollen grains (male gametes). |
| Gynoecium (female) | Carpel/pistil = stigma + style + ovary | Ovary contains ovules; each ovule has female gamete (egg). |
Pollination and fertilisation
- Pollination – transfer of pollen grains from anther to stigma.
- Self-pollination – same flower or same plant.
- Cross-pollination – between flowers of different plants of same species.
| Type | Agents | Features |
|---|---|---|
| Wind pollination | Air currents. | Light, dry pollen; feathery stigma; small petals – e.g., maize, grasses. |
| Insect pollination | Bees, butterflies, moths, etc. | Bright petals, nectar, scent – e.g., sunflower, jasmine. |
Fertilisation: After pollination, a pollen tube grows through style and reaches ovule; male nucleus fuses with egg cell to form zygote, which develops into an embryo.
From flower to fruit and seed
- Ovary → develops into fruit.
- Ovule → develops into seed (with embryo + stored food).
- Other floral parts may dry and fall.
Seed dispersal – how seeds spread
Seed dispersal helps plants to:
- Avoid overcrowding and competition.
- Colonise new areas.
- Survive in changing conditions.
| Agent | Example adaptations | Examples (Indian context) |
|---|---|---|
| Wind | Light seeds with wings or hair-like structures. | Drumstick, madar (Calotropis), cotton, dandelion. |
| Water | Light, spongy, fibrous fruit or seed. | Coconut, lotus, water lily. |
| Animals / humans | Hooks, spines or tasty fleshy fruits. | Xanthium, Urena (hooked fruits), mango, guava, jamun. |
| Explosion / splitting | Dry fruits burst open when ripe. | Pea, bean, balsam. |
Memory Line: “Wind – wings, Water – floating, Animals – hooks or fruits.” – quickly match seed features with dispersal agents.
Exam Tip: If the question shows a picture of coconut, cotton, Xanthium, pea pod – first identify the agent of dispersal, then answer. Often used in match-the-following or diagram-based items.
Sexual and Asexual Reproduction in Animals, Metamorphosis
Sexual reproduction in animals – basic outline
- Involves male gamete (sperm) and female gamete (ovum/egg).
- Fusion of gametes → zygote → embryo → new individual.
| Term | Meaning | Example / note |
|---|---|---|
| Unisexual organisms | Male and female are separate individuals. | Human, cow, dog, hen, frog. |
| Hermaphrodites | Same individual has both male and female reproductive organs. | Earthworm, tapeworm, leech (but usually cross-fertilise). |
| Internal fertilisation | Fusion of gametes inside female body. | Reptiles, birds, mammals, many land animals. |
| External fertilisation | Gametes released into water; fusion takes place outside body. | Fish, many amphibians (frog) – many eggs laid at a time. |
Asexual reproduction in animals (simple forms)
- Budding in Hydra – small bud grows on parent’s body, then detaches.
- Binary fission in protozoans – Amoeba, Paramecium.
- Some lower animals show regeneration (starfish arm growing new body) but this is limited in higher animals.
Metamorphosis – change of body form
Metamorphosis is a drastic change in body form and habits during development from young stage to adult.
| Organism | Stages | Key change |
|---|---|---|
| Frog | Egg → tadpole (aquatic, gills, tail) → adult frog (air-breathing, lungs, legs). | Change from water-living herbivore to land-living carnivore. |
| Butterfly | Egg → larva (caterpillar) → pupa → adult butterfly. | Changes in body structure, feeding method and habitat. |
Memory Line: “Metamorphosis = new body + new habit.” – juvenile and adult stages look very different and live differently.
Exam Tip: Life-cycle diagrams of frog and butterfly are common. Questions may ask to pick out the larval stage or to state whether the life-cycle involves metamorphosis.
Reproduction in a Placental Mammal – Human, and Cloning
Human reproduction – simple school-level outline
Humans are placental mammals. Development of baby takes place inside mother’s uterus with help of placenta, which supplies food and oxygen and removes wastes.
| Aspect | Simple description (school level) |
|---|---|
| Male system | Testes produce sperms and the hormone testosterone; ducts and associated glands help in transfer of sperms. |
| Female system | Ovaries produce ova and hormones (estrogen, progesterone); oviducts, uterus and vagina help in transport, implantation and birth. |
| Fertilisation | Usually occurs in oviduct; sperm nucleus and egg nucleus fuse to form zygote. |
| Pregnancy | Zygote develops into embryo, then foetus in uterus. Placenta connects foetus with mother’s blood supply. |
| Birth | After full development, foetus is delivered through birth canal. |
Placenta – simple function
- Thin, disc-like structure attached to uterus and foetus (via umbilical cord).
- Brings mother’s and baby’s blood very close (without mixing).
- Supplies oxygen and nutrients from mother and removes carbon dioxide and wastes from foetus.
Cloning – producing genetically identical copy
Cloning is the process of producing an organism that is genetically identical to another organism.
- Natural cloning – identical twins in humans (from the same zygote splitting).
- Artificial cloning (school reference) – “Dolly” the sheep (1996) was the first mammal cloned from an adult body cell in Scotland.
| Feature | Cloned organism |
|---|---|
| Genetic makeup | Same as the donor organism (no variation). |
| Benefits | Can preserve desirable qualities in animals and plants. |
| Concerns (school level) | Ethical issues, health problems, low success rate. |
Memory Line: “Clone = carbon copy of genes.” – Clones have the same genetic information as the original organism.
Exam Tip: Common question: “Name the first cloned sheep” → answer is Dolly. Also be ready to write a simple definition of cloning.
Reproductive Health, Birth Control Methods and Social Issues
Reproductive health – simple idea
Reproductive health means a state of complete physical, mental and social well-being in all matters relating to the reproductive system.
| Aspect | Key points (school level) |
|---|---|
| Physical health | Proper nutrition, hygiene, protection from infections, safe motherhood. |
| Mental health | Correct information, confidence, ability to say “no” to risky behaviour. |
| Social well-being | Freedom from discrimination, violence, exploitation; respect for both genders. |
Birth control methods – school-level classification
Used to regulate number and spacing of children and to protect health of mother and child.
| Type | Examples | Simple idea |
|---|---|---|
| Natural methods | Avoiding intercourse during fertile period, breastfeeding for spacing. | Based on knowledge of menstrual cycle; no devices or medicines. |
| Barrier methods | Condoms etc. | Prevent sperms from reaching egg. |
| Intra-uterine devices (IUDs) | Devices placed in uterus by doctors. | Prevent implantation of embryo; require medical guidance. |
| Surgical methods | Vasectomy in males; tubectomy in females. | Permanently block sperm or egg transport tubes; done for couples with completed family and with medical counselling. |
Fighting against social ills (school perspective)
- Child marriage – affects health and education; laws in India fix minimum age for marriage and punish early marriage.
- Gender discrimination – equal value and opportunities should be given to boys and girls.
- Child labour and trafficking – strict laws and social awareness are needed to protect children.
- Misconceptions and myths about menstruation and puberty should be removed through correct science education.
Memory Line: “Healthy body + correct information + respect = reproductive health.”
Exam Tip: Many questions ask about advantages of small family, ill-effects of child marriage or why awareness is important. Use points from physical, mental and social angles, not only from one side.
Adolescence and Puberty – Changes, Hormones, Reproductive Phase
Adolescence and puberty – basic meanings
| Term | Meaning |
|---|---|
| Adolescence | Period between childhood and adulthood, roughly from 11–12 years to about 18–19 years. |
| Puberty | Stage when sex organs mature and the body becomes capable of reproduction. |
In this period, both physical and emotional changes occur due to activity of hormones.
Role of hormones during puberty
- Pituitary gland – releases hormones that signal ovaries or testes to start producing sex hormones.
- Testosterone in boys – produced by testes; causes beard and moustache growth, voice change, broadening of shoulders, more muscle mass.
- Estrogen and progesterone in girls – produced by ovaries; cause development of mammary glands, broader hips, start of menstrual cycle etc.
Common physical changes (school-level description)
| Change | Both boys and girls | More in boys | More in girls |
|---|---|---|---|
| Increase in height | Yes – rapid growth spurt. | Usually reach more height by late teens. | Height increase earlier, stops earlier. |
| Body shape | Muscles develop, body becomes stronger. | Shoulders broaden; chest widens. | Hips broaden; body becomes more rounded. |
| Hair growth | Under arms and in pubic region. | On chest, face (beard, moustache). | Less facial hair. |
| Voice change | Voice quality changes. | Becomes deep due to enlarged voice box. | Becomes clearer but not as deep. |
Reproductive phase
- After puberty, individuals enter reproductive phase.
- In girls, menstrual cycle usually starts between 10–13 years and continues till about 45–50 years.
- In boys, sperm production starts at puberty and continues for long adult period.
Emotional changes and healthy response (school viewpoint)
- Adolescents may feel confused, shy, curious or stressed because of changes.
- Need correct information from parents, teachers, health workers and textbooks.
- Need guidance to develop good habits: balanced diet, exercise, rest, cleanliness, avoiding addiction.
Memory Line: “Adolescence = growth of body + growth of mind.” – both physical and mental changes must be understood and guided.
Exam Tip: Typical questions ask: “List changes at puberty”, “Why are balanced diet and hygiene important for adolescents?” or “What is reproductive health?” – always include at least one point each from physical, mental and social aspects.