Asexual reproduction and vegetative propagation
A gardener snips a stem of a money plant, puts it in a glass of water, and in a week white roots appear. No flower, no seed, no second parent was needed.
Asexual reproduction needs only one parent, and the young one is an exact genetic copy (a clone). In plants, new plants can grow from vegetative parts such as stems, leaves and buds. This is vegetative propagation. Common methods are cutting, layering, grafting and tissue culture.
In the figure : Different parts, same idea: a new plant from a parent part.
Rule 1: Vegetative parts can make new plants — A part with a node or bud, kept moist, can grow roots and shoots.
- Easy : Sugarcane pieces with nodes sprout when planted in moist soil.
- Medium : Ginger and potato are underground stems; their buds grow into new plants.
- Exam-type : Bryophyllum leaf margins grow tiny plantlets that fall and root.
Rule 2: Choose the method for the goal — Cutting and layering copy one plant; grafting joins two plants; tissue culture makes many disease-free plants from a few cells.
- Easy : A rose cutting keeps the flower colour of the parent.
- Medium : Grafting joins a sweet-fruit stem to a strong-rooted plant to get both traits.
- Exam-type : Banana growers use tissue culture to get thousands of virus-free plants quickly.
Vegetative propagation gives identical plants quickly, but the lack of variation makes all plants equally weak to one disease.
Thinking that a cutting grows from a seed, or that a grafted plant is a mix of the two plants' genes.
Memory clue: C-L-G-T — Cutting, Layering, Grafting, Tissue culture. Every one has one parent.
Spot the difference
| Method | What is used | Example |
|---|---|---|
| Cutting | Stem piece with node | Rose, money plant |
| Layering | Bent branch pressed in soil | Jasmine, lemon |
| Tissue culture | Few cells on nutrient medium | Banana, orchid |
Practice questions
- 1What is a clone?
- 2Name two plants that grow from underground stems.
- 3Why must a cutting have at least one node?
- 4Why is the branch kept attached to the parent during layering?
- 5Why does an orchard owner prefer grafting over seeds for a prize mango?
- 6Why are leaves of a cutting trimmed?
- 7A nursery makes 40 cuttings from one plant, and 3 out of every 4 root successfully. How many rooted plants will it get?
- 8A tissue culture tube gives 6 plantlets each month from one piece. How many plantlets from 5 pieces in 4 months?
Show answers (try them yourself first)
- 1An identical copy of the parent made by one-parent reproduction.
- 2Potato and ginger.
- 3Roots and shoots arise from nodes (buds).
- 4It keeps receiving water and nutrients until its own roots form.
- 5A graft copies the known good variety, while seeds show variation.
- 6To reduce water loss until roots grow.
- 740 × 3 ÷ 4 = 30 plants.
- 86 × 5 × 4 = 120 plantlets.
Budding, spores and mitosis
A speck of bread mould on a damp slice becomes a fuzzy green patch in three days. Nothing was added, yet it multiplied.
Many organisms reproduce by budding (a small bud grows on the parent and separates, as in yeast and Hydra) or by spores (tiny light cells made on hyphae of fungi such as Rhizopus). Both use mitosis, the cell division that makes two identical cells. Louis Pasteur showed that life comes from existing life.
In the figure : A spore lands, germinates and spreads into a mould.
Rule 1: Warmth and moisture help spores grow — Spores are always in air; they sprout only where it is warm and damp.
- Easy : Bread kept in a warm, damp box grows mould faster than bread kept dry in a fridge.
- Medium : Cold slows the growth of microorganisms, so cooked food lasts longer in a fridge.
- Exam-type : A dry, open window sill rarely grows mould on a dry biscuit.
Rule 2: Budding and spores both copy the parent — Mitosis gives each new cell the same number of chromosomes as the parent cell.
- Easy : A parent cell with 20 chromosomes gives cells with 20 chromosomes each.
- Medium : Yeast buds multiply fast in a warm sugar solution.
- Exam-type : Hydra often carries several buds at one time.
Asexual reproduction is fast and needs one parent, so populations grow quickly when conditions are good.
Thinking that mould appears from bread by itself, or that a spore is a seed with two parents.
Memory clue: Bud = body outgrowth, Spore = tiny traveller, and both come from mitosis.
Spot the difference
| Organism | Method | Key part |
|---|---|---|
| Yeast | Budding | Bud on parent cell |
| Hydra | Budding | Bud on body wall |
| Rhizopus | Spores | Spore case on hyphae |
Practice questions
- 1What are hyphae?
- 2Who proved that life comes from existing life?
- 3Name one organism that reproduces by budding.
- 4Why do spores need warm, damp places?
- 5Why do fungi make millions of spores?
- 6Why is a fridge useful for food?
- 7A mould colony doubles its size every day. If it covers 1 cm² on day 1, find the area on day 5.
- 8A mother cell with 24 chromosomes divides by mitosis. How many chromosomes in each daughter cell, and how many daughter cells?
Show answers (try them yourself first)
- 1Thread-like parts of a fungus.
- 2Louis Pasteur.
- 3Yeast or Hydra.
- 4They need warmth and moisture to germinate.
- 5Only a few land in a suitable place, so many are made.
- 6Low temperature slows growth of microorganisms.
- 71, 2, 4, 8, 16 cm² on day 5.
- 824 chromosomes in each of 2 daughter cells.
Sexual reproduction, meiosis and variation
Two brothers share the same parents, yet one is tall with curly hair and the other is short with straight hair. Sexual reproduction mixes the characters.
In sexual reproduction two parents make gametes (sperm and egg). They fuse to form a zygote. Gametes are made by meiosis, which halves the number of chromosomes. Humans have 46 chromosomes (23 pairs) in body cells and 23 in each gamete. The zygote gets 23 from each parent and is again 46.
In the figure : Meiosis halves, fertilisation restores.
Rule 1: Meiosis halves the chromosome number — A gamete gets one chromosome from each pair, so it is haploid; the zygote is diploid.
- Easy : A cell with 40 chromosomes makes gametes with 20.
- Medium : Sperm (23) + egg (23) gives a zygote with 46.
- Exam-type : Without meiosis, the number would double in each generation.
Rule 2: Random mixing gives variation — With n pairs of contrasting characters, the number of gamete types is 2 raised to n.
- Easy : 3 pairs give 2 × 2 × 2 = 8 types.
- Medium : 5 pairs give 2 × 2 × 2 × 2 × 2 = 32 types.
- Exam-type : Variation helps some individuals survive when the environment changes.
Meiosis makes gametes; mitosis makes body cells and clones. Fertilisation brings back the full number.
Saying that meiosis doubles chromosomes, or that a child gets all characters from only one parent.
Memory clue: Meiosis = Minus half (gametes), Mitosis = Make same (copies).
Spot the difference
| Point | Mitosis | Meiosis |
|---|---|---|
| Chromosome number | Stays the same | Becomes half |
| Makes | Body cells, clones | Gametes |
| Variation | None | Gives variation |
Practice questions
- 1Name the male and female gametes of animals.
- 2How many chromosomes are in a human body cell?
- 3What is formed when two gametes fuse?
- 4Why do children of the same parents look different?
- 5Why is meiosis necessary for sexual reproduction?
- 6How does variation help a species?
- 7A species has 30 chromosomes in each body cell. How many are in a gamete and in a zygote?
- 8How many gamete types are possible from 4 pairs of contrasting characters?
Show answers (try them yourself first)
- 1Sperm and egg.
- 246 chromosomes.
- 3A zygote.
- 4Random mixing of chromosomes gives a unique combination to each child.
- 5Otherwise the chromosome number would double every generation.
- 6It helps some individuals survive changing conditions.
- 715 in a gamete and 30 in a zygote.
- 82 × 2 × 2 × 2 = 16 types.
Flower structure and pollination
A bee lands on a bright flower, picks up yellow dust on its legs and carries it to the next flower. That dust is the start of a fruit.
The flower has four whorls: sepals (protect the bud), petals (attract pollinators), stamens (male: filament and anther that makes pollen) and the pistil (female: stigma, style, ovary with ovules). Pollination is the transfer of pollen from anther to stigma. It is self-pollination within one plant and cross-pollination between two plants.
In the figure : Stamen is male, pistil is female.
Flower structure and pollination
In the app you can move this figure with your finger.
Open in the appRule 1: Know the parts and their jobs — Anther makes pollen; ovary holds the ovules; the stigma catches pollen.
- Easy : A flower without stamens cannot make pollen.
- Medium : An ovule holds the egg cell and is found inside the ovary.
- Exam-type : A complete flower has sepals, petals, stamens and a pistil.
Rule 2: Pollinator and flower match — Bright, scented flowers use insects; light, plentiful pollen with a feathery stigma suits wind; water plants use water.
- Easy : Wheat releases a huge amount of light pollen to the wind.
- Medium : A flower with large sticky pollen is usually insect-pollinated.
- Exam-type : Vallisneria is pollinated through water.
Pollination is only the transfer of pollen; fertilisation is the next, separate step.
Mixing up pollination with fertilisation, or stamen with pistil.
Memory clue: Stamen = Sperm-side (male), Pistil = female. Anther holds pollen.
Spot the difference
| Part | Sex | Job |
|---|---|---|
| Stamen | Male | Makes pollen |
| Pistil | Female | Receives pollen, holds ovules |
| Petal | Neither | Attracts pollinators |
Practice questions
- 1Name the male part of a flower.
- 2What is pollination?
- 3Where are ovules found?
- 4Why do wind-pollinated flowers release a large amount of pollen?
- 5How does a bright, scented flower help the plant?
- 6What is the difference between self- and cross-pollination?
- 7Wheat flowers need many pollen grains. If 50 flowers each release 20000 grains, how many in all?
- 8Out of 200 pollen grains on a stigma, only 1 fertilises the ovule. What fraction fertilises?
Show answers (try them yourself first)
- 1The stamen.
- 2Transfer of pollen from anther to stigma.
- 3Inside the ovary.
- 4Much pollen is lost before it reaches a stigma.
- 5It attracts insects that carry pollen.
- 6Self uses one plant; cross uses two plants.
- 750 × 20000 = 1000000 grains.
- 81 out of 200, that is 1/200.
Fertilisation, seeds and fruits in plants
After a mango tree flowers, tiny green knobs appear where flowers were, and weeks later they are juicy mangoes with a stone inside.
After pollination, a pollen tube grows down the style to the ovule. A male gamete fuses with the egg in fertilisation to form a zygote, which becomes an embryo. The ovule becomes the seed and the ovary becomes the fruit. Seeds spread by dispersal through wind, water and animals and sprout when water, air and warmth are available.
In the figure : Pollen lands, tube grows, gametes fuse, seed forms.
Rule 1: Fertilisation changes flower parts into fruit and seed — Zygote becomes the embryo; ovule becomes a seed; ovary becomes a fruit.
- Easy : A pea pod grows from the ovary and the peas from ovules.
- Medium : No pollination means no fertilisation, fruit or seed.
- Exam-type : Fruit forms only when fertilisation has taken place.
Rule 2: Dispersal depends on seed features — Hairs or wings suit wind; floating husks suit water; hooks suit animals.
- Easy : Dandelion seeds with hairs travel by wind.
- Medium : Coconut with fibrous husk floats on sea water.
- Exam-type : Seeds with hooks stick to animal fur.
Dispersal reduces crowding, so seedlings get more water and light.
Thinking that fruits form from petals, or that seeds form without fertilisation.
Memory clue: Ovule → Seed, Ovary → Fruit. Order: Tube, Fuse, Zygote, Seed.
Spot the difference
| Part before | Becomes | After fertilisation |
|---|---|---|
| Ovule | Seed | Holds embryo |
| Ovary | Fruit | Protects seeds |
| Zygote | Embryo | Grows in seed |
Practice questions
- 1What carries the male gamete to the egg?
- 2Name the three agents of seed dispersal.
- 3What does the ovary turn into?
- 4Why is seed dispersal useful?
- 5Why do coconuts float?
- 6What is needed for a seed to germinate?
- 7A grass flower releases 400000 pollen grains and forms 100 seeds. Find the pollen grains per seed.
- 8A tree drops 5000 seeds and 2 out of every 100 sprout. How many seedlings?
Show answers (try them yourself first)
- 1The pollen tube.
- 2Wind, water and animals.
- 3A fruit.
- 4It spreads seeds so seedlings get more space, water and light.
- 5Their fibrous husk traps air and helps floating.
- 6Water, air and suitable temperature.
- 7400000 ÷ 100 = 4000 grains per seed.
- 85000 × 2 ÷ 100 = 100 seedlings.
Reproduction in animals
A frog lays a jelly-like mass of thousands of eggs in a pond, while a crow lays three or four eggs and guards them. Both are reproducing, in different ways.
In external fertilisation (frogs, most fish) eggs and sperm meet outside the body, so many eggs are laid and few survive. In internal fertilisation (birds, reptiles, mammals) they meet inside the female, so fewer eggs are laid and care is greater. The egg contains yolk. Insects pass through egg, larva, pupa and adult. The larva is a feeding stage, such as a caterpillar or tadpole.
In the figure : Fewer eggs, more care, higher survival.
Rule 1: Where fertilisation happens decides the number of eggs — Outside the body means many exposed eggs; inside means few protected eggs.
- Easy : Carp lay thousands of eggs but few young survive.
- Medium : A sparrow lays a few eggs and young ones survive better.
- Exam-type : A frog has external fertilisation, a lizard has internal.
Rule 2: More yolk means fewer, bigger eggs — A mother can give a lot of yolk only to a few eggs.
- Easy : A bird's egg has enough yolk until hatching.
- Medium : A frog egg has little yolk and hatches into a larva.
- Exam-type : A caterpillar eats leaves to store food for the pupa stage.
Species with few young give more care. Species with many young give none, but still survive through numbers.
Thinking that all animals lay eggs with equal yolk, or that a tadpole is an adult frog.
Memory clue: Outside = Many eggs, Inside = Few eggs. Butterfly: E-L-P-A (Egg, Larva, Pupa, Adult).
Spot the difference
| Animal | Fertilisation | Eggs |
|---|---|---|
| Frog | External | Very many |
| Fish | External | Hundreds to thousands |
| Bird | Internal | Few, with much yolk |
Practice questions
- 1Name an animal with external fertilisation.
- 2What is yolk?
- 3Which stage of a butterfly feeds a lot?
- 4Why do fish lay so many eggs?
- 5Why does a bird lay only a few eggs?
- 6Why is the larva stage needed?
- 7A fish lays 12000 eggs and 3 out of every 1000 survive. How many young survive?
- 8A bird lays 4 eggs and all hatch; a frog lays 600 eggs and 2% survive. Which has more survivors?
Show answers (try them yourself first)
- 1Frog or fish.
- 2Stored food in the egg for the embryo.
- 3The larva (caterpillar).
- 4External fertilisation exposes eggs, so many are lost.
- 5Each egg has a lot of yolk and needs resources.
- 6It feeds and stores nutrients before turning into an adult.
- 712000 × 3 ÷ 1000 = 36 young.
- 8Frog: 600 × 2 ÷ 100 = 12 survivors, more than the bird's 4.
Human reproductive systems and fertilisation
A science chart shows a boy and a girl of the same age. Their reproductive organs look different but follow the same plan: make gametes and bring them together.
In males, the testes (in the scrotum, slightly cooler than the body) make sperm. Sperm pass through the vas deferens and urethra; the seminal vesicles and prostate add fluid. In females, the ovaries make eggs, the oviducts carry them, and the uterus holds the developing baby. The release of an egg is ovulation; fertilisation usually occurs in the oviduct. The zygote then implants in the uterus.
In the figure : Gametes are made, meet in the oviduct, grow in the uterus.
Rule 1: Know where gametes are made — Sperm form in the testes; eggs form in the ovaries.
- Easy : The scrotum keeps the testes slightly cooler than body temperature.
- Medium : A girl is born with millions of immature eggs in her ovaries.
- Exam-type : The testes also make a hormone that causes changes at puberty.
Rule 2: Fertilisation, then implantation — Order: ovulation, fertilisation, zygote, implantation.
- Easy : Fertilisation usually takes place in the oviduct.
- Medium : The zygote divides by mitosis on its way to the uterus.
- Exam-type : A zygote has 46 chromosomes: 23 from sperm and 23 from egg.
The father's chromosome (X or Y) decides the sex of the baby; the mother always gives X.
Saying that the mother decides the baby's sex, or that fertilisation happens in the uterus.
Memory clue: Testes → Sperm, Ovary → Egg. Order: Ovulate, Fertilise, Zygote, Implant.
Spot the difference
| Organ | Sex | Role |
|---|---|---|
| Testis | Male | Makes sperm |
| Ovary | Female | Makes eggs |
| Uterus | Female | Baby develops here |
Practice questions
- 1Where are sperm made?
- 2What is ovulation?
- 3Where does fertilisation usually occur?
- 4Why are the testes kept outside the body?
- 5Which parent decides the sex of the baby, and how?
- 6How does a sperm differ from an egg?
- 7A sperm with 23 chromosomes fuses with an egg with 23. How many chromosomes in the zygote and in each body cell of the baby?
- 8A woman ovulates once in 28 days. How many eggs are released in 12 cycles?
Show answers (try them yourself first)
- 1In the testes.
- 2Release of a mature egg from an ovary.
- 3In the oviduct.
- 4Sperm formation needs a temperature slightly below body temperature.
- 5The father; he gives X or Y, the mother always gives X.
- 6A sperm is small and motile; an egg is large and non-motile with stored food.
- 746 in the zygote and 46 in each body cell.
- 812 eggs, one in each cycle.
Menstrual cycle, pregnancy and reproductive health
A girl notices that her period comes about every four weeks. Her teacher explains that this is a regular body cycle preparing for a possible pregnancy.
In the menstrual cycle, the uterus lining thickens to receive a zygote. In a 28-day cycle ovulation occurs around day 14. If the egg is not fertilised, the lining sheds with some blood in menstruation (3 to 7 days). Cycles begin at puberty and end around age 50 (menopause). Pregnancy lasts about nine months in three trimesters; the embryo is a foetus from about the ninth week.
In the figure : Egg released, travels, lining sheds if unfertilised.
Rule 1: No fertilisation means menstruation — The thickened lining is no longer needed, so it sheds.
- Easy : An egg lives about one day if not fertilised.
- Medium : If the zygote implants, menstruation stops during pregnancy.
- Exam-type : A period that began on 5 March in a 28-day cycle is next due on 2 April.
Rule 2: Care protects health — Hygiene, balanced diet, check-ups and safe practices protect mother and child.
- Easy : Sanitary pads should be changed every 4 to 6 hours and disposed of wrapped in a bin.
- Medium : Condoms reduce the spread of STIs such as HIV and help prevent pregnancy.
- Exam-type : Prenatal sex determination is prohibited by law in India to keep a balanced sex ratio.
Physical maturity comes before emotional maturity, so being able to reproduce does not mean being ready for adult responsibility.
Thinking that menstruation is a disease, or that pregnancy lasts a fixed one year.
Memory clue: Egg + no sperm = Lining out. Pregnancy: 9 months, 3 trimesters.
Spot the difference
| Event | When | What happens |
|---|---|---|
| Ovulation | About day 14 | Egg released |
| Menstruation | 3 to 7 days | Lining sheds |
| Pregnancy | About 9 months | Foetus grows in uterus |
Practice questions
- 1What is menstruation?
- 2How long does a typical pregnancy last?
- 3Name one sexually transmitted infection.
- 4Why does the uterus lining shed if the egg is not fertilised?
- 5Why is menstrual hygiene important?
- 6Why is prenatal sex determination banned?
- 7A period started on 3 June in a regular 28-day cycle. When is the next one due?
- 8Pregnancy lasts nine months in three equal trimesters. How many months in each trimester?
Show answers (try them yourself first)
- 1Shedding of the uterus lining with some blood.
- 2About nine months.
- 3HIV (also gonorrhoea, syphilis or herpes).
- 4The lining is not needed when there is no zygote.
- 5It prevents infection and keeps the person healthy.
- 6To prevent sex-selective abortion and a skewed sex ratio.
- 73 June plus 28 days is 1 July.
- 89 ÷ 3 = 3 months each.