01 · Explore
Reproduction continues a lineage
Asexual and sexual processes pass on genetic information differently.
- Reproduction
- Production of new individuals, continuing a lineage.
- Asexual reproduction
- Formation of offspring without fusion of gametes.
- Sexual reproduction
- Reproduction involving fusion of gametes.
Copying and combining are different routes
- Model
- A conceptual comparison, not actual cell dimensions. The colours identify genetic contributions; they are not observed colours of offspring.
An individual can live without reproducing, but a lineage must produce new individuals to continue across generations. Asexual reproduction usually has one parent and gives closely similar genetic copies.
Sexual reproduction combines genetic material through gametes. Usually two individuals contribute, but self-fertilising organisms show why “always exactly two parents” is not the defining rule.
Pause & Try
Think it through first. Writing and checking your answer is free with an account.
Question
Is sexual reproduction defined only by the number of parent individuals?
Sign in to see the answer
Write your own answer and compare it with ours. It’s free.
Sign inNew here? Sign up freeNCERT reference: chapter PDF pages 1, 2, 5, 17.
02 · Explore
A plant part can grow into a new plant
Seeds are not required in this asexual route.
- Vegetative propagation
- Growth of new plants from vegetative parts such as stems, roots or leaves.
Potato eyes are buds on a modified stem; ginger also has an underground stem. Sugarcane and money-plant stem pieces can produce roots and shoots. Bryophyllum can form plantlets at leaf margins.
Plants propagated this way retain a selected type efficiently. Mutations can still occur, and growth conditions can change appearance; “clone” does not mean an absolutely identical life experience.
Pause & Try
Think it through first. Writing and checking your answer is free with an account.
Question
Are potato tubers roots simply because they are underground?
Sign in to see the answer
Write your own answer and compare it with ours. It’s free.
Sign inNew here? Sign up freeNCERT reference: chapter PDF pages 2, 3.
03 · Explore
Three methods use different plant connections
Compare which part is attached and what grows next.
- Cutting
- A separated plant piece used to establish a new plant.
- Layering
- Root formation on a shoot while it remains attached, followed by separation.
- Grafting
- Joining a scion shoot to a compatible rooted stock.
Layer first; separate after roots develop
- Model
- In layering, a still-attached stem is bent to the ground and develops roots. Only after roots form is the new plant separated. Root and stem positions are schematic.
A cutting is separate from the start. In layering, the shoot stays connected while roots develop. Grafting combines a chosen shoot with a rooted stock; it does not fuse their genomes into a sexual hybrid.
Successful propagation depends on species, health and conditions. Rooting does not always take the same fixed number of days. Tissue culture can multiply selected plant material under controlled sterile conditions; healthy tested stock and care are still needed.
| Method | What stays / changes | Important distinction |
|---|---|---|
| Cutting | A piece is removed then planted | Rooting ability differs by plant |
| Layering | Shoot attached while roots develop | Separate after establishment |
| Grafting | Scion attached to rooted stock | Compatible tissues join; not genome fusion |
| Tissue culture | Small material multiplied in controlled medium | Health testing and sterile technique matter |
Pause & Try
Think it through first. Writing and checking your answer is free with an account.
Question
Which method keeps a shoot attached to its parent while it forms roots?
Sign in to see the answer
Write your own answer and compare it with ours. It’s free.
Sign inNew here? Sign up freeNCERT reference: chapter PDF pages 2, 3, 20.
04 · Explore
Small organisms reproduce in several ways
Look at where the new individual forms.
- Binary fission
- A parent cell divides into two daughter cells.
- Budding
- A small outgrowth develops and may separate.
- Asexual spore
- A dispersing reproductive unit that can germinate under suitable conditions.
Bacteria can divide by binary fission; they do not undergo nuclear mitosis because they have no nucleus. Yeast often buds. Hydra grows a multicellular bud by repeated cell division.
Mould spores can arrive through air and grow on suitable material. They do not arise spontaneously from the bread itself. Many fungi have both sexual and asexual stages. Avoid culturing or handling unknown mould as a home activity.
Pause & Try
Think it through first. Writing and checking your answer is free with an account.
Question
What differs between fission and budding in the simple picture?
Sign in to see the answer
Write your own answer and compare it with ours. It’s free.
Sign inNew here? Sign up freeNCERT reference: chapter PDF pages 2, 4, 5.
05 · Explore
Halving prevents doubling every generation
Gametes contribute one set each.
- Diploid / haploid
- Having two chromosome sets / one chromosome set.
- Meiosis
- Cell division that reduces chromosome-set number and generates genetic combinations.
One member of each homologous pair per set
- Model
- A two-pair segregation model, not all stages of meiosis. DNA replication and the full two-division sequence are omitted; it teaches the change from two sets to one.
In the usual human model, a body-cell nucleus has 46 chromosomes in 23 pairs; a sperm or egg has 23. Fusion restores 46 in the zygote. Mitosis then supports growth without halving the chromosome-set number.
In animals, meiosis is part of gamete formation. In flowering plants, meiosis first forms haploid spores, and later development produces gametes. The plant route is not identical to the animal route.
Pause & Try
Think it through first. Writing and checking your answer is free with an account.
Question
Why do gametes normally carry half the body-cell chromosome number?
Sign in to see the answer
Write your own answer and compare it with ours. It’s free.
Sign inNew here? Sign up freeNCERT reference: chapter PDF pages 5, 6, 13.
06 · Explore
New combinations can create differences
Variation is produced before selection acts on it.
- Genetic variation
- Differences in inherited genetic information among individuals.
Choose one from each independent pair
- Model
- Independent-pair selection is a mathematical chromosome model. It does not assign real human appearance traits to one chromosome or include all sources of variation.
Chromosome segregation, recombination and fertilisation generate different combinations. A simple model with three independently segregating pairs gives 2³=8 possible selections even before recombination is counted.
Traits such as human hair or eye colour are not reliably explained by one bead on one chromosome. Variation does not appear because an organism knows what it needs. Some differences can improve survival or reproduction in a particular environment; selection acts over generations.
| Pair A | Pair B | Pair C |
|---|---|---|
| A₁ | B₁ | C₁ |
| A₁ | B₁ | C₂ |
| A₁ | B₂ | C₁ |
| A₁ | B₂ | C₂ |
| A₂ | B₁ | C₁ |
| A₂ | B₁ | C₂ |
| A₂ | B₂ | C₁ |
| A₂ | B₂ | C₂ |
Pause & Try
Think it through first. Writing and checking your answer is free with an account.
Question
Does every new inherited difference help survival?
Sign in to see the answer
Write your own answer and compare it with ours. It’s free.
Sign inNew here? Sign up freeNCERT reference: chapter PDF pages 6, 7, 10, 18.
07 · Explore
Find the pollen source and the ovules
Structure tells you what each part contributes.
- Stamen
- Flower part with filament and pollen-producing anther.
- Pistil
- Female flower structure with stigma, style and ovary.
- Ovule
- Structure containing the female gametophyte and egg, usually becoming a seed after fertilisation.
Sepals commonly protect the bud; petals can help attract pollinating animals. The anther produces pollen. The stigma receives pollen, the style connects to the ovary, and ovules occur inside the ovary.
Pollen carries or produces the male gametes; the pollen grain is not simply one sperm cell. Not all flowers contain every part, and not every plant uses brightly coloured petals.
Pause & Try
Think it through first. Writing and checking your answer is free with an account.
Question
Which structure later becomes the seed: ovary or ovule?
Sign in to see the answer
Write your own answer and compare it with ours. It’s free.
Sign inNew here? Sign up freeNCERT reference: chapter PDF pages 7, 8.
08 · Explore
Pollen delivery comes before gamete fusion
Transfer to a stigma is a different event from fusion in an ovule.
- Pollination
- Transfer of pollen from anther to a stigma.
- Self- / cross-pollination
- Transfer within the same plant / between plants of the same species in the introductory model.
Distinguish the same plant from another plant
- Model
- Movement between compatible flowers on the same plant is self-pollination; transfer from plant A to another plant of the same species is cross-pollination. Flowers are symbols, not a species-specific mechanism.
Pollen on the same flower or another flower of the same plant is self-pollination in this classification. Pollen arriving from another compatible plant is cross-pollination.
Successful pollen delivery alone does not guarantee fertilisation: compatibility and subsequent pollen-tube growth matter. Some flowers have mechanisms reducing self-fertilisation.
Pause & Try
Think it through first. Writing and checking your answer is free with an account.
Question
Can pollination happen without subsequent fertilisation?
Sign in to see the answer
Write your own answer and compare it with ours. It’s free.
Sign inNew here? Sign up freeNCERT reference: chapter PDF pages 8, 9, 18, 19.
09 · Explore
Flower features suit the delivery route
Wind and animals solve the delivery problem differently.
- Pollinating agent
- A carrier such as wind, water or an animal that transfers pollen.
Wind delivery and directed visits
- Model
- A qualitative strategy comparison, not measured efficiency data. The animal visit directs contact with a flower; wind distributes pollen across a wider area.
Many wind-pollinated grasses produce abundant light pollen and expose anthers and receptive stigmas. Animal-pollinated flowers may offer nectar and use scent, colour or shape to guide visitors. Some aquatic plants use water; growing in water alone does not prove water pollination.
Compare strategies within suitable data. The source’s broad per-flower pollen/seed table mixes very different flowers and cannot serve as a universal success rate. Pollinator experiments need comparable plants, conditions, replication and counts with clear units.
| Route | Useful feature | Reason |
|---|---|---|
| Wind | Light abundant pollen; exposed stigma | Dispersed grains may reach a compatible stigma |
| Animal | Scent, nectar, suitable flower shape | Visitors can carry pollen between flowers |
| Water in particular species | Adapted pollen/flower placement | Water movement can help delivery |
Pause & Try
Think it through first. Writing and checking your answer is free with an account.
Question
Does being an aquatic plant automatically mean pollen travels in water?
Sign in to see the answer
Write your own answer and compare it with ours. It’s free.
Sign inNew here? Sign up freeNCERT reference: chapter PDF pages 9, 10, 19, 20.