ScienceCBSE Class 8 · Our Home: Earth, a Unique Life Sustaining Planet

Reproduction and the Continuity of Life: Class 8 Science

Updated 17 October 2026 · Fact-checked

Reproduction keeps each kind of living being from disappearing and passes genes from parents to offspring. In asexual reproduction one parent produces exact copies, as in vegetative propagation, binary division or budding. In sexual reproduction two parents each contribute a gamete carrying half the genetic material; fertilisation forms a zygote, so offspring are similar to but not identical with their parents.

Asexual reproduction gives exact copies from one parent; sexual reproduction mixes genes from two parents, so offspring are similar but not identical.

Illustration drawn for QuestionBuddy.

Understand Reproduction and the Continuity of Life

Why reproduce? If plants and animals did not reproduce, life would disappear. Parents pass on instructions called genetic material or genes, stored inside every cell, which guide how a single cell grows into a calf, kitten or any other being; so cows have calves and cats have kittens. Reproduction also allows small changes in these instructions, which can help survival: camels developed humps for storing fat in deserts, and some bacteria have become resistant to antibiotics. Over many generations such changes can give new features or even new types of living beings.

Asexual reproduction. A single parent produces new individuals that are exact copies of itself in terms of the instructions inside the cell.

*Vegetative propagation* in plants: a leaf, stem or root planted in soil grows into a new plant (Activity 13.3: stem cutting of a money plant, the 'eyes' of a sprouted potato, ginger). Bamboo and sugarcane grow this way.
*Binary division:* single-celled organisms such as bacteria and Amoeba divide into two identical individuals.
*Budding:* Hydra grows tiny buds on its body that break off and grow into new individuals.
*Regeneration:* Planaria, a flatworm, can regrow from a fragment of its body; some multicellular algae regrow from cut parts.

Sexual reproduction. Two parents, male and female, are involved. Flowering plants have male and female parts, and some microorganisms such as bacteria and yeast have two 'mating types'. Each parent makes specialised reproductive cells called gametes, which carry only half of the parent's genetic material. When a male and a female gamete join, the new cell has a full set: half from each parent, so the amount of instructions does not keep doubling. Each gamete carries a different set of instructions, which mix in different ways each time, so each child (even of the same parents) is unique. Sexual reproduction mixes useful features and lets new ones appear.

In flowering plants. Pollen grains inside the anther are the male gametes and ovules deep inside the flower are the female gametes. Wind, insects or animals carry pollen to another flower: pollination. When the male and female gametes combine it is fertilisation, forming a zygote that becomes the seed; the fleshy part of the flower around the ovule becomes the fruit. Animals that eat the fruit drop seeds far from the parent plant (a banyan seed in a wall crack), and given water seeds use stored nutrients to grow roots and shoots.

In animals. Gametes are sperm (male) and eggs (female). In fish and frogs both are released into water, where fertilisation takes place and the zygote develops into an embryo in water. In birds and mammals, sperm are deposited inside the female and fertilisation is internal. In birds the fertilised egg is laid and the embryo develops after it is laid, living on the large store of food put into the egg. In most mammals the embryo develops inside the mother, whose body provides food and oxygen until birth.

The features of Earth that make life possible are in the previous topic.

Reproduction and the Continuity of Life: formulas and key facts

Asexual reproduction: One parent > offspring identical to the parent; Vegetative propagation, binary division, budding, regeneration.
Sexual reproduction: Male gamete + Female gamete > Zygote (half the genetic material from each parent); Offspring similar to but not identical with the parents.
In flowering plants: Pollen (anther) + Ovule > Zygote > Seed; Ovary wall > Fruit; Pollination carries pollen; fertilisation joins gametes.
In animals: $S p er m + E g g > Z y g o t e > E mb r y o$; Fish, frogs: in water. Birds: egg laid. Most mammals: inside the mother.
Terms: $G e n es ∣ G am e t es ∣ Z y g o t e ∣ E mb r y o$; Genes are the instructions; gametes carry half.

How to solve Reproduction and the Continuity of Life questions

Use this method for reproduction questions.

1Count the parents: one means asexual, two means sexual.
2For asexual, name the type: vegetative propagation, binary division, budding or regeneration.
3For sexual, trace: gametes, fertilisation, zygote, embryo; say where it happens.
4Explain similarity (genes passed on) and variation (mixing from two parents).
5For numerical growth by division, double each time: 2 to the power of the number of divisions.
6Add an advantage or limitation of the method if asked.

Reproduction and the Continuity of Life in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Division of a microbe

Suppose one bacterium divides into two identical bacteria every 20 minutes under good conditions (an invented rate for the problem; the chapter says only that bacteria divide into two identical individuals).

(a) How many bacteria are there after 1 hour? (b) After 2 hours? (c) How many divisions give at least 1000 bacteria? (d) Are the new bacteria different from the parent?

Try it first, then show the solutionSolution

1 hour = 3 divisions: 2 × 2 × 2 = 8.
2 hours = 6 divisions: 2^6 = 64.
2^9 = 512, 2^10 = 1024, so 10 divisions give at least 1000 (200 minutes, or 3 h 20 min).
No; in this asexual method the offspring are exact copies.

Answer: (a) 8; (b) 64; (c) 10 divisions; (d) identical copies.

Memory hook: One splits to two, two to four: doubling fast.

Cuttings and eyes

Imagine a gardener cuts a potato into pieces so that each piece has at least one 'eye' and plants them in moist soil. One potato gives 6 pieces with eyes, and of the planted pieces 5 sprout.

(a) What kind of reproduction is this? (b) Find the percentage that sprouted. (c) Why will the new plants be exactly like the parent? (d) Give two other plant parts used this way.

Try it first, then show the solutionSolution

Vegetative propagation, a kind of asexual reproduction.
5 ÷ 6 × 100 = 83.3%.
A single parent gives its instructions unchanged, so the offspring are exact copies.
Stem cutting of money plant, ginger piece (also leaf, stem or root generally).

Answer: (a) Vegetative propagation; (b) about 83.3%; (c) one parent, identical genes; (d) money plant stem, ginger.

Memory hook: One parent, same plan.

Tricks to remember Reproduction and the Continuity of Life

Short memory aids. Say each one aloud once, then use it on a question the same day.

A for Alone, S for Sharing
Asexual = one parent alone. Sexual = two parents sharing genes.
Use it when: Distinguishing the types.
Half and half
Each gamete carries half; the zygote has the full set.
Use it when: Why genes do not double.
Pollination, Fertilisation, Fruit
P carries, F joins, Fruit forms.
Use it when: Order in flowering plants.
Hydra buds, Amoeba splits, Planaria regrows
Three animals three methods.
Use it when: Asexual examples.

Reproduction and the Continuity of Life: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Compare sexual and asexual reproduction · 3 marks · Short answerBoard level

Differentiate between asexual and sexual reproduction on number of parents, similarity to parents and one example each.

Try it first, then show the solutionSolution

Asexual: one parent; offspring exact copies; e.g. Hydra budding or potato eyes. (1)
Sexual: two parents; offspring share traits with both but are not identical; e.g. birds or flowering plants. (1)
Reason: in sexual reproduction instructions from two parents mix. (1)

Answer: Asexual: one parent, exact copies; sexual: two parents, mixed instructions, variation.

Example 2: Where fertilisation takes place · 1 mark · MCQBoard level

In frogs and fish, fertilisation takes place
(a) inside the female
(b) in water outside the bodies
(c) in the air
(d) only after hatching

Try it first, then show the solutionSolution

Male and female eject sperm and eggs into water where they combine.

Answer: (b)

Example 3: From flower to fruit · 5 marks · Long answerHarder board level

(a) Define pollination. (1) (b) Name the male and female gametes of a flower. (1) (c) Define fertilisation and zygote. (2) (d) What does the zygote become and what does the part of the flower around the ovule become? (1)

Try it first, then show the solutionSolution

(a) The carrying of pollen from the anther to another flower by wind, insects or animals. (1)
(b) Male gamete: pollen grain in the anther; female gamete: ovule. (1)
(c) Fertilisation: the joining of male and female gametes; the zygote is the cell formed by it. (2)
(d) The zygote becomes the seed; the fleshy part around the ovule becomes the fruit. (1)

Answer: Pollination carries pollen; pollen and ovule are gametes; fertilisation forms a zygote that becomes a seed; the fruit forms around it.

Example 4: Why siblings differ · 4 marks · Case-basedHarder board level

Read the passage and answer.

Two brothers have different eye colour and one is taller. A student says: 'Each parent gives all their genes to the child, so the child has double the instructions.'
(a) Correct the student's statement. (1)
(b) Explain why the brothers differ. (1)
(c) Why does a cow always give birth to a cow? (1)
(d) Give one advantage of variation. (1)

Try it first, then show the solutionSolution

(a) Each parent makes gametes with half the genetic material; the zygote has a full set, half from each parent. (1)
(b) Each gamete carries a different set of instructions, mixed in different ways each time. (1)
(c) Parents pass on the instructions that guide how a single cell develops into that kind of organism. (1)
(d) A useful change may help survival in a new environment (e.g. the camel's hump, bacteria resistant to antibiotics). (1)

Answer: (a) Gametes carry half; (b) different mixes; (c) genes guide development; (d) variation helps survival.

Example 5: Eggs or live birth · 4 marks · Case-basedHOTS / competency

Read the passage and answer.

A hen lays an egg that contains a large store of food. A dog's embryo develops inside its mother. A frog lays thousands of eggs in water. A student asks why dogs do not lay eggs.
(a) Where does fertilisation take place in the frog and in the hen? (1)
(b) How does the embryo of a bird get food? (1)
(c) How does the embryo of a dog get food and oxygen? (1)
(d) Give one possible advantage and one disadvantage of each strategy (any one each). (1)

Try it first, then show the solutionSolution

(a) Frog: in water outside the bodies; hen: inside the female's body. (1)
(b) From the large store of food packed in the egg by the female. (1)
(c) The mother's body supplies them until birth. (1)
(d) For example: egg-laying frees the mother after laying but needs a big store of food in each egg and the young need protection; giving birth keeps the young supplied and protected inside the mother, but the mother carries the load (the chapter asks you to discuss; any reasoned answer is accepted). (1)

Answer: (a) Water; inside the hen; (b) food in the egg; (c) mother's body; (d) reasoned advantage and disadvantage.

Where students lose marks in Reproduction and the Continuity of Life

The slips examiners see most often, and what to write instead.

Mistake: Saying a gamete carries the full genetic material.
The zygote does.
Wrong working
Each gamete carries all the genes of the parent.
Right working
Each gamete carries half of the parent's genetic material; the zygote receives half from each parent.
Do this: Gamete = half.
Usually costs: 1 mark.
Mistake: Writing pollination and fertilisation as the same.
Both occur in flowers.
Wrong working
Fertilisation is the transfer of pollen to the flower.
Right working
Pollination is the carrying of pollen; fertilisation is the joining of male and female gametes.
Do this: Pollination moves; fertilisation joins.
Usually costs: 1 mark.
Mistake: Naming bacteria as reproducing sexually in all cases.
A line about mating types is misread.
Wrong working
Bacteria only reproduce sexually.
Right working
Bacteria divide into two identical individuals (asexual); some also have two mating types.
Do this: Quote the chapter's asexual example.
Usually costs: 1 mark.
Mistake: Saying sexual reproduction gives exact copies.
Offspring look like parents.
Wrong working
Offspring of sexual reproduction are identical to the parents.
Right working
Offspring share traits with both parents but are not exactly like either.
Do this: Say 'similar but varied'.
Usually costs: 1 mark.

Exam tips

State the number of parents first when classifying reproduction.
Give the sequence gametes, fertilisation, zygote, embryo.
Use the chapter's examples: Hydra, Planaria, Amoeba, potato eyes, ginger, money plant.
Link variation to survival with the camel and antibiotic-resistant bacteria examples.
For doubling problems, write 2^n and the arithmetic.

Practice questions on Reproduction and the Continuity of Life

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 3 marks · Very short answerBoard level
Name the process in each: (a) Hydra forming a bud, (b) Amoeba splitting into two, (c) a money plant stem growing roots in water.
Hint
Budding, binary division, vegetative propagation.
Answer
(a) Budding (1). (b) Binary division (1). (c) Vegetative propagation (1).
Q2 · 1 mark · MCQBoard level
Gametes carry
(a) the full set of genetic material
(b) half of the parent's genetic material
(c) no genetic material
(d) double the genetic material
Hint
Zygote gets full set.
Answer
(b)
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Offspring from asexual reproduction are exact copies of the parent.
Reason (R): Only one parent is involved, so only one set of instructions is passed on.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
One set of instructions.
Answer
(a) R explains A.
Q4 · 4 marks · Short answerHarder board level
A single cell divides into two every 30 minutes (an invented rate). (a) How many cells are there after 3 hours? (b) After how many hours are there at least 500 cells? (c) By what factor does the number grow in 2 hours? (d) Are the cells identical to the first? Name the type of reproduction.
Hint
Every 30 minutes means 2 divisions per hour.
Answer
(a) 3 hours = 6 divisions: 2^6 = 64. (b) 2^9 = 512, which needs 9 divisions = 4.5 hours. (c) 2 hours = 4 divisions: 2^4 = 16 times. (d) Yes, identical; asexual reproduction by division (1 mark each).
Q5 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
A student plants a stem cutting of a rose and some seeds of the same rose. The cutting gives a plant exactly like the parent, but the seedlings show small differences in flower colour.
(a) Which method is sexual and which is asexual? (b) Explain why the seedlings differ. (c) Why does the cutting match the parent exactly? (d) State one advantage of the variation in seedlings.
Hint
Seeds come from fertilisation.
Answer
(a) Seeds: sexual; cutting: asexual (vegetative propagation). (b) Seeds come from gametes of two parents, whose instructions mix. (c) The cutting grows from a part of one plant and carries the same instructions. (d) A useful change may help survival in a new environment (1 mark each).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What are genes?Show answer
The instructions stored inside every cell, passed from parents to offspring.
2.What is vegetative propagation?Show answer
Reproduction of a plant from a leaf, stem or root planted in soil.
3.What is a zygote?Show answer
The cell formed when a male and a female gamete join.
4.Where do pollen grains form?Show answer
In the anther of a flower.
5.How does a mammal embryo get food?Show answer
From the mother's body, which provides food and oxygen until birth.

Reproduction and the Continuity of Life: frequently asked questions

Why do brothers and sisters look different?

Each gamete carries a different set of instructions that mix in different ways, so every child is unique.

Can all plants be grown from cuttings?

The chapter lists examples such as money plant, potato, ginger, bamboo and sugarcane; many plants reproduce when a leaf, stem or root is planted in soil.

What do seeds need to grow?

Water; they use stored nutrients to grow roots and shoots.

Why do fish lay many eggs?

This is a discussion question in the chapter, asking about advantages and disadvantages; it is not answered there.