Notes Class 9 Science Exploration Chapter 11 Reproduction – How Life Continues

🌱

Introduction: What is Reproduction?

Reproduction (प्रजनन) is a biological process by which living beings produce new individuals of their own kind. It is one of the fundamental characteristics of all living organisms. Without reproduction, a species would become extinct.

📌 Definition: Reproduction = The biological process by which living organisms produce new individuals of the same species, ensuring the continuity of life.

🎯 Why is Reproduction Important?

It ensures the continuity of life on Earth — without it, species die out.
It transfers genetic information from one generation to the next.
It creates variation (in sexual reproduction), which helps species adapt to changing environments.
Variation accumulated over many generations can even give rise to new species (evolution).

🔀 Two Main Types of Reproduction

🔵 Asexual Reproduction

A single parent produces offspring that are almost exact copies of the parent. No mixing of genetic material. Examples: bacteria, amoeba, yeast, hydra, many plants.

🟠 Sexual Reproduction

Two parents contribute genetic material. Offspring inherit a mix of characteristics. This mixing creates small differences (variations) between parents and offspring. Examples: flowering plants, most animals, humans.

💡

Real-Life Connection

A mango tree grows old and dies, but its seeds grow into new mango plants. Cows give birth to calves, dogs to puppies, and humans to children — this is how life on Earth keeps going!

🌿

Asexual Reproduction in Plants — Vegetative Propagation

Many plants can grow new individuals from their existing parts — without producing seeds! This is called Vegetative Propagation (कायिक प्रजनन). New plants arise from the vegetative (growing) parts of a plant — roots, stems, or leaves.

🔑 Key Feature: Vegetative propagation involves only ONE parent → produces genetically identical individuals (clones).

🌱 Examples of Vegetative Propagation in Nature

Plant	Part Used	How it Works
Potato	Underground stem (tuber)	Eyes of potato sprout new plants
Ginger	Rhizome (underground stem)	Sprouts new plants without seeds
Money Plant	Stem cutting	Stem pieces grow into new plants
Sugarcane	Stem cutting	Each piece grows into a new plant
Bryophyllum	Leaf	Tiny plantlets (buds) grow on leaf margins

🇮🇳

Indian Connection — Krishi Vigyan Kendras

Various Krishi Vigyan Kendras (KVKs) under ICAR (Indian Council of Agricultural Research) teach farmers modern grafting techniques. This helps farmers grow high-yield fruits and boost their income!

🔧 Artificial Methods of Vegetative Propagation

Scientists and farmers have adapted natural vegetative propagation into several useful methods:

✂️ 1. Cutting

Cut a shoot (about 10–15 cm long) with 2–3 nodes from a healthy parent plant.
Remove leaves from the lower half of the cutting.
Insert the cutting at 45–60° angle into soil mixed with compost.
Water regularly — new roots and shoots grow from nodes.

📝

Exam Tip

Examples of plants propagated by cutting: rose, sugarcane, money plant, bougainvillea. The cutting should always have at least one node (गांठ) from which new roots sprout.

🌿 2. Grafting (कलम लगाना)

Take a healthy rooted plant (Plant A = rootstock, e.g., wild rose).
Take a stem piece from another plant (Plant B = scion, e.g., yellow rose).
Create a slit/wound on Plant A’s twig.
Insert Plant B’s stem cutting into Plant A’s slit and tie with cloth/tape.
Cut the other branches of Plant A so Plant B gets all nutrients.
Water regularly — Plant B grows on Plant A’s roots.

🌹

Why Grafting is Useful

Grafting lets us combine the strong roots of one plant (rootstock) with the desirable fruits/flowers of another (scion). Mango and apple farmers use this widely to get high-quality fruits.

🌿 3. Layering (दाब कलम)

Select a flexible, thin twig of a plant (e.g., lemon, jasmine).
Bend the middle part of the twig and bury it under the soil surface.
Water regularly — new roots develop at the buried part after 10–15 days.
Once roots develop, cut the twig from the parent plant.
The rooted twig now grows as a new independent plant!

🧪 4. Tissue Culture (Micropropagation)

Tissue culture is a modern laboratory technique where tiny pieces of plant tissue (often from shoot tips) are grown on special nutrient media to produce thousands of new plants.

🍌

Real-World Impact — Banana Farming in India

Tissue culture has revolutionised banana farming in India. Farmers are now provided mass-produced, virus-free plantlets from the shoot tip (apical meristem) of banana plants. This ensures high yields and eliminates diseased plants!

📖

NCERT Definition to Remember

Vegetative Propagation= A type of asexual reproduction in plants where new plants arise from the vegetative parts (root, stem, leaf) of the parent plant, producing genetically identical offspring.

✅ Advantages of Vegetative Propagation in Agriculture

Produces genetically identical plants — desirable characters are preserved.
Plants grow faster than those from seeds — begin flowering/fruiting sooner.
Farmers can produce plants on a large scale efficiently.
Useful for plants that produce few or sterile seeds (e.g., banana, seedless grapes).

🔬

Asexual Reproduction in Other Organisms

Asexual reproduction is also seen in many unicellular and simple multicellular organisms like bacteria, amoeba, yeast, hydra, and fungi (mould). Let’s explore how each reproduces:

🍞 Budding in Yeast & Hydra

🧫 Budding in Yeast

Yeast cells develop small, round outgrowths called buds from the parent cell. The bud grows, detaches, and becomes a new individual. Yeast is active in warm conditions (25–35°C) — which is why bread rises in a warm kitchen!

🐟 Budding in Hydra

In hydra (a multicellular animal), repeated cell division at a specific site on the parent body produces a small outgrowth called a bud. The bud enlarges and separates from the parent to live independently. Many buds can grow simultaneously!

🔑 Budding = A form of asexual reproduction where a new organism grows as an outgrowth (bud) from the parent body and eventually separates to live independently.

🍄 Spore Formation in Fungi (Mould)

Have you noticed a fuzzy black or green growth on old bread or roti? That’s mould (a type of fungus)! Mould reproduces by forming tiny, lightweight structures called spores.

Spores are usually single-celled and very lightweight.
They float easily through air currents — that’s how they settle on your bread.
When warmth and moisture are present, spores germinate into new individuals quickly.
One mould colony can produce millions of spores!

⚠️

Why Do We Refrigerate Food?

Spores need warmth (25–35°C) and moisture to germinate. Low temperatures in a refrigerator slow or stop spore reproduction — this is why refrigerated food lasts much longer. Before refrigerators (about 100 years ago), fresh food lasted only 1–2 days!

Type of Mould	Spore Structure	Common Example
Rhizopus	Round sac (sporangium) at tip of hyphae	Black mould on bread (काली फफूंद)
Aspergillus	Spores on swollen vesicle on hyphae	Found on damp walls, rotting food

🌟

Fungi — Not Just Spoilers!

Moulds may look unpleasant, but fungi benefit society greatly. Many life-saving antibiotics like penicillin and amoxicillin are derived from fungi. Fungi also help decompose organic waste and even remove heavy metals from industrial effluents!

🧑‍🔬

Louis Pasteur — Disproving Spontaneous Generation

For long, people thought life arose from non-living matter. French scientist Louis Pasteur proved through experiments that new life always comes from pre-existing life. He founded the germ theory of disease and led to food sterilisation practices we still use today!

⚙️ The Central Process: Mitosis

In all forms of asexual reproduction studied above, the central process is Mitosis — a type of cell division that produces two daughter cells, each having the same number of chromosomes as the parent cell.

🔑 Asexual Reproduction → Mitosis → Genetically Identical Offspring (Clones)

Because of mitosis, offspring produced by asexual reproduction are called clones. This method is fast and helps organisms increase population quickly, especially when environmental conditions are favourable.

🧬

Sexual Reproduction & Meiosis — Creating Variation

Sexual reproduction (लैंगिक प्रजनन) involves two parents. Both parents contribute genetic material to the offspring. This mixing of characteristics leads to variation among offspring.

🤔 The Problem of Chromosome Numbers

If each generation received the full set of chromosomes from both parents, the chromosome number would keep doubling every generation! 🤯

⚠️

The Biological Problem & Its Solution

Humans have 46 chromosomes (23 pairs). If both egg and sperm had 46 each, the zygote would have 92! This problem is solved by a special cell division calledMeiosis.

🔬 Meiosis — The Special Cell Division

🔑 Meiosis = A special type of cell division that reduces the chromosome number from diploid (2n) to haploid (n) in the resulting gametes (reproductive cells).

Chromosome Numbers in Humans:

Parent body cell: 46 chromosomes (diploid, 2n)

↓ After Meiosis ↓

Gamete (sperm/egg): 23 chromosomes (haploid, n)

↓ After Fertilisation ↓

✅ Zygote: 23 + 23 = 46 chromosomes — same as parents!

🎯 Types of Gametes

In Animals:

Male gametes = Sperm (शुक्राणु) — tiny, motile

Female gametes = Eggs/Ova (अंडाणु) — large, non-motile

In Plants:

Male gametes = inside Pollen grains

Female gametes = inside Ovule (egg cell)

🎲 How Meiosis Creates Variation

During meiosis, chromosomes of each pair separate so each gamete receives only one chromosome from each pair. This random mixing provides endless combinations!

🎯

Mind-Blowing Math!

With just 3 pairs of chromosomes → 8 possible combinations. With23 pairs(as in humans) →2²³ = over 8 million combinationspossible in each gamete! This is why no two siblings (except identical twins) are exactly alike.

🌍 Why is Variation Important?

Variation helps individuals adapt better to changing environments.
Over time, accumulated variation contributes to evolution.
Example: Some people can tolerate low oxygen at high altitudes; some can digest milk in adulthood — these are results of genetic variation!

📖

Remember the Difference!

Mitosis→ identical daughter cells → used in growth, repair, asexual reproduction.

Meiosis→ haploid gametes → used only in sexual reproduction → creates variation.

🌸

Sexual Reproduction in Flowering Plants

Flowering plants (Angiosperms — आवृतबीजी) are the most diverse group of plants on Earth. In angiosperms, flowers serve as reproductive organs.

🌺 Parts of a Flower

A complete flower has four whorls (arranged from outside to inside):

1. Sepal (बाह्यदल) → Outermost green covering → Protects the flower bud

2. Petal (दल/पंखुड़ी) → Coloured/fragrant → Attracts pollinators

3. Stamen (पुंकेसर) → MALE PART = Anther (produces pollen) + Filament (stalk)

4. Pistil (स्त्रीकेसर) → FEMALE PART = Stigma + Style + Ovary (contains Ovules with egg cells)

🔵 Stamen — Male Reproductive Part

Anther→ Produces pollen grains containing male gametes
Filament→ Thin stalk supporting the anther

🔴 Pistil — Female Reproductive Part

Stigma→ Tip; flat/sticky — receives pollen
Style→ Tube connecting stigma to ovary
Ovary→ Contains ovules with egg cells (female gametes)

💨 Pollination (परागण)

🔑 Pollination = The transfer of pollen grains from the Anther to the Stigma of a flower.

Self-Pollination (स्व-परागण)

Pollen transfers to the stigma of the same flower or another flower on the same plant. Example: Pea (मटर / Pisum sativum). Fruits still form even when covered with cloth bags!

Cross-Pollination (पर-परागण)

Pollen transfers from the anther of one plant to the stigma of a different plant of the same species. Creates more variation. Example: Maize, papaya.

🐝 Pollination Strategies — How Pollen Travels

Pollinator	Plants	Adaptations
💨 Wind	Wheat, Maize, Rice	Pollen: light, small, produced in millions. Stigma: long, feathery to trap pollen.
💧 Water	Vallisneria, Hydrilla (aquatic)	Pollen: released in water currents to reach stigma.
🐝 Insects (Bees, Butterflies)	Sunflower, Hibiscus, Marigold	Flowers: brightly coloured, fragrant, produce nectar. Pollen: large, sticky or spiny.
🐦 Birds	Coral tree, Hibiscus	Pollinated by Indian white-eye and sunbirds. Bright red/orange flowers.

📝

Exam Trick — Wind vs Insect Pollination

Wind-pollinated plants produce much more pollen (5 lakh – 10 lakh per flower) but form fewer seeds (50–200). Insect-pollinated plants produce less pollen (20,000–40,000) but form more seeds (800–1,000) because delivery is more precise!

🌰 Fertilisation & Seed Formation

Pollen grain lands on a compatible stigma.
Pollen grain produces a pollen tube that grows down through the style into the ovary.
The male gamete travels through the pollen tube to reach the ovule.
Male gamete fuses with the egg cell (female gamete) → This is Fertilisation (निषेचन)!
The fertilised egg is called a Zygote (युग्मनज) → develops into an embryo.
Ovule → develops into a Seed. Ovary → develops into a Fruit.
Seeds are dispersed by wind, water, or animals → germinate in favourable conditions into new plants.

🌸 Pollination → Fertilisation → Zygote → Embryo → Seed (Ovule) + Fruit (Ovary)

🇮🇳

P. Maheshwari — Father of Indian Embryology (भारतीय भ्रूणविज्ञान के जनक)

Prof. P. Maheshwari was a leading Indian scientist in plant embryology. He developed the technique of in-vitro fertilisation in flowering plants — fusing an egg and male gamete in a test tube to create hybrid plants. His classic book “An Introduction to the Embryology of Angiosperms” (1950) is still widely used by scientists worldwide.

⚠️

Common Mistake — Seed vs Fruit

Students often confuse what becomes the seed and what becomes the fruit. Remember:OVULE → SEEDandOVARY → FRUIT. The ovary wall surrounds and protects the seeds inside.

🐸

Sexual Reproduction in Animals

Animals show wide variety in their reproductive strategies, but all face the basic challenge: ensuring male and female gametes meet, and that offspring survive long enough to reproduce.

🔄 External vs Internal Fertilisation

External Fertilisation (बाह्य निषेचन)

Fertilisation occurs outside the body, usually in water. Female releases eggs → male releases sperm over them → fertilisation happens in water. Examples:Fish, Frogs. Many eggs are laid but many are destroyed by currents or eaten.

Internal Fertilisation (आंतरिक निषेचन)

Fertilisation occurs inside the female’s body. The fertilised egg or embryo is better protected. Fewer eggs laid but survival rate is higher. Examples:Reptiles, Birds, Mammals.

📊 Variation in Animal Reproductive Strategies

Animal	Habitat	Fertilisation	Eggs Produced	Offspring Survival
Fish	Water	External	100s–1,000s at a time	🔴 Low
Frog	Water/Land	External	5,000–50,000 at a time	🔴 Low
Lizard	Land	Internal	2–20 at a time	🟡 Moderate
Bird	Water/Land	Internal	1–15 at a time	🟢 Moderate to High

🦋 Life Cycle with Larval Stage

Fish, amphibians, and insects produce many eggs. The yolk in each egg is just enough to produce a larva that hatches and then feeds and grows. This larval stage is essentially a feeding stage. Once enough nutrition is accumulated, metamorphosis (transformation) takes place and the adult body forms — as seen in butterflies and frogs.

📝

Exam Tip — Why More Eggs = Less Survival?

The rule: the more eggs an animal produces, the lower the chance of survival of each individual offspring. This is because external fertilisation and environmental exposure mean more offspring are destroyed. Internal fertilisation and parental care increase survival but require fewer offspring.

🧑‍🤝‍🧑

Reproduction in Human Beings

🔬 Male Reproductive System (पुरुष जनन तंत्र)

Testes (वृषण) → Two oval organs in scrotum → Produce sperm + male hormones (testosterone)

Scrotum (वृषणकोश) → Keeps testes slightly cooler than body temp (essential for sperm formation)

Vas Deferens (शुक्रवाहिनी) → Long tube carrying sperm from testes to urethra

Seminal Vesicles + Prostate Gland → Add fluids to nourish and activate sperm

Urethra → Common passage for urine AND sperm (semen)

Penis → External organ through which semen/urine exits

🌡️

Why is the Scrotum Outside the Body?

Sperm production requires a temperature slightly lower than normal body temperature (37°C). The scrotum keeps testes at about 34–35°C, which is ideal for sperm formation. That’s why testes are located outside the body!

🔬 Female Reproductive System (स्त्री जनन तंत्र)

Ovaries (अंडाशय) → Pair of organs → Produce eggs (ova) + female hormones (oestrogen, progesterone)

Fallopian Tubes / Oviducts (अंडवाहिनी) → Connect ovaries to uterus → Site of fertilisation!

Uterus (गर्भाशय) → Bag-like structure where foetus develops during pregnancy

Cervix (गर्भाशय-ग्रीवा) → Narrow passage connecting uterus to vagina

Vagina (योनि) → Birth canal; receives sperm during intercourse

🔬 Gametogenesis — Formation of Gametes

🔑 Gametogenesis = The process of formation of gametes (sperm and eggs) by meiosis in the testes and ovaries respectively.

Feature	Sperm (Male Gamete)	Egg / Ovum (Female Gamete)
Size	Very small (microscopic)	Large (visible to naked eye)
Number produced	Millions	One per month (few hundred in lifetime)
Stored nutrients	Absent	Present (yolk)
Motility	Actively motile (swims using tail)	Non-motile
Chromosomes	23 (haploid)	23 (haploid)

❤️ Fertilisation in Humans

Ovulation: From puberty, usually one mature egg is released from an ovary every month (~Day 14). The egg travels to the fallopian tube.
Before ovulation, the inner lining of the uterus (endometrium) becomes thick and rich in blood vessels — preparing for possible pregnancy.
During sexual intercourse, millions of sperm enter the vagina and swim through the reproductive tract.
If a sperm meets the egg in the fallopian tube and successfully fuses with it → Fertilisation!
A Zygote is formed → undergoes mitotic divisions while travelling to the uterus.
The zygote implants into the uterine lining → Pregnancy begins.

🇮🇳

India’s First Test Tube Baby!

In-vitro Fertilisation (IVF) is a technique where egg and sperm are combined outside the body in a laboratory dish, and the fertilised egg is then implanted in the uterus. In 1978, Dr.Subhash Mukhopadhyayof Kolkata pioneered India’s first test tube baby —Kanupriya Agarwal(nicknamed Durga), just 67 days after the world’s first IVF baby Louise Brown in the UK!

🔄 The Menstrual Cycle (मासिक धर्म चक्र)

If the egg is NOT fertilised, it degenerates after about a day. The thickened uterine lining is no longer needed and sheds. This is Menstruation (मासिक धर्म / period), which usually lasts 3–7 days.

Day 1–5

Menstruation

Shedding of uterine lining + blood

Day 6–14

Rebuilding

Uterine lining regrows; egg matures in ovary

Day 14

Ovulation

Ovary releases mature egg

Day 15–28

Preparation

Lining thickens; if no fertilisation → cycle repeats

📖

Key Facts to Remember

Menstrual cycle repeats every21–35 days(typically ~28 days). It begins at puberty (ages 10–14 in girls) and continues untilmenopause(around age 50).Menstruation is a sign of a healthy reproductive system— nothing to be ashamed of!

🧬

Who Determines the Baby’s Sex?

Every person has two sex chromosomes. Females: XX; Males: XY. The mother always contributes anX chromosome. The father contributes either anX (→ girl: XX)or aY (→ boy: XY)chromosome. So, it is thefather’s chromosomethat determines the baby’s biological sex!

🤰 Pregnancy & Childbirth

Human pregnancy lasts approximately 9 months and is divided into three trimesters:

Trimester	Duration	Key Events
1st Trimester	Months 1–3	Fertilised egg develops into embryo; major organs start forming. From week 9, called foetus.
2nd Trimester	Months 4–6	Foetus grows bigger and stronger; mother can feel its movements.
3rd Trimester	Months 7–9	Baby grows rapidly; gets ready for life outside the womb.

During childbirth, strong contractions of the uterus muscles push the foetus out through the birth canal (vagina). If vaginal delivery is not safe, doctors may perform a surgical procedure (C-section).

🛡️ Prevention of STIs & Unwanted Pregnancy

Sexually Transmitted Infections (STIs) include gonorrhoea, syphilis, herpes, genital warts, HIV (leading to AIDS). Some are incurable. Condoms can prevent both STI transmission and pregnancy.

Contraceptive Method	How it Works
Condoms / Vaginal Covers	Physical barrier; stops sperm from reaching egg; also prevents STIs
Oral Pills (Contraceptive Pills)	Hormones prevent ovulation; may have side effects
IUD (Copper-T)	Placed in uterus; prevents pregnancy; may sometimes irritate uterus
Surgical Methods	Block vas deferens (male) or fallopian tubes (female) permanently

⚠️

Important — Prenatal Sex Determination is Illegal in India!

Self-selective abortion (choosing to terminate based on gender) leads to a dangerous imbalance in sex ratio. Therefore,prenatal sex determination (finding out the baby’s sex before birth) is strictly prohibited by law in Indiaunder the Pre-Conception and Pre-Natal Diagnostic Techniques (PCPNDT) Act.

🇮🇳

India’s Contribution to Contraception!

Indian scientists at the Central Drug Research Institute (CDRI), Lucknow, developed the world’s first non-steroidal and non-hormonal oral contraceptive pill. Taken once weekly, it avoids common side effects like weight gain and nausea. It is provided free through the National Family Planning Programme!

📋

Quick Revision Summary — Chapter at a Glance

🌱 Reproduction

Biological process by which living organisms produce new individuals of the same species. Two types: Asexual & Sexual.

🌿 Vegetative Propagation

Asexual reproduction in plants. Methods: Cutting, Grafting, Layering, Tissue Culture. Produces genetically identical clones.

🍄 Budding & Spores

Budding in yeast & hydra; Spore formation in fungi. Central process = Mitosis → identical offspring (clones).

🧬 Meiosis

Special cell division forming gametes. Reduces chromosomes from 2n → n (diploid to haploid). Creates variation in offspring.

🌸 Flower Parts

Stamen (male) = Anther + Filament. Pistil (female) = Stigma + Style + Ovary. Pollination = anther → stigma transfer.

🌰 Plant Fertilisation

Pollen tube carries male gamete to ovule. Egg + sperm = Zygote. Ovule → Seed; Ovary → Fruit.

🐸 Animal Reproduction

External fertilisation (fish, frogs) = more eggs, less survival. Internal fertilisation (birds, mammals) = fewer eggs, more survival.

🧑 Human Male System

Testes → sperm + hormones. Scrotum keeps testes cool. Vas deferens → sperm pathway. Seminal vesicles/prostate → nourish sperm.

👩 Human Female System

Ovaries → eggs + hormones. Fallopian tube = fertilisation site. Uterus = foetal development. Menstrual cycle ≈ 28 days.

⚠️ Exam Alerts

Ovule→Seed, Ovary→Fruit. Father determines sex of baby. Meiosis in gametes; Mitosis in clones. Prenatal sex determination is illegal in India.

🤰 Pregnancy

9 months, 3 trimesters. Zygote → embryo → foetus. Breastfeeding essential after birth. Mother needs balanced diet and check-ups.

🛡️ Contraception

Condoms (prevent STIs + pregnancy), Oral pills (prevent ovulation), IUD/Copper-T (in uterus), Surgical methods (permanent).

📝

Important Exam Questions with Answers

Q1. Define vegetative propagation. Give two examples of plants reproduced by this method. (CBSE / 2 Marks)

Ans: Vegetative propagation is a type of asexual reproduction in plants in which new plants develop from the vegetative parts (root, stem, or leaf) of the parent plant, producing genetically identical individuals.

Examples: (1) Potato — new plants grow from eyes/nodes of the tuber. (2) Bryophyllum — tiny plantlets grow on the margins of leaves.

Q2. Differentiate between self-pollination and cross-pollination. (CBSE / 2 Marks)

Ans:

Self-pollination: Transfer of pollen grains from the anther to the stigma of the same flower or another flower on the same plant. No variation is produced. Example: Pea plant.

Cross-pollination: Transfer of pollen grains from the anther of a flower of one plant to the stigma of a flower of a different plant of the same species. Creates genetic variation. Example: Maize, Papaya.

Q3. What is meiosis? Why is it important in sexual reproduction? (CBSE / 3 Marks)

Ans: Meiosis is a special type of cell division in which the chromosome number of a parent cell (diploid/2n) is reduced to half (haploid/n) in the daughter cells called gametes.

Importance: (1) It ensures the chromosome number remains constant across generations — when two haploid gametes fuse during fertilisation, the zygote has the same chromosome number (2n) as the parents. (2) During meiosis, random mixing of chromosomes creates genetic variation among offspring, which is essential for evolution and adaptation.

Q4. Explain the process of fertilisation and seed formation in flowering plants. (CBSE / 3 Marks)

Ans: After a pollen grain lands on a compatible stigma, it germinates and produces a pollen tube that grows down through the style into the ovary. The male gamete travels through the pollen tube and reaches the ovule, where it fuses with the egg cell (female gamete). This fusion of gametes is called fertilisation. The fertilised egg is called a zygote, which develops into an embryo. The ovule hardens and develops into a seed, while the ovary wall enlarges and develops into a fruit.

Q5. Describe the menstrual cycle in human females. What happens when the egg is not fertilised? (CBSE / 3 Marks)

Ans: The menstrual cycle repeats every 21–35 days (typically ~28 days):

• Day 1–5: Menstruation — shedding of the thickened uterine lining with blood.

• Day 6–14: The uterine lining gradually rebuilds; an egg matures in the ovary.

• Day 14: Ovulation — a mature egg is released from the ovary.

• Day 15–28: Uterine lining becomes thicker and rich in blood vessels (preparing for implantation).

If the egg is not fertilised: It remains viable for about a day, then degenerates. The uterine lining that had prepared for a zygote is no longer needed and sheds — this is menstruation. The cycle then repeats.

Q6. Why does asexual reproduction produce offspring that are genetically identical to the parent? (CBSE / 2 Marks)

Ans: In asexual reproduction, only one parent is involved and the new organisms are produced through mitosis — a type of cell division that produces daughter cells with the exact same number and type of chromosomes as the parent cell. Since no mixing of genetic material from two parents occurs, all offspring are genetically identical to the parent and to each other. These identical organisms are called clones.

Q7. What are the differences between external and internal fertilisation? Give examples of animals that show each type. (CBSE / 3 Marks)

Ans:

External Fertilisation: Fertilisation occurs outside the female’s body, usually in water. The female releases eggs and the male releases sperm over them. Many eggs are laid but many are destroyed or eaten, so survival rate is low. Example: Fish (100s–1000s eggs), Frogs (5,000–50,000 eggs).

Internal Fertilisation: Fertilisation occurs inside the female’s body. The embryo is better protected; fewer eggs are produced but survival rate is higher. Example: Reptiles (lizards, 2–20 eggs), Birds (1–15 eggs), Mammals (humans, usually 1 offspring at a time).

Notes Class 9 Science Exploration Chapter 11 Reproduction – How Life Continues

Amresh Academy

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