Reproduction: How Life Continues Class 9 PPT & Notes (Ch 11)

• How asexual reproduction makes exact copies of a parent
• How farmers use cutting, grafting, layering and tissue culture
• Why meiosis creates variation in sexual reproduction
• How a flower turns pollen into a fruit and a seed
• How reproduction and new life work in animals and humans

Think it over: when does a farmer prefer asexual methods for crop production, and when sexual methods? Why do most complex animals and flowering plants reproduce sexually, whereas simple organisms like yeast and hydra mainly reproduce asexually? Keep these questions in mind: the chapter answers both.

Reproduction is the biological process by which living beings produce new individuals of their own kind. Every organism has a definite life span (born, grows, matures, reproduces, dies). Reproduction is why life on Earth continues: a mango tree dies, but its seeds grow into new mango plants; cows give birth to calves, dogs to puppies and humans to children.

Why small differences matter: differences build up over many generations, help living beings adapt to changing environments and sometimes even give rise to new species. This is the raw material of evolution. With no variation there is no way to cope with change.

Asexual reproduction is seen in many unicellular organisms (bacteria, amoeba, yeast), in simple multicellular organisms (hydra and sponge) and in many plants. Only one parent is involved, and the offspring are genetically identical to that parent.

• New plants arise from the vegetative (growing) parts of a plant: roots, stems or leaves
• Potato and ginger: fleshy underground stems sprout new plants without seeds
• Money plant and sugarcane: stem cuttings grow into new plants
• Bryophyllum: leaves sprout tiny plantlets along the notched edge. Each plantlet already has small leaves and roots, and when it drops off it grows into a complete new plant. No flower, no seed and no second parent are needed
• Only one parent is involved, so all the new plants are genetically identical

Asexual reproduction produces genetically identical individuals. Scientists and horticulturists adapted this into methods (cutting, grafting, layering and tissue culture) that propagate plants efficiently. They have greatly improved agricultural and horticultural practices, and farmers can cultivate desirable crops on a large scale.

• Collect shoot cuttings in the morning, and note whether the branches are cut at the end of the growing season
• Note the average length of each cutting and count its nodes and internodes
• Remove the leaves from the lower half of each cutting and plant it in soil at a slant (about 45° to 60°), not upright
• Water regularly and observe the change

1. Take a healthy rooted plant (Plant A, the stock), for example a wild rose variety
2. Cut a slit in a twig of Plant A (and cut the other branches of Plant A)
3. Insert a stem piece of Plant B (the scion), a yellow or pink rose variety, into the slit
4. Protect the joint with cotton cloth or wrapping film until it heals, and water regularly
5. The graft heals, and Plant B grows on Plant A’s roots

• Select a flexible, thin twig of a tree or shrub, such as a lemon plant
• Bury the middle part of the twig under the soil while the tip stays above the ground, and the twig stays attached to the parent
• Water regularly. After 10 to 15 days, roots develop from the buried part
• Cut the rooted twig from the parent so that it grows as a new plant

• Healthy plantlets are mass-produced from the shoot tip (apical meristem) in a sterile culture jar, and then transferred to the field
• Thousands of identical plants can be produced from one plant. Tissue-culture banana plantations are uniform and disease-free
• KVKs and ICAR: Krishi Vigyan Kendras, under the Indian Council of Agricultural Research (ICAR), teach farmers modern grafting and marketing skills, resulting in better fruit quality and higher farm income

Take 20 mL of sugar solution (1 g in 10 mL) in a test tube, add a pinch of yeast granules and keep it in a warm place so that the yeast becomes active. After 1 to 2 hours, mount a drop on a slide under a compound microscope. You see small round outgrowths (buds) on the parent yeast cells, some still attached and others separating, and sometimes a chain of buds. This is how yeast increases its numbers rapidly.

Hydra is a simple multicellular animal. At one specific site a small outgrowth called a bud is produced by repeated cell division. The bud grows, develops its own mouth and tentacles while still attached, then pinches off and lives as a new hydra. The parent is unharmed and can bud again, and many buds can grow at once. The new hydra is genetically identical to the parent.

Fruits and cooked food get spoilt by microbes such as fungi, and black patches on a damp wall are also microorganisms. For a long time people believed living things arose on their own from non-living matter, an idea called spontaneous generation. Louis Pasteur’s experiments proved that new life always comes from pre-existing life. He strengthened the cell theory (all cells arise from pre-existing cells), and his work led to food sterilisation practices.

• Place a slice of bread or roti with a few drops of water on a damp cotton and tissue-paper layer in a closed chamber, keep it in a warm, dark place away from direct sunlight, and observe daily without touching the bread. After three days, view a little of the mould under the microscope
• Rhizopus: thread-like hyphae spread across the bread. Each upright thread ends in a round sac at the tip packed with tiny round spores. When the sac bursts, the spores are released into the air
• Aspergillus: its spores are not held in a closed sac but form on a swollen vesicle at the end of a long hypha, radiating outward
• Spore formation: spores are produced in huge numbers (millions from one colony), are lightweight and usually single-celled, float easily through air, wait for moisture and nutrients, and germinate quickly into a new individual

• Fungi grow very fast and degrade organic wastes, play a role in removing heavy metals from industrial wastes, and many antibiotics (penicillin, amoxicillin) come from fungi
• Microbes grow well in warmth and moisture (about 25 to 35 °C). Lower temperatures slow down their reproduction, so refrigerators and deep freezing keep food fresh for much longer

In every organism studied so far in this chapter, asexual reproduction happens through mitosis. Mitosis produces two daughter cells, each with the same number of chromosomes as the parent cell. The offspring are therefore genetically identical and are called clones. This method is fast and builds up the population quickly when conditions are favourable.

Where you see this in real life: every rose and hibiscus plant in a nursery is grown from cuttings, mango and apple orchards are planted with grafted saplings, banana plantations use tissue-culture plantlets, and potato and ginger are planted as pieces, not as seeds.

Sexual reproduction involves two parents, and both contribute genetic material to the offspring. If each generation received a full set from both parents, the chromosome number would double every generation, which would make the species unworkable within a few generations. Nature solves this with a special cell division called meiosis.

• Each species has a fixed number of chromosomes: thread-like structures in the nucleus that carry genetic information. Humans have 23 pairs, 46 in total, and each pair has one chromosome from each of two different individuals
• Meiosis is the special cell division that forms gametes. The parent cell is diploid (it has the full set of chromosomes), and during meiosis the two chromosomes of each pair separate, so each gamete receives only one chromosome from each pair: the chromosome number is reduced to half (haploid)
• Gametes are the reproductive cells formed by meiosis. In animals the male gametes are sperm and the female gametes are eggs. In plants the pollen grain contains the male gametes, and the ovule contains the female gamete (the egg). Every human gamete carries 23 chromosomes

Take three pairs of beads, each pair standing for two contrasting characters: pair 1 (green): light green = blonde hair, dark green = black hair; pair 2 (blue): straight and curly hair; pair 3 (red): brown and black eyes. Randomly pick one bead from each pair and note the combination. Since each pair gives 2 choices, three pairs give 2 × 2 × 2 = 8 different gamete combinations.

Variation and evolution: random mixing gives a huge number of combinations, and each of us receives a unique combination of chromosomes. This creates variation among individuals, which helps some individuals adapt better to changing environments and, over time, contributes to evolution.

• Flowering plants are called angiosperms, the most diverse group of plants on Earth. Flowers are the reproductive organs of angiosperms. (Non-flowering plants such as pines also reproduce sexually)
• Leaves make food, roots absorb water, stems give strength, and flowers reproduce
• Sepals are the outermost whorl: the thin, flat green covering that wraps the bud and protects the flower. Petals are the coloured, often fragrant projections that attract pollinators
• A complete flower has four parts: sepals, petals, stamens and pistil. A flower with both stamen and pistil is bisexual. Some plants carry male and female flowers separately, as in papaya, where they are often on different trees

Select two juvenile flower buds and three freshly blossomed flowers on a pea plant. Remove the stamens from one bud and from one of the open flowers, and wrap muslin bags around four of them (the plain bud, the destamened bud, the destamened flower and one plain flower), leaving one open flower uncovered as the control. Only fruit formation tells you what happened. Fruits form in all treatments except the bud whose stamens were removed: that bud had no pollen of its own and none could enter. Conclusion: the transfer of pollen from the anther to the stigma is necessary for fruit formation. This transfer is called pollination.

Pollination is only the transfer of pollen, and fertilisation comes later. Without pollination there is no fruit and no seed. Both types produce fruits and seeds.

Night-blooming flowers cannot rely on bright colours to be seen. They are usually white or pale, so they stand out in dim light, and are strongly fragrant.

• When pollen reaches a compatible stigma, the pollen grain produces a pollen tube, which grows down through the style into the ovary. The male gamete moves through this tube, arrives at the ovule and fuses with the egg cell. This fusion of gametes is fertilisation
• The fertilised egg is called the zygote, which later develops into an embryo
• Ovule becomes the seed, and ovary becomes the fruit. The petals and stamens dry and fall away. The fruit protects the seeds and helps disperse them
• Seeds are dispersed by wind, water and animals, spread away from the parent plant, and germinate into a new plant when water, air and temperature are favourable

A hypothesis is the testable statement you set out to check, and a parameter is a condition you keep the same in every set-up so the comparison stays fair. Wind pollination uses far more pollen for far fewer seeds (a poor pollen-to-seed ratio), whereas an insect delivers pollen directly to a stigma. Producing huge amounts of pollen still works because wind delivery is cheap.

• P. Maheshwari is known as the Father of Indian Embryology (the study of plant reproductive organs). He developed the technique of in-vitro fertilisation in flowering plants (fusing an egg and a male gamete in a test tube to create new hybrid plants) and was among the first to grow plant embryos on artificial nutrient media. His book An Introduction to the Embryology of Angiosperms (1950) is still widely used
• Plant breeding uses sexual reproduction: selective breeding (farmers select plants with desirable characters), artificial hybridisation (remove the stamens, bag the flower to prevent self-pollination, then transfer chosen pollen by hand) and genetic engineering (inserting genetic material for desired characters)

In external fertilisation the female releases eggs into the water and the male releases sperm over them. Because the eggs are unprotected, producing a very large number ensures that at least a few survive to become adults.

• Fish, amphibians and insects produce several hundred eggs at a time. Each egg contains yolk, a nutritive substance that nourishes the embryo. The mother’s body cannot supply large amounts of yolk for so many eggs, so the yolk is just enough to produce a larva, an intermediate feeding stage that hatches from the egg and feeds on organic matter
• Metamorphosis is the transformation of the larva into an adult. In a butterfly: egg → larva (caterpillar, the feeding and growing stage) → pupa (the resting stage inside a case) → adult (emerges from the pupa and lays eggs again)
• Reptiles and birds lay eggs with enough yolk to nourish the embryo until it hatches, with no separate larval stage. In mammals the zygote grows inside the female body, and the mother’s body supplies nourishment directly

Care after birth: in some species the young can find their own food at once, whereas in others an extended period of feeding and care is necessary. Mammals typically feed their young with breast milk for some time. More development before birth means more care is possible. Animals choose either quantity (many eggs) or protection (few, protected young).

As a child grows into an adult, many physical and emotional changes take place and the reproductive organs mature and begin producing gametes: the sperm in males and the egg in females. When a sperm meets an egg inside the female body they form a zygote, which develops into an embryo and then a foetus in the uterus.

• Testes (singular testis) are two oval organs that produce the male gametes, the sperm, and a hormone. They lie in a pouch of skin called the scrotum, which keeps them slightly cooler than normal body temperature, necessary for sperm formation
• Sperm travel through the vas deferens, which opens into the urethra, a common passage for urine and sperm
• Glands such as the seminal vesicles and the prostate add fluids that nourish the sperm and help them stay active. Each sperm has a head containing genetic material and a long tail that helps it swim towards the egg

• A pair of ovaries produce the eggs and release hormones that bring about changes during puberty
• The oviducts (fallopian tubes) connect each ovary to the uterus and carry the egg towards it
• The uterus is a bag-like structure where the foetus develops. It opens into the vagina through a narrow passage called the cervix

• Gametogenesis is the formation of gametes in the testes and ovaries by meiosis. Human cells have 46 chromosomes but sperm and eggs have only 23, so that the zygote has the same number as the parents
• Sperm vs egg: sperm are very small, produced in millions, and actively motile; the egg is large, only a few are produced, and it is non-motile (the egg has a prominent nucleus and nutrients)
• Ovulation: at birth a girl’s ovaries already contain millions of immature eggs. From puberty, usually one mature egg is released every month from one of the ovaries, and the inner lining of the uterus becomes thick
• Fertilisation takes place in the oviduct when a sperm fuses with the egg. The egg contributes 23 chromosomes and the sperm 23, so the zygote has the full set of 46
• The zygote divides by a series of mitotic divisions while travelling to the uterus, and implants into the thickened lining to receive nourishment. This marks the beginning of pregnancy

• If the egg is not fertilised, it lasts about a day and then degenerates. The thick, blood-rich uterine lining is no longer needed, so it is shed and leaves the body through the vagina with some blood. This process is menstruation (the period)
• If fertilisation occurs, the lining is needed to nourish the embryo, so it is not shed, and the cycle stops during pregnancy
• The cycle usually begins at puberty (between ages 10 and 14) and continues till menopause, around age 50. It repeats typically every 21 to 35 days, often about 28 days, so day 14 is a typical case, not a fixed rule

Every person has sex chromosomes: females have XX and males have XY. The mother always contributes an X chromosome to the baby, while the father contributes either an X (giving a girl, XX) or a Y (giving a boy, XY). So the chromosome from the father decides the baby’s biological sex.

• Use clean menstrual products (sanitary pads, reusable or biodegradable ones), and change them as often as required
• Wash the genital area with clean water, and avoid soap, as it can disrupt the natural bacterial balance. Always wash hands with soap and water after changing a pad
• Dispose of used products properly (wrap them in newspaper or the wrapper and put them in a bin)
• Menstruation is a sign of a healthy reproductive system. It is not something to be ashamed of

• Pregnancy lasts about nine months and is divided into three trimesters. In the first, the fertilised egg develops into an embryo and major organs start forming (from about the ninth week the embryo is called a foetus). In the second, the foetus grows and the mother can usually feel its movements. In the third, the baby grows fastest and gets ready for life
• During childbirth, strong contractions of the muscles of the uterus push the foetus out through the birth canal. If a normal birth is not possible or safe, doctors may use medical or surgical procedures
• Care of the newborn and the mother: mother’s milk provides complete nutrition and protects the infant from many diseases; the baby must be kept on schedule for vaccinations and handled gently; the mother needs nutrition and adequate rest, and should avoid smoking, alcohol and any medicines without medical advice
• The mother’s health during pregnancy: regular medical check-ups, a balanced diet rich in proteins, vitamins and minerals, following the doctor’s advice, and emotional support from family

Post-partum depression: some mothers feel sadness and anxiety after delivery. It is a recognised condition that can be treated, so mothers should be encouraged to talk to a healthcare worker (a doctor, nurse or ASHA worker). ASHA workers: more than 10 lakh Accredited Social Health Activists, women trained under the National Health Mission, serve across India, especially in rural areas, promoting hygiene, immunisation and family planning and advising on maternal care and safe deliveries.

• During adolescence the body becomes capable of reproduction (sexual maturity), but emotional and social maturity take longer. Being ready is about making thoughtful and responsible decisions, which help prevent unplanned pregnancies and sexually transmitted infections, and support healthy relationships
• Sexually transmitted infections (STIs) pass from an infected person to an uninfected person during sexual contact. They include gonorrhoea, syphilis, herpes, genital warts and HIV, which can lead to AIDS. Some are not curable yet, and barrier methods such as condoms reduce the risk

• Abortion: an unwanted pregnancy can be removed by surgery, generally done only within the first trimester, when the embryo is very small
• Prenatal sex determination is prohibited by law in India, because self-selective abortion driven by a preference for a specific gender leads to an imbalance in the sex ratio
• A made-in-India pill: scientists at the Central Drug Research Institute (CDRI), Lucknow, developed the world’s first non-steroidal, non-hormonal oral contraceptive pill. It is taken once a week, avoids side effects such as weight gain, and is provided free through the National Family Planning Programme
• IVF (in-vitro fertilisation) combines an egg and a sperm outside the female body, in a laboratory dish (not a test tube), and the fertilised egg is implanted in the uterus. A baby born this way is commonly called a “test-tube baby”. Dr Subhash Mukhopadhyay is remembered for IVF in India

5-minute revision: asexual reproduction means one parent and mitosis, giving clones (budding, spores, vegetative propagation). Four propagation methods: cutting, grafting, layering and tissue culture. Pollination is the transfer, and fertilisation is the fusion. The ovule becomes the seed and the ovary becomes the fruit. External fertilisation means many eggs and low survival; internal fertilisation means few eggs and higher survival. Meiosis halves 46 to 23, so that the zygote is back to 46, and mixing creates variation. In humans: gametogenesis, then ovulation (about day 14), then fertilisation and implantation, then pregnancy of about nine months.

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