Life Processes Part 2 Class 10 Notes, Formulas, Questions | SSC

This chapter deals with reproduction, the life process that keeps a species going. It explains the methods of asexual reproduction in unicellular and multicellular organisms and sexual reproduction in flowering plants and humans. It covers the human reproductive systems, gamete formation, sex determination, the menstrual cycle and techniques such as IVF, surrogacy and sperm banks. It ends with twins, reproductive health and population explosion.

Summary

Nutrition, respiration, excretion and control keep an organism alive, while reproduction keeps the species going. Reproduction is the formation of a new organism of the same species by an existing one, and it is also one of the causes of evolution. It occurs by two methods: asexual and sexual. Asexual reproduction forms a new organism without gametes; it is uniparental, occurs by mitosis and gives offspring genetically identical to the parent. It is fast but lacks genetic recombination.

In unicellular organisms, binary fission divides the parent cell into two similar daughter cells; it is seen in bacteria, protists and in mitochondria and chloroplasts. Amoeba shows simple binary fission in any plane, Paramecium transverse and Euglena longitudinal binary fission, usually when food is plentiful. In adverse conditions Amoeba forms a cyst, its nucleus divides many times, and many amoebulae are released when conditions improve; this is multiple fission. Yeast reproduces by budding, in which a bulge on the parent cell receives one daughter nucleus and separates as a new cell.

In multicellular organisms, fragmentation breaks the body into pieces that each grow into a new individual, as in Spirogyra and Sycon. In regeneration a lost part is regrown; a wall lizard regrows its tail (limited regeneration), while Planaria splits into two parts that each form a whole animal. Hydra forms a bud from regenerative cells of its body wall that grows into a small hydra and separates. Vegetative propagation uses roots, stems, leaves or buds, such as eyes of potato, leaf-margin buds of Bryophyllum and node buds of sugarcane. Fungi like Mucor reproduce by spores released from sporangia.

Sexual reproduction involves two gametes and two main processes: gamete formation by meiosis, which halves the chromosome number, and fertilisation, in which haploid male and female gametes fuse to form a diploid zygote that develops into an embryo. Offspring carry recombined genes of both parents, so they resemble the parents in some characters and differ in others. This genetic variation helps species adapt to changing environments and avoid extinction.

The flower is the unit of sexual reproduction in plants and has four whorls: calyx (sepals), corolla (petals), androecium (stamens) and gynoecium (carpels). Androecium and gynoecium are essential whorls; calyx and corolla are accessory whorls. Flowers may be bisexual like Hibiscus or unisexual like papaya, and pedicellate or sessile. Each carpel has an ovary, style and stigma; the ovule contains an embryo sac with a haploid egg cell and two polar nuclei. Pollination by wind, water, insects or other animals brings pollen to the stigma; the pollen tube carries two male gametes. One fuses with the egg to form the zygote and the other with the two polar nuclei to form the endosperm, so it is called double fertilisation. The ovule becomes the seed and the ovary the fruit, and the seed germinates in favourable conditions.

The human male reproductive system has testes in the scrotum, where germinal epithelium of the seminiferous tubules forms sperms by meiosis. Sperms pass through rete testis, vasa efferentia, epididymis, vas deferens, ejaculatory duct and urinogenital duct, maturing on the way. Seminal vesicles, prostate gland and Cowper's glands add secretions to form semen. The female system has a pair of ovaries, a pair of oviducts, a uterus, a vagina and a pair of Bartholin's glands. A female foetus has 2 to 4 million immature oocytes, but only about 400 are released between puberty and menopause (about 45 to 50 years). Fertilisation is internal and occurs in the oviduct; the zygote divides, the embryo is implanted in the uterus, a placenta forms, and development completes in about nine months.

Germ cells have 44 + XX or 44 + XY chromosomes. Sperms are of two types, 22 + X or 22 + Y, while oocytes are only 22 + X, so the father decides whether the child is a boy or a girl. The menstrual cycle repeats every 28 to 30 days and is controlled by FSH, LH, estrogen and progesterone. FSH makes a follicle grow, the follicle secretes estrogen and the endometrium regenerates; LH causes ovulation and the burst follicle becomes the corpus luteum, which secretes progesterone that prepares the endometrium. If fertilisation does not occur within 24 hours, the corpus luteum becomes the corpus albicans, hormones stop, and the endometrium is shed with bleeding for about five days (menstruation).

Childless couples can be helped by IVF (fertilisation in a test tube and implantation of the embryo), surrogacy (the embryo is implanted in another woman, the surrogate mother) and sperm banks (stored semen from screened donors, whose names are kept secret by law). Monozygotic twins form when one embryo splits into two groups of cells within 8 days; they are identical and of the same sex, and a later split may form conjoined twins. Dizygotic twins develop from two oocytes fertilised by two sperms and may differ in sex. Reproductive health needs hygiene and awareness; syphilis and gonorrhoea are bacterial sexual diseases. Population explosion, the very fast growth of population, causes unemployment and stress on resources, and family planning is the answer.

Mind map

Menstrual cycle

Important definitions

Formulas

Key points to remember

• Asexual reproduction is uniparental and occurs by mitosis; offspring are genetically identical to the parent.
• Amoeba: simple binary fission; Paramecium: transverse; Euglena: longitudinal.
• Mitochondria and chloroplasts also divide by binary fission.
• Yeast (unicellular fungus) and Hydra reproduce by budding.
• Spirogyra and Sycon reproduce by fragmentation; Planaria by regeneration.
• Potato reproduces by eyes, Bryophyllum by leaf-margin buds, sugarcane and grasses by node buds.
• Gametes are formed by meiosis; pollen grains are formed by meiosis in the anther.
• Embryo sac has one haploid egg cell and two haploid polar nuclei.
• Testes lie in the scrotum outside the abdominal cavity.
• All male organs are paired except urinogenital duct, prostate gland, penis and scrotum.
• Epididymis is about 6 m long; a sperm is about 60 micrometres long; semen contains fructose for energy.
• Oocytes of women near menopause may divide abnormally, which can cause Down's syndrome in the child.
• The male partner decides the sex of the child, so the mother must not be blamed for a girl child.
• Monozygotic twins are identical and of the same sex; dizygotic twins may differ in sex.

Solved examples

Example 1. A human female has about 2 million oocytes at birth and releases about 400 oocytes till menopause. What percentage of oocytes is released?

Released fraction = 400 / 2,000,000 = 0.0002. Percentage = 0.0002 x 100 = 0.02 percent. The remaining oocytes degenerate.

Example 2. If a woman begins menstruating at 13 and reaches menopause at 46, and one ovum is released each month, about how many ova are released?

Years = 46 - 13 = 33. Ova = 33 x 12 = 396, which is about 400, matching the textbook figure.

Example 3. Show by cross how the sex of a child is decided.

Mother (44 + XX) forms only 22 + X ova. Father (44 + XY) forms 22 + X and 22 + Y sperms in equal numbers. Ovum 22 + X with sperm 22 + X gives 44 + XX, a girl. Ovum 22 + X with sperm 22 + Y gives 44 + XY, a boy. So the chance of each is 50 percent and the father's sperm decides the sex.

Example 4. A flowering plant has 2n = 24 chromosomes. Find the chromosome number in (a) male gamete, (b) egg cell, (c) zygote, (d) endosperm.

(a) Male gamete is haploid: n = 12. (b) Egg cell: n = 12. (c) Zygote = male gamete + egg = 2n = 24. (d) Endosperm = male gamete + two polar nuclei = 3n = 36.

Example 5. Using the census data, how much did India's population increase from 2001 (1,028,610,328) to 2011 (1,210,854,977)?

Increase = 1,210,854,977 - 1,028,610,328 = 182,244,649. Percentage growth = 182,244,649 / 1,028,610,328 x 100, which is about 17.7 percent in ten years.

Important questions and answers

Q1. Fill in the blanks: (a) In humans sperm production occurs in the ____. (b) ____ chromosome is responsible for maleness. (c) Implantation of embryo occurs in the ____. (d) ____ reproduction occurs without fusion of gametes.

(a) Testes. (b) Y. (c) Uterus. (d) Asexual.

Q2. Explain with examples types of asexual reproduction in unicellular organisms.

Binary fission: the parent cell divides into two daughter cells; simple in Amoeba, transverse in Paramecium, longitudinal in Euglena. Multiple fission: in adverse conditions Amoeba forms a cyst, its nucleus divides many times and many amoebulae are released when conditions improve. Budding: in yeast, a bulge on the parent cell receives a daughter nucleus and separates as a new cell.

Q3. Explain sexual reproduction in plants.

The flower is the reproductive unit. Pollen from the anther reaches the sticky stigma by pollination. The pollen grain grows a pollen tube with two male gametes, which travels through the style to the embryo sac. One male gamete fuses with the egg cell to form the zygote; the other fuses with two polar nuclei to form the endosperm (double fertilisation). The ovule becomes the seed and the ovary the fruit. The seed germinates and the zygote grows into a plantlet using food in the endosperm.

Q4. What is the menstrual cycle? Describe it in brief.

Changes in the female reproductive system that repeat every 28 to 30 days after puberty make up the menstrual cycle, controlled by FSH, LH, estrogen and progesterone. FSH grows a follicle, which secretes estrogen to rebuild the endometrium. LH causes ovulation; the corpus luteum secretes progesterone and the endometrium becomes ready for implantation. Without fertilisation within 24 hours, the corpus luteum becomes the corpus albicans, hormones stop and the endometrium is shed with bleeding for about five days.

Q5. Explain the concept of IVF.

In IVF the ovum and sperms are brought together in a test tube for fertilisation. The embryo formed is implanted in the woman's uterus at the right time. It helps couples with problems like low sperm count or blocked oviducts.

Q6. The gender of a child is determined by the male partner. True or false? Explain.

True. A woman forms only 22 + X ova, while a man forms 22 + X and 22 + Y sperms. If an X-bearing sperm fertilises the ovum the child is a girl (44 + XX); if a Y-bearing sperm does, the child is a boy (44 + XY). So the father decides the sex and blaming the mother for a girl child is wrong.

Q7. Distinguish between monozygotic and dizygotic twins.

Monozygotic twins come from one zygote whose embryo cells split into two groups; dizygotic twins come from two oocytes fertilised by two sperms. Monozygotic twins are genetically identical and of the same sex; dizygotic twins are genetically different and may be of the same or different sex.

Q8. Distinguish between asexual and sexual reproduction.

Asexual needs one parent; sexual needs male and female parents. Asexual does not involve gametes; sexual involves fusion of gametes. Asexual uses mitosis only; sexual uses meiosis for gametes and mitosis for growth of the zygote. Offspring of asexual reproduction are identical to the parent; those of sexual reproduction are genetically different. Asexual is fast; sexual brings variation.

Q9. Modern techniques like surrogacy, sperm bank and IVF help human beings. Justify.

Many couples cannot have children due to irregular cycles, blocked oviducts, implantation problems, absence or poor movement of sperms. IVF overcomes fertilisation problems, surrogacy overcomes implantation problems by using another woman's uterus, and sperm banks provide screened donor semen. Thus these techniques help childless couples have children.

Q10. Name: (a) hormones secreted by the ovary, (b) types of twins, (c) any two sexual diseases.

(a) Estrogen and progesterone. (b) Monozygotic and dizygotic twins. (c) Syphilis and gonorrhoea.

Q11. What precautions will you follow to maintain reproductive health?

Keep the genitals clean, take special hygiene and rest during menstruation, get correct information without shyness, avoid unsafe sexual contact to prevent diseases like syphilis and gonorrhoea, and consult a doctor for any problem.

Exam tips

• Practise labelled diagrams of the male and female reproductive systems, the flower and the menstrual cycle; they are frequently asked.
• Memorise the sperm duct sequence: rete testis, vasa efferentia, epididymis, vas deferens, ejaculatory duct, urinogenital duct.
• Pair each asexual method with its textbook example.
• In the menstrual cycle answer, mention all four hormones and the role of each.
• For sex determination, write the chromosome combinations clearly.

FAQs

Why is it called double fertilisation?

Because both male gametes take part: one fuses with the egg and the other with the two polar nuclei.

Where does fertilisation take place in humans?

In the oviduct; the embryo is then implanted in the uterus.

What are conjoined twins?

Twins born with some body parts joined and some organs shared; there is a high possibility of them when the embryo cells divide into two groups more than 8 days after zygote formation.

Which hormones control the menstrual cycle?

FSH, LH, estrogen and progesterone.

These notes were prepared with AI help from the Balbharati Science and Technology Part 2 textbook (2026-27) and checked against it.