3. Life Processes in Living Organisms Part 2

1. Binary fission: The parent cell divides into two similar daughter cells. It occurs in favourable conditions, when plenty of food is available.
   • Amoeba can divide in any plane, as it has no fixed shape – simple binary fission.
   • Paramecium divides across its body – transverse binary fission.
   • Euglena divides along its length – longitudinal binary fission.
2. Multiple fission: In adverse conditions, Amoeba becomes round and forms a protective covering (cyst). Its nucleus divides many times, then the cytoplasm divides. Many amoebulae are formed. When conditions become favourable, the cyst breaks and they are released.
3. Budding: In yeast, the nucleus divides into two. A small bulge (bud) forms on the parent cell and one nucleus enters it. The bud grows, separates and lives as a new yeast cell.

• IVF means In Vitro Fertilization, that is, fertilization in a test tube (outside the body).
• An ovum is taken from the ovary of the woman. Sperms are taken from her husband.
• The ovum is fertilized by a sperm in the laboratory, and an embryo is formed.
• At the right time, the embryo is implanted in the uterus of the woman. It develops there normally.
• IVF helps childless couples who have problems like low sperm count or obstacles in the oviduct.

• Bathe daily and keep the genitals clean and dry.
• Wear clean, dry cotton undergarments.
• During menstruation, use clean sanitary pads, change them regularly and dispose of them properly.
• Take rest and a nutritious diet during menstruation.
• Avoid unsafe sexual contact, as it spreads diseases like syphilis and gonorrhoea.
• Do not hide any problem out of shyness. Consult a doctor for infection, pain or irregular periods.
• Follow the legal age of marriage (18 years for girls, 21 years for boys).
• Get correct information from parents, teachers and doctors.

Menstrual cycle: After puberty, the female reproductive system undergoes certain changes that repeat every 28–30 days. These repeating changes are called the menstrual cycle. It is controlled by four hormones: FSH, LH, estrogen and progesterone.

This cycle repeats every month unless an embryo is implanted.

• In sexual reproduction, two parents take part. Each parent forms haploid gametes by meiosis.
• The male gamete and female gamete fuse to form a diploid zygote. So the new-born gets half its chromosomes (genes) from the father and half from the mother.
• That is why the new-born shows similarities with both parents in some characters.
• During meiosis, crossing over causes recombination of genes. So the new-born also has some characters different from both parents.

Examples:

• A child may have the father’s curly hair and the mother’s eye colour.
• Puppies of the same parents look like the parents but differ from each other in colour and spots.
• Brothers and sisters look alike in some features but are not exactly the same (except monozygotic twins).

Testosterone (secreted by testes); follicle stimulating hormone (FSH) and luteinizing hormone (LH) (secreted by pituitary gland).

Estrogen and progesterone.

Monozygotic twins and dizygotic twins. (Conjoined or Siamese twins are a special kind of monozygotic twins.)

Syphilis and gonorrhoea.

Condoms, oral contraceptive pills, Copper-T, and surgical methods (vasectomy in men and tubectomy in women).

The statement is true.

• A man has XY sex chromosomes (44 + XY). A woman has XX sex chromosomes (44 + XX).
• By meiosis, the man forms two types of sperms: (22 + X) and (22 + Y). The woman forms only one type of ovum: (22 + X).
• If a sperm with an X chromosome fertilizes the ovum, the zygote is 44 + XX and the child is a girl.
• If a sperm with a Y chromosome fertilizes the ovum, the zygote is 44 + XY and the child is a boy.

The mother always gives an X chromosome. Whether the child is a boy or a girl depends on the chromosome given by the father. So it is wrong to blame the mother for the birth of a girl child.

In plants, asexual reproduction takes place in the following ways:

1. Vegetative propagation: New plants grow from vegetative parts like root, stem, leaf and bud.
   • Root: sweet potato
   • Stem: potato (by the ‘eyes’ on the tuber); sugarcane and grasses (by buds on the nodes)
   • Leaf: Bryophyllum (by buds on the leaf margin)
2. Fragmentation: When water and nutrients are plentiful, the filaments of the alga Spirogyra grow fast and break into many fragments. Each fragment grows into a new Spirogyra.
3. Spore formation: The fungus Mucor forms spores in sporangia. When the sporangia burst, spores are released. In a moist and warm place, they germinate and form a new fungal colony.

These methods need only one parent, and the new plants are exactly like the parent.

Many couples cannot have children because of problems in the man or the woman. Modern techniques help such couples.

• IVF: Useful when there is low sperm count or an obstacle in the oviduct. The ovum is fertilized in a test tube and the embryo is implanted in the uterus.
• Surrogacy: Useful when a woman has problems in implantation of the embryo in her uterus. Her ovum is fertilized with her husband’s sperm in a test tube, and the embryo is implanted in the uterus of another woman (surrogate mother).
• Sperm bank: Useful when the man has no sperms or abnormal sperms. Semen from a medically checked donor is used for IVF. The donor’s name is kept secret by law.

Thus these techniques help childless couples to have a child. This brings happiness to the family and reduces their stress.

The flower is the structural unit of sexual reproduction in plants. It has four whorls: calyx (sepals), corolla (petals), androecium (stamens, the male whorl) and gynoecium (carpels, the female whorl). See the diagram in Q6(c).

Where to find the data: Census of India (censusindia.gov.in), the United Nations World Population Prospects, and the World Bank data website.

Steps:

1. Choose 6–8 Asian countries, for example India, China, Pakistan, Bangladesh, Nepal, Sri Lanka, Japan and Indonesia.
2. Write each country’s population for the present year and for ten years ago in a table.
3. Find the percentage growth: (new population − old population) ÷ old population × 100.
4. Draw a double bar graph: countries on the X-axis and population on the Y-axis, with two bars (old and new) for each country.

Worked example (India, from the textbook table): 2001: 1,02,86,10,328 and 2011: 1,21,08,54,977. Increase = 18,22,44,649. Growth = 18,22,44,649 ÷ 1,02,86,10,328 × 100 ≈ 17.7% in ten years.

Points to write in your conclusion: Which countries grew fastest? In which countries has growth slowed down or has the population decreased? How does population growth affect jobs, food, housing and natural resources?

Plan for the road show:

1. Form groups and prepare placards, banners and a short street play (5–7 minutes).
2. Take permission from the school and local authorities, and choose a busy place such as a market.
3. Perform the play, then explain the main message and answer people’s questions.

Main messages:

• The gender of a child depends on the father’s chromosome (X or Y). The mother is not responsible for a girl child.
• Finding out the sex of a foetus is a crime in India under the PCPNDT Act, 1994.
• Female foeticide lowers the number of girls. The 2011 Census recorded only 918 girls for every 1000 boys (age 0–6).
• Girls and boys should get equal love, food, education and opportunities.

Sample slogans: “Save the girl child, save the future.” “Son or daughter, both are equal.” “A daughter is a blessing, not a burden.”