Population | ICSE Class 10 Biology Notes

This note covers the ICSE Class 10 Biology topic Population: the population explosion in India and the world, the main reasons for the sharp rise, the terms demography, population density, birth rate, death rate and growth rate, the problems caused by rapid population growth, population education, and the methods of population control, from tubectomy and vasectomy to condoms, pills and IUDs.

What is the population explosion?

A population explosion is a very rapid rise in the number of people in a short period. In the last century, all-round development improved the quality of life, and better health facilities and living conditions had an explosive impact on population growth.

The world population was around 2 billion in 1900, rose to about 6 billion by 2000 and to 7.2 billion in 2011. According to United Nations estimates, it passed 8 billion in November 2022.

India followed the same trend. Its population was about 350 million at independence, came close to the billion mark by 2000 and crossed 1.2 billion in May 2011. The 2011 Census counted 1,210 million people. According to UN estimates, India overtook China as the world's most populous country in 2023.

In India, population data come from the Census, which is held every 10 years. The first census was conducted in 1872, but the first complete census was held only in 1881. The table shows that India's population grew about five times in the 110 years from 1901 to 2011, with the fastest growth between 1951 and 1981.

How has India's population grown over the last century?

India's population growth over the twentieth century falls into four distinct phases, each shaped by the balance between the birth rate and the death rate.

The key idea is that a population explodes when the death rate falls quickly while the birth rate stays high. The gap between the two, the natural increase, widens, and the population grows fast even if families are no larger than before.

The states are shaded in five classes of growth rate: above 25 per cent, 20 to 25, 15 to 20, 10 to 15, and less than 10 per cent. Kerala, at the south-western tip, is in the lowest class. Much of the south is in the 10 to 20 per cent classes, a broad belt across the north and centre is in the 20 to 25 per cent class, and the darkest class appears in parts of the east and north-east.

See Fig. 1.3 in your NCERT textbook

What are the main reasons for the sharp rise in population?

The population grows when births exceed deaths. In India and the world, the sharp rise came mainly from a fall in deaths, while births remained high for a long time. The main reasons are:

1. A rapid decline in the death rate: better medical care, vaccination, control of epidemics, improved sanitation and a more secure food supply mean fewer people die young.
2. Lower maternal and infant mortality: a fall in the maternal mortality rate (MMR) and the infant mortality rate (IMR) means that more mothers and babies survive childbirth and infancy.
3. More people of reproductive age: as more children survive to adulthood, the number of people in the reproductive age group rises, and they in turn have children.
4. Longer life expectancy: with better health facilities and living conditions, people live longer, so the total population rises even without more births.
5. Social and economic factors that keep the birth rate high: early marriage, illiteracy, poverty (where children are seen as extra earning hands and support in old age), the preference for a male child, and a lack of awareness or use of family planning.

The first four reasons are signs of progress: they come from better health and living conditions. The fifth explains why births stayed high after deaths fell. That is why education, especially of girls, and access to family planning are at the centre of population control.

Note: A rising population does not mean that families are having more children than before. In India's explosive phase, the main change was that far fewer people were dying, while the birth rate fell only slowly.

What do demography and population density mean?

Demography is the scientific study of human populations: their size, composition and distribution, and how these change through births, deaths and migration. The data on which demography depends in India come mainly from the Census.

Population density is the number of people per unit area of land, usually measured in persons per square kilometre. Each unit of land has a limited capacity to support people, so density shows the pressure of population on land.

Density of population = Population ÷ Area

Worked example 1. Region X has an area of 100 sq km and a population of 1,50,000.

Answer: Density = 1,50,000 ÷ 100 = 1,500 persons per sq km.

The density of population in India was 382 persons per sq km in 2011. It has risen steadily, from 117 persons per sq km in 1951, an increase of more than 200 persons per sq km in about 50 years.

Density is not the same everywhere. People prefer areas with fresh water, flat plains, a comfortable climate and fertile soil, and areas with minerals, industries and cities. The Ganga plains are among the most densely populated areas of the world, while the Himalayan mountain zones are scarcely populated.

What are birth rate, death rate and growth rate?

The crude birth rate (CBR) is the number of live births in a year per thousand of the population:

CBR = (B ÷ P) × 1,000, where B is the number of live births in the year and P is the estimated mid-year population.

The crude death rate (CDR) is the number of deaths in a year per thousand of the population:

CDR = (D ÷ P) × 1,000, where D is the number of deaths in the year and P is the estimated mid-year population.

Worked example 2. A town has a mid-year population of 50,000. In one year there are 1,000 live births and 400 deaths. Find the birth rate, death rate and rate of natural increase.

Answer: CBR = (1,000 ÷ 50,000) × 1,000 = 20 per thousand. CDR = (400 ÷ 50,000) × 1,000 = 8 per thousand. The natural increase is 20 − 8 = 12 per thousand, or 1.2 per cent a year.

Growth of population

• Growth of population is the change in the number of people in an area between two points of time. For example, India's population rose from 102.86 crore in 2001 to 121.02 crore in 2011, a growth of about 18.16 crore.
• Growth rate is this change expressed as a percentage. The decadal growth rate is (p₂ − p₁) ÷ p₁ × 100, where p₁ is the population of the base year and p₂ that of the present year.
• Natural growth = births − deaths. Actual growth = births − deaths + in-migration − out-migration.
• Growth is positive when the birth rate exceeds the death rate or people migrate in permanently, and negative when the birth rate falls below the death rate or people migrate out.

The annual growth rate of India's population was 1.64 per cent in 2011. Population doubling time is the time a population takes to double itself at its current annual growth rate; the faster the growth, the shorter this time.

What problems does the population explosion cause?

An alarming growth rate can lead to a scarcity of even the basic requirements of food, shelter and clothing, in spite of significant progress in producing them. The main problems are:

Rapid growth also puts pressure on schools, hospitals, housing, transport and sanitation. Cities grow crowded as people migrate from villages in search of work, and slums spread. A growing population needs ever more food, so the land is farmed more intensively. Much of the gain in production has to go into supporting the added numbers instead of raising living standards.

What is population education?

Population education is education that helps people understand the population situation, its causes, and its effects on the quality of life of the individual, the family and the nation, so that they can make informed and responsible decisions about family size.

It is built into school subjects and awareness programmes, and it covers:

• Awareness of the problem: how uncontrolled population growth affects food, jobs, health, housing and the environment.
• The small family norm: the benefits of a small, planned family for the health of the mother and child and for the family's income and education.
• Reproductive health: correct information about reproductive organs, adolescence, safe and hygienic sexual practices, and sexually transmitted diseases, so that young people do not believe myths.
• Family planning: knowledge of the available birth control methods, especially for couples of marriageable age.
• Care of mother and child: care of pregnant mothers, post-natal care and the importance of breast-feeding.
• Gender equality: equal opportunities for the male and female child, which reduces the pressure to keep having children until a son is born.

Parents, relatives, teachers and friends, as well as audio-visual and print media, all have a role in spreading this information. Introducing sex education in schools helps give young people the right information.

How can population growth be controlled?

Because rapid growth strains food, jobs, resources and living standards, control measures are needed, and the government was forced to take serious steps to check the growth rate. India was among the first countries in the world to begin national action plans for reproductive health. These programmes, called family planning, began in 1951. Wider programmes now run as the Reproductive and Child Health Care (RCH) programmes. Through them the growth rate came down, though only marginally at first.

The government's measures include:

• Motivating smaller families through the media, with posters of a happy couple and two children under the slogan Hum Do Hamare Do (we two, our two). Many young, urban, working couples have even adopted a one child norm.
• Raising the legal age of marriage to 18 years for females and 21 years for males.
• Incentives to couples with small families.
• Contraceptive methods made widely available to prevent unwanted pregnancies and to space children.

An ideal contraceptive should be user-friendly, easily available, effective and reversible, with no or least side-effects, and should not interfere with the sexual drive, desire or act of the user. Contraceptive methods fall into these groups: natural or traditional, barrier, intra-uterine devices (IUDs), oral contraceptives, injectables, implants and surgical methods.

A suitable method should always be chosen in consultation with qualified medical professionals. Possible ill-effects of some methods, such as nausea, abdominal pain, irregular menstrual bleeding or even breast cancer, are not very significant but should not be ignored.

Which contraceptive methods help prevent pregnancy?

Condoms

Condoms are thin rubber or latex sheaths that cover the penis in the male, or the vagina and cervix in the female, just before coitus, so that semen does not enter the female reproductive tract. Both male and female condoms are disposable and can be self-inserted, giving privacy to the user. Their use has increased because they also protect against sexually transmitted infections and AIDS.

Intra-uterine devices

IUDs are inserted by doctors or expert nurses into the uterus through the vagina. Hormone-releasing IUDs also make the uterus unsuitable for implantation and the cervix hostile to sperm. IUDs are ideal for women who want to delay pregnancy or space children, and are among the most widely accepted methods in India.

A photograph of a small T-shaped plastic device with copper wire wound on its stem, and two thin threads hanging from the base of the stem.

See Fig. 3.2 in your NCERT textbook

Oral contraceptive pills

The pills contain small doses of progestogens or progestogen-estrogen combinations. They are taken daily for 21 days, starting preferably within the first five days of the menstrual cycle, then stopped for 7 days, during which menstruation occurs, and the pattern is repeated. They are very effective, have fewer side effects and are well accepted.

A photograph of a hand holding several thin, flexible rods, the implants that are placed under the skin to release hormones slowly.

See Fig. 3.3 in your NCERT textbook

What are vasectomy and tubectomy?

Surgical methods, also called sterilisation, are generally advised as a terminal method for a male or female partner who wants no more pregnancies. The surgery blocks the transport of gametes and so prevents conception.

1. Vasectomy is sterilisation of the male.
2. A small incision is made on the scrotum.
3. A small part of each vas deferens is removed or tied up.
4. Sperm can no longer travel from the testes to be released in the semen.

1. Tubectomy is sterilisation of the female.
2. A small incision is made in the abdomen, or the approach is through the vagina.
3. A small part of each fallopian tube is removed or tied up.
4. The ovum can no longer travel down the tube to meet the sperm, so fertilisation cannot occur.

(a) The male reproductive system, with the vas deferens on each side marked "tied and cut". (b) The female reproductive system, with arrows pointing to both fallopian tubes, labelled "fallopian tubes tied and cut".

See Fig. 3.4 a and b in your NCERT textbook

Both techniques are highly effective, but their reversibility is very poor, so they are chosen by couples who have completed their families. Neither affects the production of hormones or the sexual act.

Glossary

• Population explosion — A very rapid rise in population in a short period, as in India between 1951 and 1981.
• Demography — The scientific study of human populations: their size, composition and distribution, and how these change.
• Census — The official count of a country's population; in India it is held every 10 years.
• Population density — The number of people per unit area of land, usually in persons per square kilometre.
• Crude birth rate — The number of live births in a year per thousand of the mid-year population.
• Crude death rate — The number of deaths in a year per thousand of the mid-year population.
• Growth rate — The change in population between two points of time, expressed as a percentage.
• Natural growth — The increase in population from the difference between births and deaths.
• Population doubling time — The time a population takes to double itself at its current annual growth rate.
• Population education — Education that helps people understand population issues and make informed decisions about family size.
• IUD — An intra-uterine device, such as the Copper T, placed in the uterus by a doctor to prevent pregnancy.
• Sterilisation — A surgical, terminal method of contraception: vasectomy in males and tubectomy in females.

Common errors and misconceptions

• Misconception: The population explosion happened because families started having more children. Correct: It happened mainly because the death rate fell rapidly while the birth rate stayed high.
• Misconception: Birth rate is the number of births in a year. Correct: It is the number of live births in a year per thousand of the population, so places of different sizes can be compared.
• Misconception: Population density measures how many people a country has. Correct: It measures people per unit area, so a small country can be denser than a large one with more people.
• Misconception: Vasectomy is done on the fallopian tubes. Correct: Vasectomy blocks the vas deferens in males; tubectomy blocks the fallopian tubes in females.
• Misconception: Sterilisation can be easily reversed. Correct: Surgical methods are highly effective but their reversibility is very poor, so they are terminal methods.
• Misconception: All contraceptives protect against sexually transmitted infections. Correct: Among the methods listed, condoms protect against sexually transmitted infections and AIDS.
• Misconception: A growth rate that is falling means the population is falling. Correct: A lower positive growth rate still adds people every year; the population falls only when growth is negative.

Exam-style questions with model answers

Q1. Define demography and population density. [2 marks]

1. Demography is the scientific study of human populations: their size, composition and distribution, and how these change through births, deaths and migration.
2. Population density is the number of people living per unit area of land, usually expressed in persons per square kilometre.

Q2. Name the surgical method of population control in (a) males, (b) females, and the structure blocked in each. [2 marks]

1. (a) In males the method is vasectomy, in which a small part of each vas deferens is removed or tied up through a small incision on the scrotum.
2. (b) In females the method is tubectomy, in which a small part of each fallopian tube is removed or tied up.

Q3. Give three main reasons for the sharp rise in human population in India. [3 marks]

1. A rapid decline in the death rate, due to better medical care, control of epidemics, sanitation and a more secure food supply.
2. A fall in maternal and infant mortality rates, so more mothers and babies survive, and more people reach the reproductive age group.
3. A birth rate kept high by social and economic factors such as early marriage, illiteracy, poverty, the preference for a male child and a lack of awareness of family planning.

Q4. A town of 50,000 people records 1,000 live births and 400 deaths in a year. Calculate its birth rate, death rate and natural growth rate. [3 marks]

1. Birth rate = (1,000 ÷ 50,000) × 1,000 = 20 live births per thousand per year.
2. Death rate = (400 ÷ 50,000) × 1,000 = 8 deaths per thousand per year.
3. Natural growth = birth rate − death rate = 20 − 8 = 12 per thousand per year, that is, 1.2 per cent a year.

Q5. Explain four problems caused by the population explosion. [4 marks]

1. Unemployment: the number of people seeking work grows faster than jobs are created.
2. Over-exploitation of natural resources: land, water, forests and minerals are used faster than they can be replaced.
3. Low per capita income and price rise: national income is shared among more people, and demand for goods outstrips supply, pushing prices up.
4. Pollution: more people, vehicles, industries and waste pollute the air, water and land, especially in crowded cities.

Q6. Describe the methods of population control, with examples of how each prevents pregnancy. [5 marks]

1. Barrier methods: condoms are thin rubber or latex sheaths used by males or females to stop semen from entering the female tract; they also protect against sexually transmitted infections and AIDS.
2. Intra-uterine devices: IUDs such as the Copper T are placed in the uterus by a doctor; they increase phagocytosis of sperm, and copper ions reduce sperm motility and fertilising capacity.
3. Oral contraceptive pills: small doses of progestogens or progestogen-estrogen are taken daily for 21 days; they inhibit ovulation and implantation and alter the cervical mucus.
4. Surgical methods: vasectomy (cutting or tying the vas deferens) and tubectomy (cutting or tying the fallopian tubes) block gamete transport; they are highly effective but very poorly reversible.
5. Government measures support these methods: raising the marriage age to 18 for females and 21 for males, incentives for small families, and the Hum Do Hamare Do campaign.

Key takeaways

• India's population grew from about 350 million at independence to 1,210 million in the 2011 Census; the world passed 8 billion in 2022.
• India's growth passed through stagnant, steady, explosive (1951 to 1981) and slowing phases, set by the balance of birth and death rates.
• The population explosion came mainly from a rapid fall in death, maternal and infant mortality rates while birth rates stayed high.
• Demography studies populations; density is people per sq km, which was 382 in India in 2011, up from 117 in 1951.
• Birth rate and death rate are counted per thousand of the population per year; growth rate expresses the change as a percentage.
• Rapid growth causes unemployment, over-exploitation of resources, low per capita income, price rise, pollution and unequal distribution of wealth.
• Population education builds awareness of the problem, the small family norm, reproductive health and gender equality.
• Control methods include condoms, pills, IUDs such as the Copper T, and the terminal surgical methods of vasectomy and tubectomy.

Test yourself

How often is the Census held in India, and when was the first complete census?

The Census is held every 10 years. The first census was in 1872, and the first complete census was in 1881.

What was the density of population of India in 2011?

The density of population of India in 2011 was 382 persons per square kilometre, up from 117 in 1951.

Which period is called the population explosion in India, and why?

The period 1951 to 1981, when a rapid fall in the death rate with a high birth rate pushed annual growth to about 2.2 per cent.

What is the legal age of marriage in India?

The legal age of marriage is 18 years for females and 21 years for males, a measure also used to slow population growth.

What does the slogan Hum Do Hamare Do promote?

It means "we two, our two" and promotes a small family of two children, shown in posters of a happy couple.

How do copper-releasing IUDs prevent pregnancy?

They increase phagocytosis of sperm in the uterus, and the copper ions released reduce sperm motility and fertilising capacity.

What is population doubling time?

The time a population takes to double itself at its current annual growth rate; faster growth means a shorter doubling time.

Which contraceptive method also protects against AIDS?

Condoms, used by males or females, also protect the user from sexually transmitted infections and AIDS.