Grade 12 Zoology Note
Population can be defined as the total number of individuals occupying at a particular area at a particular time. The organisms are capable of interbreeding among themselves. The size and the density of a population depends on different factors;
1.Birth or Natality rate
2.Mortality or death rate
Human population growth:
History of human being is only about 50,000 years old. But there are no records available about the human population since that period. Global human population growth amounts to around 75 million annually, or 1.1% per year. The global population has grown from 1 billion in 1800 to 7 billion in 2012. It is expected to keep growing, where estimates have put the total population at 8.4 billion by mid-2030, and 9.6 billion by mid-2050. The population growth rate is the rate at which the number of individuals in a population increases in a given time period as a fraction of the initial population. Specifically, population growth rate refers to the change in population over a unit time period, often expressed as a percentage of the number of individuals in the population at the beginning of that period.
Population in Nepal:
Like other countries the population of Nepal is also increasing day by day.
The population of Nepal is estimated to be 30,494,504 people based on the 2014 census, with a population growth rate of 1.596% and a median age of 21.6 years. Female median age is estimated to be 22.5 years, and male median age to be 20.7 years. Only 4.4% of the population is estimated to be more than 65 years old, comprising 681,252 females and 597,628 males. Sixty one per cent of the population is between 15 and 64 years old, and 34.6% is younger than 14 years. Birth rate is estimated to be 22.17 births/1,000 populations with an infant mortality rate of 44.54 deaths per 1,000 live births. Life expectancy at birth is estimated to be 67.44 years for females and 64.94 years for males. Death rate is estimated to be 681 deaths per 100,000 people. Net migration rate is estimated to be 61 migrants per 100,000 people. According to the 2001 census, only 48.6% of the total population is literate of which 62.7% are male and 34.9% are female. According to doubling time rate of population, the population of Nepal double within 33 years.
Patterns of population growth (growth curves):
The mathematical models of population growth are basically two types;
The J-shaped growth pattern of population is shown in the given figures. This type of population growth is seen in algae, some insects, annual plants and lemmings of tundra. Finally this growth curve shows rapid increases in mortality rate. It consists of two phases namely lag phase and exponential phase.
Fig; population growth in j-shaped curve
2.S-shaped curve (Sigmoid curve):
This type growth is observed in yeast cell and most of the organisms including human. Finally this growth curve shows slow zero growth rate as birth rate equals to death rate. It consists of three phases namely lag phase, exponential phase and stationary phase.
Fig; population growth in s-shaped curve
Different between J-shaped curve and S-shaped curve
1.Finally this growth curve shows rapid increases in mortality rate.
1.Finally this growth curve shows slow zero growth rate as birth rate equals to death rate.
2.examples- Bacteria, some insects, lemming of tundra.
2.examples- yeast cells, most of the organisms including human.
3.It consist of two phases namely lag phase and exponential phase.
3.It consists of three phases namely lag phase, exponential phase and stationary phase.
Reason or causes of Increase in Human population
1.Advancement in agricultural technology: due to Advancement of science and technology production of food has been enhanced.
2.Better public health: Due to better health care and greater medical medical attention life expectancy of people is increasing.
3.Control of various epidemic diseases.
4.Lack of education because the ratio of increase is more in rural area.
5.Misbelieves like in male dominant society, people prefer to have more sons then daughter.
6.In some reason polygamy is very common.
7.Early the marriage sooner the child.
Problems or Consequences of over population:
a.Space: New towns and cities are coming up to accommodate the growing population. This put a great strain on agricultural lands and forest areas.
b.Food supply: It will lead to the food crises resulting in famines, hunger and poor health.
c.Unemployment: Rise in population has resulted in large scale unemployment.
d.Education: Higher population decreases the quality of education.
e.Poverty: Birth of every child adds the poverty.
F. increases in social crimes.
2.Shortages the natural resources:
a.Energy crises: Increases in the population has created greater demand for energy.
b.Drinking water: Drinking water is the major problem in over populated areas.
a.pollution: Rise in the population causes environmental pollutions.
b.Sanitation and epidemic diseases: Poor sanitation caused by overpopulation leads to the development of various epidemic diseases.
c.Deforetation: Forest trees are cut and forest areas are encroached.
Control of over population
The people are suggested following ways of controlling over population;
1.Education about population must be focused in the curriculum of al grades.
2.Late marriage can help in reducing population growth.
3.Abortion is usually applied to the deliberate destruction of a foetus by drug, Which help to control over population.
4. Family planning is also main way to control population.