Page 34 - Science Coursebook

2.6 Populations

You have probably heard that the human
population is growing fast. The United Nations
estimated there were more than 7 billion
people on Earth in early 2012. Some scientists
think that our population will reach 10 billion How will we cope
by 2050. (10 billion is 10 000 000 000.) when there are
an extra 3 billion
No-one can be sure what will happen to people on Earth?
our population in the future. The size of a
population increases when the number of births per year is greater than the number
of deaths per year. In many countries, better health care, and better supplies of food
and water, are reducing the number of deaths per year. To keep the population steady,
the number of births must also decrease.

12 high prediction

10 medium prediction

8 low prediction
world
population 6
/ billions
4

2

0
1 500 1000 1500 2000 2200
year
This graph shows how the human population has changed in the last 2000 years (yellow
background), and how it is predicted to change by 2200 (purple background).

Questions

A+I 1 Look at the graph. What can you conclude about the number of
births and deaths per year between the year 1 and the year 1000? increasing
A+I 2 Suggest reasons for the shape of the graph between 1500 and 2000. population

A+I 3 There are three different lines showing the predicted population size falling
in the future. Suggest why. birth rate
rising rising
Factors affecting the size of animal populations birth rate death rate

We can define a population as the number of organisms of a
particular species that are living in the same place at the same time. falling
death rate
Look back at the diagram of the food web in the Southern Ocean, on falling
page 28. Let’s think about the population of penguins. population
How birth rate and death

rate affect population size.

32 2 Living things in their environment