HUMAN BIOLOGY

488 Chapter 25

expLore on your oWn

conservation and the development of alternative, renewable

energy sources will be crucial.

Human population growth and related activities also are

contributing to the rapid loss of other species.

revieW Questions

1. Describe at least two ways that human activities are
   altering air quality.


2. Explain the difference between global warming and global
   climate change.


3. Describe the greenhouse effect. Make a list of twenty
   agricultural and other products that you depend on. Are
   any implicated in global warming?


4. What is deforestation, and how does large­scale deforestion
   damage an ecosystem?

seLF-Quiz Answers in Appendix VI

1. The number of individuals that can be sustained indefinitely
   by the resources in a given region is the.
   a. biotic potential
   b. carrying capacity
   c. environmental resistance
   d. density­dependent control


2. shields organisms against the sun’s UV
   wavelengths.
   a. A thermal inversion c. The ozone layer
   b. Acid rain d. The greenhouse effect


3. Acid rain is one outcome of.
   a. coal burning c. some industrial processes
   b. gas and oil burning d. all of the above


4. Greenhouse gases.
   a. slow the escape of heat from Earth into space
   b. are produced by natural and human activities
   c. are at higher levels than they were 100 years ago
   d. all of the above


5. All the following are renewable energy sources except
   .
   a. hydropower c. natural gas
   b. wind d. solar energy

summary

section 25.1 Recent, rapid growth of
the human population has been due mainly
to advances in agri culture, industrialization,
sanitation, and health care. Differences in
growth among countries correlate partly
with levels of economic development and partly with
demographics such as population density and age structure.
Populations of countries with a large reproductive base
generally grow the fastest.

section 25.2 Carrying capacity is the
number of individuals of a species that can
be sustained long­term by the available
resources in an area.
Populations initially show logistic
growth—rapid growth that levels off when
carrying capacity is reached. Carrying
capacity, competition, and other factors limit population
growth. Density­dependent controls on growth include
competition for resources, disease, and predation.

section 25.3 An ecological footprint
is the sum total of resources used by a
population or person, together with the
resulting wastes. If renewable resources
are replenished, they may be available
indefinitely. Nonrenewable resources (such
as fossil fuels) can’t be readily replenished.
A pollutant is a substance that harms the health, activities,
or survival of a population.

sections 25.4–25.9 Exponential
growth of the human population has
brought increased pollution and demands
for energy, water, food, and waste dis­
posal sites.
Air pollutants are present in industrial
and photo chemical smog and acid rain.
Long­lasting chlorofluorocarbons (CFCs), once widely used
as coolants and propellants in aerosol sprays, have played a
major role in the seasonal thinning of the Earth’s protective
ozone layer. Widespread deforestation is associated with
leaching of soil nutrients, erosion, and possible disruption of
the global carbon cycle.
Fossil fuels are nonrenewable and are major sources of
air pollution. To meet the increasing demand for energy,

Section 25.3 discussed the ecological footprint concept—the total resources a population
consumes and the resulting wastes that are returned to the environment. You may also have heard
about the personal “carbon footprint” we each have with respect to climate change. The idea is that each of us does
things that produce lots of carbon dioxide emissions, such as driving a car or taking a plane to a vacation spot.
Many websites provide information on assessing one’s carbon footprint and offer suggestions for reducing it.
Do some online research to learn more about this concept and then list at least five things you think you could
realistically do to reduce yours.

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