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Chapter 21 Populations and Communities-Section1 Living Things and
the Environment
Different types of organisms must live in different types of environments. AN organism obtains food,
water, shelter, and other things it needs to live, grow, and reproduce from its environment. An
environment that provides the things the organism needs to live, grow, and reproduce is called its
One area may contain many habitats and organisms live in different habitats because they have
different requirements for survival.
Biotic Factors
To meet its needs, an organism must interact with more than just the same type of organism. An
organism interacts with both the living and nonliving parts of its habitat. The living parts of a habitat
are called biotic factors. Any living thing in a habitat is a biotic factor.
Abiotic Factors
Abiotic factors are the nonliving parts of an organism’s habitat. They include water, sunlight. oxygen,
temperature, and soil.
Levels of Organization
Populations-A species is a group of organisms that are physically similar and can mate with each
other and produce offspring that can also mate and reproduce.
All the members of one species in a particular area are referred to as a population.
Communities-All the different populations that live together in an area make up a community.
In order to be considered a community, the different populations must live close enough
together to interact. In order to interact, they must be able to share the same resources, for
example, a pond for getting water.
Ecosystem-The community of organisms that live in a particular area, along with their nonliving
surroundings, make up an ecosystem.
The smallest level of organization is a single organism, which belongs to a population, that
includes other members of its species. The population belongs to a community of different
species. The community and abiotic factors together form an ecosystem.
Because the population in an ecosystem interacts with one another, any change affects all the
different populations that live there. The study of how living things interact with each other and
their environment is called ecology. Ecologists study how organisms react to change in their