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8D
Summary Sheets
Habitats and environments
A habitat is the area where an organism lives. The surroundings of an organism are called
its environment. Non-living factors (e.g. light, dampness, temperature) that affect what an environment is
like are called physical environmental factors. Living things that affect what an environment is like are
called living factors.
All the plants and animals that live in a habitat make up a community. Within a community, the total
number of one species is called a population.
In order to survive in a habitat, organisms need various resources. An animal needs food, water,
oxygen and shelter, and it needs to find a mate to reproduce. Plants need light, water and carbon dioxide in
order to make food. They also need mineral salts (nutrients), oxygen and space to grow.
Adaptations
The organisms living must be adapted to survive in a habitat. Members of the same community may have
similar adaptations to cope with the problems of their habitat. Organisms that are
better adapted to survive in an area will have a better chance of survival. Since a habitat contains many
different environments, many organisms are not spread evenly through a habitat. All the places where an
organism is found are its distribution. If it is not spread evenly through the
habitat it is said to have uneven distribution. If it is spread evenly it has even distribution.
Classifying living organisms
There are so many species that we need classify them. The Summary Sheets for Unit 7D show how members of
the animal kingdom are classified into groups.
Members of the plant kingdom can make their own food by photosynthesis. There are four main plant
groups. Mosses reproduce by spores, have thin leaves and no roots or xylem vessels. Ferns reproduce by
spores held in containers under their leaves. Conifers reproduce using seeds found
in cones and have needle-shaped leaves. Flowering plants reproduce using seeds found in fruits, have flowers
and large, flat leaves.
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Summary Sheets (continued)
Sampling methods
Ecologists are scientists who study habitats. They catch organisms using various sampling
methods, then use keys and field guides to identify them.
Ecologists often need to know the size of a population. It would be impossible to count all the organisms
in a habitat, so they take samples and then estimate the total population.
A quadrat is a sampling square used to estimate plant populations. It is placed randomly on the ground and the
number of plants inside it is counted each time. The more samples that are taken, the more reliable an estimate
will be.
Ecologists measure physical environmental factors, like how warm it is and how much oxygen is
dissolved in pond water, using sensors and data loggers. They see if there are any relationships
(links) between the factors, such as the warmer the water, the lower the oxygen level is.
Feeding relationships
Animals depend on plants or other animals for food. Food chains and food webs show the
feeding relationships in a habitat (see the Summary Sheets for Unit 7C). However, living organisms depend on
other organisms in other ways. For example, plants depend on insects for pollination.
The populations of the organisms at each level in a food chain can be shown as a pyramid of numbers.
The size of each bar represents the number of organisms. Usually there are fewer organisms as you go along
a food chain because energy is lost at each level (e.g. through movement, faeces). Sometimes the pyramid
has an unusual shape if the organisms are very different in size.
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Summary Sheets (continued)
Populations
The size of a population is affected by several factors.
• Animals compete with each other for resources such as food, water and shelter.
• Plants compete for light, water, nutrients (mineral salts) and space.
• Competition for resources may cause populations of some organisms to decrease.
• Disease can kill organisms.
• Poisons may kill organisms, or kill the organisms that they depend on. Poisons can build up in
the animals as you go along a food chain.
• Changes in living factors affect populations. For instance, the populations of predators and prey
are linked. When there are a lot of prey organisms, the number of predators increases because
they have plenty of food. This decreases the number of prey, which then leads to a decrease in
the number of predators.
• Changes in physical environmental factors can also affect populations. For instance, when
it gets cold in winter, some animals alter their behaviour and migrate. Their populations decrease.
If populations of an organism get too low the organisms may become endangered or even extinct. For
instance, changes in physical environmental factors 65 million years ago probably caused the dinosaurs to
become extinct. Humans hunting dodo birds helped them to become extinct. Today, hunting and
overfishing have caused many animals to become endangered.
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