HABITATS AND ENVIRONMENTS
Food chains
The table describes some common terms used to describe living things in their
environment:
Term
Description
Environment
All the conditions that surround a living organism
Habitat
The place where an organism lives
Population
All the members of a single species that live in a habitat
Community
All the populations of different organisms that live together in a habitat
Ecosystem
Interaction between living organisms and the environment
A food chain shows the different species of an organism in an ecosystem, and what eats what.
Producers and consumers
A food chain always starts with a producer, an organism that makes food. This is
usually a green plant, because plants can make their own food by photosynthesis.
A food chain ends with a consumer, an animal that eats a plant or another animal.
Here is an example of a simple food chain:
grass → cow → human
(The arrows in food chains show the way in which energy is moving. They do not show what eats what )
Other words in a food chain
There are several words used to describe the
organisms in a food chain.
A food chain from grass to hawk
The plant is the producer and the animals are consumers:



the first consumer in the chain is also called the primary consumer
the next one is the secondary consumer
the one after that is the tertiary consumer
A consumer that only eats plants is called a herbivore, and a
consumer that only eats other animals is called a carnivore.
An omnivore is an animal that eats both plants and animals.
Pyramids of numbers
The population of each organism in a food chain can be shown
in a type of bar chart called a pyramid of numbers. The bars are drawn
to scale – the more organisms it represents, the wider the bar. The
producer in the food chain always goes at the bottom of the pyramid of
numbers. Think about this food chain:
clover → snail → thrush → hawk
Clover is a plant and it is the producer in this food chain. Its bar goes
at the bottom of the pyramid:
Food webs
When all the food chains in an ecosystem are joined up together, they form a food web. Here
is an example of a food web:
Although it looks complex, it is just several food chains joined together. Here are
some of the food chains in this food web:
grass → insect → vole → hawk
grass → insect → frog → fox
grass → insect → vole → fox
Notice that:
 the rabbits and slugs have just one predator
 the frogs and voles have two predators (the foxes and hawks)
 the insects have three predators (frogs, voles and thrushes)
This leads to some interesting effects if the population of a particular organism in the food
web decreases. Some animals can just eat more of another organism if food is in short supply,
while others may starve and die. This in turn can affect the populations of other organisms in
the food web.
Adaptation
Living things are adapted to their habitats. This means that they have special
features that help them to survive. An African elephant, for example, lives in a hot habitat
and has very large ears that it flaps to keep cool.
A polar bear, on the other hand, lives in a cold habitat and has thick fur to keep warm.
It’s not just animals that are adapted to their environment, plants are too. A cactus is well
adapted for survival in the desert. They have long roots to collect water from a large area and
a stem that can store water for a long period of time.
The animals and plants in one habitat are suited to live there and may not be able to
survive in other habitats. When a habitat changes, the animals and plants that live there are
affected. See the PPT for the other examples of adaptation.
IMPACT OF HUMAN ACTIVITY
The Earth is our only source of resources, and these are limited. As the population
keeps growing, recycling becomes more important. Increased levels of carbon dioxide are
linked to climate change.
The impact of humans
The Earth is the source of all the resources we need, such as metals, plastics and fuels.
Humans are very successful living things. We compete with other organisms for many natural
resources. These include:
 land (for farms, buildings and roads)
 water (for drinking, watering fields, and industry)
The world’s human population is increasing, and this means that we are using more resources
all the time.
Population growth
The human population in the year 1800 was about 1 billion, and now it is more than 7
billion (more than 7,000,000,000).
Deforestation
Humans have been cutting down trees for thousands of years. We do this to clear land
for farming and building, and for wood to use as a fuel or building material.
Forestry is sustainable as long as forests are allowed to replace themselves, or are replanted
after felling, but often this is not done. The result is that the world’s forests are steadily
shrinking. The maps show the loss of forest across the world over the last 10,000 years:
Map showing the forest areas of the world about 10,000 years ago
Map showing the forest areas of the world today. There is now much less forest in the Americas, Asia and
Europe.
Pollution
We produce waste whenever we make or transport objects and substance. Waste materials
include:
 household and industrial rubbish
 chemicals from industrial processes
 smoke from burning fuels
 harmful gases from burning fuels
They damage the environment and are a waste of resources.
Many harmful gases are emitted from motor vehicles
Greenhouse effect
Some thermal energy from the Earth’s surface escapes into space. If too much thermal
energy escaped, the planet would be very cold. However some gases in the atmosphere,
called greenhouse gases, trap escaping thermal energy. This causes some of the thermal
energy to pass back to the surface. This is called the greenhouse effect, and it keeps our
planet warm. Carbon dioxide is an important greenhouse gas.
Increasing carbon dioxide levels
Humans burn fossil fuels to power cars and other machines, to generate electricity,
and to keep buildings warm. Waste gases are released during combustion, including carbon
dioxide. As the human population increases, more fuel is used, and more carbon dioxide is
released.
Human activities have caused the percentage of carbon dioxide in the atmosphere to increase
Global warming
Extra carbon dioxide in the atmosphere increases the greenhouse effect. More thermal
energy is trapped by the atmosphere, causing the planet to become warmer than it would be
naturally. This increase in the Earth’s temperature is called global warming.
The average temperature of the planet has increased in recent years
The majority of climate scientists agree that there is a link between the increasing levels of
carbon dioxide and the increasing temperatures. Global warming is having an effect on the
world’s climates.
The impact of climate change
The weather includes the wind, sunshine and rain you see from day to day. The climate is
the sort of weather seen over years and decades. Climate change and its effects as a result of
global warming includes:
 ice melting faster than it can be replaced in the Arctic and Antarctic
 the oceans warming up – their water is expanding and causing sea levels to rise
 changes in where different species of plants and animals can live
Resources and recycling
Sustainable development involves making sure that the way we behave now does not
make life difficult or impossible for future generations. You will remember that the Earth’s
resources are limited so, to achieve sustainable development, we need to carefully consider
how we use resources. Recycling is an important way to help us achieve sustainable
development. We can recycle many resources, including:
 glass
 metal
 paper
 plastic
Used objects need to be sorted before they can be recycled
a. Glass
Glass is easily recycled. It can be melted and remoulded to make new objects, such as
bottles. The energy needed to do this is less than the energy needed to make new glass from
its raw materials. However, we need to sort different coloured glass ready for recycling, and
transport it to the recycling plant.
b. Metal
Just like glass, it takes less energy to melt and remould metals than it does to extract new
metals from their ores. Aluminium is a valuable metal that melts at a relatively low
temperature, so it is particularly attractive for recycling.
Metal drinks cans ready to be recycled
c. Paper
Paper is not melted when it is recycled. Instead, it is broken up into small pieces and
reformed to make new sheets of paper. This takes less energy than making new paper from
trees. However, paper can only be recycled a few times before its fibres become too short to
be useful. Recycled paper is often only good enough for toilet paper or cardboard, but it can
be used as a fuel or compost instead.
d. Plastic
Many plastics (but not all) can be recycled. For example, some plastic bottles can be
recycled to make fleece for clothing. Recycling means that we use less crude oil, the raw
material needed for making plastics. Different types of plastics have to be sorted out and this
can be difficult, but recycling plastic does stop much of it ending up in landfill sites.
A lot of waste still ends up in landfill sites, which is a waste of valuable resources