Chapter 5

Web of Life

Interactions

within an
environment
examples

interactions interactions between living things
between living and the physical characteristics
things of the environment
such as between
such as
producers and consumers between

and producers and light energy
from the Sun
predators and prey
Copyright © 2010 Horizon Education, publishing as M. KOYLU

Primary Energy Source
• Organisms that first capture solar energy, the
producers, include plants, some kinds of bacteria,
and algae.

• Consumers are those organisms that consume
plants or other organisms to obtain the energy
necessary to build their molecules.


Where do these organisms get their
food and energy from?


• The path of energy through
the trophic levels of an
ecosystem is called a food
chain.
• The lowest trophic level of
any ecosystem is occupied by
the producers, such as plants,
algae, and bacteria.
• Producers use the energy of
the sun to build energy-rich
carbohydrates.

Food Chain in an Antarctic
Ecosystem


Plants are food
producers.

Animals are food
consumers.

Energy is transferred through a food
chain, from food producer to food
Prey are animals eaten by
consumer.
other animals.

A food chain
Predators are animals
that eat other animals.


A food chain shows the food relationships
among organisms and the transfer of energy
through organisms in the form of food.

Example:
Grass  Zebra  Lion


A food chain shows what is eaten.

The lettuce is eaten by the rabbit.

The fly is eaten by the thrush.

Food chains always start with a plant.

The lettuce is eaten by the slug, the slug is eaten
by the bird.


Food chains also show predator-prey relationships.
Identify the predators and prey below.


Put on your thinking cap…

Can a predator be a prey of another animal?
Give an example to support your answer.


A predator can also be a prey!


Write a food
chain based on
this photograph.

Which is the
producer?

Which is the
consumer?


Write a food chain based on the photographs below.
Identify the producer, consumers, predator and prey.


Meat-eaters are bigger
than plant-eaters. Predators
are larger
than prey!

Do you agree with Tom and Corrine? Why?


Quaternary
consumers

• Food Chain: Carnivore
Carnivore

Tertiary
– set of food (energy) consumers

Carnivore Carnivore
transfer from
trophic level to Secondary
consumers
trophic level Carnivore Carnivore

Primary
consumers

Herbivore Zooplankton

Producers

Plant Phytoplankton
A terrestrial food chain A marine food chain


Do you eat only one type of food?
What is the advantage of eating a variety of food?

• At the second trophic
level are herbivores,
animals that eat plants or
other primary producers.
They are the primary
consumers.

• A herbivore must be
able to break down a
plant’s molecules into
usable compounds.


• At the third trophic level are secondary consumers,
animals that eat herbivores. These animals are called
carnivores.


• Some animals, such as bears, are both herbivores
and carnivores; they are called omnivores.


• Detritivores are organisms that obtain their energy
from the organic wastes and dead bodies that are
produced at all trophic levels.


• Bacteria and fungi are known as decomposers
because they cause decay.

• Decomposition of bodies and wastes releases
nutrients back into the environment to be recycled by
other organisms.

• In most ecosystems, energy does not follow simple
straight paths because animals often feed at several
trophic levels. This creates an interconnected group of
food chains called a food web.


Food web – formed by interlinking
food chains
Food chains:
• Rice plant  Sparrow
• Rice plant  Locust  Sparrow

Food web:
Locust

Rice plant Sparrow

Food webs
• Formed by interlinking food chains

• Show the food relationships among organisms

• Show how energy is transferred through
organisms in the form of food

• Show predator-prey relationships


• In the wild, animals may eat more than one thing, so
they belong to more than one food chain.
• To get the food they need, small herbivores may eat
lots of different plants, and carnivores may eat many
different animals.
fox
owl

mice
rabbits

seeds berries
grass


Quaternary,
tertiary,
and secondary
consumers

Tertiary and

secondary
consumers

Secondary
and
primary
consumers

Primary
consumers

Producers
(plants)


Construct a garden food web from the
following food chains.

• Grass  Grasshopper  Lizard

• Grass  Grasshopper  Toad

• Grass  Praying mantis  Lizard

• Grass  Grasshopper  Praying mantis 
Toad


Identify the predators and prey in
the above food web.

A food web
in an African
grassland


African grassland food web

• Identify the producers, plant-eaters and meat-
eaters.

• Write down three food chains from the food
web which involve the impala.

• Give an example of a prey and predator in the
food web.



If the population of zebras increases in the
African grassland, what will happen to the
population of lions?

Will the populations of the other organisms in
the food web be affected? Explain.


The farmers
complain that
the sparrows
are eating too
much rice grains
Easy! Killing
and this affects
the sparrows
their harvests.
will solve the
problem!

Do you agree with Corrine? Why?

Is it true…
• … only large animals are consumers?

• … an organism higher in a food chain is a
predator of all the organisms below it?

• … a change in the population of an organism
in a food web only affects the populations of
organisms directly linked to it?


How are the organisms in a food web in a habitat
affected when new types of organisms are
introduced into the habitat?


What is the missing link?
provide energy and nutrients to
Producers Consumers

nutrients death death

?

Decomposers

Decomposers are organisms which break down
dead and waste matter into simple substances, such
as mineral salts, carbon dioxide and water.

E.g. Certain types of bacteria and fungi


Are the following decomposers?


What would happen if there were no
decomposers?


Decomposers help to…

• … break down dead and waste matter so that
they would not pile up on Earth.

• … recycle nutrients in the environment so that
they will not run out.


The missing link – Decomposers!


Returned to
Simple substances like carbon
which the environment
dioxide, water and nutrients are

into
Dead plants, animals and waste

breakdown

Fungi Bacteria


All
decomposers
are micro- I don’t think so. Dung
organisms. beetles are not micro-
organisms.

Do you agree with Tom and Corrine? Discuss.

Organism A living thing

Population Group of plants or animals of the same type,
live and reproduce in the same place and in
the same period of time.

Community Made up of many populations living
together at the same time.

Leaf Litter
Community
Different
populations of
organisms can
hide among the
decaying leaves
as it provides
food and shelter.


Rotting log
Community
Fungi and mosses grow on the log providing food for slugs and snails, while
the log provide shelter for both.


Habitat Examples of habitats
Place where population can
find everything it needs to live
and reproduce. Can you name
the habitats?

Different habitats can have Therefore support different
different living conditions. communities.


Open fields receive
sunlight and water
plant populations food
and shelter to many other
organisms.
Plants provide animals below with shelter and place to
reproduce.


•The insects
feed on
wood.
•The animals
feed on
leaves, fruit
and branches.
•The leaves
also protect
them from
predators.


Food chains & Food webs

Chapter 
• link food producers to food
consumers
• show transfer of energy from
WRAP-UP food producers to food
consumers
• predator-prey relationship

Habitat place where organisms
can find everything it needs to
live and reproduce

Decomposers (bacteria and
fungi) breakdown dead matter
into simple substances
Community
consists of different
populations living in the
same place. Population group of organisms
of the same type, living and
reproducing in the same surroundings


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