ECOSYSTEMS
7.3 Food Chains and food webs:
interactions of life
Food chains and food webs:
interactions of life
 Please write down any notes/questions that are in this
colour thanks! 
 All living things require energy. This energy is used by
organisms for growth, repair and reproduction to help
the organism survive.
What is the source of this energy?
The SUN
 The Sun is one big nuclear reaction where hydrogen is
being made into helium. This releases a LOT of energy
(light, heat, gamma radiation, X-rays, microwaves and
radiowaves.)
Food chains and food webs:
interactions of life
7.3 Question 2
‘The Sun is the source of all life on Earth.’ Do you
agree with this statement? Why or why not? (write
your answers in your workbook)
‘Yes’, because the Sun provides the initial source of
energy for plants to grow.
Food chains and food webs:
interactions of life
 Plants, green algae & a
number of microorganisms
(i.e the ruffled sea slug),
use light from the Sun to
provide the energy for life.
They convert carbon
dioxide and water into food
(sugar-called glucosechemical energy). This is
known as photosynthesis.
Food chains and food webs:
interactions of life
 Sunlight is absorbed by
chlorophyll (this is what
makes the leaf look green)
in the leaf, providing
energy required to convert
the carbon dioxide (taken
in through the leaves) and
the water (taken in through
the roots) into glucose and
oxygen.
Food chains and food webs:
interactions of life
Photosynthesis
Carbon dioxide + water  glucose + oxygen
(in the presence of
sunlight and chlorophyll)
Producers or Autotrophs- organisms that produce
their own food.
They are essential because they provide food for all
the other organisms in the ecosystem.
Food chains and food webs:
interactions of life
7.3 Question 3
So you think the term ‘producer’ is an accurate
description of a green plant? Explain your reasoning.
(please write the answer in your text book)
‘Yes’, because it produces its own food.
7.3 Question 4
Complete the following statement:
light energy from the Sun
During photosynthesis, _______
chemical
is converted into _________energy
within plants.
The flow of nutrients
through an ecosystem
Consumers or heterotrophs cannot produce their own
food.
Animals that eat plants are called primary consumers or
herbivores. e.g. Kangaroo
Animals that eat herbivores are called secondary
consumers or carnivores. e.g. Dingo
Consumers that eat both plants and animals are called
omnivores. e.g. Humans
The flow of nutrients
through an ecosystem
Complete the following questions quietly in your text
book:
7.3 (page 177)
Question 1
Question 5
Question 6
The flow of nutrients
through an ecosystem
The nutritional sequence between producers, primary,
secondary and tertiary consumers is called a food chain.
(each organism links to another.)
The flow of nutrients
through an ecosystem
Food chains rarely have more than six links called
trophic levels.
The interactions between the food chains and their
various food sources are known as a food web.
The flow of nutrients
through an ecosystem
The flow of nutrients
through an ecosystem
The flow of nutrients
through an ecosystem
Please complete the following questions in your work
book quietly:
Question 7
Question 8
Question 9
The flow of nutrients
through an ecosystem
Biodiversity
 refers to the number of species present in a community.
Communities with high biodiversity (many species of
plants and animals) can survive environmental changes
better than those with low biodiversity (only a few
different species of plants and animals living together). As
there are more options for food if one organism is
destroyed. Lets look at the crane/bird in the slides
example. (previous slide).
What options does it have to eat? Would it survive if say
frogs disappeared?
 What would not survive if the plant in the pond
disappeared?
The flow of nutrients
through an ecosystem
Biodiversity
 In the video when the frogs
disappeared what did the
grasshoppers do?
 By removing the natural
vegetation of an area and
replacing it with one specific type
of plant (wheat) humans have
reduced the biodiversity of many
ecosystems and some species are
now extinct.
The flow of nutrients
through an ecosystem
Please complete the following questions in your work
book quietly:
Question 12
The flow of energy
through an ecosystem
• Read this information together from the text book
page 174.
Decomposers: the last link in the food chain
• Organic matter- all matter in the biosphere that
comes from living organisms and contain the element
carbon.
•Decomposers- recycle organic material (dead
plants/animals)
•Eg bacteria & fungi
•Question 10 & 11 (p177)
Relationships between
organisms
Read through “Relationships between organisms”
together. (p 175-176)
The different types of interaction include:
1. Mutualism (symbiosis)
2. Commensalism
3. Amensalism
4. Competition
5. Exploitation (a- predation b- herbivory cparasitism)
Please complete the remainder of the questions in
Your book (Questions 13-19).