Transcript Food chains and food webs

Food chains and food webs
Ena Haniff
Food Chains
• A food chain is a simple sequence which shows the
flow of energy through an ecosystem (in the form
of food)
• Energy from the sun is converted to plant matter
by producers during the process of photosynthesis
• Energy is transferred as the nutrients in food
• Each organism is a link and each link is called a
feeding level or “trophic level”
Food Chains
• A food chain can be represented by a simple
diagram as follows:
• Grass
Deer
Tiger
• Arrow
denotes “ is eaten by”
• Arrows are used to show the flow of energy from
one trophic level to another
Food Chains
• Feeding relationships are shown in a food chain
• Food chains begin with a plant or producer
(usually)
• All other organisms in a food chain are animals or
consumers
Questions
• How is the sun’s energy transferred to plants?
• Plants use the sun’s energy during photosynthesis
to produce carbohydrates which is sugar and is a
store of energy
• How do animals (consumers) obtain their energy?
• Animals obtain their energy by eating plants and
other animals and use the energy from the
carbohydrates. They also build more complex
substances (such as proteins) which also stores the
energy they obtained from producers
Questions
• Why do organisms need energy?
• Organisms need energy to carry out all the
functions of living things:
• Growth
• Repair
• Reproduction
• Movement (animals)
Activity
• From the list of organisms, choose three suitable
organisms and construct a food chain.
• Crab, butterfly, shark, fish, cat, snake, grass, bird,
rat, flower, octopus, pig, tiger, deer, lettuce, cow,
human, seaweed,
• You can construct more than one food chain
• Can you spot the producers?
• Which organisms are herbivores?
• Omnivores?
• Carnivores?
Activity
Producers
Consumers
Grass, flower, lettuce, seaweed Crab, butterfly, shark, fish, cat,
snake, bird, rat, octopus, pig,
tiger, deer, cow, human
Herbivores
Omnivores
Carnivores
Butterfly, deer, cow
Pig, human, bird,
crab, fish, rat,
Shark, snake, tiger,
octopus
A little more on producers and
consumers
• Producers make their own food using the sun’s
energy
• They include green plants, mosses, aquatic plants,
phytoplankton in water and certain bacteria
• Phytoplankton are microscopic algae that live in
water that use photosynthesis to produce their
own food and which forms the base of marine food
chains
A little more on producers and
consumers
• Consumers cannot make their own food and need
to eat other organisms to obtain energy
• There are many types of consumers in a food
chain:
• Primary
• Secondary
• Tertiary
• Quaternary
A little more on producers and
consumers
Type of
Symbol
consumer
Description
Primary
1°
Organisms that consume producers (green plants). They
are the first set of consumers and they occupy the 2nd
trophic level
Secondary
2°
Organisms that consume primary consumers. The are the
2nd set of consumers and they occupy the 3rd trophic
level
Tertiary
3°
Organisms that consume secondary consumers. They are
the 3rd set of consumers and they occupy the 4th trophic
level
Quaternary
4°
Organisms that consume tertiary consumers. They are
they 4th set of consumers and they occupy the 5th trophic
level.
An example
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Grass
Deer
Human
Tiger
In this food chain, the grass is the producer.
The Deer is the primary consumer
Can you identify the secondary and tertiary
consumers?
Human: Secondary
Tiger: Tertiary
Can you name the 2nd feeding or trophic level?
The deer
An unusual food chain
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Recall that in the beginning of the lesson I said that
food chains usually begin with producers? Well, here is
an exception:
Leaf litter
Earthworm
Bird
In this food chain, a producer is not at the beginning.
This food chain begins with detritus (decaying organic
matter)
The Earthworm is a detritivore here (decomposer)
It fills the role of returning organic material to
inorganic material where it can be used again by plants
Food webs
Ena Haniff
Introduction
• In the pop up chart, what would happen if I
introduced a bird, a rabbit and a snake into the
Jungle?
Food webs
• In reality, organisms have more than one source of
food
• Organisms can be a link in more than one food
chain
• For example the tiger can eat both the deer and
the rabbit
• And plants are eaten by both the deer and the
butterfly
• This makes the feeding interactions more
complicated
Food webs
Activity
• From the food web shown
• Construct a food chain with three links and one
with four links
Food web
• A food web shows a network of interconnected
food chains
• It shows the transfer of energy through an
ecosystem
• It uses arrows to show the transfer of energy
Question
• What would happen if all the rats were suddenly
removed from this food web?
Activity
Possible results
• There will be an explosion in the populations of all
the organisms that the rat feeds on including
grasshoppers, caterpillars, grubs and beetles
• These are herbivores; they will consume more
plants
• Food supplies could be affected
• The amount of oxygen produced and carbon
dioxide removed from the air could be affected
• The owl population would be affected because rats
were half of their food supply
Equilibrium
• Predators limit the number of prey in an ecosystem
and prey limit the number of predators as well.
• There is a delicate balance in an ecosystem that
can be easily upset if the population of the various
organisms are disturbed
• An example: swarms of locusts happen under
conditions which are favourable to their
reproduction; and it wreaks havoc on the food
crops when this occurs
Assessment activity
• Using any of the organisms provided, construct a
simple food web.
• Crab, butterfly, shark, fish, cat, snake, grass, bird,
rat, flower, octopus, pig, tiger, deer, lettuce, cow,
human, seaweed