Food chains and food webs

About how energy moves through food chains and webs.

WAL:

All

Most

Some

• How does energy enter an ecosystem and become transferred between organisms?

• What is meant by the terms: trophic level, food chain, food web, producer, consumer and decomposer?

• How is energy lost from the ecosystem?

Today we are covering from the specification:

Pages 61-63 of the textbook.

How does energy enter an ecosystem and become transferred between

organisms?

• The ultimate source of energy for organisms found in an ecosystem is sunlight.

• This is converted to chemical energy by photosynthesising organisms and passed as food between other organisms.

Radiation from the Sun (solar or light energy)

is the main source of energy for all living things. The suns light

energy is ‘captured’ and used by green plants and algae during photosynthesis, to make new

biomass. 6CO2 + 6H20 C6H12O6 + 6O2

Light energy

Key words

Producer Primary consumer

Secondary consumer Tertiary consumer

Quaternary consumer Herbivore

Omnivore Carnivore

Food chain Food web

Trophic level Autotroph

Heterotroph Decomposer

TASK: try to write a definition for each of these terms.

What is a food chain?

• Organisms need energy to live

• They get this energy by eating other organisms– E.g. A rabbit gets energy from the carrots it eats

• A food chain shows how energy is passed through a series of animals– E.g. Carrot Rabbit Fox

Methods of Obtaining Energy

• Organisms may be autotrophs (like plants) or heterotrophs (like animals).

• Autotrophs use energy from the sun to produce their own materials for growth etc.

• Heterotrophs use organic substances from other organisms for growth etc.

http://www.youtube.com/watch?v=O7eQKSf0LmY

i.e. autotrophs are producers and heterotrophs are consumers.

Draw this diagram:

Omnivores

CarnivoresHerbivores

What do they eat?Put these organisms into the correct categories:

Grizzly bear Human

Caterpillar Crow

Fox Cat

Grasshopper Pig

Frog Slug

Sparrowhawk Lion

Horse Deer

What do they eat?Herbivore Omnivore Carnivore

Caterpillar Grizzly bear Fox Grasshopper Human Frog

Slug Crow Sparrowhawk

Horse Pig Lion

Deer Cat

Stoat

Toad

Caterpillar

GrassProducer• Makes food from sun using

photosynthesis

Primary Consumer• Gains energy by eating

producers. • Usually herbivores

Secondary Consumer• Gains energy by eating primary

consumers. • Usually carnivores but can be • omnivores

Tertiary Consumer• Gains energy by eating

secondary consumers. • Usually predators but may be

scavengers or parasites

Trophic level – position in the food chain.

1st trophic level

4th trophic level

Food chains

• Food chains are diagrams that show what animals eat.

• In habitats all animals and plants depend on each other.

• If one animal or plant dies out it might affect the other animals .

Human

Cow

Grass

What would happen to the cows if all the grass died out?

What are detritivores?

Things that feed on detritus (dead or decaying material) giving it a bigger surface area for microorganisms to work on.

LL 2008

Name some examples of detritivores

LL 2008

Decomposers feed by releasing enzymes outside of their ‘body’, digesting the food externally and then absorbing the nutrients.

Decay is caused by saprobionts.

Bacteria & fungi are saprobionts.

LL 2008

Constructing an ecosystem

• A food chain is quite unrealistic – food webs are much better.

• Within any ecosystem there are two main processes to consider:– The flow of energy through the ecosystem.– The cycling of elements through the

ecosystem.

• We are going to construct an ecosystem based on these two main principles.

LettuceMakes its own food using

energy from the sun.

GrassMakes its own food using

energy from the sun.

SlugEats lettuce.

AphidEats grass.

GrasshopperEats grass.

CaterpillarEats lettuce.

RabbitEats lettuce and grass.

SpiderEats aphids.

HedgehogEats slugs and caterpillars.

ThrushEats slugs and spiders.

VoleEats grasshoppers.

FrogEats grasshoppers.

Grass snakeEats frogs.

SparrowhawkEats voles and thrushes.

FoxEats hedgehogs, voles and

rabbits.

Constructing an ecosystem

• As well as the cards provided, you will also have to draw/add your own elements to the ecosystem as some are missing.

Constructing an ecosystem

• Cut out all of the cards and try to arrange them in a logical ecosystem.

• Once you’re happy, glue them down.• Draw arrows between organisms to show

the flow of energy (and therefore feeding relationships) within the ecosystem.

• Around the outside, list any abiotic factors which could affect the individuals in the ecosystem.

An example ecosystem

Food chains and food webs

About how energy moves through food chains and webs.

WAL:

All

Most

Some

• How does energy enter an ecosystem and become transferred between organisms?

• What is meant by the terms: trophic level, food chain, food web, producer, consumer and decomposer?

• How is energy lost from the ecosystem?

5,4,3,2,1 go… can you talk about food chains and food webs for 60 seconds mentioning as many as the key words

as possible?Producer Consumer

Food chain

Food web

Omnivore

Habitat

Trophic level

Energy loss

Heat

Quaternary consumer

Decomposer

Respiration

Tertiary consumer

Secondary consumer

Primary consumer

Detritivore

Carnivore Herbivore

Ecology Bingo

Draw a 2 x 3 grid and fill it with 6 key words from todays lesson...

Ecosystem CarnivoreConsumer ProducerFood chain Energy flow