Biology

Food Chains

Thousands of years ago huge beasts roamed the Earth, but most died out with the end of the last ice age. A new discovery about their diet suggests another possible cause for their disappearance. It also shows us the importance of understanding the way that many species depend on others for food.

This is a print version of an interactive online lesson. To sign up for the real thing or for curriculum

details about the lesson go to

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Introduction: Food Chains

Imagine an animal that stands three times taller than you and weighs as much as �ve cars. That’s how big a woolly

mammoth, an early relation of the elephant, was. With its long curved tusks, it must have been a frightening sight! The

woolly rhino was almost as big and looked like an oversized modern rhinoceros but with a shaggy coat and even longer

horns.

Both animals lived in the icy Arctic region during the Pleistocene epoch, more than 10,000 years ago. They belonged to a

group called megafauna, which means “big animals”. But despite looking scary, these animals only used their horns to

defend themselves and, like modern rhinos and elephants, were vegetarians.

Scientists have found lots of fossilized grass pollen in soil from that time and, until now, thought that this was what the

huge animals lived on. But it looks as if the scientists may have missed a key piece of the puzzle.

Grass produces more pollen than other types of plants and so it looked like that was all that was there. But now scientists

have found the remains of another plant deep in the permanently frozen soil. With modern DNA testing, they worked out

that the most common thing growing in the area was not grass, but leafy protein-rich plants called forbs. These would make

much better food for a big beast than grass.

And there's other evidence that these forbs might have been the animals' main diet. The forbs died out about 10,000 years

ago – about the same time as many megafauna.

Read the full Cosmos Magazine article  here.

Woolly mammoths and woolly rhinos are just a couple of the now extinct

species that roamed the Northern Hemisphere during the Pleistocene epoch.

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Question 1

Propose: It's likely that a number of causes contributed to the extinction of the Arctic megafauna. What causes can you

suggest?

Hint: The above introduction suggests one possible cause.

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Gather: Food Chains

All living things need energy to survive. It helps grass grow, enables lions to roar and is even helping you read this right now.

But where does energy come from?

Plants get their energy from sunlight. Via a special process called photosynthesis, plants are able to turn the energy they

receive from the Sun into glucose, a form of sugar, which they can then use to grow. Because plants produce their own

food they are called producers.

Animals get their energy from the food they eat and are called consumers. An antelope is a consumer because it eats grass

to get its energy. Similarly, a lion is a consumer because it eats antelope to get its energy.

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Question 1

Classify: Label each of the organisms below as either a producer or a consumer.

A food chain shows the �ow of energy from organism to organism in an ecosystem. A simple example of a food chain is:

grass → antelope → lion

As in the above example, food chains typically start with a producer, in this case grass. The consumer that eats the

producer is called a primary consumer (in this case, the antelope), and the consumer that eats the primary consumer is

called a secondary consumer (in this case, the lion).

Question 2

Identify: Label the Pleistocene food chain below with the terms primary consumer, secondary consumer and producer.

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When plants and animals die they return to the earth and become detritus – dead organic matter – which is eventually

consumed by decomposers such as fungi and bacteria. Detritus is an important element in many food chains, as you're

about to see.

Credit: Dead stu�: The secret ingredient in our food chain – John C. Moore by TED-Ed (YouTube).

0:00 / 3:50

Question 3

Notes: Use this space to take notes for the video.

Note: This is not a question and is optional, but we recommend taking notes – they will help you remember the main points of the

video and also help if you need to come back to answer a question or review the lesson.

Question 4

Recall: Over 30% of plant matter across the globe is eaten

while it's still alive.

True

False

I'm not sure

Question 5

Recall: Most organisms in an ecosystem are directly or

indirectly nourished by dead matter, or detritus.

True

False

I'm not sure

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Question 6

Recall:  What's the di�erence between a green food chain and a brown food chain?

Question 7

Draw: The above video showed how multiple food chains can be joined together to make a food web. Use the arrow tool

to show the �ow of energy between the organisms below to create a food web. Use green arrows to show green food

chains, brown arrows to show brown food chains and red arrows to show the �ow of energy to generate the detritus.

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Process: Food Chains

The arrows in a food chain show how energy is transferred through an ecosystem. Only about 10% of an organism's energy

is passed on to the organism that consumes it. The rest is used up in growth, reproduction, repair and movement, to name

a few. 

Question 1

Calculate: Energy is measured in joules. If the producer in a particular food chain has 13,500 joules of energy, how much

energy will be passed on to the secondary consumer?

Hint: First work out how much would be passed on to the primary consumer.

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Credit: From the top of the food chain down: Rewilding our world – George Monbiot by TED-Ed (YouTube).

0:00 / 5:27

Question 2

Notes: Use this space to take notes for the video.

Note: This is not a question and is optional.

Question 3

Describe: What impact did reintroducing wolves into Yellowstone National Park have on its ecosystem?

Left: A wolf in Yellowstone National Park. Right: Yellowstone National Park on a world map.

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Question 4

Re�ect: What can we learn about the relationship between species in a food web from the reintroduction of wolves into

Yellowstone National Park?

Question 5

Explain: Rewilding is the process of restoring ecosystems to their natural state – for example, restoring farmland into the

forests that were originally cut down to create the farmland. Why can't rewilding bring back the megafauna?

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Project: Food Chains

Saving endangered animals

The Tasmanian devil, bilby and corroboree frog are all endangered Australian species.

Is it worthwhile discovering the causes behind the extinction of the megafauna? If scientists can prove that their extinction

was caused by humans, would it change how we treat endangered animals today?

Many organizations want governments to do more to help endangered animals. To do this, they need to raise awareness

among the general public and encourage people to contact a government representative to plead their case.

The more people that contact the government, the more likely the government is to take notice. 

Question 1

Create: Write a letter or design a presentation that could be sent to a government representative outlining your concerns

about the extinction of a local endangered animal. The following checklist will guide you in writing your letter or

presentation:

1. Choose a local endangered animal. The following websites may help you: EPBC Act List of Threatened

Fauna (Australia), Endangered Species Foundation (New Zealand), U.S. Fish and Wildlife Service (United States) or

IUCN Red List (International).

2. Choose an appropriate government representative.

3. Find out the postal address of your chosen government representative.

4. Research information about your endangered species, such as how many individuals of this species are currently

alive and why the population is in decline.

5. Think about whether or not you can refer to the death of the megafauna in your letter or presentation to

strengthen your argument.

6. Think about what you want the government to do and be explicit about this in your letter or presentation.

Use a formal style of writing and do your best to convince your government to take action!

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Career: Food Chains

Professor Alan Cooper is an evolutionary biologist who loves to play detective. He uses ancient DNA to solve evolutionary mysteries that have stumped the world for decades.

Alan grew up in New Zealand, where as a child he would

roam the wilderness with his father, a palaeontologist, and

his mother, a botanist. They would hunt for fossils, explore

caves, study plants, and talk about the geology of the

landscape. It was during a caving expedition that he found

bones from the now extinct moa – a large �ightless bird

similar to the emu. The discovery helped him realize that

he could combine his love for caving with scienti�c

research. Today, Alan analyses DNA extracted from

ancient bones, teeth, leaves, seeds and faeces aged

anywhere from 100 to 300,000 years old. Using this DNA,

he reveals long-lost details about extinct animals and

humans.

In one of his studies, Alan looked back into the lives of ice

age mammoths – elephant-like animals with shaggy hair

that weighed up to 8,000 kg. Mammoths moved into the

Arctic about two million years ago and had to adapt to the

cold. Using DNA from mammoth bones, Alan cultivated

mammoth haemoglobin, the protein in blood that carries

oxygen around the body. Haemoglobin normally gets

'sticky' at cold temperatures and doesn't release oxygen to

the body's tissues easily. But Alan found that mammoth

haemoglobin had special adaptations that allowed it to

function at colder temperatures, which would have been

critical for the mammoths' survival.

Alan does a lot of his work from his lab at Adelaide

University in South Australia. However, his search for

specimens takes him travelling around the world,

particularly to cold places "because that’s where bones are

preserved the best". He doesn't unearth all specimens in

the �eld, though – he says "you’d be surprised what you

can �nd in the back room of a museum!".

For Alan, the joy of his job as an evolutionary biologist lies

in studying "amazing animals and amazing things that

have happened and using DNA to get a completely new

way of looking at them”.

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Research: Alan's passion for caving as a boy helped lead him into a career as an evolutionary biologist. What activities do

you enjoy in your spare time? What career in science do you think best matches your passion?

Hint: If you can't think of many di�erent careers in science, the career lists on the Science Buddies website may help you.

Image credits

Introduction: Woolly mammoths, Mauricio

Antón/Wikipedia; Process: Getty Images, wolf in

Yellowstone National Park, Wikipedia; Project: iStock, Gallo

Images/Getty Images & National Geographic/Getty Images;

Career: University of Adelaide/Randy Larcombe. Test:

phytoplankton, Detlef Kramer;  northern krill, Øystein

Paulsen; Blue whale, NOAA.

Question 1

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Test: Food Chains

Note: There may be more than one correct answer to the multiple-choice questions below.

Question 1 (1 mark)

Organisms that are able to make their own food are

called: 

photosynthesis

producers

consumers

detritus

I'm not sure

Question 2 (1 mark)

Plants create glucose using energy from ____________ in a

process called ____________ .

soil, photosynthesis

sugar, absorption

soil, growth

sunlight; photosynthesis

I'm not sure

Questions 3 – 8 refer to the following ocean food chain.

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Question 3 (1 mark)

Phytoplankton are microscopic organisms that �oat in the

surface waters of the ocean, where they carry out

photosynthesis. They live by:

consuming other, smaller organisms

using energy from chemicals in the seawater

using energy from sunlight

consuming small particles of dead �sh remains

I'm not sure

Question 4 (1 mark)

Which organisms in the food chain are producers?

phytoplankton

krill

blue whales

None of the above

I'm not sure

Question 5 (1 mark)

Which organisms in the food chain are consumers:

phytoplankton

krill

blue whale

None of the above

I'm not sure

Question 6 (1 mark)

In this food chain, the blue whales are:

producers

decomposers

primary consumers

secondary consumers

I'm not sure

Question 7 (1 mark)

Consumers get their energy:

by converting it from the energy in sunlight

by producing it themselves using chemical

processes

from animals, but not plants, that they eat

from plants, but not animals, that they eat

from plants and/or animals that they eat

I’m not sure.

Question 8 (1 mark)

The food chain above is an example of a ____________ food

chain because ____________ .

blue; it is in the ocean

green; it starts with a living organism

green; sea water sometimes looks green

brown; phytoplankton are brown

I'm not sure

Question 9 (1 mark)

In land ecosystems, __________ plant matter gets eaten

while the plants are still alive.

all

most

only a small proportion of

no

I'm not sure

Question 10 (1 mark)

Once a plant dies, there is no useful energy in its remains.

True

False

I'm not sure

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Question 11 (1 mark)

Organisms such as fungi and bacteria that live on dead

organic matter are called:

decomposers

detritus

consumers

scum

I'm not sure

Question 12 (1 mark)

Which of the following are features of brown food chains?

They end with animals that have fur (typically

brown)

They always include decomposers

They always include detritus

They always include green plants

I’m not sure

Question 13 (1 mark)

A plant grows from a seed and after several months,

�owers. A woolly mammoth pulls the entire plant out of

the ground and eats it.

All of the energy that the plant converted from sunlight in

its life is now in the mammoth.

True

False

I'm not sure

Question 14 (1 mark)

You eat some mushrooms. You are part of a:

green food chain, because mushrooms are

living things

green food chain, because mushrooms get

energy directly from the Sun

brown food chain, because mushrooms grow

in soil

brown food chain, because mushrooms get

their energy from detritus

I'm not sure

Question 15 (1 mark)

Food webs have multiple food chains within them, but

within any web there are only ever brown or green food

chains, not both.

True

False

I'm not sure

Question 16 (1 mark)

The ultimate source of energy in detritus is:

soil

bacteria

the Sun

plants

animal waste

I'm not sure

Question 17 (1 mark)

Learning goal 1: Describe where plants and animals get their energy to survive, and how.

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Total available marks: 19

Question 18 (1 mark)

Learning goal 2: Describe three roles organisms play within green food chains.

Question 19 (1 mark)

Learning goal 3: What is the di�erence between green and brown food chains? Explain.

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