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Understand Energy Transfer in the Carbon Cycle

Worksheet Overview

QUESTION 1 of 10

We eat food to make sure that we have enough energy to survive. Over the course of the evolution of all organisms, we have become more and more efficient - saving energy where we can, so we have to waste less energy hunting food. There is one problem, however - where does that energy come from in the first place? 

 

The Sun is the ultimate source of energy for all organisms.

Plants are producers because they make their own food. Part of the energy they make this way is transferred to the herbivore animals that eat plants, the primary consumers.

Secondary consumers get their energy from eating the herbivores and they are called carnivores because they eat other animals.

There are also tertiary consumers (and yes you guessed right... they eat secondary consumers!).

Some animals (like humans) eat both plants and animals and they are called omnivores

 

The feeding relationships described above are shown through food webs and food chains which, in turn, can be shown with the use of pyramids of numbers and biomass.

Not much of the energy made initially by plants is transferred to animals. A lot of it is lost during the transfer and by the daily functions of organisms.

Some elements like carbon and nitrogen are recycled in the environment, with all this eating!

Let's explore all this in more detail in the questions that follow.

This is a food chain. The arrows start from the organism eaten and point to the organism that eats it.

A food chain

The plants and animals in a food chain can be shown in pictures or just with their names written before and after the arrows, so don't be confused if you see just names in your exam. Even if you have not heard of those organisms before, you know a lot about them because of their position in the food chain or the food web. Remember, you know what they eat and what eats them!

 

 Match the organisms above with their status in the food chain. 

Column A

Column B

Grass seed
Primary consumer
Vole
Secondary consumer
Barn owl
Producer

This is a food web. It is made of different chains put together.

 

Tick any options that show a correct food chain from this food web.

A food web 

Trees → moose → hawk

Shrubs → rabbit → snake

Grasses → insects → frog → owl → hawk

Grasses → mice → snake → hawk

Grasses → mice → snake → moose

Food pyramids show the different trophic levels of a feeding relationship. Trophic means food in Greek, so do you see the connection? Energy passes from one trophic level to another. One organism of a food chain occupies a trophic level. Here is a pyramid of biomass:

 

A pyramid of biomass

 

Look at the pyramid of biomass. Tick the food chain it was made from.

Elder tree → aphids → lacewings → starling

Elder tree → lacewings → aphids → starling

Elder tree → aphids → lacewings → starling → hawk

Look at the pyramid of numbers from the same food chain. The sequence of the organisms is the same, but the boxes differ in size. It does not even look like a pyramid anymore! Why

 

Pyramid of numbers

 

Note: Pyramids of biomass show the living (bio) mass that passes from organism to organism and that is a better reflection of the amount of energy that passes through. Pyramids of numbers are good for showing the actual numbers of organisms (or a relationship between the numbers).

There are five elder trees that the aphids feed on

One elder tree feeds a large number of aphids. There is only one but it is massive

Many lacewings (but fewer than aphids) are the source of food for one starling

Too many starlings eat the lacewings

Check the pyramid of numbers below (at least this one looks like a pyramid!).

 

Pyramid of numbers

 

Which sentence describes the numbers of organisms correctly?

Many lettuce plants are eaten by snails which are eaten by fewer thrushes.The thrushes are eaten by one sparrowhawk

One lettuce feeds all those snails

One hundred sparrowhawks eat fifty thrushes

In a specific environment in the ocean, zooplankton creatures eat phytoplankton. Phytoplankton makes its own energy. Sardines feed on zooplankton and are eaten by dolphins and sharks.

 

Tick the food chains described here.

 

Do not panic in an exam if you have not heard of the organisms before. They always give you clues. Have a go at the answer and look at the explanation if you get it wrong.

Phytoplankton → zooplankton → sardines → shark

Phytoplankton → zooplankton → sardines → dolphin

Zooplankton → phytoplankton → sardines → shark

Phytoplankton → zooplankton → shark → dolphin

Remember pyramids of biomass? Here is one. Pay special attention to the energy units on the right hand side.

 

Tropic Levels

 

What do you notice?

 

Complete the sentence with one of the words below.

 

The energy passed from one trophic level to another __________.

Stays the same

Increases

Decreases

Plants use or lose most of the energy they make: about 90% of it. Some energy is lost through water evaporating into the atmosphere from the leaves and some energy is reflected back to the atmosphere as soon as it touches the leaf. A little bit of the Sun's energy is used in photosynthesis.

In animals, 90% of the energy they take from their food is also lost through heat and waste, or used for growth, movement and other functions. The efficiency of this energy transfer can be calculated using this formula:

 

Efficiency equation

 

If you multiply the result by 100, you will get the percentage of energy used.

The unit of energy is either joules (J), kJoules (1 kJ = 1000 J) or calories. Think of the problem below and put your maths hat on.

 

A cow takes 3056 kJ from the grass. 1022 kJ are lost through heat and 1909 kJ are lost in waste. Only 125 kJ are used for growth.

 

Calculate the energy efficiency of this energy transfer and tick the correct answers. 

0.04

4%

0.4

The Carbon Cycle

Carbon is recycled in the environment. There is already a lot of carbon in the atmosphere, mainly from burning fossil fuels. Plants use that carbon for photosynthesis, but plants, like animals, also respire, releasing more carbon.

When organisms die, their bodies decay and decompose. There are organisms called detritivores that feed on dead plants and animals, but some of the carbon from the bodies go back to the ground.

 

The carbon cycle

 

Study the picture carefully because you must be able to describe the carbon cycle.

 

Tick the ways in which carbon is released into the environment.

Photosynthesis

Respiration

Decay and decomposition

Burning fossil fuels

The Nitrogen Cycle

Like carbon, nitrogen is also recycled. There is nitrogen in the soil in the form of nitrates used by plants and also in proteins formed by plants and animals.

 

The nitrogen cycle

 

Look at the picture and choose the main source of nitrogen for plants.

Atmospheric nitrogen

Nitrogen from decaying material

Plant proteins

  • Question 1

This is a food chain. The arrows start from the organism eaten and point to the organism that eats it.

A food chain

The plants and animals in a food chain can be shown in pictures or just with their names written before and after the arrows, so don't be confused if you see just names in your exam. Even if you have not heard of those organisms before, you know a lot about them because of their position in the food chain or the food web. Remember, you know what they eat and what eats them!

 

 Match the organisms above with their status in the food chain. 

CORRECT ANSWER

Column A

Column B

Grass seed
Producer
Vole
Primary consumer
Barn owl
Secondary consumer
EDDIE SAYS
The grass seed is the plant and produces its own food using energy from the Sun - so it's called a producer! The vole consumes grass seed and is in turn consumed by the barn owl, so they are primary and secondary consumers, respectively.
  • Question 2

This is a food web. It is made of different chains put together.

 

Tick any options that show a correct food chain from this food web.

A food web 

CORRECT ANSWER
Grasses → insects → frog → owl → hawk
Grasses → mice → snake → hawk
EDDIE SAYS
If you found this tricky, it is possible that you missed something from the food web above. Although snakes do sometimes eat rabbits, in this food web there is no arrow from the rabbit to the snake so rabbits are not eaten by snakes in this specific environment. There is no arrow from the snake to the moose either, so moose do not eat snakes.
  • Question 3

Food pyramids show the different trophic levels of a feeding relationship. Trophic means food in Greek, so do you see the connection? Energy passes from one trophic level to another. One organism of a food chain occupies a trophic level. Here is a pyramid of biomass:

 

A pyramid of biomass

 

Look at the pyramid of biomass. Tick the food chain it was made from.

CORRECT ANSWER
Elder tree → aphids → lacewings → starling
EDDIE SAYS
Elder trees feed aphids which are eaten by lacewings. Lacewings are eaten by starlings. The organisms with the greatest biomass are the producers, then the primary consumers, then the secondary and so on!
  • Question 4

Look at the pyramid of numbers from the same food chain. The sequence of the organisms is the same, but the boxes differ in size. It does not even look like a pyramid anymore! Why

 

Pyramid of numbers

 

Note: Pyramids of biomass show the living (bio) mass that passes from organism to organism and that is a better reflection of the amount of energy that passes through. Pyramids of numbers are good for showing the actual numbers of organisms (or a relationship between the numbers).

CORRECT ANSWER
One elder tree feeds a large number of aphids. There is only one but it is massive
Many lacewings (but fewer than aphids) are the source of food for one starling
EDDIE SAYS
Did you understand this pyramid? The size of the boxes reflects the number of the organisms involved at each step of the food chain. There is only one elder tree that many aphids feed on and also many lacewings that are eaten by one starling. A pyramid of numbers will always start with the producer - there could be one or one million of them.
  • Question 5

Check the pyramid of numbers below (at least this one looks like a pyramid!).

 

Pyramid of numbers

 

Which sentence describes the numbers of organisms correctly?

CORRECT ANSWER
Many lettuce plants are eaten by snails which are eaten by fewer thrushes.The thrushes are eaten by one sparrowhawk
EDDIE SAYS
Many lettuce plants are eaten by snails which are, in turn, eaten by thrushes. There are fewer thrushes than there are snails. The thrushes are then eaten by one sparrowhawk. This is why the numbers are constantly going down.
  • Question 6

In a specific environment in the ocean, zooplankton creatures eat phytoplankton. Phytoplankton makes its own energy. Sardines feed on zooplankton and are eaten by dolphins and sharks.

 

Tick the food chains described here.

 

Do not panic in an exam if you have not heard of the organisms before. They always give you clues. Have a go at the answer and look at the explanation if you get it wrong.

CORRECT ANSWER
Phytoplankton → zooplankton → sardines → shark
Phytoplankton → zooplankton → sardines → dolphin
EDDIE SAYS
Right then, how did you get on with your detective work here? Here are the clues: phyto in Greek means plant (remember that because phytoplankton is used in exam questions). Zoo means animal. The question also tells you that phytoplankton make their own food, so it has to be a producer, i.e. a plant, which always goes first in a food chain. So options one and two are correct.
  • Question 7

Remember pyramids of biomass? Here is one. Pay special attention to the energy units on the right hand side.

 

Tropic Levels

 

What do you notice?

 

Complete the sentence with one of the words below.

 

The energy passed from one trophic level to another __________.

CORRECT ANSWER
Decreases
EDDIE SAYS
Only 10% of energy is transferred to the next trophic level, so the amount of energy decreases as you go up the food chain or the pyramid. This is why there can only be a limited number of top predators - there just isn't the energy to sustain them.
  • Question 8

Plants use or lose most of the energy they make: about 90% of it. Some energy is lost through water evaporating into the atmosphere from the leaves and some energy is reflected back to the atmosphere as soon as it touches the leaf. A little bit of the Sun's energy is used in photosynthesis.

In animals, 90% of the energy they take from their food is also lost through heat and waste, or used for growth, movement and other functions. The efficiency of this energy transfer can be calculated using this formula:

 

Efficiency equation

 

If you multiply the result by 100, you will get the percentage of energy used.

The unit of energy is either joules (J), kJoules (1 kJ = 1000 J) or calories. Think of the problem below and put your maths hat on.

 

A cow takes 3056 kJ from the grass. 1022 kJ are lost through heat and 1909 kJ are lost in waste. Only 125 kJ are used for growth.

 

Calculate the energy efficiency of this energy transfer and tick the correct answers. 

CORRECT ANSWER
0.04
4%
EDDIE SAYS
How did you manage with this complicated maths related question? It's just a question of using the equation given: energy efficiency = energy used ÷ energy supplied The energy used = 125 kJ The energy supplied = 3056 kJ energy efficiency = 125 ÷ 3056 = 0.04 Or, we can turn it into a percentage by multiplying it by 100 = 4%
  • Question 9

The Carbon Cycle

Carbon is recycled in the environment. There is already a lot of carbon in the atmosphere, mainly from burning fossil fuels. Plants use that carbon for photosynthesis, but plants, like animals, also respire, releasing more carbon.

When organisms die, their bodies decay and decompose. There are organisms called detritivores that feed on dead plants and animals, but some of the carbon from the bodies go back to the ground.

 

The carbon cycle

 

Study the picture carefully because you must be able to describe the carbon cycle.

 

Tick the ways in which carbon is released into the environment.

CORRECT ANSWER
Respiration
Decay and decomposition
Burning fossil fuels
EDDIE SAYS
Photosynthesis is the only wrong answer because during this process plants take carbon from the atmosphere in the form of carbon dioxide. Carbon dioxide is also taken in by the sea, and the animals that use it make shells.
  • Question 10

The Nitrogen Cycle

Like carbon, nitrogen is also recycled. There is nitrogen in the soil in the form of nitrates used by plants and also in proteins formed by plants and animals.

 

The nitrogen cycle

 

Look at the picture and choose the main source of nitrogen for plants.

CORRECT ANSWER
Nitrogen from decaying material
EDDIE SAYS
Nitrogen in decaying material and animal waste is the main source of nitrogen for plants. Bacteria break down the plant material so that it is able to be used by other plants and animals. How did you feel about this activity? Don't worry if you found some of the later questions a bit tricky - there is a lot to remember with the carbon and nitrogen cycles. The more you study the diagrams on these last two questions, the easier it should be to understand the processes that are taking place.
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