IGCSE Biology

Section 4: Ecology and the environmentc. Cycles within Ecosystems

2. Carbon Cycle4.9 describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion

Ref:Pg. 163 15.10 “Decomposers release minerals from dead organisms”

15.11 “Carbon is recycled”

Carbon Cycle AnimationsFor each animation, you are only interested in finding out about the four words from the objectives. After you have watched the animations you should be able to describe in detail each of the following processes and where they occur.1. Respiration2. Photosynthesis3. Decomposition4. Combustion

Similar to the one you watch on the water cycle.Work through animationTry the quiz at the end.http://epa.gov/climatechange/kids/carbon_cycle_version2.html

Detailed carbon cycle animation with audio explanationshttp://www.nodvin.net/snhu/SCI219/demos/Chapter_3/Chapter_03/Present/animations/51_1_2_1.html

Another detailed site, has quite a few numbers that you DON’t need to remember.http://www.ebex21.co.nz/enlargement.asp

In the above diagram can you identify and explain the four processes from your objective:

1. Respiration2. Photosynthesis3. Decomposition4. Combustion

Decomposers, like all living things, produce carbon dioxide during respiration. The carbon dioxide is released into the atmosphere where it may be used by plants during photosynthesis to make sugars and starch.

1. Carbon is in the air in the form of Carbon Dioxide

2. Plants take in carbon dioxide during photosynthesis; they use it to produce glucose and oxygen.

3. When animals digest plant or animal material the glucose is broken down in the process of respiration. The carbon is then breathed out as carbon dioxide.

4. Plants also release carbon dioxide at night in the process of respiration.

5. During the day plants photosynthesis quicker than they respire so they take in more carbon dioxide than they produce.

6. Plants balance the carbon dioxide and oxygen for earth.

7. The burning of fossil fuels contribute to the greenhouse effect, which releases carbon dioxide into the atmosphere.

8. Photosynthesis takes in the carbon dioxide from the air and returns oxygen to the air. Respiration takes in oxygen and returns carbon dioxide.

9. Decomposers also respire producing carbon dioxide.

Carbon Cycle – Quick Self Test

Use the diagram on the following page, along with the following text to fill in the missing words in BOTH the text and on the diagram.

You may use the same word more than once.

In the atmosphere carbon is in the form of a gas called 1. _______________________. Green plants are the only living organisms which can convert this gas into an organic compound. They do this by the process of 2. ____________________, which produces 3. ____________________ and oxygen. The oxygen is released back out into the atmosphere. The 3. ____________________ is stored in plants in the form of starch and can be transferred to animals through 4. ____________________. Animals need the 3. ____________________ for the important process of 5. ____________________, which will release the 1. ____________________ back into the atmosphere.

All plants and animals will eventually die and be broken down by fungi and bacteria which are 6. ____________________. As plants and 6. ___________________ are living organisms they also carry out the process of 7. ____________________, which releases 1. ____________________ back into the atmosphere.

8. ____________________ is the process by which dead vegetation from millions of years ago formed 9. ____________________ such as oil, coal, peat and gas. During 10. ___________________, the 9. ____________________ are burnt and release 1. ____________________ into the atmosphere.

Carbon Cycle – Quick Self Test

1._____________ in the atmosphere

3. ________ is stored as starch

Plants and animals will eventually die and be broken down by 6. _________________________

5.

4.

2.

9. ___________________ were produced millions of years ago from the remains of dead vegetation.

8.

10.

7.

7.

Questions

1. In a stable community, the processes which remove materials are balanced by processes which return materials. These materials are constantly cycled within the community.

a. Name:

i. process X (1)

ii. process Y (1)

iii. the group of organisms Z which bring about decay. (1)

b. Choose words from this list to complete the sentences below. (3)

decomposition fermentation microbes plants purification sewage

Waste from human bodies is treated at a ...................................................... works.

It is broken down into simpler substances by ...........................................................

This process is called .................................................................................................

2. A gardener was told to let more air into his heap of garden waste.

a. Explain why this would help decay. (1)

b. Write down two further conditions which speed up the decay of garden waste in a compost heap. (2)

3. Mushrooms can be grown on compost. The compost is made by mixing straw and manure which rot down.

a. Write down three things which are needed for the straw and manure to rot.

(3)

b. Some substances, like plastic, are not biodegradable. What does this mean? (1)

4. The diagram shows part of the carbon cycle.

What are the processes shown as A, B, C and D? (4)

(i) Process A is ................................................................................................................

(ii) Process B is ................................................................................................................

(iii) Process C is ...............................................................................................................

(iv) Process D is ...............................................................................................................

5. Use words from the box to complete the sentences about the water cycle. (6)

boils condenses evaporates freezesmelts rain sea Sun wind

Water .............................. from the surface of the ............................ . Heat from the ................................. speeds up this process and so does the .................................. . Water vapour in the atmosphere cools down and ........................ to form billions of tiny water droplets. Some of the droplets join together and fall as ........................ .

6. The diagram shows some processes in the carbon cycle.

a. What is the name of substance X? (1)

b. Which process, A, B, C, D or E, takes the longest? (1)

7. Compost heaps are used to recycle waste plant materials.

Complete the sentences by choosing the correct words from the box. (4)

The waste plant materials ............................. because they are broken down by microorganisms. The waste plant materials are broken down faster when the conditions are ................................ and ............................... . This process releases substances that can be used by other plants to .................................. .

8. The diagram below shows the mass of carbon involved each year in some of the processes in the carbon cycle.

a. Complete the equation for plant respiration. (2)

b. Calculate the mass of carbon removed from the atmosphere each year. (Show your working.) (1)

c. Calculate the percentage of this total which is removed by the photosynthesis of land plants. (Show your working.) (1)

d. Calculate the net gain of carbon by the atmosphere in one year. (Show your working.) (2)

9. The diagram shows some of the stages by which materials are cycled in living organisms.

a. In which of the stages, A, B, C or D: (3)

i. are substances broken down by microbes; ....................

ii. is carbon dioxide made into sugar; ....................

iii. are plants eaten by animals? ....................

10. Each autumn, many trees lose their leaves.

a. Describe how carbon compounds in the leaves can be recycled so that they can be used again by the trees. (4)

b. Give two environmental conditions which speed up the processes you have described in part (a). (2)