JESEI
teacher’s notes student’s notes

Cycling carbon: seeing how plants use carbon dioxide in the lab

(teacher’s notes)

Level

This material is designed for students aged 12 to 14 (years 8 and 9) .

Topic

This activity is one of five aimed to teach students about the nature of carbon, the different types of compounds it exists in (eg charcoal,

glucose, carbon dioxide), the biochemical reactions it takes part in (photosynthesis and respiration), the range of processes that carbon and

carbon compounds are involved in on Earth, and how these link together to form the carbon cycle.

The other activities are

Carbon cycle: where is this crucial carbon?; a teacher-led discussion interspersed with demonstrations in which the teacher burns a range of

materials over a Bunsen flame, forming charcoal, to illustrate that they contain carbon.

Carbon cycle in the lab: carbon products and the processes that link them; which involves working in small groups to place examples of the

carbon cycle products in the correct places on a diagram of the cycle.

Carbon cycle: releasing dinosaur breath in the lab; a short pupil practical exploring the storage of carbon in the fossils that make up limestone

and chalk.

Carbon cycle: exchanging carbon dioxide between the atmosphere and ocean; a short pupil practical comparing how well carbon dioxide

dissolves in sea water compared with fresh water.

Context

An understanding of the carbon cycle is essential to the debate about global warming, an environmental issue that most students will have

heard about. Since the Earth’s atmosphere formed, it seems to have always contained carbon dioxide in varying amounts Carbon dioxide is a

‘greenhouse gas’ through which light radiation can pass but which absorbs some of the heat radiation produced by light irradiating the Earth’s

surface. This causes the Earth’s surface and atmosphere to be warmer than it would otherwise be and without the ‘greenhouse effect’ the Earth

would probably be completely frozen. Humans, as all life on Earth, have always been part of the carbon cycle, but now (since the industrial

revolution) the large scale burning of oil, coal and natural gas, along with deforestation, is leading to increasing atmospheric carbon dioxide

levels. This in turn is related to an enhanced greenhouse effect and consequent climatic change. An understanding of the factors affecting

global warming leads to an understanding of the measures required to reduce their impact. This can link into economic and political debates

on the subject. Students should have already covered photosynthesis and respiration in order to do this activity effectively.

Teaching points

This activity demonstrates the uptake of carbon dioxide by plants, using Elodea as the example. Elodea is a pond plant that lives below the

water surface and thus extracts dissolved carbon dioxide from the water rather than directly from the atmosphere as terrestrial plants do.

Carbon exchange between living things and the atmosphere mostly happens through photosynthesis and respiration. During the growing

season leaves take up carbon dioxide. Carbon is stored in the living biomass.

Students should work in pairs for this activity.

Apparatus and materials

Each group of pupils will need:

3 boiling tubes

A drinking straw

Boiled water

Phenol red indicator (which is red and goes yellow in the presence of carbon dioxide)

A sprig of Elodea

Bright light

Carbon cycle diagram (Figure 1)

Safety

Pupils should blow through the straw and not suck. Only one person in the group should use the straw. Dispose of the straws at the end of the

activity.

Activity

Pour about 2- 3 cm depth of water into each boiling tube (the same depth in each).

Add a few drops of indicator to each.

Breathe out gently through the straw into two of the tubes until the indicator colour changes to yellow.

Put the sprig of Elodea into one tube.

Place all three in bright light and leave them for about 40 minutes.

After this time (during which the students could be doing another related activity), they should observe the boiling tubes’ contents and record

their observations by answering the following questions:

Q 1. What happened to the indicator in the tube containing Elodea? = Went back to red.

Q 2. What does this mean? = CO2 gone/decreased.

Q 3. How do you know it was due to the Elodea? = Because there was no change in other tube.

Q 4. What caused this to happen? = Photosynthesising Elodea took in CO2.

Q 5. Shade in the stage of the carbon cycle on the diagram that this relates to.

Q 6. State two ways in which this carbon can be returned to the atmosphere. = Decay of plant when dead, respiration by plant. Animal eating

plant and respiring/ decaying.

JESEI
teacher’s notes student’s notes

Cycling carbon: seeing

how plants use carbon

dioxide in the lab

(teacher’s notes)

Level

This material is designed for students aged 12 to

14 (years 8 and 9) .

Topic

This activity is one of five aimed to teach

students about the nature of carbon, the

different types of compounds it exists in (eg

charcoal, glucose, carbon dioxide), the

biochemical reactions it takes part in

(photosynthesis and respiration), the range of

processes that carbon and carbon compounds

are involved in on Earth, and how these link

together to form the carbon cycle.

The other activities are

Carbon cycle: where is this crucial carbon?; a

teacher-led discussion interspersed with

demonstrations in which the teacher burns a

range of materials over a Bunsen flame, forming

charcoal, to illustrate that they contain carbon.

Carbon cycle in the lab: carbon products and the

processes that link them; which involves working

in small groups to place examples of the carbon

cycle products in the correct places on a diagram

of the cycle.

Carbon cycle: releasing dinosaur breath in the

lab; a short pupil practical exploring the storage

of carbon in the fossils that make up limestone

and chalk.

Carbon cycle: exchanging carbon dioxide

between the atmosphere and ocean; a short

pupil practical comparing how well carbon

dioxide dissolves in sea water compared with

fresh water.

Context

An understanding of the carbon cycle is essential

to the debate about global warming, an

environmental issue that most students will have

heard about. Since the Earth’s atmosphere

formed, it seems to have always contained

carbon dioxide in varying amounts Carbon

dioxide is a ‘greenhouse gas’ through which light

radiation can pass but which absorbs some of the

heat radiation produced by light irradiating the

Earth’s surface. This causes the Earth’s surface

and atmosphere to be warmer than it would

otherwise be and without the ‘greenhouse effect’

the Earth would probably be completely frozen.

Humans, as all life on Earth, have always been

part of the carbon cycle, but now (since the

industrial revolution) the large scale burning of

oil, coal and natural gas, along with

deforestation, is leading to increasing

atmospheric carbon dioxide levels. This in turn is

related to an enhanced greenhouse effect and

consequent climatic change. An understanding of

the factors affecting global warming leads to an

understanding of the measures required to

reduce their impact. This can link into economic

and political debates on the subject. Students

should have already covered photosynthesis and

respiration in order to do this activity effectively.

Teaching points

This activity demonstrates the uptake of carbon

dioxide by plants, using Elodea as the example.

Elodea is a pond plant that lives below the water

surface and thus extracts dissolved carbon

dioxide from the water rather than directly from

the atmosphere as terrestrial plants do.

Carbon exchange between living things and the

atmosphere mostly happens through

photosynthesis and respiration. During the

growing season leaves take up carbon dioxide.

Carbon is stored in the living biomass.

Students should work in pairs for this activity.

Apparatus and

materials

Each group of pupils will need:

3 boiling tubes

A drinking straw

Boiled water

Phenol red indicator (which is red and goes

yellow in the presence of carbon dioxide)

A sprig of Elodea

Bright light

Carbon cycle diagram (Figure 1)

Safety

Pupils should blow through the straw and not

suck. Only one person in the group should use

the straw. Dispose of the straws at the end of the

activity.

Activity

Pour about 2- 3 cm depth of water into each

boiling tube (the same depth in each).

Add a few drops of indicator to each.

Breathe out gently through the straw into two

of the tubes until the indicator colour changes to

yellow.

Put the sprig of Elodea into one tube.

Place all three in bright light and leave them

for about 40 minutes.

After this time (during which the students could

be doing another related activity), they should

observe the boiling tubes’ contents and record

their observations by answering the following

questions:

Q 1. What happened to the indicator in the

tube containing Elodea? = Went back to red.

Q 2. What does this mean? = CO2

gone/decreased.

Q 3. How do you know it was due to the

Elodea? = Because there was no change in other

tube.

Q 4. What caused this to happen? =

Photosynthesising Elodea took in CO2.

Q 5. Shade in the stage of the carbon cycle on

the diagram that this relates to.

Q 6. State two ways in which this carbon can

be returned to the atmosphere. = Decay of plant

when dead, respiration by plant. Animal eating

plant and respiring/ decaying.