In this practical students will be able to see photosynthesis and cellular respiration in action.

This test can be done with and without snails. However both ways will demonstrate how photosynthesis produces oxygen, and cellular respiration uses oxygen and create Carbon dioxide.

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• Elodea and snails
• Just Elodea
• Questions

Elodea and Snails

Materials per group

• 8 x Test tubes
• 2 x test tube rack
• 6 x Elodea
• 6 x Snail
• Bromthymol blue
• Aluminium foil or a box
• 8 x test tube stoppers

Method

1. Get the 8 test tubes and label the first four

1D, 2D, 3D and 4D.

1. Label the next 4:

1L, 2L, 3L and 4L.

1. Pour Bromthymol blue into all the test tubes.
2. Place one elodea plant in 2D, 3D, 2L and 3L
3. Place one snail in 3D, 4D, 3L and 4D
4. Place stoppers on all the test tubes.
5. Test tubes marked L are left in the Light.
6. Test tubes marked D are left in the dark (wrapped in aluminium foil or placed in a box)

Questions

State the hypothesis?

What is the independent variable?

What is the dependant variable?

What is the control?

What is Bromthymol blue and why are we using it?

What gas does the snail release

What gas does Elodea release

Why do we place some test tubes in the light, while other are placed in the dark. Explain how this might affect the results.

If no carbon dioxide is present in your test tube it will be a ____________ colour. If a medium amount of CO2 is present, your test tube will be a _______________ colour. If a large amount of CO2 is present, your test tube will be __________________.

Explain three reasons why plants and animals rely on each other (think back to ecology)

In what cellular organelles is each of the two processes occurring? Are plant and animals both equipped to do cellular respiration and photosynthesis or not? Explain

What is the chemical and worded equation for Photosynthesis?

What is the worded equation for the light and dark stages of photosynthesis?

What is the chemical and worded equation for cellular respiration

Are there any other organisms, other than plants or snails which could have altered the results of the experiment?

Under what circumstances would you expect cellular respiration to stop in all tubes?  

How was carbon dioxide supplied to the plant?

Just Elodea

Materials per group

• 4 x Test tubes
• 2 x test tube rack
• 2 x Elodea
• Bromthymol blue
• Aluminium foil

Method

1. Get the 4 test tubes and label the first two

1D and 2D.

1. Label the next 2:

1L and 2L.

1. Pour Bromthymol blue into all the test tubes.
2. Place one elodea plant in 2D and 2L, and nothing in 1D and 1L
3. Test tubes marked L are left in the Light.
4. Test tubes marked D are left in the dark (wrapped in aluminium foil or placed in a box)
5. Leave them over night and observe the change in bromthymol blue the next day.

Bromthymol blue?

So why do we use bromthymol blue? Well this is an indicator which changes colour in the presence of carbon dioxide.

Notice the video to the right. Bromthymol blue 0.4%, mixed with water creates a green liquid (You must mix it with water).

Watch what happens when I blow carbon dioxide into the beaker.

Notice the colour change.

WARNING: Plant respire at night, thus the Bromthymol blue might still be yellow in the early morning.