Lesson 11 The Breathing Leaf
Completion requirements
The Breathing Leaf
The leaf is the location of both photosynthesis and gas exchange in a plant.
The leaf is designed not only for photosynthesis, but for gas exchange as well. This gas exchange allows photosynthesis to happen more effectively and ensures the plant has the materials it needs.
In order for photosynthesis to occur, carbon dioxide must be brought into the plant in the presence of sunlight. When sunlight hits the leaf, the guard cells on the underside of the leaf open the stomata to allow carbon dioxide to enter the leaf.
This carbon dioxide is stored in the spongy mesophyll tissue until it is needed for photosynthesis in the palisade tissue cells. The palisade tissue cells use both the sunlight and the carbon dioxide (along with water from the roots) to produce
glucose and oxygen. The oxygen is then released through the stomata to the environment or transported down the stem to the rest of the plant through the ground tissue. Lenticels also allow for gas exchange in locations other than the leaf.
In the next lesson, we will look at the transport of materials through the xylem and phloem vascular tissues.
In the next lesson, we will look at the transport of materials through the xylem and phloem vascular tissues.
A11.10 Gas exchange through the stomata
Virtual Lab
Plants and Snails © Explore Learning
Background Information:
In this lab, you will place plants and snails in sealed tubes to see what gases they emit through photosynthesis and cellular respiration.
Plants and Snails © Explore Learning
Background Information:
Please note: if you scroll down while in the Gizmo you will see a list of questions. You DO NOT need to complete these questions. You are able to complete them for extra practice if you would like.
- Launch the Gizmo by clicking on the play button.
- Check off the “Show oxygen and «math»«msub»«mi»CO«/mi»«mn»2«/mn»«/msub»«/math» values (in ppm)” box.
- Place one Elodea sprig in test tubes A and B.
- Place one snail in test tubes B and C.
- Leave test tube D empty as your control.
- Move the oxygen and carbon dioxide reader to each of the four test tubes and record the original levels of these chemicals.
- Click on the play button at the bottom of your screen.
- Record the oxygen and carbon dioxide levels in each of the four test tubes. Write down what happened to the plants and snails in each tube.
- Click the reset button at the bottom of your screen and turn off the lights by clicking on the light switch.
- Click the play button again.
- Record the oxygen and carbon dioxide levels in each of the four test tubes. Write down what happened to the plants and snails in each tube.
- Please return to the top of this page and click on analysis to complete the analysis questions.
©Explore Learning
A11.12 Light Switch
A11.12 Light Switch
- What happened to the levels of carbon dioxide and oxygen in each tube with the lights on? Why did this happen?
Tube A: Carbon dioxide got very low and oxygen got very high. This is because the carbon dioxide was used for photosynthesis and converted into oxygen.
Tube B: Carbon dioxide and oxygen stayed very close to where they started. This is because the plant converted carbon dioxide to oxygen, and the snail converted the oxygen back to carbon dioxide.
Tube C: Carbon dioxide got very high and oxygen got very low. This is because the snail used the oxygen to breathe and perform cellular respiration, converting the oxygen into carbon dioxide.
Tube D: Nothing changed, as it was the control.
Tube B: Carbon dioxide and oxygen stayed very close to where they started. This is because the plant converted carbon dioxide to oxygen, and the snail converted the oxygen back to carbon dioxide.
Tube C: Carbon dioxide got very high and oxygen got very low. This is because the snail used the oxygen to breathe and perform cellular respiration, converting the oxygen into carbon dioxide.
Tube D: Nothing changed, as it was the control.
- What happened to the levels of carbon dioxide and oxygen in each tube with the lights off? Why did this happen?
Tube A: Carbon dioxide increased and the oxygen decreased. This is because the plant could not perform photosynthesis in the dark, so no oxygen was created. The plant was only able to perform cellular respiration.
Tube B: Carbon dioxide got very high and the oxygen got very low. This is because the plant could not perform photosynthesis, so both the plant and the snail performed cellular respiration. This used up the oxygen and converted it to carbon dioxide.
Tube C: Carbon dioxide got very high and oxygen got very low. This is because the snail used the oxygen to breathe and perform cellular respiration, converting the oxygen into carbon dioxide.
Tube D: Nothing changed, as it was the control.
Tube B: Carbon dioxide got very high and the oxygen got very low. This is because the plant could not perform photosynthesis, so both the plant and the snail performed cellular respiration. This used up the oxygen and converted it to carbon dioxide.
Tube C: Carbon dioxide got very high and oxygen got very low. This is because the snail used the oxygen to breathe and perform cellular respiration, converting the oxygen into carbon dioxide.
Tube D: Nothing changed, as it was the control.
- What happened to the plants and snails in each of the tubes at the end of each experiment? Why did this happen?
In the light experiment, the plant in tube A and the snail in tube C died. The plant and snail in tube B survived. This is because the snail and plant in tube B were performing complimentary processes, and so the levels of carbon dioxide
and oxygen were able to stay balanced. In tube A, the plant ran out of carbon dioxide and thus starved. In tube C, the snail ran out of oxygen.
In the dark experiment, the plant in tube A survived, but the plants and snails in tubes B and C did not. The plant in tube A only used a bit of oxygen for cellular respiration and so did not run out of either oxygen or carbon dioxide. The plant and snail in tube B ran out of oxygen for cellular respiration, as the plant was not able to perform photosynthesis to replenish the oxygen. The snail in tube C also ran out of oxygen.
In the dark experiment, the plant in tube A survived, but the plants and snails in tubes B and C did not. The plant in tube A only used a bit of oxygen for cellular respiration and so did not run out of either oxygen or carbon dioxide. The plant and snail in tube B ran out of oxygen for cellular respiration, as the plant was not able to perform photosynthesis to replenish the oxygen. The snail in tube C also ran out of oxygen.
Around 23 to 25 degrees Celsius was the best temperature no matter what light colour was used. You will learn more about how temperature affects photosynthesis in this lesson.