Lesson 11 The Breathing Leaf
| Site: | MoodleHUB.ca đ |
| Course: | Science 10 [5 cr] - AB Ed copy 1 |
| Book: | Lesson 11 The Breathing Leaf |
| Printed by: | Guest user |
| Date: | Sunday, 7 September 2025, 6:46 PM |
Introduction
Plants, just like animals, exchange gases. They exchange oxygen for carbon dioxide.
A11.1 The mitochondria is the location of cellular respiration.
All plant cells undergo cellular respiration, just like animal cells. This is the process where glucose and oxygen are used to create energy, carbon dioxide, and water. It is essentially the opposite process to photosynthesis. The chemical equation for
cellular respiration is
This process is used to create the energy the cells need to perform the basic life functions. To review what cells use energy for, reread Lesson 4 on the parts of the cell and Lesson 6 on the cell membrane.
Plants create all the glucose they need through photosynthesis and, depending on the amount of sunlight available, produce all the oxygen they need as well. In fact, they often produce more oxygen than is needed and release the extra into their environment. This means while plants use oxygen and undergo gas exchange just like animals, they tend to do it backward. They take in carbon dioxide and release oxygen.
By the end of this lesson, you will understand how a plant exchanges gases.
This process is used to create the energy the cells need to perform the basic life functions. To review what cells use energy for, reread Lesson 4 on the parts of the cell and Lesson 6 on the cell membrane.
Plants create all the glucose they need through photosynthesis and, depending on the amount of sunlight available, produce all the oxygen they need as well. In fact, they often produce more oxygen than is needed and release the extra into their environment. This means while plants use oxygen and undergo gas exchange just like animals, they tend to do it backward. They take in carbon dioxide and release oxygen.
By the end of this lesson, you will understand how a plant exchanges gases.
Targets
By the end of this lesson, you will be able to- explain the gas exchange system in plants and how diffusion is used in this system
- identify the structure and function of the lenticels, guard cells, and stomata
Interactive Activity
Cell Energy Cycle © Explore Learning
Background Information:
This activity gives a great visual for how photosynthesis and cellular respiration are complementary processes. It will help you understand what reactants are needed for each process.
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 âShow formula of chemical equationâ at the bottom of your screen.
- This will take you to the âPhotosynthesisâ tab. In this tab, you need to drag the two chemicals needed for photosynthesis into the chloroplast.
- Once you have dragged the chemicals needed over, add light by clicking on the âAdd lightâ button.
- This will show you the chemicals photosynthesis creates.
- Click on the âRespirationâ tab.
- Check off âShow formula of chemical equationâ at the bottom of your screen.
©Explore Learning
A11.2 How to switch tabs
A11.2 How to switch tabs
- In this tab, you need to drag the two chemicals needed for cellular respiration into the mitochondrion.
- Once you have dragged the chemicals needed into the mitochondrion, click the âNextâ button in the top right-hand corner.
- Read the explanations in the bottom left corner of your screen and keep clicking the âNextâ button to see the process of cellular respiration.
- Click on the âCycleâ tab.
- Drag the chemicals to the processes they are needed for. The animation will move the chemicals in place for you to show how these two processes create a cycle.
- Please return to the top of this page and click on analysis to complete the analysis questions.
- Explain why cellular respiration and photosynthesis are complementary processes.
They are complimentary processes because the products of one are the reactants of the other. This means photosynthesis produces the chemicals needed for cellular respiration and cellular respiration produces the chemicals needed for
photosynthesis.
- What gases are exchanged when an animal breathes? What gases do plants exchange when they perform photosynthesis?
The lungs of animals breathe in oxygen and breathe out carbon dioxide because the cells in an animal body perform only cellular respiration. A plant will release oxygen and absorb carbon dioxide. We will look at how plants exchange
these gases in this lesson.
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.
Gas Exchange in the Dermal Tissue
How are the stomata and guard cells involved in gas exchange?
A11.3 Electron micrograph of stomata
Due to the waxy cuticle and the epidermis, it is very hard for a plant to get all the gases it needs through diffusion. Plants have solved this problem by having specialized cells called guard cells. Guard cells control the opening and closing of
small holes in the underside of the leaf called stomata. The stomata allow gases to pass into or out of the cell, depending on their concentration gradient. If there is more oxygen inside the leaf than outside, the oxygen will move to the outside
of the leaf through the stomata.
How big the stomata are and when they are open or closed is controlled by the guard cells. It is extremely important that the guard cells do this job, as water can also escape through the stomata. If the stomata were left open all of the time, the plant would quickly dry out and die. If the stomata were never open, though, the plant would not get enough carbon dioxide to undergo photosynthesis. The plant would then starve and die.
The guard cells open and close the stoma depending on how much sunlight is reaching them. When light hits the leaves, it stimulates the guard cells to bring potassium ions into the cell through active transport. This creates a high concentration of potassium inside the cell, so water flows into the cell through osmosis to try to dilute that concentration. The side of the cell away from the stoma has a thinner membrane, so the water is able to push out farther in that direction, giving the cell a crescent shape and opening the stoma. Each stoma have two guard cells surrounding it, when the stoma is open, both these guard cells have a crescent shape, forming the stoma in the centre.
How big the stomata are and when they are open or closed is controlled by the guard cells. It is extremely important that the guard cells do this job, as water can also escape through the stomata. If the stomata were left open all of the time, the plant would quickly dry out and die. If the stomata were never open, though, the plant would not get enough carbon dioxide to undergo photosynthesis. The plant would then starve and die.
The guard cells open and close the stoma depending on how much sunlight is reaching them. When light hits the leaves, it stimulates the guard cells to bring potassium ions into the cell through active transport. This creates a high concentration of potassium inside the cell, so water flows into the cell through osmosis to try to dilute that concentration. The side of the cell away from the stoma has a thinner membrane, so the water is able to push out farther in that direction, giving the cell a crescent shape and opening the stoma. Each stoma have two guard cells surrounding it, when the stoma is open, both these guard cells have a crescent shape, forming the stoma in the centre.
A11.4 Open and closed stoma
When the stomata are open, carbon dioxide and oxygen can flow into and out of the leaf, but so can water. This loss of water out of the stomata is called transpiration.
When there is not enough water left to flow into the guard cells, they go limp and the stomata close. This lack of water signals the cell to allow the potassium ions to move out of the guard cells. This changes the concentration gradient of the potassium
ions and water leaves the guard cells to try to dilute the now high concentration of potassium ions outside the cell. The guard cells go back to their original shape and the stomata close.
The number of stomata found in the epidermis of a leaf is dependent on the plants environment. Plants in a hot and dry environment have fewer stomata to stop the loss of water through transpiration. Plants in a wet environment will have more stomata
since water loss is not as big of an issue. Stomata are also sensitive to the amount of carbon dioxide in the air. If there is not enough carbon dioxide in the air, the stomata will open as wide as the can to try to allow all the carbon dioxide
possible into the leaf so the plant can continue with photosynthesis.
A11.5 Comparison of plants in a hot and dry vs. wet environment
Watch This
Stomatal Closure in Tradescantia Leaf Cells © YouTube davcjal
This video will show you a stomata closing in a leaf. From this video, you can see the stomata does not snap open or closed; instead it slowly closes as the water moves out of the guard cells into the surrounding cells.
Did You Know?
A11.6 Maple tree
The underside of a leaf can have anywhere from 10,000 to 100,000 stomata per cm2! On a hot day, when all these stomata are open, an average size maple tree may lose up to 200 L of water. Just imagine how much water that maple tree needs to survive.
Read This
Please read page 309 and the top of page 311 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on how the guard cells open and close the stomata and what the function of the stomata is. Remember,
if you have any questions or you do not understand something, ask your teacher!
Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.- In your own words, explain how a stoma opens and closes.
Your answer should be a variation of the following:
- When the sunlight touches the guard cells, the guard cells begin to actively transport potassium ions into themselves.
- This creates a high concentration of potassium inside the cell, so water moves into the cell through osmosis.
- This creates a high water pressure inside the guard cells and causes them to move into a crescent shape.
- This opens the stoma.
- As the water pressure begins to go down, the cell actively transports potassium out of the cell.
- The water then follows the potassium ions through osmosis and the guard cells go back to their original shape.
- This closes the stoma.
- Why is it important that the stomata open and close in response to the amount of sunlight present?
Photosynthesis requires light to occur, so it is important that during that time, the plant has the carbon dioxide it needs in order to perform photosynthesis. Note: There are parts of photosynthesis that occur in the dark, but those parts do not require carbon dioxide like the parts that occur in the light.
Gas Exchange in the Ground Tissue
Why are the stomata located on the underside of the leaf?
A11.7 Gas exchange through the stomata
You may remember on the lower side of the leaf, the dermal tissue is next to the spongy tissue cells (also called spongy mesophyll tissue). You may also remember that there are lots of air pockets between these cells. The stomata are located just below
this layer in the epidermis on the lower side of the leaf, so the gas that enters through the stomata can go straight into the air pockets within the spongy mesophyll tissue. This gives the carbon dioxide needed for photosynthesis a place to be stored
before it is used by the palisade tissue cells that are directly above the spongy mesophyll tissue layer.
The spongy tissue cells will move oxygen toward the stomata so the oxygen can escape the leaf easily, and they will move carbon dioxide closer to the palisade tissue cells to be used for photosynthesis. This makes the diffusion of these gases very efficient within the leaves and the stem. The gases needed are able to travel through these air pockets, guided by the spongy tissue cells, around the leaf and down the stem to where ever they are needed.
The spongy tissue cells will move oxygen toward the stomata so the oxygen can escape the leaf easily, and they will move carbon dioxide closer to the palisade tissue cells to be used for photosynthesis. This makes the diffusion of these gases very efficient within the leaves and the stem. The gases needed are able to travel through these air pockets, guided by the spongy tissue cells, around the leaf and down the stem to where ever they are needed.
Read This
Please reread the section called âGround Tissueâ on pages 311 to 313 in your Science 10 textbook. Make sure you take notes on your readings to study from later. This time, you should focus on the spongy tissue cells and how the spongy mesophyll layer
helps with the diffusion of oxygen and carbon dioxide. Remember, if you have any questions or you do not understand something, ask your teacher!
Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.- Why are the stomata located on the underside of the leaf?
The stomata are located on the underside of the leaf so the gases entering the leaf can go straight into the spongy tissue layer where there are many air pockets for the gases to be stored in. The palisade tissue cells have to be at the
top of the leaf in order to catch as much sunlight as possible, so the spongy tissue layer with its air pockets have to be located under the palisade tissue layer.
- What is the purpose of the air pockets between the spongy tissue cells?
The air pockets are for gas storage. They also get the gases closer to the palisade tissue cells where the gases are needed for photosynthesis. This way, the plant does not have to transport the gases; they naturally move up toward the
palisade cells.
Lenticels
Are the leaves the only place gas exchange happens in plants?
Gas exchange happens through diffusion in all plants; there are no specific organs associated with this function. It does, however, happen in the stems or trunks of plants as well as in the leaves.
Have you ever noticed small blisters or splits on the stems or trunks of plants? These are very small and can be difficult to see, but they are another location of gas exchange. These blisters or splits are called lenticels. Lenticels are very similar to stomata, except they are always open. They allow for gas exchange and transpiration to occur.
Read This
Please read the section called âGas Exchange in Plantsâ on page 313 in
your Science 10 textbook. Make sure you take notes on your readings to
study from later. You should focus on what lenticels are and what their
function is. Remember, if you have
any questions or you do not understand something, ask your teacher!
Have you ever noticed small blisters or splits on the stems or trunks of plants? These are very small and can be difficult to see, but they are another location of gas exchange. These blisters or splits are called lenticels. Lenticels are very similar to stomata, except they are always open. They allow for gas exchange and transpiration to occur.
Read This
Please read the section called âGas Exchange in Plantsâ on page 313 in
your Science 10 textbook. Make sure you take notes on your readings to
study from later. You should focus on what lenticels are and what their
function is. Remember, if you have
any questions or you do not understand something, ask your teacher!Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.- How are lenticels similar to stomata? How are they different?
Similarities: Both are involved in gas exchange and transpiration. Differences: Stomata are open and closed by guard cells that react to the amount of sun and water present. Lenticels are always open.
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 âShow oxygen and «math»«msub»«mi»CO«/mi»«mn»2«/mn»«/msub»«/math» values (in ppm)â 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.
1.6 Assignment
Unit A Assignment Lessons 10-13
It is now time to complete the Lesson 11 portion of 1.6 Assignment. Click on the button below to go to the assignment page.
1.6 Assignment