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Lesson 12 Transport in Plants

  Tonicity and Photosynthesis

How does tonicity affect photosynthesis?


You may remember the terms “hypertonic,” “hypotonic,” and “isotonic” from Section 2 of this unit. A hypertonic solution is a solution that has a higher concentration of particles. A hypotonic solution is one that has a lower concentration of particles, and an isotonic solution is one that has the same concentration of particles.

A cell that is in a hypertonic solution will have its water leave to try to dilute that hypertonic solution. Just like you saw in the lab “Osmosis, Diffusion and Paramecium Homeostasis” in Lesson 6, this will cause the cell to shrivel and pull away from the cell wall. In plants, this effect is called plasmolysis and it causes the leaf to go limp. There is not enough pressure from the cells to cause the leaf to stay rigid, so it flops down. This stops photosynthesis from happening as effectively since the leaf is not outstretched to catch as much light as possible.

A12.11 Wilted plant


A12.12 A plant with turgor pressure
A cell that is in a hypotonic solution will have water enter the cell to try to dilute the solution inside the cell. Again, just like you saw in the lab “Diffusion and Osmosis,” this will cause the cell to be turgid, or full of water. This turgor pressure causes the leaf to be stiff and outstretched, allowing the leaf to catch as much sunlight as possible. A plant that is in a hypotonic solution will be the most effective at photosynthesis.

Read This


Please read page 320 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on how hypertonic and hypotonic solutions affect photosynthesis. Remember, if you have any questions or you do not understand something, ask your teacher!

  Digging Deeper


A12.13 Pine needles

Pine trees photosynthesize as much as deciduous trees do. Plants do not have to have big flat leaves to photosynthesize efficiently. For information on how pine trees photosynthesize, go to the following link.

Learn More

  Did You Know?


A12.14 A maple tree with fall colours

Deciduous trees lose their leaves in the fall and go dormant in the winter time. Many people think it is the cold weather that tells the trees to change colours and drop their leaves, but it is actually the change in the length of sunlight each day.

  Virtual Lab


Osmosis, Diffusion, and Paramecium Homeostasis © Explore learning


Background Information:
These labs will allow you to observe how osmosis and diffusion work. You will complete a lab on osmosis, a lab on diffusion, and then a lab on a paramecium (a small single-celled organism) to see these two processes in action. They will also let you observe what happens in a hypertonic and a hypotonic solution.

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.

  1. Open the Osmosis Gizmo by clicking on the play button in this section.
  2. The pink square represents a cell, the green dots represent water molecules, and the blue dots represent a large molecule such as starch or sugar.
  3. Check that the simulation has loaded with the default settings of five large molecules outside the cell and an initial cell volume of 30%. Take note of the initial concentrations inside and outside of the cell and the initial number of solute and solvent particles inside and outside of the cell. These are found on the right-hand side of the simulation. (You can take a screenshot of this information using the camera icon if you wish.)
  4. Click the play button located at the bottom of the screen to run the simulation. Watch what happens to the size of the cell as the simulation plays out. What is happening to the concentration inside and outside of the cell?
  5. After 20 seconds, take note of the final concentrations inside and outside of the cell, what happened to the size of the cell, and the number of solute and solvent particles inside and outside of the cell. (You can take a screenshot of this information using the camera icon if you wish.)
  6. Click on the reset button found next to the pause/play button.
  7. Change the solute outside to 10 molecules and the initial cell volume to 60%. Record or screenshot the initial information.
  8. Click on the play button to run the simulation. Watch what happens to the size of the cell as the simulation plays out. What is happening to the concentration inside and outside of the cell?
  9. After 67 seconds, click the pause button and record or screenshot the final information.
  10. Repeat steps 6 to 9, changing the initial cell volume to 20% and leaving the solute outside at 10 molecules. You only need to run this simulation for 30 seconds.


Simulation:

©Explore Learning
A6.18 Default Settings



©Explore Learning
A6.18 Camera icon

  1. Open the Diffusion Gizmo by clicking on the play button in this section.
  2. Make sure the simulation opens with the default settings shown in image A6.19. The clear space in this simulation represents water, and the purple dots represent small particles.
  3. Click the play button in the bottom right half of the simulation. What happens to the number of particles in region B?
  4. Run the simulation for 60 seconds. What has happened to the number of particles in regions A and B?
  5. Click the reset button next to the pause/play button.
  6. Increase the number of y in B to 50 and decrease the wall height to 25%. You will now see purple and green particles.
  7. Click on the play button to run the simulation. What happens to the number of particles in regions A and B?
  8. Run the simulation for 120 seconds. What has happened to the number of particles in regions A and B? What has happened to the number of x and y particles in each region?


©Explore Learning
A6.19 Default settings in Diffusion lab

  1. Open the Paramecium Homeostasis Gizmo by clicking on the play button in this section.
  2. Check that the simulation has opened with a water solute concentration of 1% and paramecium controlled.
  3. Click on the play button located in the bottom left side of the simulation. What is happening to the contractile vacuole (the pink sphere)? Why do you think this is happening?
  4. Pause the simulation and change the water solute concentration to 2%. Click on the play button and observe what happens to the contractile vacuole.
  5. Pause the simulation again and change the water solute concentration to 0%. Click on the play button and observe what happens to the contractile vacuole.
  6. Pause the simulation and change the water solute concentration back to 1%. Change the simulation from “Paramecium controlled” to “User controlled.” You are now in charge of when the contractile vacuole does its job.
  7. Click the play button and observe what happens to the contractile vacuole and size of paramecium. Do not click on the contract button. What eventually happens to the paramecium?
  8. Reset the simulation, making sure the simulation is still user controlled. Click on the play button and try to click on the contract button at the right time to keep the paramecium healthy. If you would like a challenge, change the water solute concentration to 0%.
  9. Pause the simulation and change the water solute concentration to 2%.
  10. Click the play button and observe what happens to the size of the cell. (This is a small difference, so you really have to watch to see it!)


  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.

  1. Is a hypertonic or hypotonic solution better for photosynthesis? Why?
A hypotonic solution is better for photosynthesis because the water moves into the plant cells through osmosis. This increases the turgor pressure in the leaves and helps them to stretch out to catch as much sunlight as possible.