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Lesson 12 Transport in Plants

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Course: Science 10 [5 cr] - AB Ed copy 1
Book: Lesson 12 Transport in Plants
Printed by: Guest user
Date: Sunday, 7 September 2025, 6:46 PM

Table of contents

  Introduction

How do the vascular tissues work?



A12.1 Xylem and phloem in a buttercup plant
The xylem vascular tissue and the phloem vascular tissue are in charge of the movement of materials, such as water and glucose, around the plant. This may seem very similar to our veins and arteries that carry blood around our bodies, but they work in a very different way. The xylem tissue uses the special properties of water to transport it and any dissolved minerals from the roots to the leaves.

In this lesson, we will study these special water properties and, by the end of the lesson, you will be able to explain how the xylem vascular tissue and the phloem vascular tissue work.

  Targets

By the end of this lesson, you will be able to

  • explain the transport system in plants
  • explain the xylem and phloem tissues and the processes of transpiration, including turgor pressure, osmosis, diffusion, active transport, and root pressure in root hairs
  • explain the cohesion and adhesion properties of water

  Watch This

GCSE Biology: Transport in Plants © Cognito 


Watch this video for a quick introduction to the two types of vascular tissues in plants, the xylem, and phloem. We will go into greater detail of how these tissues work in this lesson.

  Water Properties

What are the special water properties the xylem tissue uses?


Water is a unique compound and, as such, has some unique properties. If you fill a glass to the brim with water, you may notice how the water is actually above the edge of the glass. How does this happen? Why doesn’t the water overflow? It will eventually, but water is very attracted both to itself and to other substances. This helps water “hold on” to the glass (adhesion) and to itself (cohesion) so it does not overflow as quickly as you may think it will.

A12.2 Water sits above the edge of the glass.


© dnak, via Wikimedia Commons
A12.3 Water droplets on a leaf
Cohesion is the property of water that allows it to be attracted to itself. Image A12.3 shows water molecules that have attached to each other to form small water droplets on the surface of a leaf. This is a great example of cohesion.

Water molecules are slightly polar in nature. This means one end of the water molecule has a very slight positive charge while the other end has a very slight negative charge. Remember, opposites attract, so the positive end of one water molecule is attracted to the negative end of another, allowing the molecules to cling to each other. If we look back at the glass, this attraction can only hold for so long. Eventually the weight of all the water particles clinging together will become too much and the water will overflow from the glass.


© JĂŒ, via Wikimedia Commons
A12.4 Oxygen is slightly positive and the hydrogens are slightly negative

  Did You Know?


 A12.5 Gerridae insect sitting on the surface of a lake

A variety of bugs use the property of cohesion to sit on the surface of the water without sinking. They have adapted so they do not break the bonds used in cohesion when they sit on the surface.


©Horla Varlan via flickr
A12.5 Water along the edges of the glasses is higher than in the middle
Adhesion is the property of water that allows it to be attracted to other substances. This property is also due to water’s polar nature. The positive and negative ends of the water molecule are attracted to the slightly positive and negative ends in other substances. If you look closely at water in a glass, you will see the water along the glass itself is higher than the water in the middle of the glass. This is because the water is attracted to the glass, so more molecules are found along the glass wall. This causes the water to sit higher as there are more water molecules in that location. Water can actually “climb” a short distance by using this property. The water molecules that are higher up on the glass wall pull other water molecules up behind it due to the cohesion property.


  Read This

Please read the section called “Cohesion and Adhesion” on page 316 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on how the properties of cohesion and adhesion work. 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.

  1. If you were to place droplets of water on a penny, which property keeps the droplets from falling off the penny? How does it work?

Cohesion helps to keep the water droplets from falling off the penny. Cohesion works by keeping the water molecules attracted to each other so they hold on to each other rather than falling off the penny.

You could also suggest adhesion helps to keep the water droplets from falling off the penny. Adhesion keeps the water attracted to the surface of the penny so the droplets do not slide off the penny.
  1. How does water “climb” up the side of a glass?
Water uses the properties of both adhesion and cohesion to move up the side of the glass. The water molecules are attracted to the side of the glass, so they all try to align themselves along that surface. This pushes the molecules up the side of the glass. The property of cohesion keeps the water molecules attached to each other, so as the molecules are pushed up the side of the glass, they pull other molecules with them.

  From Root to Leaf

How does water get from the soil to the leaf, where it is needed for photosynthesis?


A12.6 Root pressure
The root hairs of a plant absorb minerals from the soil through active transport. This creates a higher concentration of minerals in the roots, so water moves into the roots through osmosis. This increases the pressure of water inside the roots and creates what is called root pressure. Root pressure is responsible for some of the movement of water from the roots to the leaves of the plant. This pressure in the roots causes water to be forced up the xylem. Water is pushed from the high pressure in the roots to the lower pressure in the stem or trunk. Root pressure can push water to a maximum of a few metres up the stem or trunk of a plant.

Water is also pulled up the xylem to the leaves by tension or transpiration pull. As water leaves through the stomata and lenticels though the process of transpiration, the water molecule behind it is pulled in to take its place. The water molecule behind that one is then pulled to take that one’s place and so on. This occurs because of the properties of cohesion and adhesion. The water molecules are attracted to each other, so as one moves up and out of the stomata or lenticel, it pulls molecules behind it along with it. The water molecules are also attracted to the walls of the xylem, helping the molecules “climb” up the stem or trunk.

As the water fills the air pockets in the ground tissue, it is used by the palisade tissue cells for photosynthesis. This creates the same kind of pull as transpiration. As a water molecule is used, the molecule behind is pulled in to take its place and so on.

A12.7 Transpirationpull

  Digging Deeper


A12.8 Tree growth rings

Trees build new xylem as their trunks get larger. The old xylem becomes blocked with age, and the trunk grows around them. These old tubes are an essential part of the tree’s support system. The growth rings in a tree trunk are actually the old xylem tissues. Go to the following link for more information. https://www.britannica.com/science/xylem

Learn More

A12.9 Process of transpiration
A large amount of the water that is pulled from the roots up to the leaves exits the plant through transpiration and is not used for photosynthesis. This is needed to keep the pull strong enough to continue to pull water up to the leaves to be used in photosynthesis.

Transpiration is regulated by the temperature in the plant’s environment and the opening and closing of the stomata. If the plant is in a hot and dry environment, transpiration occurs quickly and water is pulled from the roots rapidly. This allows photosynthesis to occur quickly as well since the leaf has a constant flow of water to use.

If the plant starts to lose too much water through transpiration, the stomata close. However, once the stomata close, the rate of photosynthesis drops significantly, as there is a reduced transpiration pull and water does not make it to the leaves as quickly.

  Read This

Please read pages 316 to 318 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on how water moves from the roots of a plant to its leaves. 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.

  1. What happens to the movement of water if the plant lives in a cool or wet environment? Why?
If the plant lives in a cool or wet environment, the stomata can stay open for longer, increasing the transpiration pull. This allows more water to be pulled to the leaf and allows more photosynthesis to occur. In this environment, plants will not have as strong of a transpiration pull as in a hot and dry environment, so photosynthesis cannot occur as quickly. This type of environment does allow for photosynthesis to take place over a longer period of time as the plant can leave the stomata open for longer without worrying about losing too much water.
  1. Does transpiration and photosynthesis occur at night?
The stomata are only open when sunlight is present, so transpiration does not occur at night. Photosynthesis needs water to occur, so if there is no transpiration pull, there is very little photosynthesis occurring.

Note: Some of the reactions of photosynthesis can occur at night; these are called the light-independent reactions. You will learn more about these reactions in Biology 20.
  1. Draw a diagram that shows how water moves from the roots to the leaves of the plant. Be sure to include the type of cell transport used at each location.


A12.10 Movement of water



  Try This

A Visual of Water Movement


Background Information

We know water moves from the roots to the leaves of plants, but can we see it? This activity will give you a visual of how water moves in plants and will help you see the xylem. Both of these activities will require you to gather materials from your home or a store. These are not mandatory activities but are a great addition if you can do them. There are videos for each activity if you cannot complete them otherwise.

  1. Collect two small vases or cups, a sharp knife, food colouring and one white carnation with a fairly long stem.
  2. Fill the two small vases or cups with water. Add a couple of drops of food colouring to one vase or cup.
  3. Using the sharp knife, very carefully split the stem down the middle.
  4. Place one half of the stem in the clear water vase and the other half in the coloured water.
  5. Leave the carnation for a couple of days before observing the results.
  6. Please click on Procedure 2 to complete the next experiment.



©YouTube, Sick Science!

Colour Changing Carnations
  1. Collect a stalk of celery with leaves on the top, food colouring, and a water glass.
  2. Fill the cup about half full with water and add a few drops of food colouring.
  3. Cut the bottom end off the celery and place it in the coloured water.
  4. Leave the celery in the water for a couple of days before observing the results. Make sure you observe what happens to the leaves of the stalk and what the bottom of the celery looks like.
  5. You can complete this experiment with other vegetables as well!
  6. Please click on the analysis tab to complete the analysis questions.


©YouTube MUNBotnicalGarden

Celery Straws – A Growing Experiment
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  1. Explain the results of the carnation experiment.
Half of the carnation stayed white while the other half turned the colour of the food colouring. This happened because the xylem on the stem in the food colouring absorbed the food colouring as well as the water. This food colouring was transported up the stem into the flower through transpiration pull, dying the half of the flower that got its water from that half of the stem. This shows how water moves up the stem of the flower and how the xylem only takes water to part of the plant. Each xylem tissue takes water to a specific end point; it does not take water all over the plant.

  1. What part of the celery is dyed darker when you look at the bottom of the stalk?
The xylem was dyed darker. This is because the xylem is what transported the water up the celery stalk, so it had the most exposure to the dye.

  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. 

  Sugar Transport

How is glucose transported from the leaves to the rest of the plant?


A12.15 Sieve tube cells
The phloem tissue is responsible for transporting the glucose produced during photosynthesis to the rest of the cells in the plant. All cells need glucose to produce energy for life functions. This energy is produced through cellular respiration in the mitochondria.

The phloem tissue is made up of sieve tube cells that have perforated ends. These perforated ends allow the cytoplasm to flow from one cell to the next. These cells do not have a nucleus, so they must be connected with companion cells that do contain a nucleus. These companion cells control the function of the sieve tube cells by using carrier proteins and active transport to move glucose into the sieve tube cells. Since the concentration of glucose is now higher in these cells, water follows through osmosis to try to even out the concentration. This mixture of water and glucose is then transported down the phloem following a theory called the pressure-flow theory.

The pressure-flow theory suggests that as more water and glucose enter the sieve tube cells in the leaves, the water and glucose that is already in the sieve tube cells get pushed farther down the phloem tissue. Due to the pressure behind them, the water and glucose look for a way to move out of the sieve tube cells to an area of lower concentration. They find this area in parts of the plant that need glucose. In these locations, the glucose is actively transported out of the cells into the adjacent cells that need it. Again, due to osmosis, the water follows the glucose out of the phloem and into the surrounding cells.
 

A12.16 Pressure-flow theory
The sugars are then used for life functions by the cells or stored as starches or oils in the roots, stems, or fruits of the plant. The water leaves the plant through transpiration, gets pulled into another cell through osmosis, or enters the xylem to go back up to the leaves.

Due to the glucose and water leaving the phloem where they are needed, the pressure is always less in those locations. This means the glucose and water are constantly being pushed from the leaves to the locations where they are needed the most.

  Digging Deeper


A12.17 Venus flytrap

Carnivorous plants eat meat to get the nutrients they otherwise would not have. This is an adaptation to living in environments with poor soil. There are a variety of ways the plants digest the meat they trap, but once it is digested, it is absorbed and transported along with the rest of the nutrients that are absorbed in the soil. Go to the following link for more information on carnivorous plants.

Learn More

  Read This

Please read pages 320 and 321 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on how glucose is transported through the phloem. 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.

  1. Why would damage to the phloem potentially kill a plant?
Damage to the phloem would stop the transportation of glucose. Since glucose is used by all cells for cellular respiration, the cells would start to die if they were not able to get it. The energy created during cellular respiration is used in many different important cell functions, such as active transport, protein synthesis, and digestion.

  1. Describe the structure of the phloem tissue.
The phloem tissue is made up of a bunch of sieve tube cells lined up end to end. The ends of these cells are perforated, so the cytoplasm can flow from one cell to another. Each cell has a companion cell attached to it that directs the function of the sieve tube cell. These cells make long tubes that run from the leaves to the rest of the plant. There are many of these tubes bundled together along with the xylem tissue to make up the vascular tissue.

  1. Draw a diagram that shows how glucose moves from the leaves to the rest of the plant. Be sure to include the type of cell transport used at each location.
Active transport is used in the leaf; glucose is actively transported from the palisade cells into the phloem. The water follows the glucose into the phloem through osmosis. When the glucose reaches the low pressure area, it is actively transported out of the phloem into the cells that require it. Water again follows through osmosis.


A12.16 Pressure-flow theory


  Transport in Plants

Plants must transport water and minerals from the roots to the leaves and glucose from the leaves to the rest of the plant.



A12.18 Vascular tissues in a pumpkin stem
Plants accomplish the transport of water, minerals, and glucose through the xylem vascular tissue and the phloem vascular tissue. The xylem tissue transports water and dissolved minerals from the roots through root pressure and transpiration pull. The phloem transports glucose and water from the leaves following the pressure-flow theory. Both types of vascular tissue use active transport and osmosis to move these materials around.

Both glucose and water are needed for the growth of plants, but how do plants know what direction to grow roots and leaves in? How can they tell without eyes where the sun will be and where the soil is? The next lesson will explore the systems in plants that control where leaves and roots grow.

  Watch This

Transport in Plants Parts 1-3 © YouTube FuseSchool- Global Education


Watch this series of videos for a review of how transport in the xylem and phloem work.


© YouTube FuseSchool - Global Education
Xylem and Phloem - Transport in Plants

Part 1 provides an overview of the xylem and phloem and what they transport.

 
© YouTube FuseSchool - Global Education
Xylem and Phloem - Part 2 - Transpiration - Transport in Plants

Part 2 goes into more detail on how the xylem works to transport water from the roots to the leaves of the plant.

 
© YouTube FuseSchool - Global Education
Xylem and Phloem - Part 3 - Translocation - Transport in Plants

Part 3 goes into more detail on how the phloem works to transport sugars around the plant.

1.6 Assignment

Unit A Assignment Lessons 10-13

It is now time to complete the Lesson 12 portion of 1.6 Assignment. Click on the button below to go to the assignment page.

1.6 Assignment