Lesson 12 Transport in Plants
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.
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.
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.- 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.
- 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.
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.
- 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