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Passive & Active Absorption of Water in Plants

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Adrianne Baron

Adrianne has a master's degree in cancer biology and has taught high school and college biology.

Expert Contributor
Christianlly Cena

Christianlly has taught college Physics, Natural science, Earth science, and facilitated laboratory courses. He has a master's degree in Physics and is currently pursuing his doctorate degree.

Explore the passive and active absorption processes plants use to obtain water. Discover the roles of root hairs and osmosis in active absorption, and investigate the roles of transpiration and the apoplast pathways in passive absorption. Updated: 01/05/2022

Absorption in Plants

When your throat is very dry and you feel dehydrated, you'll most likely reach for a bottle or a glass of water. Just like you need water to feel and function at your best, plants need water to grow and thrive.

But unlike you, plants can't just grab a bottle of water, so what do they do? Plants absorb water from their environment, particularly the soil in which they're rooted. They accomplish this through two types of absorption: active and passive absorption.

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  • 0:04 Absorption in Plants
  • 0:32 Active Absorption
  • 2:25 Passive Absorption
  • 3:16 Lesson Summary
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Active Absorption

Any time you hear the word 'active' you know that it's something that requires energy and effort. The same holds true in the case of active absorption, which is the absorption of water through the activity of a plant's root hairs.

Root hairs are thin, hair-like structures that extend from the roots of the plant. The root hairs increase the surface area through which the plant can take up water. For example, they're like having many instead of a few straws.

In a high water concentration, the root hairs will absorb water through osmosis. Osmosis is the movement of water from an area of high concentration to an area of low concentration. When the concentration of water in the soil is higher than the concentration of water in the roots, the water will move into the root hairs. This action does not require a lot of energy.

On the other hand, there are times when the concentration of water in the soil is lower than the concentration of water in the roots. To overcome this obstacle, the root hairs use energy in the form of adenosine triphosphate, or ATP, to create a concentration gradient that will allow the water to move into the roots.

The root hairs create this gradient through endocytosis, the sodium/potassium pump, and exocytosis in order to move the molecules of solutes into the cells of the root hairs. This causes a shift in the concentration gradient to a point where the concentration of water is higher in the soil than it is in the plants, allowing the water to flow into the cells of the root hairs.

Once the root hairs have done their part, the water has to make its way into the plant. This happens through the symplast pathway, which is the movement of water from cell to cell through the plasmodesmata of the cell.

Recall that the plasmodesmata is the network of cytoplasm in plant cells. Water enters the cell sap and then flows into the cell, moving from one cell to the next until it reaches the root. From there, it can make its way to the rest of the plant.

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Additional Activities

Passive & Active Absorption in Plants: True or False Activity

This activity will help you assess your knowledge regarding the two types of water absorption in plants.

Directions

Determine whether the following statements are true or false. To do this, print or copy this page on a blank paper and underline or circle the answer.

True | False 1. Adenosine diphosphate is an energy-carrying molecule found in plants that aids in water absorption.

True | False 2. Water helps move nutrients from the soil into the plant, helping it grow and thrive.

True | False 3. Osmosis is the spontaneous water movement across a concentration gradient, which requires a minimal amount of energy.

True | False 4. Stomata are small channels that directly connect the cytoplasm of neighboring plant cells.

True | False 5. Exocytosis is the process of moving water into the cells of the root hairs.

True | False 6. Active absorption refers to the absorption of water by the leaves with the help of ATP.

True | False 7. The evaporation of water from the shoots and leaves is known as transpiration.

True | False 8. Passive absorption of water takes place when the rate of transpiration is usually high.

True | False 9. The symplast pathway is the path in which the water moves between cell membranes.

True | False 10. Passive water absorption is carried out without the utilization of energy.


Answer Key

  1. False, because the correct statement is: Adenosine triphosphate is an energy-carrying molecule found in plants that aids in water absorption.
  2. True
  3. False, because the correct statement is: Osmosis is the spontaneous water movement across a concentration gradient, which requires a large amount of energy.
  4. False, because the correct statement is: Plasmodesmata are small channels that directly connect the cytoplasm of neighboring plant cells.
  5. True
  6. False, because the correct statement is: Active absorption refers to the absorption of water by the root hairs with the help of ATP.
  7. True
  8. True
  9. False, because the correct statement is: The apoplast pathway is the path in which the water moves between cell membranes.
  10. True

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