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introduction
introduction
Have you visited or at least heard about the giant California redwoods? These amazing trees can grow up to 100 m tall! In Alberta, even the trees in the central and north central regions of the province consist of tall aspens that can reach heights of up to 25 m.
How do trees like the California redwoods and the aspens of Alberta get water and minerals from their roots to their leaves way up at the top?
Many factors are involved in the movement of water in plants. In this section you will learn about these factors: cohesion & adhesion, root pressure, transpiration pull, sugar transport, pressure-flow theory.
cohesion and adhesion
cohesion and adhesion
Cohesion- The attraction of water molecules to other water molecules.
Adhesion- The attraction of water molecules to molecules of other substances.
Through cohesion and adhesion, water molecules (due to their polar nature), are able to pull themselves up through the xylem tubes.
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root pressure and transpiration pull
root pressure and transpiration pull
Other ways through which water moves up the stem to the leaves in plants are root pressure and transpiration pull. Roots draw water and minerals from the soil. This creates a greater pressure in the roots than there is in the stem and leaves, thus forcing the water up the stem. Transpiration pull results from the evaporation of water through the leaves. This creates a pull on the water within the stem and leaves.
learning activities
learning activities
Turn to pages 316 to 318 of the textbook and read “Root Pressure” and “From Root to Leaf: Water Transport in Plants.”
18. What evidence is there that root pressure occurs?
19. Through what process is water drawn into the roots?
20. How does transpiration pull work to move water up the stem of a plant?
21. How does temperature affect transpiration pull?
effect of tonicity on plant cells
effect of tonicity on plant cells
Tonicity refers to the concentration of solute particles in any solution. If the environment of a cell has a higher concentration of solute particles than the cell contents, the cell environment is said to be hypertonic or to have higher tonicity. Living cells continuously respond to the tonicity of their environment.
learning activities
learning activities
Turn to page 320 of the textbook and read “The Effect of Tonicity on Plant Cells.”
Study the photographs in Figure C3.21 closely.
a. Describe plasmolysis.
b. What is the effect of plasmolysis on a leaf of a plant?
What happens to a plant that has been in a salt solution for a few minutes when it is returned to fresh water?
3. Why is turgidity important to green plants?
from source to sink: sugar transport in plants
from source to sink: sugar transport in plants
In addition to water, plants need a supply of food (sugars) to survive. Xylem and phloem cells are the mechanism for transport of sugars throughout the plant.
learning activities
learning activities
Read “From Source to Sink: Sugar Transport in Plants” on pages 320 and 321 of the textbook. Study Figure C3.22 on page 321 carefully.
1. Why are xylem and phloem cells important to the survival of the plant?
2. What terms are used for where sugars are manufactured and where they are used or stored?
3. Describe the mechanism by which the sugars are moved from the leaves to the rest of the plant.
4. What are the sugars used for when they are passed on to the rest of the plant?
5. How is the constant flow of sugar down the phloem maintained?
Next: You are now ready to move on to complete section A3.5
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