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introduction
introduction
Air can enter cells by passive diffusion. However, it would take along time to get the needed volume of air into a plant that way, especially with the cuticle covering the surface of most of the plant. To solve this problem, the leaf has specialized cells to maximize its ability to exchange gases. There are also other specialized cells that function to provide the reactants and remove the products of th leaf's cellular activities.
Pages 309-314
leaf tissue anatomy
leaf tissue anatomy
leaf: dermal tissue
leaf: dermal tissue
The epidermis on both the top and underside of the leaf is clear and very thin.
Specialized cells called guard cells form tiny openings or pores called stomata that allow gas exchange to happen easily.
These guard cells are able to open and close, thus controlling the amount of gas that can move through.
Some gases can enter by diffusion, but it is the stomata that control most of the gas exchange. The mechanism for opening and closing the stomata involves light and increasing and decreasing the concentration of potassium ions (K+) in the guard cells
learning activities
learning activities
Read the introduction to “The Leaf Tissues and Gas Exchange” and the information in “Dermal Tissue” on pages 309 and 311 of the textbook.
You will discover how the mechanism for opening and closing the stomata works. Closely study the sequence of events in Figure C3.13 on page 309.
1a. Describe what causes guard cells to absorb water from surrounding cells.
b. What happens to guard cells when water enters?
2. Which gases important to the survival of plants pass through the stomata?
3. What causes stoma to close?
4. What is the process of water loss through leaves called?
5. How do guard cells protect the plant from losing too much water through its leaves?
6. How do plants adapt to environmental conditions with regard to number of stomata?
leaf: Ground tissue
leaf: Ground tissue
Pages 311-313
The upper epidermis and lower epidermis form the outside layers of a leaf. Between these two layers are two different types of cells that form the ground tissue of the leaf. This tissue is called mesophyll.
There are two very different types of mesophyll tissues
palisade tissue cells
where chloroplasts are found
tightly bound cell layers
spongy mesophyll tissue
many air spaces for diffusion of gases
The process of diffusion is very efficient in plants because of the3 air spaces present in the spongy mesophyll of the leaf and within the stem. Air diffuses through the stomata and into the air spaces in the leaf, through the intercellular spaces and own the stem.
leaf: vascular tissue
leaf: vascular tissue
The vascular tissue provides the leaf with wate rneeded for transpiration and for photosynthesis, and also removes the sugars formed in photosynthesis. If you observe a leaf, you will see a network of ribs running through it. .These ribs, called leaf veins, contain the vascular tissue of the leaf. The xylem and the phloem tissues are bunched together like a handful of straws in a vascular bundle.
The xylem transports water necessary for photosynthesis.
The phloem transports the sugar that was made during photosynthesis to the res tof the plant.
learning activities
learning activities
Read “Ground Tissue” and “Vascular Tissue” on pages 311 to 313 of the textbook.
Study the diagram and the light micrograph of a leaf in Figure C3.15 on page 312 closely.
1. What are the names of the two types of cells in the region between the upper epidermis and the lower epidermis?
2. Why are palisade cells arranged in such a regular way?
3. How do the spaces between the cells in the spongy mesophyll layer help with diffusion of gases?
4. a. Where is the vascular tissue located in leaves?
b. What is the purpose of vascular tissue in leaves?
5. Answer questions #5, 7, & 10 from the Check and Reflect on page 314.
Once you have completed the required readings and learning activities for sections C3.1-C3.3, you are now ready to complete the following lab:
Lab:
"C3 Plant Systems Lab and Investigation"
Next: You are now ready to move on to complete section C3.4
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