1. Leaf Tissues and Gas Exchange
With a waxy cuticle, how do the cells inside the plant get air?

2. Dermal Tissue Air enters plant cells through passive diffusion
Plants have specialized cells which allow more efficient gas exchange within the leaf called guard cells which surround the stomata
Guard cells open into ground tissue to allow for efficient gas exchange
Movement of gas depends on its concentration gradient

3. Dermal Tissue
The majority of stomata on a leaf are found on the underside
Depending on conditions the guard cells will open or close
Open – guard cells swell because K+ is pumped into cell by active transport and the water follows the K+. The wall on the outside of the guard cell is thinner than the inside wall causing the cell to bend into a crescent shape
Closed – K+ exits guard cells and water follows, guard cell goes limp

4. Dermal Tissue
Stomata allow for easy movement of gases but also protect plant from water loss
Plants need water because…
All gas in the leaf is absorbed into the cells by dissolving in a thin film of water
Needed as a product for photosynthesis
This thin film of water causes plants to loose water vapor, which is called transpiration

5. Dermal Tissue Stomata are sensitive to environmental conditions
Plants that live in hot, dry climates have adapted to having fewer stomata
Plants in environments with little carbon dioxide have adapted by keeping stomata as wide as they can and for long periods of time

6. Ground Tissue
Located between the upper and lower epidermis, there is ground tissue called mesophyll (2 types)
Palisade tissue cells
found below upper epidermis
long, rigid rectangular cells tightly packed together (maximizes number of cells in contact with the sun)
responsible for photosynthesis
Spongy mesophyll tissue
between palisade tissue cells and lower epidermis
loosely packed with space in-between (gas exchange)

7. Ground Tissue

8. Transportation system in plants.
Vascular Tissue
Transportation system in plants.
Xylem
Phloem
Xylem and phloem are bunched together like a bundle of straws and form a vascular bundle.

9. Gas Exchange In plants, gas exchange occurs by diffusion
Stomata increase gas movement
Loose ground tissue maximizes diffusion
The leaf is not the only location of gas exchange
Trees have natural “slashes” and “blisters” on them called lenticels.

12. Homework Read p. 309- 313 Do Check and Reflect P. 314 # 5,7,8,9,10
Do worksheet C3.3- Leaf tissues and gas exchange