Transcript File
Leaf Tissues and Gas Exchange With a waxy cuticle, how do the cells inside the plant get air? 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 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 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 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 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) Ground Tissue Vascular Tissue Transportation system in plants. Xylem Phloem Xylem and phloem are bunched together like a bundle of straws and form a vascular bundle. 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. 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