Presentation on theme: "Figure 23–18 The Internal Structure of a Leaf"— Presentation transcript:
1 Figure 23–18 The Internal Structure of a Leaf CuticleVeinsEpidermisPalisade mesophyllXylemVeinPhloemSpongy mesophyllEpidermisStomaGuard cells
2 Leaf Structures & Functions Epidermis – layer of tough, irregularly shaped cells; covered by cuticle; form waterproof barrier that protects tissues and limits water loss through evaporationMesophyll – photosynthesis in most plants occurs herePalisade mesophyll – tall columnar, cells; closely packedSpongy mesophyll – loose; many air spaces that connect to exterior through stomata
3 Stomata – porelike openings in the underside of the leaf; allows carbon dioxide and oxygen to diffuse into and out of leafGuard cells – control the opening and closing of stomata by responding to changes in water pressurePlants keep their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of waterIn general, stomata are open during the daytime when photosynthesis is active, and closed at night.May be closed during hot, dry conditions to reduce water loss.
4 Vein – vascular tissue connected to vascular tissue of stems; transport system xylem – carries water from roots to rest of plantphloem – carries nutrients and food made by photosynthesis
5 Function of Guard Cells Section 23-4Guard cellsGuard cellsInner cell wallInner cell wallStomaStoma OpenStoma Closed
6 Function of Guard Cells Section 23-4Guard cellsGuard cellsInner cell wallInner cell wallStomaStoma OpenStoma Closed