1. End Show Slide 1 of 32 Copyright Pearson Prentice Hall Biology

2. End Show Slide 2 of 32 Copyright Pearson Prentice Hall 23–4 Leaves

3. End Show 23-4 Leaves Slide 3 of 32 Copyright Pearson Prentice Hall Leaf Structure How does the structure of a leaf enable it to carry out photosynthesis?

4. End Show 23-4 Leaves Slide 4 of 32 Copyright Pearson Prentice Hall Leaf Structure The structure of a leaf is optimized for absorbing light and carrying out photosynthesis.

5. End Show 23-4 Leaves Slide 5 of 32 Copyright Pearson Prentice Hall Leaf Structure To collect sunlight, most leaves have thin, flattened sections called blades. Blade Stem Bud Petiole Simple leaf Compound leaf Leaflet

6. End Show 23-4 Leaves Slide 6 of 32 Copyright Pearson Prentice Hall Leaf Structure The blade is attached to the stem by a thin stalk called a petiole. Blade Stem Bud Petiole Simple leaf Compound leaf Leaflet

7. End Show 23-4 Leaves Slide 7 of 32 Copyright Pearson Prentice Hall Leaf Structure Simple leaves have only one blade and one petiole. Blade Stem Bud Petiole Simple leaf Compound leaf Leaflet

8. End Show 23-4 Leaves Slide 8 of 32 Copyright Pearson Prentice Hall Leaf Structure Compound leaves have several blades, or leaflets, that are joined together and to the stem by several petioles. Blade Stem Bud Petiole Simple leaf Compound leaf Leaflet

9. End Show 23-4 Leaves Slide 9 of 32 Copyright Pearson Prentice Hall Leaf Structure Leaves are covered on the top and bottom by epidermis. Epidermis

10. End Show 23-4 Leaves Slide 10 of 32 Copyright Pearson Prentice Hall Leaf Structure The epidermis of many leaves is covered by the cuticle. Epidermis Cuticle

11. End Show 23-4 Leaves Slide 11 of 32 Copyright Pearson Prentice Hall Leaf Structure The cuticle and epidermal cells form a waterproof barrier that protects tissues inside the leaf and limits the loss of water through evaporation. The vascular tissues of leaves are connected directly to the vascular tissues of stems.

12. End Show 23-4 Leaves Slide 12 of 32 Copyright Pearson Prentice Hall Leaf Structure In leaves, xylem and phloem tissues are gathered together into bundles that run from the stem into the petiole. In the leaf blade, the vascular bundles are surrounded by parenchyma and sclerenchyma cells.

13. End Show 23-4 Leaves Slide 13 of 32 Copyright Pearson Prentice Hall Leaf Structure All these tissues form the veins of a leaf. Xylem Phloem Vein

14. End Show 23-4 Leaves Slide 14 of 32 Copyright Pearson Prentice Hall Leaf Functions Most leaves consist of a specialized ground tissue known as mesophyll. Palisade mesophyll Spongy mesophyll

15. End Show 23-4 Leaves Slide 15 of 32 Copyright Pearson Prentice Hall Leaf Functions The layer of mesophyll cells found directly under the epidermis is called the palisade mesophyll. These closely-packed cells absorb light that enters the leaf. Palisade mesophyll

16. End Show 23-4 Leaves Slide 16 of 32 Copyright Pearson Prentice Hall Leaf Functions Beneath the palisade mesophyll is the spongy mesophyll, a loose tissue with many air spaces between its cells. Spongy mesophyll

17. End Show 23-4 Leaves Slide 17 of 32 Copyright Pearson Prentice Hall Leaf Functions The air spaces connect with the exterior through stomata. Stomata are porelike openings in the underside of the leaf that allow carbon dioxide and oxygen to diffuse into and out of the leaf. Stoma

18. End Show 23-4 Leaves Slide 18 of 32 Copyright Pearson Prentice Hall Leaf Functions Each stoma consists of two guard cells. Guard cells are specialized cells that control the opening and closing of stomata by responding to changes in water pressure. Guard cells

19. End Show 23-4 Leaves Slide 19 of 32 Copyright Pearson Prentice Hall Leaf Functions Transpiration The surfaces of spongy mesophyll cells are kept moist so gases can enter and leave the cells easily. Water evaporates from these surfaces and is lost to the atmosphere.

20. End Show 23-4 Leaves Slide 20 of 32 Copyright Pearson Prentice Hall Leaf Functions Transpiration is the loss of water through its leaves. This lost water is replaced by water drawn into the leaf through xylem vessels in the vascular tissue.

21. End Show 23-4 Leaves Slide 21 of 32 Copyright Pearson Prentice Hall Leaf Functions Gas Exchange How does gas exchange take place in a leaf?

22. End Show 23-4 Leaves Slide 22 of 32 Copyright Pearson Prentice Hall Leaf Functions Plant leaves allow gas exchange between air spaces in the spongy mesophyll and the exterior by opening their stomata. Plants keep their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of water.

23. End Show 23-4 Leaves Slide 23 of 32 Copyright Pearson Prentice Hall Leaf Functions Guard cells are specialized cells that control the stomata. Stomata open and close in response to changes in water pressure within guard cells.

24. End Show 23-4 Leaves Slide 24 of 32 Copyright Pearson Prentice Hall Leaf Functions When water pressure within guard cells is high, the stoma open.

25. End Show 23-4 Leaves Slide 25 of 32 Copyright Pearson Prentice Hall Leaf Functions When water pressure within guard cells decreases, the stoma closes.

26. End Show 23-4 Leaves Slide 26 of 32 Copyright Pearson Prentice Hall Leaf Functions Plants regulate the opening and closing of their stomata to balance water loss with rates of photosynthesis. Stomata are open in daytime, when photosynthesis is active, and closed at night, to prevent water loss. In hot, dry conditions stomata may close even in bright sunlight, to conserve water.

27. End Show - or - Continue to: Click to Launch: Slide 27 of 32 Copyright Pearson Prentice Hall 23–4

28. End Show Slide 28 of 32 Copyright Pearson Prentice Hall 23–4 A compound leaf is one that has a.a blade attached by several petioles. b.two or more blades. c.a blade that is divided into many leaflets. d.many blades, each with its own petiole.

29. End Show Slide 29 of 32 Copyright Pearson Prentice Hall 23–4 The layer of cells in a leaf that absorb light is the a.phloem. b.vein. c.palisade mesophyll. d.epidermis.

30. End Show Slide 30 of 32 Copyright Pearson Prentice Hall 23–4 The structure of a leaf allows it to a.maximize sun exposure and maximize water loss. b.maximize sun exposure and minimize water loss. c.minimize sun exposure and maximize water loss. d.minimize sun exposure and minimize water loss.

31. End Show Slide 31 of 32 Copyright Pearson Prentice Hall 23–4 A process in which water is lost through the leaves of a plant is called a.transpiration. b.photosynthesis. c.glycolysis. d.cellular respiration.

32. End Show Slide 32 of 32 Copyright Pearson Prentice Hall 23–4 Gas exchange in a leaf occurs through the a.cuticle. b.epidermis. c.mesophyll. d.stomata.

33. END OF SECTION