1. 1 Review Describe how the structure of the leaf is adapted to make photosynthesis more efficient Form a Hypothesis The leave of desert plants often have two or more layers of palisade mesophyll rather than one. How might this modification be advantageous to a desert plant 2 Review How do stomata help plants maintain homeostasis Predict Are stomata more likely to be open or closed on a hot day- explain

2. Ch 23 Plant Structure and Function
23.4 Leaves

3. Anatomy of a Leaf Blade Petiole
Thin, flattened part of leaf to collect sunlight
Petiole
Thin stalk that attaches stem to blade
Have dermal, ground, and vascular tissues.

4. Dermal Tissue
Epidermis is covered by a waxy cuticle that protects the leaf and limits water loss through evaporation
Tough irregular cells with thick cell walls.

5. Vascular Tissue
Xylem and phloem tissues are gathered together into bundles called leaf veins.

6. Ground Tissue Palisade mesophyll Spongy mesophyll
Closely packed cells that absorb light that enters the leaf
Spongy mesophyll
Has many air spaces between its cells.

7. Stomata Small openings in the epidermis
Allow carbon dioxide, water, and oxygen to diffuse into and out of the leaf
Connects to spongy mesophyll.

8. Transpiration Loss of water through leaves due to evaporation
Replaced by water drawn into the leaf through xylem
Mesophyll cells are kept moist so that gases can enter and leave the cells easily
Helps to cool leaves on hot days.

9. Gas Exchange
Leaves take in carbon dioxide and give off oxygen during photosynthesis
Cells take in oxygen and give off carbon dioxide during cellular respiration
Gas exchange uses stomata.

10. Stomata always open Stomata always closed
Water loss would be so great, few plants would be able to survive
Stomata always closed
Air exchange couldn’t occur
Keep stomata open just enough to allow photosynthesis to occur but not enough that they lose excessive water.

11. Guard Cells Highly specialized cells surround stomata
Control their opening and closing
Regulate gases exchange.

12. Open Stomata
Carbon dioxide can enter
Water is lost by transpiration.

13. Open Stomata
When water is abundant, it flows into the leaf, raising water pressure in the guard cells, which opens the stomata.

14. Closed Stomata Carbon dioxide cannot enter
Water is no lost by transpiration.

15. Closed Stomata
When water is scarce, water pressure within the guard cells decreases, the inner walls pull together, and the stoma closes.

16. Homeostasis
Stomata open during the day for photosynthesis, and close at night to limit water loss
May close in bright sunlight under hot, dry conditions to conserve water.

17. Transpiration and Wilting
Osmotic pressure keeps a plant’s leaves and stems rigid
High transpiration rates can lead to wilting.

18. Adaptations of Leaves Pitcher Plant:
Leaf is modified to attract and digest insects and other small
Typically live in nutrient-poor soils and rely on animal prey as their source of nitrogen.

19. Rock Plant Two leaves are rounded to minimize exposure to air
Have few stomata.

20. Spruce
Narrow leaves contain waxy epidermis and stomata that are set below the surface of the leaf
Reduce water loss.

21. Cactus leaves are nonphotosynthetic thorns Protect against herbivores
Photosynthesis carried out in stem.

22. Examining Stomata Obtain different kinds of leaves from your teacher
Spread a thick coating of clear nail polish on the underside of each leaf
Wait about 10 minutes for the polish to dry completely
Attach a strip of clear tap to the polish and gently peel off the tape and the dried polish
Tape the polish to a clean microscope slide and examine under a 40x lens
For each leaf, move the microscope stage so you can count stomata from three distinct fields of view

23. Examining Stomata
Calculate What is the average number of stomata per square cm for each leaf
Graph Make a graph that compares these averages
Form a Hypothesis Write a hypothesis that could account for differences in stoma density among plants