Presentation on theme: "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."— Presentation transcript:
11 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
3Anatomy of a Leaf Blade Petiole Thin, flattened part of leaf to collect sunlightPetioleThin stalk that attaches stem to bladeHave dermal, ground, and vascular tissues.
4Dermal TissueEpidermis is covered by a waxy cuticle that protects the leaf and limits water loss through evaporationTough irregular cells with thick cell walls.
5Vascular TissueXylem and phloem tissues are gathered together into bundles called leaf veins.
6Ground Tissue Palisade mesophyll Spongy mesophyll Closely packed cells that absorb light that enters the leafSpongy mesophyllHas many air spaces between its cells.
7Stomata Small openings in the epidermis Allow carbon dioxide, water, and oxygen to diffuse into and out of the leafConnects to spongy mesophyll.
8Transpiration Loss of water through leaves due to evaporation Replaced by water drawn into the leaf through xylemMesophyll cells are kept moist so that gases can enter and leave the cells easilyHelps to cool leaves on hot days.
9Gas ExchangeLeaves take in carbon dioxide and give off oxygen during photosynthesisCells take in oxygen and give off carbon dioxide during cellular respirationGas exchange uses stomata.
10Stomata always open Stomata always closed Water loss would be so great, few plants would be able to surviveStomata always closedAir exchange couldn’t occurKeep stomata open just enough to allow photosynthesis to occur but not enough that they lose excessive water.
11Guard Cells Highly specialized cells surround stomata Control their opening and closingRegulate gases exchange.
12Open StomataCarbon dioxide can enterWater is lost by transpiration.
13Open StomataWhen water is abundant, it flows into the leaf, raising water pressure in the guard cells, which opens the stomata.
14Closed Stomata Carbon dioxide cannot enter Water is no lost by transpiration.
15Closed StomataWhen water is scarce, water pressure within the guard cells decreases, the inner walls pull together, and the stoma closes.
16HomeostasisStomata open during the day for photosynthesis, and close at night to limit water lossMay close in bright sunlight under hot, dry conditions to conserve water.
17Transpiration and Wilting Osmotic pressure keeps a plant’s leaves and stems rigidHigh transpiration rates can lead to wilting.
18Adaptations of Leaves Pitcher Plant: Leaf is modified to attract and digest insects and other smallTypically live in nutrient-poor soils and rely on animal prey as their source of nitrogen.
19Rock Plant Two leaves are rounded to minimize exposure to air Have few stomata.
20SpruceNarrow leaves contain waxy epidermis and stomata that are set below the surface of the leafReduce water loss.
21Cactus leaves are nonphotosynthetic thorns Protect against herbivores Photosynthesis carried out in stem.
22Examining Stomata Obtain different kinds of leaves from your teacher Spread a thick coating of clear nail polish on the underside of each leafWait about 10 minutes for the polish to dry completelyAttach a strip of clear tap to the polish and gently peel off the tape and the dried polishTape the polish to a clean microscope slide and examine under a 40x lensFor each leaf, move the microscope stage so you can count stomata from three distinct fields of view
23Examining StomataCalculate What is the average number of stomata per square cm for each leafGraph Make a graph that compares these averagesForm a Hypothesis Write a hypothesis that could account for differences in stoma density among plants