1 review describe how the structure of the leaf is adapted to make photosynthesis more efficient...
TRANSCRIPT
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
CH 23 PLANT STRUCTURE AND FUNCTION
23.4 Leaves
Anatomy of a Leaf
Blade Thin, flattened part of leaf to collect sunlight
Petiole Thin stalk that attaches stem to blade
Have dermal, ground, and vascular tissues.
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.
Vascular Tissue
Xylem and phloem tissues are gathered together into bundles called leaf veins.
Ground Tissue Palisade mesophyll
Closely packed cells that absorb light that enters the leaf
Spongy mesophyll Has many air spaces between its cells.
Stomata
Small openings in the epidermis Allow carbon dioxide, water, and oxygen to diffuse
into and out of the leaf Connects to spongy mesophyll.
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.
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.
Stomata always open 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.
Guard Cells
Highly specialized cells surround stomata Control their opening and closing Regulate gases exchange.
Open Stomata
Carbon dioxide can enter Water is lost by transpiration.
Open Stomata
When water is abundant, it flows into the leaf, raising water pressure in the guard cells, which opens the stomata.
Closed Stomata
Carbon dioxide cannot enter Water is no lost by transpiration.
Closed Stomata
When water is scarce, water pressure within the guard cells decreases, the inner walls pull together, and the stoma closes.
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.
Transpiration and Wilting
Osmotic pressure keeps a plant’s leaves and stems rigid
High transpiration rates can lead to wilting.
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.
Rock Plant Two leaves are rounded to minimize exposure to air Have few stomata.
Spruce Narrow leaves contain waxy epidermis and stomata
that are set below the surface of the leaf Reduce water loss.
Cactus leaves are nonphotosynthetic thorns Protect against herbivores Photosynthesis carried out in stem.
Examining Stomata
1. Obtain different kinds of leaves from your teacher2. Spread a thick coating of clear nail polish on the
underside of each leaf3. Wait about 10 minutes for the polish to dry
completely4. Attach a strip of clear tap to the polish and gently
peel off the tape and the dried polish5. Tape the polish to a clean microscope slide and
examine under a 40x lens6. For each leaf, move the microscope stage so you
can count stomata from three distinct fields of view
Examining Stomata
1. Calculate What is the average number of stomata per square cm for each leaf
2. Graph Make a graph that compares these averages
3. Form a Hypothesis Write a hypothesis that could account for differences in stoma density among plants