Objective – To continue our learning about the leaf

• Warm Up – Put your leaf lab in the center of the table– What are smart things to do while taking an exam

Reminder – today is the regents practice test

Epidermis

• Out layer of cells covering the leaf• Boundary with the outside world• Often transparent (no chloroplasts – allows light through to

photosynthesizing cells)• Often covered with a waxy coat (sometimes reduced on the

underside)• Functions:

– Protection against water loss– Regulation of gas exchange (has openings call stoma or stomata –

plural = stomates)– Secretion of metabolic compounds– In some species it may help in water absorption

Stoma – (Opening and Guard Cells)

• Openings in the leaf surface• Zone of gas exchange (Carbon Dioxide, Oxygen

and Water)• Bordered by Guard Cells– Specialized cell that respond to the environment to

control gas exchange– Especially sensitive to water conditions and regulating

water loss. (They close to prevent the greatest amount of water loss. Especially important in succulents that grow in arid environments.)

Mesophyll

• Palisade Layer– Generally cells are very close – Most concentrated chloroplasts– Site of Photosynthesis

• Spongy Layer– More space exists between cells (for air)– Cells contain chloroplasts– Site of Photosynthesis– Veins run through this layer of cells

Comparison

Plant• Protection• Regulated exchange with

the environment• Responds to the

environment (guard cells especially)

• Region of primary food production

Animal (Human)• Protection• Regulated exchange with

the environment• Responds to the

environment (goose bumps, etc.)

• No food production