Leaf Structure and Photosynthesis Purpose of a Leaf

Leaf Structure and Photosynthesis

Purpose of a Leaf • Gas exchange- CO 2 and O 2 • Plants need CO 2 to carry out photosynthesis • Must release O 2 as a byproduct of photosynthesis • Capturing light that leads to Photosynthesis • Plants turn light energy into food

Leaf Structure • Cuticle • The waxy covering of the leaf used for protection and to prevent water loss • Epidermis • • Used for protection Includes the stoma and guard cells • Stoma • • • Opening where water vapor and gases leave and enter the plant Consist of two guard cells that open and close Usually located on the bottom of the leaf

Leaf Structure • Veins • Provide support • Transport water (through the xylem) and food (through the phloem) • Mesophyll • The middle layer of the cell where photosynthesis occurs • Spongy Mesophyll: loosely packed for gas exchange • Palisade Mesophyll: column-like and the area of the most • photosynthesis Contains the chloroplast

Chloroplast • Organelle that is the site of photosynthesis • Thylakoids • Disc-like sacs that are arranged in stacks called grana • Stroma • Fluid part of the chloroplast that surrounds the thylakoids

Chlorophyll • 2 Types of chlorophyll • Chlorophyll a • Chlorophyll b • A pigment used to absorb sunlight • Located in the thylakoids

Absorption of Chlorophyll Absorption Wavelength

Photosynthesis • Used by plants to turn sunlight into “food” in the form of glucose • 6 CO 2 + 6 H 2 O → C 6 H 12 O 6 + 6 O 2 • Consists of Light-Dependent and Light-Independent Reactions

Light-Dependent Reactions • Directly involved with sunlight • Reactions occur in the thylakoids • Use the sunlight to: • produce O 2 • Convert ADP and NADP+ into ATP and NADPH

Photosystems • Made up of chlorophyll and proteins • Absorb light to begin the process of photosynthesis • 2 types • Photosystem II • Photosystem I

Light Reactions • Water molecules (H 2 O) are split into O 2, H+ ions, and electrons • Oxygen released into the atmosphere • Electrons and H+ ions are used to form ATP and NADPH

Light-Independent Reactions • Also known as the Calvin Cycle • No light necessary • Uses the ATP and NADPH from the light-dependent reactions along with CO 2 to make sugars

Calvin Cycle • CO 2 molecules taken in from the atmosphere are combined to form 3 -carbon compounds • 3 -carbon compounds are used to form sugar • ATP and NADPH from the light-dependent reactions provide the energy to make the cycle “turn” • Takes 6 turns of the cycle to produce 1 molecule of glucose

Importance of Photosynthesis • Plants use the sugars for energy and for growth and development • Ex. Cellulose • Animals that consume plants can use this stored energy

Factors Affecting Photosynthesis • Temperature • Extreme temps can affect the enzymes that increase the rate of photosynthesis • Light • Increased amounts of light can increase the rate of photosynthesis • Water • A shortage of water can slow down or stop photosynthesis

C 4 Plants • Specialized chemical pathways that helps capture CO 2 at low levels • Can keep photosynthesis working at extreme temperatures • Ex. Corn, sugar cane

CAM Plants • Seen in very dry environments • Air is only let into the leaves at night to help prevent water loss during the day • Ex. Cacti, pineapple trees