Photosynthesis and the Leaf

EnergyA. The sun is the source of energy

for almost all life on Earth

B. The sun’s energy is transferred into a useable form through photosynthesis

C. Photosynthesis uses energy from the sun to convert water and carbon dioxide into high-energy sugar and oxygen

Photosynthesis & Respiration

• 3 Kinds of Respiration– 1) external respiration- breathing, exchange of

gases between atmosphere and lungs– 2) internal respiration – exchange of O2

between blood and body cells– 3) cellular respiration – chemical reaction

where O2 molecules and broken down food molecules react to produce ATP in the mitochondria

Formula for RespirationC6H12O6+ 6O2 6H2O + 6CO2 + energy

Glucose + oxygen = water + carbon dioxide + ATP

• This is the process by which glucose molecules are broken down to release energy (ATP)

• Occurs inside the mitochondria of cells

The Respiration/Photosynthesis Cycle

Produced by Respiration Used in Photosynthesis

CO2 + energy

Glucose + O2

Used in Respiration Produced by Photosynthesis

PhotosynthesisWhat kind of organisms carry out photosynthesis?

A. They have pigments = light absorbing molecules

B. Plants and other green organisms have specialized organelles that help with this process. This organelle is called chloroplast

C. Photosynthesis takes place inside the chloroplast within leaf cells

Formula for PhotosynthesisWhat goes in? What goes out?

Start with the equation:6CO2 + 6H2O C6H12O6+ 6O2

Carbon dioxide + water = glucose + oxygen

Light-dependent Reactions

• These reactions require light

• Take place in the thylakoid membranes

• Produces ATP, NADPH (electron carrier), and oxygen

Calvin cycle

• The second cycle of photosynthesis

• Products from light-dependent reactions are synthesized into high energy glucose

• These reactions are also known as the light-independent reactions, because they do not require light

Leaf Structure

A. Epidermis • the top and

bottom layers of the leaf

• Protects the inner tissue from injury or drying out

Leaves

B. Cuticle• waxy covering on the leaves secreted by the

epidermis cells, prevents water from escaping

• Important because plants need water for photosynthesis

Leaves

C. Stomata (pl. stoma)• Pores scattered through the leaf epidermis

• Carbon dioxide enters through stoma and Oxygen is released through stoma

• Water vapor can also pass in and out of the stoma (dew)

• Stoma are generally open at night and closed during the day. Typically on underside of leaf

Leaves

D. Guard Cells• Crescent shaped cells which guard the stoma

• Responsible for opening and closing the stoma

• Guard cells pull stoma open when they become turgid (full of water)

Leaves

E. Mesophyll• Layers of cells inside the epidermis

• Most photosynthesis takes place inside this part of the leaf where the cells contain chloroplasts.

Leaves

F. Leaf veins• Vascular tissue in the leaves that contain xylem

and phloem

• Evaporation from the leaves (transpiration) produces the suction that pulls water up the xylem delivering nutrients to other parts of the plant.

http://www.youtube.com/watch?v=mYbMPwmwx88&feature=rel

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