Photosynthesis

Plants

Leaf Structure

Stomata

Plant Adaptations for Photosynthesis

Desert Plant Adaptations

Solar Energy • Solar energy travels to Earth in different

wavelengths of light

Pigments

• A pigment is a protein molecule that absorbs light

• The primary pigments in green plants are chlorophyll a and chlorophyll b

Chlorophyll Pigments • Chlorophyll pigments absorb blue-violet and

red regions of the visible spectrum best

Other Plant Pigments • Cooler temperatures cause plants to produce

less chlorophyll, revealing “hidden” pigments

• Carotenes – red and orange

• Xanthophylls – yellow

• Anthocyanins – purple, red, blue (pH dependent)

• Fucoxanthins - brown

Purpose of Photosynthesis

• To convert solar energy into a form of energy that is useable to all organisms

• Solar energy is stored in the chemical bonds of glucose (chemical energy)

Photosynthesis Reaction

“putting together with light”

Photosynthetic Organisms

• Green plants

• Algae

• Cyanobacteria

Simple Story of Photosynthesis and Food

Reactants and Products for Photosynthesis

• Identify the reactants:

• Identify the products:

Photosynthetic Organelle

• Photosynthetic reactions occur within the chloroplast

• Contains the green pigment chlorophyll

Summary of Photosynthesis

Photosynthesis Summary

• The reactions of photosynthesis use solar energy to convert carbon dioxide and water into high energy sugars (glucose) and oxygen gas

Photosynthesis Reaction

1. Light absorption by chlorophyll molecules

2. Light dependent reactions

3. Calvin Cycle

Chloroplast

Light Absorption by the Chlorophyll Molecules

• Clusters of chlorophyll pigments called

photosystems absorb light energy

• Light energy “excites” or energizes the electrons of the chlorophyll pigments

• Shorter wavelengths of light have more energy and are therefore more effective at “exciting” electrons

Photosystems are embedded within the thylakoid membranes of chloroplasts

Light Dependent Reactions

• Occur within the thylakoid membranes of the chloroplasts

• “energy building” reactions

• Require light in order to occur

Light Dependent Reactions

Light Dependent Reactions Summary

• Light energy splits water molecules into hydrogen ions (H+) and oxygen gas (photolysis)

• Two high energy compounds, ATP and NADPH, are also produced

• ATP and NADPH transfer energy (“excited” electrons) to the Calvin cycle

Light Dependent Reactions

Light Dependent Reactions Products

• Oxygen gas – released into the atmosphere (waste product)

• ATP and NADPH – to the Calvin cycle

Calvin Cycle

• Occur in the stroma of the chloroplasts

• “sugar building” reactions

Calvin Cycle

Calvin Cycle

• Inorganic carbon (from CO2) is incorporated into organic carbon (carbon fixation)

• CO2 combines with a five-carbon sugar called RuBP (forms an intermediate 6-carbon compound)

• Energy stored in ATP and NADPH is used to convert the temporary 6-C intermediate compound into carbohydrates