Today’s Objectives

•Given information and/or diagrams on the process of photosynthesis, write and/or identify the equation, raw materials, sites, products, factors affecting the process, and the role of chlorophyll in the light and dark reactions.

ATP: The Cell’s Currency

•Adenosine Triphosphate•Energy from food is converted into high energy bonds in ATP

•ADP + P + energy ATP

Photosynthesis

• 6 CO2 + 6 H2O + Light Energy C6H12O6 + 6 O2

• Basis of most of the earth’s food chains• Produces and maintains all of the earth’s atmospheric

oxygen• Most oxygen produced in the oceans

Photosynthetic Pigments

•Mostly chlorophyll a and chlorophyll b•Accessory pigments:

•Carotenoids•Anthocyanins

•Each pigment absorbs a particular wavelength of light in the visible spectrum

Photosynthesis:Reactants & Products

Chloroplast Structure

Pigment Absorption

Pigments – protein molecules that absorb specific colors of light.

• Most plants have at least 3 pigments:• 1. Chlorophyll A • 2. Chlorophyll B• 3. Carotenoids

* Why do leaves change color in the fall?

Overview of Photosynthesis

Step I: Light Reactions

• Involves the splitting of water (photolysis)

•12 H2O + Energy 6 O2 + 24 H+ + 24e-

•Requires light for the energy to split the water molecule

•Also forms a highly energetic compound, adenosine triphosphate (ATP)

Overview of the Light Reactions

•Think of the light reaction, as a process by which organisms "capture and store" radiant energy as they produce oxygen gas. This energy is stored in the form of chemical bonds of compounds such as NADPH and ATP.

Light Reaction = Electron TransportWhen Sunlight is absorbed by Photosystem II, electrons

are “kicked out”. Water is “split” to replace lost electrons.Electrons are passed along a chain of molecules to

Photosystem I.Energy from moving electrons is used to pump protons

inside the thylakoid.

Light Reaction - Analogy

Light-Dependent Reaction – Summary

• Water and Light are converted into ATP & NADPH.

• Occurs in the Thylakoid Membrane.

• Oxygen is released as a waste product.

• NADPH – an energy (electron) carrying molecule

Step II: Dark Reactions

• Does not require light but can happen at any time of day.

• The energy from NADPH and ATP is used for carbon fixation

• 6 CO2 + 24 H+ + 24 e- ------> C6H12O6 + 6 H2O

• The chemical bonds present in glucose also contain a considerable amount of stored (potential) energy.

Dark Reaction – Calvin Cycle

• Energy stored from the light reaction (ATP & NADPH) is used to power the production of sugar.

• Carbon Dioxide and Hydrogen are converted into ½ of a glucose = PGAL

Calvin Cycle – another diagram

Calvin Cycle (Light-Independent Reaction) – Summary

• CO2 is converted into carbohydrate (PGAL).

• Occurs in the Stroma.• ATP and NADPH provide the energy.

• PGAL = 3 carbon sugar that is used to make Glucose or other carbohydrates.

Overview of the Dark Reactions

• Carbon dioxide is broken and “fixed” into glucose or fructose molecules in the CALVIN CYCLE!!!!

• Glucose subunits can make cellulose or other polysaccharides, such as fruit sugars.

• The carbon skeleton in glucose also helps to synthesize other important biochemical compounds such as, lipids, amino acids, and nucleic acids.

Diagram of Photosynthesis