PHOTOSYNTHESIS

The most important biochemical process on Earth.

What types of organisms can perform the reactions of PHOTOSYNTHESIS?

1. All Plants (Plant Kingdom)

2. Algae (Protist groups: red algae, brown algae, green algae, diatoms, dinoflagellates)

3. Cyanobacteria (Bacteria Kingdom)

Reaction of Photosynthesis:

Although the reaction looks simple, the process is complex. There are 2 stages:1. Light Dependent Reactions2. Calvin Cycle = Light Independent Reaction

What is the initial energy source?

Where do the reactants come from? Where do products go?

Chloroplast = organelle that is the site of photosynthesis (both stages)

Pigments are held in the thylakoids of a chloroplast:chlorophyll a, chlorophyll b, and accessory pigments (orange, red, blue)

Simplified View of Light Dependent Reactions:

Light Dependent Reactions

ATP = cellular energy

Summary of Light Dependent Reactions:

1. water is used up and oxygen is produced 2. Photosystem II captures sunlight and absorbs electrons from water splitting to replace electrons from chlorophyll 3. Photosythem I also captures sunlight and carries electrons from proteins 4. Electron is captured by NADP+ along with H+ ions to form higher energy NADPH.

Summary of Light Dependent Reactions (cont):

5. ATP is produced by H+ ions moving through an enzyme called ATP Synthase

6. Light Dependent Reactions occur in green parts of a plant = leaves (and not in the roots underground)

Also: algae and cyanobacteria contain pigments to absorb sunlight and conduct photosynthesis

Calvin Cycle

Summary of Calvin Cycle = Light Independent Rx:

1. The 2 high energy molecules produced in Light Dependent Rx are used up: ATP and NADPH

2. CO2 is used up 3. One organic sugar, glucose, is

produced for each 6 CO2 used. 4. RuBP is regenerated at the end of

each cycle and ready for the next CO2

Light Dependent Reactions and Calvin Cycle are the 2 stages of PHOTOSYNTHESIS

Why is photosynthesis THE most important biochemical process on Earth?

1. source of atmospheric oxygen

2. source of all organic molecules, starting with glucose (a carbohydrate)

3. mitigates global warming by absorbing CO2