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• Photosynthesis – Energy from Sunlight– Photosynthesis - the

process by which autotrophs convert sunlight into a usable form of energy. (Food!!!)

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• Autotrophs that perform photosynthesis require pigments to trap the energy in light. The most common photosynthetic pigment is chlorophyll.

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• Chlorophyll is a green pigment that absorbs violet, blue, and red light. These wavelengths of light are necessary for photosynthesis

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• Autotrophs also contain other pigments called accessory pigments. (yellow,red,orange)

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Chloroplasts

In many organisms chlorophyll and other pigments are located in specialized organelles inside the cell. These are called chloroplasts.

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• A photosynthetic cell may contain several thousands chloroplasts. Inside this tiny organelle is where photosynthesis takes place.

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• Inside the chloroplasts are stacks of disk shaped structures called grana.

• The individual disk shaped structures are called thylakoids.

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• Chlorophyll is housed inside of the thylakoids.

• Inside the thylakoids, hundreds of chlorophyll molecules and other pigments are organized into units called photosystems.

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The Big Picture 

• The process of photosynthesis can be summed up by the following chemical equation. 

6CO2 + 6H2O+ energy C6H12O6 + 6O2

Reactants Products

(glucose)

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• In this equation the sugar glucose is a product.

• The energy stored in glucose can be used later to produce ATP.

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Two Cycles• Light-dependent reactions -

Photosynthesis begins when light is absorbed by the grana in the chloroplast. This starts the light dependent reactions:

- Takes place in the thylakoid membranes1. Water is split into hydrogen ions (H+), electrons, and oxygen (O2)2. Oxygen diffuses out of the chloroplast3. ATP and NADPH are produced

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Calvin Cycle – construction of carbohydrates from CO2 - Takes place in the stromaThis follows the light dependent reactions. The products ATP and NADPH are used in the Calvin cycle.

The Calvin cycle requires an input of CO2 to make sugars.

One glucose molecule is built for every six CO2 molecules that enter the cycle.

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Why?• Plants use glucose for growth, they create molecules

such as cellulose by linking chains of glucose molecules.

• Most plants store glucose as starches. Starches are found in plant foods such as wheat and potatoes.

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• When heterotrophs consume autotrophs they breakdown starches to glucose and use the energy in glucose for their own energy and structural needs.

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