4.2 Overview of Photosynthesis

The overall process of photosynthesis produces sugars that store chemical energy.

6CO2 + 6H2O C6H12O6 + 6O2

4.2 Overview of Photosynthesis

Photosynthetic organisms are producers.

• Producers make their own source of chemical energy (food).

• Plants use photosynthesis and are producers.

• Photosynthesis captures energy from sunlight to make sugars.

4.2 Overview of Photosynthesis

• Chlorophyll is a molecule that absorbs light energy.

chloroplast

leaf cell

leaf

• In plants, chlorophyll is found in organelles called chloroplasts.

• Chlorophyll reflects green light!

4.2 Overview of Photosynthesis

Photosynthesis in plants occurs in chloroplasts.

• Photosynthesis takes place in two parts of chloroplasts.

– grana (stack of thylakoids)

– Stroma (chloroplast fluid)

chloroplast

stroma

grana (thylakoids)

4.2 Overview of Photosynthesis

There are 2 stages of photosynthesis

• Light Dependent Reactions (uses light) (Light Reactions)

•Light Independent Reactions (doesn’t use light) (Dark Reactions)

4.2 Overview of Photosynthesis

The light-dependent reactions capture energy from sunlight.

– take place in thylakoids– water and sunlight are needed– chlorophyll absorbs energy– energy is transferred along thylakoid membrane then to

light-independent reactions (dark reactions)– oxygen is released

4.2 Overview of Photosynthesis

• The light-independent (dark) reactions make sugars.

– take place in stroma– needs carbon dioxide from atmosphere– use energy from light reactions to build a sugar in a

cycle of chemical reactions

4.2 Overview of Photosynthesis

The equation for the overall process is:

6CO2 + 6H2O C6H12O6 + 6O2

C6H12O6

granum (stack of thylakoids)

thylakoid

sunlight

1 six-carbon sugar

6H2O

6CO2

6O2

chloroplastchloroplast1

2

43

energy

stroma (fluid outside the thylakoids)