Biology Chapter 4.2

Photosynthesis

KEY CONCEPTThe overall process of photosynthesis produces sugars that store chemical energy.

Photosynthetic organisms are producers.• Producers make their own

source of chemical energy.• Plants use photosynthesis and

are producers.• Photosynthesis captures energy

from sunlight to make sugars.

• Chlorophyll is a molecule that absorbs light energy.

chloroplast

leaf cell

leaf

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

Photosynthesis in plants occurs in chloroplasts.

• Photosynthesis takes place in two parts of chloroplasts.– grana (thylakoids)– stroma

chloroplast

stroma

grana (thylakoids)

• 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– oxygen is released

• The light-independent reactions make sugars.– take place in stroma– needs carbon dioxide from atmosphere– use energy to build a sugar in a cycle of chemical reactions

• 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

chloroplast1

2

43

energy

stroma (fluid outside the thylakoids)

Photosynthesis (19 min)

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Dark Reactions of Photosynthesis

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