Unit 3: Photosynthesis

Photosynthesis

•Photosynthesis is an anabolic pathway where
light energy is converted to chemical energy in the
chloroplasts of plant leaves
-Light energy, carbon dioxide and water are used
to form glucose molecules and oxygen
-The energy in glucose can be transferred to other
organisms when eaten or used by the plant for
food

Where does photosynthesis take place?

Chloroplasts in leaves

Sunlight is absorbed
by a pigment
molecule called
chlorophyll.
Chlorophyll gives
plants their green
color, as it reflects
green wavelengths
and absorbs other
wavelengths.

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CO2 enters leaves and O2 exits through
stomata

Stomata are small pores, or openings, in the plant leaves.

Photosynthesis Formula

Carbon dioxide + water + sunlight →glucose + oxygen

How Does it Work?

A complex series of chemical reactions takes place in two main
steps:

Step one- Light Reactions: absorb light energy from the sun,

take in water

Step two- Calvin Cycle: Take in CO2
and convert into glucose

Transfer of energy

sunlight→chemical energy

Transfer of matter

Carbon from carbon dioxide (CO2)→ carbon in glucose (C6H12O6)

Light Reactions

NADPH is an
electron carrier

Sunlight absorbed and water
molecules are split, releasing
oxygen and electrons.
Electrons carried to Calvin Cycle.

O H-H

Calvin Cycle (Dark Reactions)

Electrons are used to
build glucose using the
carbon from carbon
dioxide.

Photosynthesis

Why do we care about photosynthesis?

• Oxygen to breathe
• Plants take in CO2, which can cause climate change in large

amounts (which it is)

• Makes sugars, which we eat
• Can use photosynthetic organisms like algae to make fuel

• Algae can store their energy in oils instead of sugars

Short Video Version

Long Version