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Photosynthesis
Biology 2
D. Mitchell
All life requires energy.
Almost all energy for life is derived from the
sun.
Energy from the sun enters. living systems
when autotrophs absorb sunlight.
Autotrophs (producers)-Organisms
that can make their own food.
Examples – plants, algae, and some
bacteria
Heterotrophs (consumers)
-must feed on autotrophs, one another, or
organic wastes in order to obtain energy.
-cannot make their own food.
Examples: other bacteria, many protists,
fungi and animals.
Photosynthesis
Process by which plants, algae and some
bacteria use light energy to make organic
compounds (sugar-glucose).
EQUATION FOR PHOTOSYNTHESIS
Light
ENERGY
6CO2 + 6H2O
C6H12O6 +
CARBON
DIOXIDE
GLUCOSE
WATER
Reactants
6O2
OXYGEN
Gas
Products
The equation is read six molecules of carbon
dioxide is added to six molecules of water
which yields one molecule of glucose and six
molecules of oxygen gas.
Photosynthesis takes place in the
chloroplast of plants and the cytoplasm
of bacteria.
•Chloroplasts are the specialized
organelles in plants and some
algae where photosynthesis
occurs.
•Most chloroplasts are in leaf cells
that are specialized for
photosynthesis.
Parts of the chloroplast:
1. Thylakoids: disc-shaped stacks
(granum) inside the chloroplast.
1. Stroma: dark fluid that surrounds
the grana inside the chloroplast
Chloroplast
Thylakoid membrane
Stroma (fluid)
Pigments involved in Photosynthesis
The primary pigment - chlorophyll
 Plants contain two types of
chlorophyll -chlorophyll a and
chlorophyll b
Each pigment absorbs certain wavelengths of
light (red and blue) and reflects others (green
and yellow).
Photosynthesis: The Process
•Occurs in 2 main phases
Light Dependent Reactions
•Photosystem II
•Photosystem I
Light Independent (Calvin
Cycle) Reactions
Light Dependent Reactions
•Occur in the thylakoids of the
chloroplasts during times of light
•Purpose is to absorb sunlight and
convert it to ATP that can be used
in the Calvin cycle.
Summary of Light Dependent
a) Sunlight enters the chloroplast when
pigments in the thylakoids absorb the
light.
a) Some excited electrons are released.
b) Water molecules are split into H+ and
Oxygen gas (O2) .
Summary of Light Dependent
d) Some excited electrons pass to the
Electron Transport Chain and travel
across the thylakoid membranes.
d) Energy provided in the ETCs is used
to make ATP.
f) Some excited electrons travel
down another electron transport
chain.
g) Energy is used to make NADPH
And now what….
•The ATP and the NADPH of the
light dependent reactions are
used for the next main step, the
Calvin cycle (Light independent
reactions)
Light Independent Reactions
• USES Carbon dioxide (CO2), H+, and
the energy in ATP and NADPH
• CO2 is fixed/mixed with the Hydrogen
ions to make glucose.
• Occurs in the stroma in the chloroplast
Calvin Benson Cycle
• the most common method of
carbon-dioxide fixation
• function -to produce a single
molecule of glucose (C6H12O6)
•3 phases:
1.Carbon Fixation
2.Reduction
3.Regeneration of RuBP
Summary of Light Independent Reactions
• Using ATP and NADPH from the light
dependent reactions, Carbon dioxide
(CO2) is used to make glucose (C6H12O6).
Environmental factors that affect photosynthesis
are:
•Light quality
•Light intensity
•Light availability
•Carbon dioxide availability
•Water availability