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BIOLOGY:
Class Notes #1= Photosynthesis
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Autotrophs vs. Heterotrophs
Autotrophs make their own food/energy
Ie) Plants use the light energy from the sun to produce food
Heterotrophs eat other things for food/energy
Ie) Animals cannot use the sun’s energy directly so they consume food
Mushrooms decompose other organisms
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The chemical process that produces food for autotrophs is photosynthesis.
The breaking down of food to release energy for cell work is cellular respiration.
Chemical equation for PHOTOSYNTHESIS:
Chlorophyll / enzymes
Chemical equation for RESPIRATION:
C6H12O6 + 6O2
6CO2 + 6H2O + 36ATP (38 ATP, in some prokaryote cells)
C reduced + O oxidized ----------> C Oxidized + O reduced
II. The molecule which temporarily stores
energy for the cell until it is needed is called
adenosine triphosphate (ATP).
This molecule consists of three different parts:
 adenosine adenine: a nitrogen
containing double ring molecule
 ribose:
a five carbon sugar

3 phosphates: the inorganic portion of
the molecule, containing the elements, P and O
The chemical bonds joining one phosphate to the next are high energy bonds. It takes
a lot of energy to form them and a lot of energy can be released if they are broken.
Energy from food
ADP + P ----- ATP (enzyme that catalyzes this reaction is ATP Synthetase)
ATP  ADP + P + energy to do cell work ( enzyme that catalyzes this reaction is called
ATPase)
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PLANTS
 Plants have an organelle called chloroplasts.
 This organelle contains a pigment called chlorophyll which absorbs the light
energy from the sun (these give them their green color).
 Photosynthesis occurs in the chloroplasts.
 Most photosynthesis occurs in the green leaves and some occurs in the green
stems.
Photosynthesis is a process in which green plants convert energy
from sunlight into chemical energy!
 In the chloroplast there are membranes called thylakoids
which are arranged in stacks called grana.
 The space outside the thylakoids is called the stroma.
2 parts to chloroplast:
a. Grana- Contains chlorophyll.
Looks like coin stacks.
Where light dependent reactions occur.
b. Stroma- No chlorophyll. Surrounds grana.
Where sugar is made.
Where light independent (DARK) reactions occur.
Photosynthesis is in 2 parts:
1) Light Dependent Reactions=
(AKA Light Reactions)
take place in the thylakoids
2) Light Independent Reactions=
(AKA Calvin Cycle) (Dark)
take place in the stroma
Location of Photosynthesis
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1 —Light Reactions
 Sunlight hits the chlorophyll in a leaf.
 This light energy energizes electrons in the chlorophyll which are passed into the
Electron Transport Chain. These high energy electrons move through the
ETC freeing energy with each step in the form of ATP.
 Water molecules are split to replace the electrons lost from the chlorophyll (in
the form of Hydrogen) & Oxygen from the water molecule is released.
(This is what we breathe!)
 Hydrogen atoms from the water are picked up the enzyme NADP+ which then
becomes NADPH.
 NADPH carries the hydrogen to the next step (Calvin Cycle = Dark Reaction) and
is then returned to NADP+.
st
Summary
 The products of the light reaction are Oxygen
(waste product from splitting water),
 NADPH (carrying hydrogen to the next step), &
 ATP (which is carrying energy to the next step).
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2 —Light Independent Reactions (AKA Calvin Cycle) = (DARK Reaction)
 CO2 enters the cycle from the atmosphere and combines
with carbon molecules which are already in the cycle.
nd
(The plant “breathes” in CO2 through opening in the leaves
called stomata. )
 The ATP and NADPH from the Light Reactions
are used to give these new carbon molecules more
energy. (ATP becomes ADP and goes back to the
light reactions in order to become ATP again. NADPH becomes NADP+
and goes back to the light reactions to get more hydrogen.)
 Some of these molecules are used to produce sugars, lipids, amino aids, and
other compounds needed for plant metabolism and growth. (This is where the
six-carbon glucose is made!)
 Left over carbon molecules cycle back around and join with new CO2 coming in.
Summary
 The Calvin Cycle uses ATP and NADPH from
the light reactions &
 CO2 from the environment to
produce high-energy sugars (glucose).
Formula
6CO2 + 6 H2O  C2H12O6 + 6O2 + 6H2O
 CO2 from air
 H2O from ground

 Glucose (C6H12O6) is a CARBOHYDRATE –
Carbon comes from CARBON DIOXIDE!
 O2 out (what we breathe)
Factors affecting the rate of photosynthesis
1)Sunlight - its Intensity & wavelength. 2) H2O and CO2 – availability
3) Temperature (0 –35O C) 4) Minerals 5) Any factor that influences the
production of chlorophyll, enzymes, or energy carriers(ATP and NADPH).
The rate of photosynthesis will always correspond to that factor which is in least
supply. Its rate will only increase when its supply is increased.