PHOTOSYNTHESIS
Photos (light) + synthesis (put together or manufature)
Plants…
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Harness energy from the sun through chloroplasts
Then store the energy converted into carbohydrate
molecules in the cell wall and vacuoles
Undergo PHOTOSYNTHESIS - the process by which
plants convert energy from the sun to provide
energy for themselves and almost all life forms
Photosynthesis…
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Allows plants to create organic molecules
they use as fuel.
Basis of all food chains
Occurs mostly in LEAVES, which are the
main organs for photosynthesis
Photosynthesis
Chloroplasts
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Organelles specialized for photosynthesis
Have two membranes surrounding the
liquid in its interior called the STROMA
Inside the inner membrane are series of
flattened interconnected sacs called
GRANA
Each of these flattened sacs is called a
THYLAKOID
Chloroplasts (cont’d)
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A closer look at the thylakoid will reveal its membrane
separating it with the stroma or the liquid part of the
chloroplast – it is in this membrane that light trapping
molecules are located
LIGHT DEPENDENT REACTION of photosynthesis –
aka PHOTOCHEMICAL STAGE
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occurs in thylakoid membrane (because of the light trapping
molecules)
LIGHT INDEPENDENT REACTION of photosynthesis –
aka DARK REACTION/CALVIN CYCLE
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occurs in the stroma
Photosynthesis
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LIGHT and WATER are needed to
perform this process (sun heats water in
plant leaves)
Chlorophyll in chloroplasts (scattered
throughout each plant cell), absorb
energy in the form of light from the sun
Plants take in carbon dioxide – obtained
through tiny openings known as stomata
Plants absorb water and nutrients
dissolved in the soil through their root
system and its network of conducting cells
called xylem vessels
Words to Know: Photosynthesis
ATP Adenosine Triphosphate
ADP Adenosine Diphosphate
NADPHNicotinamide Adenine
Dinucleotide Phosphate
(Hydrogen acceptor)
Reactant
- substances that undergo
chemical reaction
Product
- outcome of the reaction
Photosynthesis Equation
Photosynthesis
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Is the reverse of the reactions that occur in
animals during cellular respiration
CELLULAR RESPIRATION – the splitting
apart of glucose by water to produce
carbon dioxide and energy
PHOTOSYNTHESIS – the splitting apart
of water by energy to produce glucose
from carbon dioxide, with oxygen given
off
Two Stages of Photosynthesis: Light
Dependent Stage
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Occurs in thylakoid membrane
Energy from the sun (light energy) is absorbed by
the chlorophyll and then converted into chemical
energy.
Light energy is needed to split the water molecules
into hydrogen and oxygen.
Oxygen is released as a waste product.
These reactions are called photochemical light
reactions because they require light to occur.
Light Dependent Stage
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Involves two groups of light absorbing
molecules found in the thylakoid
membranes: Photosystem I and
Photosystem II
Both capture solar energy to energize
electrons.
Both cooperate in the light reactions.
Photosystem II functions first.
Light Dependent Stage
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When excited by light from the sun, chlorophylls
release energized electrons. The photosystems
transfer the energized electrons to electron
transport chains.
Electrons in Photosystems II that were shuttled to
Photosystem I provide energy to make ATP.
Electrons from Photosystem I reduce the coenzyme
NADP+ (NAD = Nicotinamide adenine dinucleotide)
to NADPH.
Photosystem II regains electrons by splitting water
and releasing oxygen.
Steps: Light Dependent Reaction
1
Light energy
is absorbed by
2
3
Chlorophyll A
that becomes
Energized chlorophyll
supplies energy to
split
4
5
5
that are trapped by
6 NADP (H acceptor)
forms
combine
4
water
into
H2
(becomes an energy carrier)
phosphate
with
5
O
ADP
to form
is released
7 NADPH2 to be used for dark reaction
6
ATP
to be used for dark reaction
Light Independent Stage
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Second stage of photosynthesis
Formation of glucose from carbon dioxide
doesn’t directly require light.
Aka Calvin Cycle for Melvin Calvin
Occurs in stroma
Consists of cyclical series of reactions that
assembles sugar molecules from carbon
dioxide and the energy-containing
products of the light-dependent reaction
with the aid of enzymes.
Light Independent Stage
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In the stroma, the enzymes combine carbon dioxide with
ribulose phosphate (RuBP) which is a five-carbon sugar and
produce glyceraldehydes-three-phosphate (G-3-P), an
energy-rich, three-carbon sugar formed by the splitting of
sugar.
G-3-P can be used by a plant cell to make glucose and
other organic molecules.
The glucose produced during photosynthesis is used by plans
as fuel for cellular respiration, and starting material to make
cellulose.
Excess sugar is combined with a large carbohydrate
molecule and stored as starch in their roots, tubers or fruits.
Steps :
Light Independent Reaction
1
6 CO2 molecules
combines with
2
RuDP
(CO2 acceptor)
forms
3
4
6-C sugar
(unstable sugar)
splits to form
2 molecules of PGA (3- C compound)
-called:
Biochemical Pathway
combines with
5
2H
(from light reaction (NADPH))
forms
6
2 molecules of PGAL
is converted into
7
RuDP
to be reused
to combine with
CO2
Glucose
6
H2O
by-product used
in light reaction
Comparison of the two
Reaction
Site of Occurence
Light
Thylakoid-grana
Dark
stroma
Initial Requirement
(Reactants)
Light Energy, water, ATP, NADPH, and
and chlorophyll A
CO2,
End Product
ATP, NADPH,
Oxygen
Glucose, water, NADP,
ADP and inorganic
phosphate
Both reactions thus form a cycle in which the reactants: water and
carbon dioxide produce oxygen and sugar (glucose) as products
Plants need:
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Carbon dioxide
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Water
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Oxygen (for cellular respiration)
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Hydrogen
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Nitrogen
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Potassium
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Phosphorus
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Calcium
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Magnesium
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Sulfur
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Boron
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Copper
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Iron
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Molybdenum
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Zinc