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Photosynthesis
3.1 Overview of Photosynthesis
Humans, along with almost every other living organism, owe their continued
existence to photosynthesis
The energy we use, whether it comes from food when we respire or from the
wood, coal, oil or gas we burn in or homes, has been captured by
photosynthesis from…

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o An arrangement of leaves on the plant that minimises overlapping and
so avoids the shadowing of one leaf by another
o Thin, as most light is absorbed in the first few millimetres of the leaf
and so the diffusion distance is thus kept short
o A transparent cuticle and…

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They are surrounded by a double membrane and inside the membrane there
are 2 distinct regions
o The grana are stacks of up to 100 disclike structures called
thylakoids where the lightdependent stage of photosynthesis takes
place. Within the thylakoids is the photosynthetic pigment called
chlorophyll. Some thylakoids have tubular…

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3.2 The LightDependent Reaction
The lightdependent reaction of photosynthesis involves the capture of light
whose energy is used for two purposes:
1) To add an inorganic phosphate molecule to ADP, thereby making ATP
2) To split water into H+ ions (protons) and OH ions. As the splitting is
caused by…

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The loss of electrons when light hits a chlorophyll molecule leaves it short of
electrons
If the chlorophyll molecule is to continue absorbing light energy, those
electrons must be replaced
The replacement electrons are provided from water molecules that are split
using light energy
This photolysis of water also yields…

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3.3 The LightIndependent Reaction
The products of the lightdependent reaction, namely ATP and reduced NADP,
are used to reduce CO2 in the 2nd stage
Unlike the 1st stage, this stage doesn't require light directly and, in theory,
occurs whether or not light is available
It is therefore called the lightindependent…

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7) Most triose phosphate molecules are used to regenerate ribulose
bisphosphate using ATP from the lightdependent reaction

Site of the LightIndependent Reaction

The lightindependent reaction takes place in the stroma
The chloroplast is adapted to carrying out the lightindependent reaction of
photosynthesis in the following ways:
o The fluid of…

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o At this point a different factor, such as temperature, is the limiting
factor and only an alteration in its level will affect the rate of
photosynthesis
Processes such as photosynthesis are made up of a series of small reactions
It is the slowest of these reactions that determines the…

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It's still one of the rarest gases present and is often the factor that limits
the rate of photosynthesis under normal conditions
The optimum concentration of CO2 for a consistently high rate of
photosynthesis is 0.1% and growers of some greenhouse crops, such as
tomatoes, enrich the air with more…

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