Energy transfers AQA A2 Biology PART 1 of 4 TOPICS: Photosynthesis

This resource includes light dependant reactions and light independant reactions and the factors that affect the rate of photosynthesis 

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TOPICS: Photosynthesis Respiration
Energy and ecosystems Nutrient cycles
Energy transfers (AQA A2 Biology) PART 1 of 4
TOPICS
PHOTOSYNTHESIS…read more

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Light dependant reactions:
Non-cyclic photophosphorylation
The chlorophyll in photosystem 2 undergoes photoionisation where 2 electrons are excited when it absorbs
light energy (it is important that you say the chlorophyll in photosystem 2 and not just
photosystem and light energy in the exam and not just light as in both these cases you will
lose a mark). These electrons are accepted by an electron acceptor and are sent down an electron
transport chain where the electron carriers go through a series of redox reactions to photosystem 1.
During this, the electrons lose energy which is used for chemiosmosis. This is when protons are
actively transported into the thylakoid from the stroma. A concentration gradient is created and
therefore the hydrogen ions move back into the stroma down their concentration gradient via ATP
synthase (an enzyme and a carrier protein). This makes the ions lose energy which is used by the
enzyme to make ATP from ADP and Pi. The chlorophyll in photosystem 1 also undergoes
photoionisation by light energy making two electrons get excited and leave the chlorophyll (the same
rule in the bracket applies to this photosystem as well). The electrons are accepted by an
electron acceptor and are sent down a shorter electron transport chain where no ATP is made. The
electrons are given to NADP as well as 2H+ from photolysis of water to reduce it to make
NADPH/Reduced NADP. Other products from photolysis such as ½O2 is released into the
atmosphere and 2 electrons which are put into photosystem 2. NB: This reaction takes place in the
thylakoid membrane.…read more

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Light dependant reactions: Cyclic
photophosphorylation
Cyclic photophosphorylation involves only
photosystem 1 where the chlorophyll absorbs light
energy causing 2 electrons to get excited and
leave and be accepted by an electron acceptor.
The electrons go to the electron transport chain
between photosystem 2 and photosystem 1. This
is so more ATP can be made by chemiosmosis.
NB: This reaction takes place in the thylakoid
membrane.…read more

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Light independent reaction: Calvin
Cycle
This takes place in the stroma and does not involve light. This means that this
reaction involves enzymes. RuBP reacts with CO2 in the presence of the
enzyme rubisco to make 2 glycerate-3-phosphate molecules. These are
both reduced into 2 triose phosphate molecules by the oxidation of
NADPH/Reduced NADP. The reduction reaction also needs energy which is
given by hydrolysis of ATP into ADP and Pi. One carbon is used to make
glucose, other carbohydrates and proteins. The five remaining carbons are
used to make RuBP again and this needs energy which is provided by the
hydrolysis of another ATP molecule into ADP and Pi. NB: The name of
RuBP does not need to be known and glycerate-3-phosphate can be
abbreviated into GP as well as triose phosphate into TP. Always know
what you are talking about however.…read more

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Factors affecting the rate of
photosynthesis: Temperature
If temperature is low then the rate of photosynthesis is low so temperature is the
limiting factor. As temperature increases to the optimum the rate of
photosynthesis increases to the fastest showing that temperature is no
longer the limiting factor. When temperature starts to go over the optimum
temperature rate begins to decline as more water will leave by evaporation
than water coming in. High temperatures causes the enzymes involved to
denature therefore making the reaction come to a halt.…read more

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Factors affecting the rate of
photosynthesis: CO2
Low levels of CO2 means rate of photosynthesis will be low
making CO2 the limiting factor. CO2 levels at optimum and
above means photosynthesis will be at its fastest as CO2 will
not affect the rate of photosynthesis in a negative way. The
rest of the graph from the turning point is a plateau showing
that CO2 is no longer the limiting factor.…read more

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Comments

JuwairiyahZaman

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Love your powerpoints. They're very helpful :)

bennyg28

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Some good stuff, but generally too many words per slide for to be useful in a classroom situation

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