F214 OCR A2 Biology Module 3 Photosynthesis

Here is a very detailed document of the F214 photosynthesis module. It answers every part of the specification and is along the same lines as the other F214 and F215 documents I have put on here. 

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  • Created on: 21-06-11 11:13
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F214 Communication, Homeostasis and Energy
Module 3 Photosynthesis
4.3.1 Photosynthesis
a. Define the terms autotroph and heterotroph
o Organisms that can synthesise complex molecules like carbohydrates,
lipids, proteins, nucleic acid and vitamins from inorganic molecules as a
source of energy.
o They also use light energy and chemical energy.
o Organisms which cannot make their own food.
o They digest complex organic molecules into simpler soluble ones which
they then use to synthesise complex molecules such as lipids, proteins and
nucleic acids.
o The chemical potential energy is released from the complex organic
b. State that light energy is used during photosynthesis to produce complex organic
Summarised equation: 6CO2 + 6H2O (+ light energy) C6H12O6 + 6O2
c. Explain how respiration in plants and animals depends upon the products of
Oxygen needed for aerobic respiration first appeared in the atmosphere due
to photosynthesis.
It allows phototrophs and heterotrophs to release the chemical potential
energy in complex organic molecules which were made during photosynthesis.
d. State than in plants photosynthesis is a two-stage process taking place in
Photoautotrophs have organelles called chloroplasts where photosynthesis
takes place.
There are two stages to photosynthesis: the light dependant stage and the light
independent stage.
e. Explain how the structure of chloroplasts enables them to carry out their functions

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Most chloroplasts are disk shaped and between 2-10m long.
Each chloroplast has an envelope which below is an intermembrane space about
10-20nm wide.
The outer membrane is permeable to many small ions.
The inner membrane is less permeable with transport proteins embedded. It is
folded into lamellae which are stacked up to form a granum.
The grana are attached by intergranal lamellae.
The stroma is a fluid filled matrix where the light dependant stage takes place
due to it containing the enzymes needed.…read more

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They are arranged in funnel shaped structures called photosystems.
g. Explain the importance of photosynthetic pigments in photosynthesis
o Chlorophyll is a mixture of pigments.
o They have a long hydrocarbon chain and a porphyin group.
o When light hits them it causes a pair of electrons associated with
magnesium to become excited.
o There are two forms of chlorophyll a both of which appear green: P680
and P700.…read more

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Non-cyclic photophosphorylation
o When light shines on photosystem II, it excites a pair of electrons which
leave the chlorophyll molecule from the primary pigment reaction centre.
o The electrons then pass through a chain of electron carriers, which
releases energy which is used to synthesis ATP.
o The light also strikes photosystem I where a pair of electrons is lost.
o Along with protons formed at photosystem II due to photolysis of
water, the electrons join NADP to form reduced NADP.…read more

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Pairs of TP molecules combine to form hexose sugars e.g. glucose.
o Some glucose molecules can be isomerised to form the hexose sugar
o Glucose and fructose molecules may combine to make sucrose which is a
o Hexose sugars can be polymerised to make other carbohydrates.
o TP can be converted to glucose which may be combined with fatty acids
formed from GP to make lipids.
m. State that TP can be used to make carbohydrates, lipids and amino acids.…read more

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If there is little or no light available then the light dependant stage will
not happen and so it will also stop the light independent stage because it
will not have the products needed.
o Increasing the temperature will have little effect on the light-dependant
reaction apart from the photolysis of water because it is not dependant
on enzymes.…read more

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Above 25oC the rate of photosynthesis levels and then falls because
enzymes work less efficiently.
o High temperatures can also limit carbon dioxide availability because it
can cause the closure of the stomata to limit water loss.
q. Describe how to investigate experimentally the factors that affect the rate of
Light intensity
o You use a photosynthometer or an Audus microburette.
o It has to be airtight and there needs to be no bubbles in the capillary
tubing.…read more


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