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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.…

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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…

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o 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…

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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…

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o 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.

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o 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…

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o 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…


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