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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 in the thylakoid membranes.
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…

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o The excited electrons pass to an electron acceptor and back to the
chlorophyll molecule it was from.
o There is no photolysis of water and no generation of reduced NADP.
o Small amounts of ATP which may be used in the light dependant reaction
or used in guard cells…

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o The carbon dioxide combines with the 5 carbon compound ribulose
bisphosphate (RuBP) which is catalysed by ribulose bisphosphate
carboxylase-oxygenase (rubisco). RuBP is carboxylated which is when it
is combined with carbon dioxide to have a carboxyl group.
o This makes two 3 carbon compounds glycerate 3 phosphate (GP). The…

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close. So carbon dioxide uptake is reduced as is the rate of
o If carbon dioxide concentration is lower than 0.01% it allows RuBP to
build up so levels of GP and TP are reduced.
Light intensity
o It gives us a measure of how much energy is associated…

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Light intensity
o As light intensity increases, the rate of photosynthesis increases. It is
directly proportional.
o Light causes stomata to open to allow carbon dioxide into the leaves, it
is trapped by chlorophyll to excite electrons and it splits water
molecules to produce protons which are involved in


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