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Unit 4 – The Natural Environment and Species Survival
PHOTOSYNTHESIS
What is the process of photosynthesis?
-It is one that converts light energy into chemical energy to synthesise large organic molecules from
smaller inorganic substrates
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What components are inside chloroplasts?
-Starch molecule
-Ribosomes
-Granum
-DNA loop
-Stroma
-Thylakoid space
-Thylakoid membranes
-Smooth outer and inner membrane
What is their function?
-Starch molecule stores the product of photosynthesis
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-DNA loop contains the chloroplasts’ genes for some of their proteins
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Proteins are
embedded in the membranes and are involved in the light-dependent reactions
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It contains all the enzymes needed to
carry out the light-independent reactions of photosynthesis
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-A network of proteins in the grana hold the pigments in a very precise manner that forms the
photosystems allowing for maximum absorption of light
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LIGHT-DEPENDENT REACTIONS
How do the light–dependent reactions start?
-Light is absorbed by the chlorophyll in the thylakoid membranes of the chloroplast
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What state are the chlorophyll molecules now in?
-An excited state
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What do these molecules constitute?
-The electron transport chain
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How is the energy lost through these reactions used?
-It is used in the synthesis of ATP, in a process called photophosphorylation
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What does the enzyme catalyse within the thylakoid space and what does it produce?
-The splitting of water (photolysis) gives oxygen gas, hydrogen ions and electrons
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What does this result in?
-The chlorophyll molecule is no longer positively charged
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What do the electrons that have passed along the ETC combine with?
-Co-enzyme NADP and hydrogen ions from the water
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-The products are simple sugars that are used by plants, animals and other organisms in respiration
and the synthesis of new biological molecules
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What is Carbon dioxide reduced to?
-Carbohydrate
What does NADP act as?
-It acts as a hydrogen carrier
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-This is so that it can’t react with oxygen as it is transferred from water to carbon dioxide
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What is formed as a result and what is its state?
-A 6-carbon compound is formed
-It is in an unstable state
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What happens to this 3-carbon compound?
-It is reduced to form a 3-carbon sugar phosphate called Glyceraldehyde 3-phosphate (GALP)
Where does the hydrogen for the reduction come from?
-It comes from reduced NADP from the light-dependent reactions
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Two out of every 12 GALP’s formed are used in the creation of what?
-It creates a 6-carbon sugar (hexose)
What can this be converted to?
-Other organic compounds e
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amino acids and lipids
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How is RuBP formed after this?
-Phosphorylation using ATP

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