Section 4: The chemistry of photosynthesis The need for light, chlorophyll and carbon dioxide

Problem to solve What substances are required for photosynthesis? -light -chlorophyll -carbon dioxide How would you prove chlorophyll and carbon dioxide are necessary for photosynthesis using the apparatus on the desk? (Hint: you have completed a similar practical in S1) Carry out experiment

What are we learning today? We are learning to: -state that photosynthesis is a two stage process -explain why light and chlorophyll are necessary for photosynthesis -explain why carbon dioxide is necessary for photosynthesis Success criteria -Two stages photolysis and carbon fixation -Photolysis, light trapped by chlorophyll to split water in to hydrogen and oxygen -Carbon fixation, carbon dioxide source of carbon for glucose

The need for light From S1 Physical science you learned that visible light is split in to the colours you can see here During photosynthesis plants convert light energy in to chemical energy (glucose)

How do plants trap light? reflected absorbed transmitted The absorbed light is used for photosynthesis Video clip - Light and starch - Science & Plants for Schools

Structure of a leaf xylem phloem Guard cells

Structure of the leaf continued The palisade mesophyll and spongy mesophyll cells have chloroplasts Chloroplasts contain the green pigment chlorophyll which is required to trap light

Chloroplasts Chloroplasts are the site of photosynthesis Video clip - chloroplasts and starch - Science & Plants for Schools Video clip - chloroplasts and starch - Science & Plants for Schools Stroma – liquid filling Grana membranes containing pigments e.g. chlorophyll Starch grains – store of glucose

Two stages of photosynthesis Photosynthesis is more than the one line word equation we know so far. Photosynthesis is a series of enzyme controlled reactions that enable plants to make their own food. There are two stages of photosynthesis. The two stages of photosynthesis are: -photolysis -carbon fixation

Photolysis – occurs in grana Waste product of photosynthesis NADP is a hydrogen acceptor that is used to transport the hydrogen to the stroma for carbon fixation Light energy is use to make ATP (energy molecule) also used in carbon fixation = photophosphorylation Light energy is used to split water in to hydrogen and oxygen

Why is carbon dioxide required for photosynthesis? Revision!! Carbon dioxide is required as the source of carbon to make glucose Carbon dioxide + Water Glucose + Oxygen CO 2 H 2 O C 6 H 12 O 6 O 2

Carbon fixation – occurs in stroma Several enzyme controlled reactions Requires energy in the form of ATP from photolysis Carbon (from CO 2 ) becomes ‘fixed’ into carbohydrate The carbon combines with hydrogen from photolysis to form glucose

Carbon fixation Carbon dioxide (CO 2 ) NADPH 2 NADP ATP ADP + Pi Glucose

What happens to the glucose? Revision!! Glucose converted into storage carbohydrate – starch Glucose also converted into cellulose - a component of cell walls

What have I learned today? Exit ticket On your exit ticket write down (if you can) the summary of photolysis and carbon fixation