Photosynthesis 4.3

Chloroplasts Are found in plant cells Mostly within palisade mesophyll cells Chloroplasts work as transducers by converting inorganic CO2 into carbohydrates (glucose)

On whiteboards in pairs draw and label a chloroplast

C B A D E F

The Chloroplast Has a double membrane Is filled with the stroma Has Thylakoids – stacked together called grana Spaces inside the thylakoids are connected together forming the thylakoid space Acts as a transducer – converts light energy to chemical energy in the form of ATP

Different stages of photosynthesis take place in different regions of the chloroplast

Light Harvesting Photosynthetic pigments trap light energy Chlorophyll a Chlorophyll b Carotenoids – Xanthophyll and carotene They are arranged in clusters in the thylakoid membrane – the antenna complex Their arrangement ensures maximum light harvesting

Antenna Complex The arrangement funnels light to chlorophyll a Chlorophyll a is the reaction centre The other pigments are accessory pigments Reaction centre + accessory pigments = photosystem

Position of the Photosystem in the thylakoid membrane

Wavelengths of light Light photons travel in waves Each colour of light has a different wavelength (nm) All the colours combine to form white light

Wavelength of light Not all light is used by the chlorophyll Reflected Transmitted

Absorption Spectrum Shows which light is absorbed by each pigment No pigment absorbs green-yellow Hence plants look green

Action Spectrum Shows the rate of photosynthesis at each wavelength Most photosynthesis where most light is absorbed Measure O2 production to indicate rate of photosynthesis

Chromatography

Questions to check your understanding Page 15 Q 1- 10

Photosystems There are two types of photosystem Each absorbs light at a different wavelength Photosystem II – P680 , absorbs light at 680nm(orange-red light) Photosystem I – P700, absorbs light at 700nm(red light)

Biochemistry of Photosynthesis Light dependent stage Light independent stage

Photosynthesis A series of biochemical pathways In the chloroplast Light dependent stage – thylakoid membrane Cyclic and non-cyclic photophosphorylation Light independent stage - stroma

Location of each step

Light dependent stage

Light dependent stage Electrons excited and emitted Electrons accepted by electron acceptors Electrons moved down ETCs Losing energy (linked to ATP production) Production of reduced NADP and ATP Both needed in the next stage

Cyclic or non-cyclic?

Comparison Cyclic Non-Cyclic Photosystem I is final e- acceptor Only ATP produced NADP is final e- acceptor ATP and reduced NADP produced

Box activity Complete the order for light dependent photosynthesis.

Light independent Stage CALVIN CYCLE Occurs in the stroma of the chloroplasts Involves a variety enzyme catalysed reactions. Uses the products of the light dependent stage (ATP as an energy source and reduced NADP as a source of the reducing power to reduce CO2 and synthesise hexose sugar.

Check the typing on yours:

Light independent Stage Enzyme reactions RuBISCO ‘fixing’ of CO2 Needs ATP and reduced NADP to take place – from LDS. ATP 

In Pairs on a whiteboard – 6 minutes to answer these questions

Ribulose bis phosphate palisade Calvin cycle Ribulose bis phosphate Absorb light Absorption spectrum: % light absorbed by the pigments at different wavelengths Action spectrum: the rate of photosynthesis of a plant at

Box Activity Photosynthesis sort/order

Research Methods How has photosynthesis been studied

Engleman

Jun 08 a) Fully explain the results of this experiment (3)

Calvin

Explain how the hydrogen is being formed during photosynthesis (1) What would be the normal hydrogen acceptor in the chloroplast? (1) What conclusions may be drawn from the results shown in the table? (2)