Photolysis of water During the photolysis of water, photons of split water forming oxygen gas (O 2 ), (hydrogen ions or protons) and.

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1 A2 Light-dependent reactions of photosynthesis: ATP; thylakoid; energy; Pi; electrons; grana; reduce; electron; water; chlorophyll; transport; oxidising; carriers; ADP; oxygen; NADP; light; H + ; The light dependent reactions of photosynthesis take place in the membranes of the chloroplast. These membranes are organised in stacks called. 1. absorbs energy. 2. This excites to a higher level, so they are removed from chlorophyll, it. 3. Electrons are passed to in an chain, reducing each one in turn. 4. Energy is released and used to join and to form. 5. of water produces protons, electrons and ; 6. is reduced by the electrons and protons (hydrogen). Photolysis of water During the photolysis of water, photons of split water forming oxygen gas (O 2 ), (hydrogen ions or protons) and O H e- The electrons are passed to, replacing those it lost when oxidised. The hydrogen ions and further electrons are used to NADP.

2 A2 Light-dependent reactions of photosynthesis: ATP; thylakoid; energy; Pi; electrons; grana; reduce; electron; water; chlorophyll; transport; oxidising; carriers; ADP; oxygen; NADP; light; H + ; The light dependent reactions of photosynthesis take place in the thylakoid membranes of the chloroplast. These membranes are organised in stacks called grana. 1. Chlorophyll absorbs light energy. 2. This excites electrons to a higher energy level, so they are removed from chlorophyll, oxidising it. 3. Electrons are passed to carriers in an electron transport chain, reducing each one in turn. 4. Energy is released and used to join ADP and Pi to form ATP. 5. Photolysis of water produces protons, electrons and oxygen; 6. NADP is reduced by the electrons and protons (hydrogen). Photolysis of water During the photolysis of water, photons of light split water forming oxygen gas (O 2 ), H + (hydrogen ions or protons) and electrons. 2 H 2 O O H e- The electrons are passed to chlorophyll, replacing those it lost when oxidised. The hydrogen ions and further electrons are used to reduce NADP.

3 A2 Interference with the light-dependent reactions of photosynthesis What no carriers! In the absence of electron carriers in the chloroplast, electrons lost from when it absorbs light, return to a lower energy level releasing and (fluorescence). Herbicides Some herbicides (weed killers) are effective at killing plants because they inhibit transfer during photosynthesis. Suggest why such chemicals are effective at reducing plant growth

4 A2 Interference with the light-dependent reactions of photosynthesis What no carriers! In the absence of electron carriers in the chloroplast, electrons lost from chlorophyll when it absorbs light, return to a lower energy level releasing heat and light (fluorescence). Herbicides Some herbicides (weed killers) are effective at killing plants because they inhibit electron transfer during photosynthesis. Suggest why such chemicals are effective at reducing plant growth. No/less ATP and reduced NADP are produced during the light-dependent reactions of PS. This means that glycerate phospahte (GP) cannot be reduced to triose phosphate (TP). Less/no organic carbon compounds such as glucose/cellulose can be synthesised, reducing productivity/growth/ resulting in death.

5 A2 Photosynthesis and ATP: ADP; moved; protons; respiration; more; gradient; Synthase; single; Pi; chlorophyll; immediate; active transport; energy; dark; produce ATP production in the chloroplast The mechanism used to produce ATP is similar to that found in mitochondria and is called chemiosmosis. Energy from the transfer of electrons in the light dependent reactions, pumps into the space within grana. Movement of protons down the electrochemical occurs via ATP, allowing to bond with to make ATP. GIVE ME SOME ENERGY NOW! ATP is often described as an source of energy because energy release from it only involves a reaction or step. ATP + + ATP production via respiration too. Plants synthesise ATP via the light dependent reactions of photosynthesis. However, they also synthesise ATP during. Plants cannot just rely on ATP production via photosynthesis because. 1. In the no ATP production can occur by photosynthesis. 2. Some tissues are unable to photosynthesise and so produce ATP (they may lack or be underground). 3. ATP cannot be from cell to cell or stored (it s not very stable). 4. Plants use ATP than they in photosynthesis. Some uses of ATP in plants include for of mineral ions and the synthesis of proteins.

6 A2 Photosynthesis and ATP: ADP; moved; protons; respiration; more; gradient; Synthase; single; Pi; chlorophyll; immediate; active transport; energy; dark; produce ATP production in the chloroplast The mechanism used to produce ATP is similar to that found in mitochondria and is called chemiosmosis. Energy from the transfer of electrons in the light dependent reactions, pumps protons into the space within grana. Movement of protons down the electrochemical gradient occurs via ATP synthase, allowing ADP to bond with Pi to make ATP. GIVE ME SOME ENERGY NOW! ATP is often described as an immediate source of energy because energy release from it only involves a single reaction or step. ATP ADP + Pi + energy ATP production via respiration too. Plants synthesise ATP via the light dependent reactions of photosynthesis. However, they also synthesise ATP during respiration. Plants cannot just rely on ATP production via photosynthesis because. 1. In the dark no ATP production can occur by photosynthesis. 2. Some tissues are unable to photosynthesise and so produce ATP (they may lack chlorophyll or be underground). 3. ATP cannot be moved from cell to cell or stored (it s not very stable). 4. Plants use more ATP than they produce in photosynthesis. Some uses of ATP in plants include for active transport of mineral ions and the synthesis of proteins.

7 A2 Synoptic thoughts! Extraction of chloroplasts Leaves can be homogenised in a blender in the presence of cold, isotonic buffer. The extract can then be filtered. Explain the importance of each process/step in bold. Homogenisation: Cold: Isotonic: Buffer: Filtration: Chloroplasts can be separated from the filtered homogenised plant tissue by differential. Spinning the extract at low speed will make a pellet of cell debris and. Removing the and spinning it at a higher speed will separate out the into a pellet, whilst mitochondria and less dense remain in the supernatant.

8 A2 Synoptic thoughts! Extraction of chloroplasts Leaves can be homogenised in a blender in the presence of cold, isotonic buffer. The extract can then be filtered. Explain the importance of each process/step in bold. Homogenisation: breaks open the cells by damaging the cell walls. Cold: Low temperatures reduce the kinetic energy of molecules, slowing down enzyme catalysed reactions. This helps to preserve the chloroplasts so they can still function. Isotonic buffer has the same water potential as the chloroplasts. As a result there is no net movement of water by osmosis into the chloroplasts, preventing them from bursting. Buffer keeps the ph constant helping to prevent the denaturation of proteins and enzymes. Filtration helps to remove intact plant tissue and larger cell debris. Chloroplasts can be separated from the filtered homogenised plant tissue by differential centrifugation. Spinning the extract at low speed will make a pellet of cell debris and nuclei. Removing the supernatant and spinning it at a higher speed will separate out the chloroplasts into a pellet, whilst mitochondria and less dense organelles remain in the supernatant.