Photosynthesis occurs in chloroplasts．You are going to investigate the effect of light intensity on the rate of photosynthesis in a chloroplast suspension． The blue dye DCPIP can be used to investigate photosynthesis．During photosynthesis，the dark－blue colour of the DCPIP changes and eventually disappears so that it becomes colourless． Read all the instructions but DO NOT DO THEM until you have drawn a table for your results in the space provided in 1（a）（i）． You should use the safety equipment provided while you are doing the practical work． Step 1 Tear the leaves into small pieces and place them into the mortar（bowl）． Step 2 Pour the ice－cold solution from the beaker labelled isolation medium into the mortar （bowl）． Step 3 Use the pestle（or spoon）to grind the leaves in the isolation medium for one minute． Step 4 Place three layers of muslin cloth into the funnel．Put the funnel into the empty beaker labelled chloroplast suspension，as shown in Fig．1．1． Step 5 Carefully hold the edges of the muslin cloth to prevent it slipping．Pour the crushed leaves and isolation medium mixture into the funnel lined with muslin cloth．Allow the mixture to filter for three minutes．Place the muslin cloth and funnel in the container labelled waste． Fig． 1.1 © UCLES 2024 0610／52／0／N／24 Step 6 Label one test-tube A and the other test-tube B. Step 7 Raise your hand when you are ready for ice-cold water to be added to the beaker labelled water-bath. Step 8 Use the small syringe to put $$\(1 \mathrm{~cm}^{3}\)$$ of the green chloroplast suspension into test-tube $$\(\mathbf{A}\)$$ and into test-tube B. Step 9 Put test-tubes $$\(\mathbf{A}\)$$ and $$\(\mathbf{B}\)$$ into the water-bath and wait for two minutes before starting step 10. Step 10 Use the large syringe to put $$\(2.5 \mathrm{~cm}^{3}\)$$ of the blue DCPIP solution into test-tube A. Put test-tube A into the test-tube rack. Place the test-tube rack 10 cm from the lamp. Position the lamp so that the light from the lamp will shine directly onto the test-tube when you switch the lamp on. Step 11 Switch the lamp on and start the stop-clock. Step 12 Measure the time taken for the blue liquid in test-tube $$\(\mathbf{A}\)$$ to return to a green colour. Record the time taken in seconds in your table in 1(a)(i). If the contents of the test-tube remain blue after 10 minutes, stop timing and record $$\(> 600\)$$ in your table in 1(a)(i). Step 13 Reset the stop-clock to zero. Step 14 Move the test-tube rack so that it is 30 cm from the lamp. Step 15 Use the large syringe to put $$\(2.5 \mathrm{~cm}^{3}\)$$ of the blue DCPIP solution into test-tube B. Put test-tube B into the test-tube rack and start the stop-clock. Step 16 Measure the time taken for the blue liquid in test-tube $$\(\mathbf{B}\)$$ to return to a green colour. Record the time taken in seconds in your table in 1(a)(i). If the contents of the test-tube remain blue after 10 minutes, stop timing and record $$\(> 600\)$$ in your table in 1(a)(i). Some types of weedkiller prevent seeds from germinating. Plan an investigation to determine the effect of weedkiller concentration on the germination of seeds. ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . ............................................................................................................................................... . .........................................................................................................................................

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