Biology · May / June 2024 · Paper 61 · Question 1

Cooking fruit and vegetables in water reduces their vitamin C content. The vitamin C is transferred from the fruit and vegetables to the water by diffusion. DCPIP can be used to estimate the concentration of vitamin C. The blue DCPIP solution reacts with the vitamin C solution and becomes colourless. A student investigated the effect of cooking time on the vitamin C content of the water. Step 1 A piece of foil was wrapped around a beaker so that the base and sides of the beaker were covered. The top of the beaker was not covered. Step 2 A piece of citrus fruit was put into the beaker. Step 3 Hot water was added to the beaker so that the piece of citrus fruit was covered. Step 4 A stop‑clock was started. Step 5 1 cm3 samples of the liquid in the beaker were taken every minute for five minutes. Each sample was put into a separate test‑tube. Step 6 A 5 cm3 syringe was filled with DCPIP solution. Any air bubbles present in the syringe were removed. Step 7 One drop of the blue DCPIP solution was added to the test‑tube containing the first sample. The test‑tube was shaken for five seconds to mix the contents. The colour of the sample in the test‑tube was observed. Step 8 The student repeated step 7 until the sample remained blue. The volume of DCPIP solution remaining in the syringe was recorded. Step 9 The syringe was refilled with 5 cm3 of DCPIP solution. Step 10 Steps 7 to 9 were repeated with the rest of the samples. Fig 1.1 shows the student’s notebook, where they recorded their results and calculated values. volume of DCPIP remaining in the syringe: 1 minute = 3.6 2 minutes = 2.8 3 minutes = 2.2 4 minutes = 1.8 5 minutes = 1.6 volume of DCPIP added: 1 minute = 1.4 2 minutes = 2.2 3 minutes = 2.8

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