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 $$$51 \mathrm{~cm}^{3}$$$ 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 $$$5 \mathrm{~cm}^{3}$$$ 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 $$$5 \mathrm{~cm}^{3}$$$ 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. Fig. 1.1 State the independent variable in this investigation. ................................................................................................................................. (ii) State the purpose of wrapping the beaker in foil in step 1. ....................................................................................................................................... . ....................................................................................................................................... . ................................................................................................................................. (iii) Explain why it was important to remove the air bubbles from the syringe in step 6. ....................................................................................................................................... . ....................................................................................................................................... . .................................................................................................................................

Biology

IGCSE&ALevel

CAIE

Exam No：0610_s24_qp_61 Year：2024 Question No：1(b)

Answer:

Knowledge points:

4.1.1 List the chemical elements that make up: – carbohydrates – fats – proteins

4.1.10 Describe the roles of water as a solvent in organisms with respect to digestion, excretion and transport

4.1.2 State that large molecules are made from smaller molecules, limited to: – starch and glycogen from glucose – cellulose from glucose – proteins from amino acids – fats and oils from fatty acids and glycerol

4.1.3 Describe the use of: – iodine solution to test for starch – Benedict’s solution to test for reducing sugars – biuret test for proteins – ethanol emulsion test for fats and oils – DCPIP test for vitamin C

4.1.4 Describe the use of: – iodine solution to test for starch – Benedict’s solution to test for reducing sugars – biuret test for proteins – ethanol emulsion test for fats and oils – DCPIP test for vitamin C

4.1.5 Describe the use of: – iodine solution to test for starch – Benedict’s solution to test for reducing sugars – biuret test for proteins – ethanol emulsion test for fats and oils – DCPIP test for vitamin C

4.1.6 State that water is important as a solvent

4.1.7 Explain that different sequences of amino acids give different shapes to protein molecules

4.1.8 Relate the shape and structure of protein molecules to their function, limited to the active site of enzymes and the binding site of antibodies

4.1.9 Describe the structure of DNA as: – two strands coiled together to form a double helix – each strand contains chemicals called bases – cross-links between the strands are formed by pairs of bases – the bases always pair up in the same way: A with T, and C with G (full names are not required)

5.1.1 Define the term catalyst as a substance that increases the rate of a chemical reaction and is not changed by the reaction

5.1.10 Explain the effect of changes in temperature on enzyme activity in terms of kinetic energy, shape and fit, frequency of effective collisions and denaturation

5.1.11 Explain the effect of changes in pH on enzyme activity in terms of shape and fit and denaturation

5.1.2 Define enzymes as proteins that function as biological catalysts

5.1.3 Describe why enzymes are important in all living organisms in terms of reaction speed necessary to sustain life

5.1.4 Describe enzyme action with reference to the complementary shape of an enzyme and its substrate and the formation of a product (knowledge of the term active site is not required)

5.1.5 Investigate and describe the effect of changes in temperature and pH on enzyme activity

5.1.6 Investigate and describe the effect of changes in temperature and pH on enzyme activity

5.1.7 Investigate and describe the effect of changes in temperature and pH on enzyme activity

5.1.8 Explain enzyme action with reference to the active site, enzyme-substrate complex, substrate and product

5.1.9 Explain the specificity of enzymes in terms of the complementary shape and fit of the active site with the substrate

6.3.1 Describe the importance of: – nitrate ions for making amino acids – magnesium ions for making chlorophyll

6.3.2 Explain the effects of nitrate ion and magnesium ion deficiency on plant growth

Answer:

Knowledge points:

Solution:

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