Biology 9700/34 May/June 2023: question paper and mark scheme

Question

Milk is a source of protein and reducing sugars. Different types of milk contain different concentrations of protein. The concentration of protein in milk can be measured using potassium hydroxide solution and copper sulfate solution. You will investigate the protein content of milk. You are provided with the materials shown in Table 1.1. Table 1.1 labelled contents hazard volume / cm3 milk containing a 5.0% M none 50 concentration of protein W distilled water none 100 harmful K potassium hydroxide solution 20 irritant C copper sulfate solution none 20 milk containing an unknown U none 20 concentration of protein If any solution comes into contact with your skin, wash off immediately under cold water. It is recommended that you wear suitable eye protection. You will prepare a range of known concentrations of protein, using the milk containing a 5.0% concentration of protein, M. You will need to carry out a serial dilution of the milk containing 5% protein, M, to reduce the concentration of protein by half between each successive dilution. You will need to prepare four concentrations of protein in addition to 5.0% protein, M. After the serial dilution is completed, you will need to have 10 cm3 of each concentration available to use. (a) (i) Complete Fig. 1.1 to show how you will prepare your serial dilution. Fig. 1.1 shows the beakers you will use. For each beaker, add labelled arrows to show: • the volume of protein solution transferred • the volume of distilled water, W, added. Under each beaker, state the concentration of protein solution. 0 cm3 of W 20 cm3 of 5.0% protein solution, M 10 cm3 of 5.0% protein solution to use Fig. 1.1 [3] Carry out step 1 to step 7. step 1 Prepare the concentrations of protein, as shown in Fig. 1.1, in the beakers provided. Mix well. step 2 Label the test-tubes provided with the concentrations of protein prepared in step 1. step 3 Put 2 cm3 of each concentration of protein solution into the appropriately labelled test-tube. step 4 Put 2 cm3 of K into each of the labelled test-tubes. Shake gently to mix. step 5 Put 2 cm3 of C into each of the labelled test-tubes. Shake gently to mix. step 6 Leave for 2 minutes for the colour to change. step 7 Observe the colour in each test-tube and compare with the colours in Fig. 1.2. You will see the same colour in more than one test-tube. Record your observations in (a)(ii) using only the colours shown in Fig. 1.2. dark purple purple light purple blue Fig. 1.2 (ii) Record your observations in an appropriate table. You may record the same colour for more than one test-tube. [3] Carry out step 8 to step 9. step 8 Stir U and put 2 cm3 of U into a test-tube. step 9 Repeat step 4 to step 7 with U. Record the colour in (a)(iii). (iii) State the colour for sample U …… [1] (iv) Use your results in (a)(ii) and (a)(iii) to estimate the protein concentration in U. …… [1] (v) Describe one significant source of error when carrying out step 7 and suggest an improvement to reduce this error. source of error …… improvement …… [2] (vi) Suggest how you would modify the experiment to determine the concentration of reducing sugars in a sample of milk. …… [3] (b) Milk can be made from plant sources. A scientist compared the protein content in milk from cows with milk produced from different plants. The results are shown in Table 1.2. Table 1.2 type of milk protein content / g per 100 cm3 cow (C) 3.400 almond (A) 0.575 cashew (H) 2.250 oat (O) 0.400 soya (S) 3.325 Plot a bar chart of the data shown in Table 1.2 on the grid in Fig. 1.3. Use a sharp pencil. Fig. 1.3 [4] (c) One of the reducing sugars found in cow’s milk is lactose. Some people are intolerant to lactose and cannot digest it. A method of producing lactose-free milk is to treat cow’s milk with the enzyme lactase. Lactase hydrolyses lactose to produce glucose and galactose. A scientist investigated the effect of different lactase concentrations on the mass of lactose converted to glucose and galactose in 10 minutes. The scientist plotted a graph of the results, shown in Fig. 1.4. 100 80 60 mass of lactose converted /g 40 20 0 0.0 0.1 0.2 0.3 0.4 0.5 lactase concentration / mmol dm–3 Fig. 1.4 (i) Use the graph in Fig. 1.4 to determine the mass of lactose converted when 0.16 mmol dm–3 of lactase is used. Show your working on the graph. mass of lactose = …… g [1] (ii) Calculate the rate of lactose conversion when 0.16 mmol dm–3 of lactase is used. …… g min–1 [1] (iii) Explain the shape of the graph between 0.1 mmol dm–3 and 0.2 mmol dm–3 of lactase. …… [3] [Total: 22]

Question

N1 is a slide of a stained transverse section through a plant stem. (a) (i) Draw a large plan diagram of the region of the stem on N1 indicated by the shaded area in Fig. 2.1. Use a sharp pencil. Use one ruled label line and label to identify the xylem in one vascular bundle. draw this region Fig. 2.1 [5] (ii) Observe the cells in the central tissue of the stem on N1. Select a group of four adjacent cells that make up this tissue. Each cell must touch at least two of the other cells. • Make a large drawing of this group of four cells. • Use one ruled label line and label to identify the cell wall of one cell. [5] (b) Fig. 2.2 is a photomicrograph of a stained transverse section of a stem from a different plant species to the stem on N1. Fig. 2.2 Identify three observable differences, other than colour, between the stem in N1 and the stem in Fig. 2.2. Record these three observable differences in Table 2.1. Table 2.1 feature N1 Fig. 2.2 [4] (c) Fig. 2.3 shows a photomicrograph of a stage micrometer scale that is being used to calibrate an eyepiece graticule. One division, on either the stage micrometer scale or the eyepiece graticule, is the distance between two adjacent lines. The length of one division on the stage micrometer in Fig. 2.3 is 0.50 mm. 0 10 20 30 40 50 60 70 80 90 100 Fig. 2.3 (i) Calculate the actual length of one eyepiece graticule unit shown in Fig. 2.3. Give your answer in micrometres (μm). Show your working. actual length = …… μm [2] Fig. 2.4 shows a magnified section of the stem shown in Fig. 2.2. This was taken with the same microscope and the same lenses used to take the photomicrograph in Fig. 2.3. X 0 10 90 80 70 60 50 40 30 20 10 0 Fig. 2.4 (ii) Use the calibration of the eyepiece graticule unit from (c)(i) to calculate the actual length of the trichome labelled X in Fig. 2.4. Show your working. actual length = …… [2] [Total : 18]