Biology 0610/53 October/November 2019: question paper and mark scheme

Question

Photosynthesis occurs in chloroplasts. A chloroplast suspension can be made by extracting the chloroplasts from green leaves. You are going to investigate the effect of light on 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 CARRY THEM OUT until you have drawn a table for your results in the space provided in 1(a)(i). You should wear the gloves and eye protection provided during the practical work in question 1. Step 1 You are provided with eight green leaves. Tear the leaves into small pieces and place them into the mortar (bowl). Step 2 Pour all of 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 three minutes. Step 4 Place three layers of muslin into the funnel. Put the funnel into the large test‑tube labelled C. ground leaves funnel and isolation medium mixture three layers of muslin cloth large test-tube C filtrate C (chloroplast suspension) Fig. 1.1 Step 5 Carefully hold the edges of the muslin and pour the ground leaves and isolation medium mixture from the mortar (bowl) into the muslin‑lined funnel. When most of the liquid has filtered into the large test‑tube, as shown in Fig. 1.1, place the muslin and funnel in the waste container. Step 6 Raise your hand when you are ready for ice‑cold water to be added to the water‑bath. Step 7 Wrap aluminium foil around one empty test‑tube to exclude light. Leave the opening at the top of the test‑tube uncovered. Do not wrap the second test‑tube. Place both test‑tubes into the test‑tube rack. Step 8 Use the plastic pipette to add 2 cm3 of filtrate C to each of the empty test‑tubes. Step 9 Use a 5 cm3 syringe to add 5 cm3 of DCPIP solution to each of the two test‑tubes. Place a stopper in both test‑tubes. Stand both test‑tubes in the water‑bath and position the water‑bath near a bright light source or lamp. Step 10 Start the stop‑clock and wait five minutes. Step 11 After five minutes observe the colour in the uncovered test‑tube and record it in your table in 1(a)(i). Step 12 Remove the aluminium foil from the other test‑tube. Immediately observe the colour of the liquid in the test‑tube. Record this in your table in 1(a)(i). (a) (i) Prepare a table to record your results. [3] (ii) Identify the variable that was changed (independent variable) and the variable that was measured (dependent variable) in this investigation. independent variable …… dependent variable …… [2] (iii) State two variables that have been kept constant in this investigation. 1 …… 2 …… [2] (iv) State a conclusion for these results. …… [1] (b) The investigation was not repeated. (i) Suggest why it would be advisable to repeat the investigation. …… [1] (ii) Identify two other sources of error in this investigation. error 1 …… error 2 …… [2] (iii) Suggest an improvement for one of the errors you have identified in 1(b)(ii). …… [1] (c) A student wanted to investigate the effect of temperature on the rate of photosynthesis in a chloroplast suspension. Describe how the student could carry out this investigation using DCPIP. …… [6] [Total: 18]

Question

Fig. 2.1 is a photomicrograph of part of the lower epidermis of a leaf. M stoma guard cell epidermal cell N magnification ×400 Fig. 2.1 (a) (i) Make a large drawing of Fig. 2.1. Do not label your drawing. [4] (ii) Measure the length of the line MN on Fig. 2.1. length of line MN ……mm Calculate the actual width of the guard cells and the stoma indicated by line MN in Fig. 2.1. Use the equation and information in Fig. 2.1. length of line MN on Fig. 2.1 magnification = actual width of the guard cells and the stoma Give your answer to two decimal places. ……mm [3] (b) A student investigated the effect of sucrose concentration on stomatal opening. Strips of epidermis from leaves were placed in different concentrations of sucrose solution for one hour. The student measured the width of 10 stomatal openings from the epidermis in each sucrose solution. The results are shown in Table 2.1. Table 2.1 percentage width of stomatal opening / μm concentration of sucrose 1 2 3 4 5 6 7 8 9 10 average 0 5 6 7 5 5 6 7 5 7 6 5.9 5 3 4 3 3 4 3 2 3 3 2 20 1 2 1 2 1 1 5 1 2 1 1.7 (i) Circle one measurement in Table 2.1 that could be anomalous. [1] (ii) Calculate the average width of stomatal opening in the 5% sucrose solution. Include the unit. [2] (c) Pineapple plants are adapted to grow in hot dry conditions. Scientists investigated the number of stomata open, in pineapple plants, at different times of day. The data is shown in Table 2.2 (00:00 is midnight). Table 2.2 average number of time of day stomata open per mm2 00:00 77 04:00 61 08:00 22 12:00 4 16:00 10 20:00 51 (i) Calculate the percentage change in the average number of open stomata per mm2 between 16:00 hours and 20:00 hours. Space for working. ……% [2] (ii) Plot a bar chart on the grid to show the data in Table 2.2. [3] (iii) Describe, using your graph, how the average number of open stomata per mm2 changes throughout the day. …… [2] (d) When fruit ripens the starch contained within it is converted into reducing sugars. (i) State the name of the substance that is used to test for the presence of starch. …… [1] (ii) Describe how you could safely show a reducing sugar was present in a sample of pineapple fruit juice. procedure …… safety …… …… [4] [Total: 22]