Biology 2025 · May/June · Paper 52

Phosphatases are enzymes that catalyse the removal of phosphate from other molecules, releasing inorganic phosphate (P ). A phosphatase can be extracted from mung bean seedlings, Vigna radiata. Fig. 1.1 shows mung bean seedlings. mung bean seedlings A student found a published method to extract phosphatase from mung bean seedlings. to make a paste. lid of centrifuge tube plastic centrifuge tube liquid phosphatase extract solid pellet Fig. 1.2 * 0000800000002 *

State two other variables that should be standardised in the published method so that extracts with the same concentration of phosphatase can be produced.

The student read that the optimum pH for phosphatase extracted from mung bean seedlings is less than pH 7.0. The student decided to investigate phosphatase activity , using the substrate phenolphthalein phosphate (PPP). In the first four steps of the method, the student: of pH 6.0 buffer solution with 1 cm of a 1.0% solution of PPP in a test-tube of the phosphatase extract to the test-tube and started a timer of 10.0% solution of sodium carbonate. Sodium carbonate solution is alkaline.

The buffered PPP solution and the phosphatase extract were mix ed and then placed in the water-bath. The student identified this as a source of error in the method. Explain why this is a source of error and state how you would modify the method to remove this source of error. explanation modification [2] * 0000800000003 *

Suggest how the addition of 10.0% solution of sodium carbonate stops the enzyme reaction.

The phosphatase catalyses the removal of inorganic phosphate from PPP as shown by: phosphatasePPP phenolphthalein + inorganic phosphate The 10.0% solution of sodium carbonate added at the end of the experiment also causes any phenolphthalein to turn pink. The intensity of the pink colour is an indication of the concentration of phenolphthalein. T o estimate the concentration of phenolphthalein produced by the reaction, the student decided to make a proportional dilution using a 2.0% stock solution of phenolphthalein. The student made 50 cm of each diluted solution. Describe a method the student could use to make a proportional dilution of the 2.0% stock solution of phenolphthalein to get a range of concentrations.

Describe how the student could use the dilutions from

and a colorimeter to estimate the concentration of phenolphthalein in a reaction mixture.

The student decided to determine the optimum pH for phosphatase extract from the mung bean seedlings. Describe a method the student could use to determine the optimum pH for phosphatase. Y our method should be set out in a logical order and be detailed enough to allow another person to follow it. Details of how to extract phosphatase from the mung bean seedlings and how to make the dilutions of phenolphthalein solutions should not be included.

The student investigated the effect of a competitive inhibitor on the activity of a phosphatase. Fig. 1.3 shows a graph of the initial rates of enzyme reaction against PPP concentration for the enzyme with no inhibitor and the enzyme with inhibitor.Key enzyme with inhibitor enzyme with no inhibitor 0.000 0.0 0.5 1.0 1.5 PPP concentration / mmol dm 2.0 2.5 3.0 0.002 0.004 0.006 0.008 0.010 initial rate enzyme reaction / mmol 0.012 0.014 0.016 0.018 0.020

One of the data plots in Fig. 1.3 is anomalous. Circle the anomalous data plot in Fig. 1.3 and explain why you think it is anomalous.

Use Fig. 1.3 to determine the Michaelis-Menten constant (K ) for the enzyme with no inhibitor and for the enzyme with inhibitor. Include the correct units in your answers. for the enzyme with no inhibitor = for the enzyme with inhibitor =

Calculate the percentage increase in the K that occurs in the presence of the inhibitor. Show your working. percentage increase = % [2] [Total: 20] * 0000800000007 * BLANK PAGE * 0000800000008 *

Sponges are immobile, aquatic animals that live on rocks and sediment at the bottom of salt water environments. Fig. 2.1 shows an example of a sponge, growing on the seabed, in a marine habitat. scuba diver photographing sponges sponge There are many dif ferent species of sponge. Most species of sponge are sensitive to environm ental stress. Human activity causes some environmental stress. * 0000800000009 * Scientists sampled the marine habitats along a length of coastline in Algeciras Bay in southern Spain to study the species diversity of sponges. The scientists selected 12 sampling stations, A to L, as shown in Fig. 2.2. The scientists noted the land use or human activity along the coast next to each sampling station. land sampling stations marine habitat Algeciras Bay land Key to diagram: sampling station type of land use or human activity A natural habitat B natural habitat C tourist beach D housing E shipping port F tourist beach G thermal power station H oil industry I ship building and repairs J tourist boats K tourist boats L natural habitat The sampling stations were chosen to compare the ef fects of land use or human activity on the species diversity of sponges in the bay. At each marine sampling station, the scientists:

The scientists standardised some variables. State two other variables that the scientists should standardise in this investigation.

The scientists compared the species diversity of sponges between dif ferent sampling stations using an index of diversity known as beta diversity. The higher the beta diversity index, the higher the species diversity at a sampling station. Fig. 2.3 shows a graph of the beta diversity index for each sampling station. 0.6 A C E G sampling station I KB D F H J L 0.8 1.0 1.2 1.4 1.6 beta diversity index 0.7 0.9 1.1 1.3 1.5 1.7 A simplified formula for beta diversity is shown: beta diversity = x - 1 Key to symbols: n = the number of sponge species recorded at a sampling station x = the mean number of sponge species across all sampling stations At sampling station A, 37 sponge species were recorded (n = 37). Use Fig. 2.3 and the formula for beta diversity to calculate the mean number of sponge species across all sampling stations (x ). Show your working. W rite your answer to the nearest whole number. mean number of sponge species across all sampling stations (x ) = [2] * 0000800000011 *

(i) A student concluded that the species diversity of sponges was higher in the sampling stations where there was less human activity. Using the information in Fig. 2.2 and in Fig. 2.3, evaluate this conclusion. Use the values in Fig. 2.3 to support your answer.

Use the information in Fig. 2.2 and in Fig. 2.3 to state two other conclusions about the species diversity of sponges in Algeciras Bay. Use the values in Fig. 2.3 to support your answer. [Total: 10] The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country , territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries. Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable ef fort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Local Examinations Syndicate (UCLES), which is a department of the University of Cambridge. * 0000800000012 *