2025 AS Level Biology A H020/02 Depth in biology (Verified Question Paper With Mark Scheme Combined June 2025)

Thursday 22 May 2025 – Morning AS Level Biology A H020/02 Depth in biology Time allowed: 1 hour 30 minutes (Verified Question Paper With Mark Scheme Combined June 2025) INSTRUCTIONS •Use black ink. You can use an HB pencil, but only for graphs and diagrams. •Write your answer to each question in the space provided. If you need extra space use the lined pages at the end of this booklet. The question numbers must be clearly shown. •Answer all the questions. •Where appropriate, your answer should be supported with working. Marks might be given for using a correct method, even if your answer is wrong. INFORMATION •The total mark for this paper is 70. •The marks for each question are shown in brackets [ ]. •Quality of extended response will be assessed in questions marked with an asterisk (*). •This document has 24 pages. ADVICE •Read each question carefully before you start your answer. © OCR 2025 [601/4261/3] DC (PQ/SW) 350639/7 OCR is an exempt Charity Turn over 1 (a)The table describes features of molecules. Complete the table. Use ticks () to identify if the feature describes starch or cellulose. Description Starch Cellulose Is made of amylose and amylopectin Is a long unbranched chain Is made from β glucose molecules [3] (b)Students complete paper chromatography on carbohydrates. The table shows the Rf values for known carbohydrates. © , ResearchGate. Item removed due to third party copyright restrictions. Link to material - The measurements recorded for an unknown carbohydrate were: Distance travelled by solvent = 8.50 cm Distance travelled by carbohydrate = 4.34 cm Calculate the Rf value of the unknown carbohydrate and use the table to identify it. Give your answer to 2 decimal places. Rf value = ............................................................... Name of carbohydrate = ............................................................... [2] (c)Outline the role of the solvent in paper chromatography. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... . [2] 2 (a)Students use a model cell to investigate the effect of the thickness of the exchange surface membrane on the rate of diffusion across the membrane. The students are provided with dialysis tubing of different thicknesses, grade 1, grade 3 and grade 5, where grade 5 is the thickest. They set up the apparatus as shown. The students remove a sample of the external solution at 30 second intervals and determine the concentration of glucose (mmol dm–3) in the sample. Glass rod String Dialysis tubing Glucose solution External solution Beaker The table shows their results. Grade of dialysis tubing Concentration of glucose found in the samples of external solution taken at 30 s intervals (mmol dm–3) 0 s 30 s 60 s 90 s 120 s 1 0.00 1.31 2.52 3.59 4.80 3 0.00 0.82 2.24 2.39 3.31 5 0.00 0.31 0.64 0.96 1.22