AS BIOLOGY Paper 1 2020 -Question

AS BIOLOGY Paper 1 2020 - scan Materials For this paper you must have:  a ruler with millimetre measurements  a scientific calculator, which you are expected to use where appropriate. Instructions  Use black ...

AS BIOLOGY Paper 1 2020 - scan Materials For this paper you must have:  a ruler with millimetre measurements  a scientific calculator, which you are expected to use where appropriate. Instructions  Use black ink or black ball-point pen.  Fill in the boxes at the top of this page.  Answer all questions.  You must answer the questions in the spaces provided. Do not write outside the box around each page or on blank pages.  All working must be shown.  Do all rough work in this book. Cross through any work you do not want to be marked. Information  The marks for questions are shown in brackets.  The maximum mark for this paper is 75. For Examiner’s Use Question Mark 1 2 3 4 5 6 7 8 9 10 TOTAL Do not write outside the box 2 *02* 1 2 Answer all questions in the spaces provided. 0 1 Figure 1 shows part of a DNA molecule. Figure 1 . How many nucleotides are shown in Figure 1? [1 mark] . Name the type of bond labelled X in Figure 1. [1 mark] 0 1 0 1 Do not write outside the box 3 *03* 6 0 1 . 3 The enzymes DNA helicase and DNA polymerase are involved in DNA replication. Describe the function of each of these enzymes. [2 marks] DNA helicase DNA polymerase 0 1 . 4 Adenosine triphosphate (ATP) is a nucleotide derivative. Contrast the structures of ATP and a nucleotide found in DNA to give two differences. [2 marks] 1 2 Turn over ► Do not write outside the box 4 *04* A student investigated the effect of three types of disinfectant on the growth of Lactobacillus bacteria. During the investigation, the student:  boiled the agar before pouring the agar plates  transferred 0.5 cm3 of a diluted liquid culture of Lactobacillus onto each agar plate  left some agar plates as controls  added to other agar plates different concentrations of the disinfectants as shown in Table 1 on page 5. After 2 days, she counted the number of colonies of bacteria on each agar plate. 0 2 . 1 Explain the purpose of: [2 marks] boiling the agar transferring the same volume of liquid culture onto each agar plate. 0 2 Do not write outside the box 5 *05* 2 The three disinfectants used by the student were Lysol, propan-2-ol and ammonia. Table 1 shows the student’s results. Table 1 Concentration of disinfectant / arbitrary units Number of colonies of bacteria Lysol Propan-2-ol Ammonia 0 300 300 300 5 0 290 300 10 0 195 295 15 0 0 275 20 0 0 240 . The liquid culture the student transferred was diluted by 1 in 10 000 (10–4 ). Use information in this question to calculate how many bacteria were present in 1 cm3 of undiluted liquid culture. [2 marks] Answer = Question 2 continues on the next page Turn over ► 0 2 Do not write outside the box 6 *06* 3 6 . The student concluded that the minimum concentration of propan-2-ol needed to stop the growth of Lactobacillus was 15 units. This conclusion is incorrect. Describe how you could obtain a more accurate estimate of the minimum concentration of propan-2-ol needed to stop the growth of this species of bacterium. [2 marks] 0 2 Do not write outside the box 7 Turn over for the next question DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED