Biology_7401 Marking Scheme Paper 2.

Biology_7401 Marking Scheme Paper 2. Question Marking Guidance Mark Comments 01.1 1. Select at random; 2. Large sample/number (of snails)/>10; 2 1. Accept description of random technique 2. Ignore ‘many’ 01.2 Mean and standard deviation; 1 Accept 2 correct statistical values for 1 mark Accept any order Accept average for mean Accept standard error for standard deviation Accept interquartile range 01.3 (Littorina -) genus and (littorea -) species; 1 Accept phonetic spelling Accept genera 01.4 1. No (significant) difference between (mean) height (in these populations); 2. (Students) t-test; 2 Accept suitable null hypothesis TOTAL 6 MARK SCHEME – AS BIOLOGY – 7401/2 – JUNE 2020 6 Question Marking Guidance Mark Comments 02.1 1. Condensation (reaction)/loss of water; 2. (Between) phosphate and deoxyribose; 3. (Catalysed by) DNA polymerase; 2 max 3. Reject if DNA polymerase joins AT/GC OR complementary nucleotides/bases OR forms hydrogen bonds 02.2 Correct answer for 2 marks = 70;; Accept for 1 mark, A = 42 and T = 42 OR 420 (total bases in gene) OR 210 (bases in template strand) 2 02.3 Histone; 1 02.4 1. DNA helicase; 2. Breaks hydrogen bonds between base pairs/ AT and GC/complementary bases OR Breaks hydrogen bonds between polynucleotide strands; 2 2. Reject hydrolysis of hydrogen bonds TOTAL 7 MARK SCHEME – AS BIOLOGY – 7401/2 – JUNE 2020 7 Question Marking Guidance Mark Comments 03.1 1. Muscle contracts; 2. Constricts/narrows arteriole/lumen; 2 2. Accept decreases for constricts/narrows 2. Accept vasoconstriction for 1 mark 03.2 (Ventricles and arteries) 1. Ventricle (muscles) relaxed OR Arteries recoiled; 2. No (blood) backflow (into ventricles) OR No blood movement to/in/from arteries; (Atria and ventricles) 3. Atria (muscle) contracted; 4. Blood movement from atria (into ventricles); 4 Accept references to ventricle, artery or atrium (singular) 1. Accept no muscle activity OR Diastole OR Arteries smoothing blood flow 2. and 4. Accept flow/pumped for movement