Biology_7401 Marking Scheme Paper 1.

Biology_7401 Marking Scheme Paper 1. Question Marking Guidance Mark Comments 01.1 Letter Statement B; is a monomer in an enzyme’s active site D; is a monomer in cellulose C; is produced during photosynthesis and respiration B; forms a polymer that gives a positive result with a biuret test 4 Must be in correct order 01.2 C = 18, H = 32, O = 16; 1 Accept only these answers 01.3 1. Heat with acid and neutralise; 2. Heat with Benedict's (solution); 3. Red precipitate/colour; 3 Accept boil/water bath for heat Accept named alkali for neutralise 1. Accept named examples, eg HCl, NaHCO3 3. Accept other colours eg orange/ brown/green TOTAL 8 MARK SCHEME – AS BIOLOGY – 7401/1 – JUNE 2020 6 Question Marking Guidance Mark Comments 02.1 1. Bilayer OR Water is present inside and outside a cell; 2. Hydrophobic (fatty acid) tails point away/are repelled from water OR Hydrophilic (phosphate) heads point to/are in/are attracted to water; 2 1. Accept annotated diagram for ‘bilayer’ Accept cytoplasm/tissue fluid for water Accept for two marks, annotated diagram of bilayer with water labelled on each side Ignore hydrophilic/phosphate heads protect hydrophobic/fatty acid tails 02.2 1. Condensation (reaction) OR Loss of water; 2. Between of glycerol and fatty acid; 2 Accept labelled diagram 02.3 1. High (specific) heat capacity; 2. Buffers changes in temperature; 2 2. Accept ideas such as a lot of energy needed/gained to change temperature TOTAL 6 MARK SCHEME – AS BIOLOGY – 7401/1 – JUNE 2020 7 Question Marking Guidance Mark Comments 03.1 1. Engulfs; 2. Forming vesicle/phagosome and fuses with lysosome; 3. Enzymes digest/hydrolyse; 3 1. Accept endocytosis OR Description 1. Ignore ‘taken in’ 3. Accept lysozymes for ‘enzymes’ 03.2 1. (Cells from) other organisms/transplants; 2. Abnormal/cancer/tumour (cells); 3. (Cells) infected by virus; 2 max Accept ‘own cells’ if autoimmune response suggested Accept APCs Accept non-self 03.3 ‘X’ written at either or both ends of Y shape; 1 03.4 Joins two (different) polypeptides; 1 Accept holds/attaches Accept ‘prevents polypeptide chains separating’