WJEC Biology for AS: Student Bk

Exam practice questions Unit 1 1 (a) The level of protein structure is decided by the folding of the molecule and the types of bonds present. Tick the boxes in the table to show all the bonds present at each level of protein structure. (3) Level of protein structure Types of bonds Peptide Hydrogen Disulphide Ionic Primary Secondary Tertiary (b) (i) Give an example of a protein with secondary structure and of a protein with quaternary structure. (1) (ii) How does the quaternary structure of a protein differ from the tertiary structure? (1) (c) The diagram shows a molecule which can be split by an enzyme to produce two amino acids: (i) Name the molecule. (1) (ii) Name the bond which is broken by the enzyme. (1) (iii) Name the type of reaction which causes the bond to break. (1) (iv) The two amino acids formed are not identical. How do their structures differ? (1) (d) Following a biuret test to assess protein concentration, five solutions had the following absorbance when placed in a colorimeter containing a 550 nm filter: Solution Absorbance at 550 nm / AU 1 0.55 2 0.39 3 0.84 4 0.87 5 0.15 (i) Suggest two factors that must be controlled when performing this test, to ensure that the comparison between the readings is valid. (2) (ii) Place the solutions in order of concentration, with the most dilute first and the most concentrated last. (1) (iii) Explain how you chose this order of concentrations. (2) (iv) Why might the reading be unreliable at very low concentrations of protein? (1) (Total 15 marks) 2 (a) Distinguish between a tissue and an organ, giving an example of each in a flowering plant. (1) (b) Name an organic compound, which is found in the internal membranes of the chloroplast, but not in any other plant or animal organelle. (1) Fig ST06 R H O C C N O C OH H N R’ H C H H WJEC AS Level Biology: Unit 1 124