SAJC_2013_H2-Bio-TYS-ANS

2013 UCLES ‘A’ Level H2 Biology Mark Scheme 1 2013 ‘A’ Level H2 Biology Mark Scheme PAPER 1 (MCQ)

2013 UCLES ‘A’ Level H2 Biology Mark Scheme 2 PAPER 2 (CORE) QUESTION 1 (a) Describe the processes that occur in the golgi body. [3] 1 Receive proteins and lipids from the ER (rER and sER) and chemically modifies them / Further chemically modifies glycoproteins and glycolipids; e.g. short carbohydrate chains or oligosaccharides are added to the proteins and lipids to form glycoproteins and glycolipids / enzymes of the Golgi body cleave a sugar from a chain or modify one or more of the sugars; 2 Various molecules are sorted and packaged; Then, they are targeted to various cellular locations; or secreted out of the cell; 3 Hydrolytic enzymes of the lysosome will be sorted and packaged together; To form lysosomes; 4 Synthesis of carbohydrates e.g. non-cellulose polysaccharides such as pectin; For formation of plant cell walls; Examiner’s comment: The majority of candidates correctly described protein modification and most went on to provide further details. (b) Describe the roles of the vesicles that fuse with the forming face of the golgi body. [3] 1 The vesicles are made up of membranes; which buds off from the endoplasmic reticulum; 2 These vesicles transport proteins and lipids synthesized in rER and sER ; To be further chemically modified in the Golgi body ; 3 The vesicles has proteins which recognize and bind to specific receptors on the forming face of golgi body; Before membranes of vesicles fuse with membrane of the forming face of golgi body, emptying their contents into the lumen of the Golgi body; Examiner’s comment: Most candidates were able to provide full responses. However, some candidates omitted to mention the involvement of proteins. (c) Outline two roles of the vesicles that are formed from the maturing face of the golgi body. [4] 1 Secretory vesicles migrate toward the plasma membrane ; Membrane of the vesicles fuse with the plasma membrane ; 2 Substances (e.g. hormones, digestive enzymes of the gut) released to the outside of the cell; via exocytosis; 3 Lysosomes contain hydrolytic enzymes; which are introduced to food vesicles produced by phagocytosis or autophagosomes containing worn-out organelles upon fusion of both membranes; 4 Hydrolytic enzymes break down the food molecules / worn-out organelles; Digested substances are then assimilated back into the cell to be re-used; Examiner’s comment: The majority of candidates provided detailed responses. Some candidates confused the enzyme lysozyme with the hydrolytic enzymes found in lysosomes.

2013 UCLES ‘A’ Level H2 Biology Mark Scheme 3 QUESTION 2 (a) State what happens if a cell loses control of the cell cycle. [1] 1 It undergoes uncontrolled cell division and may result in cancer;; Examiner’s comment: A few candidates referred mistakenly to uncontrolled cell growth. (b) With reference to Fig 2.1,