SAJC_2015_H2-Bio-TYS-ANS

2015 UCLES ‘A’ Level H2 Biology Mark Scheme 1 2015 ‘A’ Level H2 Biology Mark Scheme PAPER 1 (MCQ)

2015 UCLES ‘A’ Level H2 Biology Mark Scheme 2 PAPER 2 (CORE) QUESTION 1 Fig.1.1 shows a diagram of a hepatocyte, which is a type of cell found in the liver. Fig. 1.1 (a) Identify the structures labelled A and B, as shown in Fig. 1.1, [6] For each structure, state two features that can be seen in Fig. 1.1. structure A: mitochondrion feature 1 : double membrane feature 2 : cristae structure B : rough endoplasmic reticulum feature 1 : cisternae / flattened membrane-bound sacs feature 2 : bound ribosomes Examiner’s comment: The question stated that features of the identified structures should be visible in Fig.1.1. A few candidates mentioned features that could not be seen, e.g. the presence of DNA. A very small number of candidates confused the cristae of the mitochondria with the cisternae of the rough endoplasmic reticulum.

2015 UCLES ‘A’ Level H2 Biology Mark Scheme 3 (b) Describe two functions of the Golgi body. [2] 1 Further post-translational modifications of proteins and lipids received from the ER (rER and sER) e.g. formation of glycoprotein, glycolipid ; 2 Sorting and packaging of proteins before being targeted to various cellular locations ; 3 Synthesis and transport of lipids ; 4 Formation of secretory vesicles (containing enzymes or proteins for release outside cell) or lysosomes ; 5 Involved in carbohydrates synthesis for the formation of cell walls in plants (Ref: 9648/P1/2010) Examiner’s comment: Candidates were able to describe a wide range of valid functions of the Golgi body. (c) Suggest two advantages to eukaryotic cells of having membrane -bound organelles. [2] 1 Provides a boundary between the cytoplasm and specific contents within the membrane-bound organelles so that separate compartments can be formed within a cell ; 2 Increase surface area for reaction to occur ; E.g. Folding of inner mitochondrial membrane results in a greater surface area for attachment of more proteins and enzymes of the electron transport chain and ATP synthase for higher rates of ATP synthesis. Examiner’s comment: Many candidates considered compartmentalisation to be an advantage of having membrane-bound organelle. Since compartmentalisation is only another way of describing this feature, responses citing compartmentalisation required further qualification and relevant details. (d) Explain the role of glycogen in animal cells. [2] 1 Stored in large quantities without having any great effect on the water potential of cells and can be prevented from diffusing out of cells ; 2 Stored in large quantities within the limited space in animal cells ; 3 Ease of breakdown allow glycogen to be a good energy source for respiration and to raise glucose levels quickly when blood sugar level drop