DHS 2022 Y5 H2 Promo Answer Scheme (Paper 1 and 2)

1 DUNMAN HIGH SCHOOL Promotional Examination Year 5 H2 Biology Promo Exam 2022 Mark Scheme Paper 1: Multiple Choice Question 1 B 6 C 11 C 2 C 7 D 12 A 3 A 8 D 13 D 4 A 9 D 14 B 5 B 10 B 15 A Q Explanation 1 Region P refers to the nucleoid region and region Q the nucleolus. Option A is incorrect because DNA in the bacterial nucleoid region (region P) is coiled around histone-like proteins, not histone proteins. Option C is incorrect because ATP synthesis does not occur in the bacterial nucleoid region (region P). The nucleolus (region Q) is also not the site of protein synthesis. Option D is incorrect because DNA is present in nucleolus (region Q). 2 The larger the organelle, the lower the centrifugal speed required for the organelle to sediment. Diagram shows the size of organelle. Sediment 1 will be the largest organelle – nucleus Sediment 2 – mitochondria Sediment 3 – endoplasmic reticulum Sediment 4 – ribosome 3 Statement 1 is correct: The reducing group is not bound in the first glucose. Statement 2 is correct: The first glucose is beta glucose. Statement 3 and 4 are false: The bond is a 1,2 glycosidic bond and this is not the bond in cellulose formation (1, 4 glycosidic bond). 4 The q uestion is indirectly asking for the change in membrane structure that increases the membrane fluidity. More cholesterol and more C=C double bonds in the hydrocarbon chain (aka higher unsaturation level) will increase membrane fluidity. 5 Option A addit ion of lysine will increase inhibition of the enzyme that converts aspartate to aspartylphosphate. This will lead to decrease in all downstream process/product, including methionine. Option B addition of aspartate semialdehyde will lead to increase in al l downstream process/product, including methionine.

2 Option C addition of threonine will increase isoleucine production. But will also lead to inhibition of enzyme that converts aspartate to aspartylphosphate. This will lead to decrease in all downstream process/product, including methionine. Option D addition of isoleucine inhibits the enzyme that converts threonine to α -oxobutyrate, which does not interfere with methionine synthesis pathway. 6 Change in quantity over time can be simplified as the rate of reaction. Especially change in product or substrate quantity over time. As quantity of product should increase over time, the graph should be 1, where the rate of reaction increases with incre asing temperature, until optimum temperature of the enzyme. Beyond optimum temperature, the rate decreases. Graph 3 is the reflection of graph 1. It represents the quantity of substrate because substrate decreases over time, hence the change is negative. But the change in rate of reaction with changing temperature is the same as product (graph 1). Graph 2 shows how enzyme quantity decreases with increasing temperature. 7 The strand on the left is ru