TKGS Prelim paper 2 ANS

TKGS SEC 4 BIO PRELIM P2 2025 MARKING SCHEME Paper 2 (50 m) Q Ans Mark Remarks 1 (a) Temperature of solutions; Particles move faster at higher temperature / cells or cell membrane are destroyed at higher temperature; Duration of experiment; Longer duration allows more time for substances to diffuse; R – size of tissue / type of tissue / freshness of tissue / concentration of solution /volume of solution / container size / humidity / temperature of room / location 2 This was not answered well with poor reference to the question context. Answers were vague and not specific. Explanations were also not specific. For example, temperature of solutions is correct, but students did not explain in relation to kinetic energy of molecules in solution. (b) Active transport; As concentration of oxygen increases from 0 to 20 arbitrary units, rate of potassium ion uptake increases from 7 to 100 arbitrary units; Increased rate of aerobic respiration to release more energy; R – no units in description of data 3 Many answers did not include reference to data. Some data lacked units. Common mistakes include interpreting the main method as diffusion. (c) Discs from the same root tissue will have minimal differences in concentration of K+ ions; To improve reliability of data; R – improve accuracy / make the experiment fair 2 It is incorrect to write that all discs from the same root tissue have the same concentration / water potential. Reference should be made that the concentration / water potential difference is at a minimum compared to using discs from different root tissues. (d) Drawing of a plasmolysed cell; Correct labelling of nucleus and cytoplasm; 2 Many answers did not include vacuoles. Those that did, the size of

the vacuoles were too big. A plasmolysed cell’s vacuole should be smaller in size. 2 (a) Urea; 1 This was well answered. (b) Glomerular filtrate has higher water potential than urine; Water molecules are selectively reabsorbed along the tubules; Into the blood; By osmosis; Max 3 Most answers stated the correct comparison of water potential between glomerular filtrate and urine. Many answers failed to include “reabsorbed”, into the blood and by osmosis. (c) (i) Glomerulus membrane (basement membrane) becomes fully permeable; No longer prevent large molecules e.g. proteins from moving out of the blood; Into Bowman’s capsule; Max 2 Many answers were not specific to link the damaged glomeruli to its partially permeability membrane. Many answers did not interpret that proteins are large molecules. Instead, they explained incorrectly that the proteins cannot be selectively reabsorbed. Many answers also failed to mention that the glomerulus filtrate was first formed in the Bowman’s capsule. (ii) Carbon, hydrogen, oxygen, nitrogen; Amino acids; 2 This was well answered. 3 (a) Proteins in faeces are broken down/de