PLMGS 2016 Bio Prelim P2 MS

Sec 4 Exp Bio Preliminary Exam 2016 Marking Scheme Paper 2 Mark schemes will use these abbreviations: ; separates marking points 
 / alternatives 
 () contents of brackets are not required but should be implied 
 R reject 
 A accept (for answers correctly cued by the question, or guidance for examiners)
 AW alternative wording (where responses vary more than usual) 
 AVP alternative valid point (where a greater than usual variety of responses is expected) ORA or reverse argument 
 underline actual word underlined must be used by candidate (grammatical variants excepted) max indicates the maximum number of marks that can be given 
 + statements on both sides of the + are needed for that mark Sec A No. Expected Answer Mark Remarks 1a P: Epidermal cell Q: Guard cell R: Stoma Max 3 R: Stomata Bi Open: potassium ions lowers the water potential of the cell Q, causing water molecules to move into the guard cell by osmosis. This causes the guard cells to be turgid and hence opening the stoma. Close: Potassium ions leaving the cell Q increases the water potential, causing water molecules to move out of the cell by osmosis. This causes the guard cells to be plasmolysed and hence closing the stoma 1 1 1 1 1 1 Max 2 each 526 trendylineplasmolysedplasmolysed and henceclosingclosi the stomaoma 1 Max 2Max 2 each ne

Total 4 Bii Cell Q has cell wall of unequal thickness. / Thicker on the inside, thinner on the outside. Cell wall is a rigid structure that does not change shape easily. This allows the cell to expand more on the outside and less on the inside when it is turgid, causing the stomata to be open or close. 1 1 1 Max 2 Must state one property and how it helps Allow for large central vacuole, allowing the changes in water potential biii Both have the ability to respond to a stimulus. Animals have a nervous system that transmit nerve impulses to effector for response, but plants do not have a nervous system and response to changes by changing the turgor pressure in their cells. 1 1 1 Max 2 A: Speed of responses Complexity of coordination Total 10 2(a) Inhaled – CO2 0.03 % and O2 21% Exhaled – CO2 4% and O2 16% 1 1 Either 1 or 2 marks only. Allow 3 – 4% for CO2 (b) O 2 diffuses from the alveoli into the haemoglobin of RBC at the blood capillaries surrounding the alveoli Oxygen rich blood is transported to the heart and Then blood pumped by the heart to the muscles At the muscles, (aerobic) respiration; release energy from glucose; for contraction; Max 4 R produce AW energy C anaerobic (respiration); less energy released; (produces) lactic acid; (muscle) becomes fatigued / tired / ref. cramp / pain; Max 2 d rapid breathing mechanism / deeper breathing; modified lung structure or described; more (efficient) haemoglobin/increase O2 carrying capacity more efficient blood supply to organs / tissues or e.g.; larger heart/thicker heart muscl