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 muscles/ more red blood cells; faster heart rate / faster circulation of blood; Max 4 Total 12 527 trendyline;; Max 4 Max 4 neTotalTota 1122trendylinnneeene

3a no chlorophyll ; no photosynthesis ; cannot make carbohydrates/ carbohydrates obtained from other organism /; Nutrients from the nearby green plants. Fungi function as a link for nutrients to reach ghost plant Max. 3 ORAfor vein B how the flower is pollinated: insect / self ; reason (insect): 1. stigma / carpel + enclosed ; 2. anthers / stamens + enclosed ; 3. anthers / stamens + small ; 4. white colour may attract (insects) ; reason (self): 5. anthers and stigma close ; 6. white / not brightly coloured + doesn’t attract (insects); 1 1 1 Max 2 C sucrose transported (to underground stems) ; through phloem/ translocation ; sucrose converted to starch ; stem swells ; Max 2 Total 8 4(a) More black moths are consumed by their predators; This is because the black moths are not able to camouflage / blend in with the tree bark. 1 1 Bi Both moths have a heterozygous genotype, Gg; 1 bii (i)Parental phenotype pale speckled moth pale speckled moth Parental genotype Gg Gg Gametes G g G g Random fertilisation Offspring genotype GG Gg Gg gg Offspring phenotype pale speckled pale speckled black speckled black Proportion of black moth: 1/4 or 25% 1 1 1 1 528 trendylinegg Offspring phenotype pale speckled pale speckled Offspring phenotype pale speckled pale speckled black speckled black ack speckled black Proportion of black moth: 1/4 or 25% Proportion of black moth: 1/4 or 25%ye

C The trees were blackened with soot air pollution; White moth more easily seen Get eaten by predators Black moth adapt better to the environment survive to reproduce and pass on their alleles to the next generation. Frequency of alleles for black pigment increases as natural selection selects for these alleles Increasing number of black moth Max 3 Reverse argument applies Total 10 5a A – tongue; B – larynx/voice box; 2 b peristalsis; 1 C closes/covers; trachea/windpipe/air passage/larynx/voice box/B; helped by raising of larynx AW; preventing the entry of food / preventing food going to lungs or respiratory system / prevents choking AW / allows food to enter oesophagus Max 3 d High blood pressure might damage the vessels of the kidney and causes the kidney to be unable to carry out ultrafiltration Lowering water intake, will lower the blood pressure, As volume of blood decreases This reduces the pressure of the blood flowing to the kidney, hence reducing damage of glomerulus at kidney Salt reduces the water potential of the cells, hence causing more ADH to be released to increase reabsorption of water, causing the volume of blood to increase and hence salt intake should be reduced. 1 1 1 1 1 Max 4 Total10 Sec B No. Expected Answer Mark Remarks 529 trendylineExpected AnswerExpected Answer MarkMarktrendylinnneyn

6a A labelling of axes; [Time : temperature/ o C; Y :heat loss/production S scale; [needs to be even and to fill more than half of the printed grid] P plot; [+/- half a small printed square] L line; [an accurate curve connecting all points or joined point to point by a ruled line and no extrapolation] max. 5m B During vigorous exercise, from 0 min to 20 min respiration occurs at a higher rate to release large amounts of energy. Some of the energy is lost as heat energy, causing the body temperature to rise This cause the thermoreceptor send a nervous impulse to the hypothalamus which starts a corrective mechanism for heat loss to decrease body temperature back to normal Vasodilation of arterioles near the skin - Increase blood flow to the skin - h e a t c a n b e l o s t t h r o u g h c o n d u c t i o n , convection & radiation Production of sweat - Removes heat through latent heat of vapourisation As the heat production is higher than heat loss, as the person stop exercising, heat production decrease and heat loss continues to be higher than heat production to bring body temperature back to normal. 1 1 1 1 1 1 1 1 Max 5m Total 10 7a Mesophyll cells uses the carbon dioxide For photosynthesis 1 530 trendylinenesophyll cells uses the carbon dioxide For sophyll cells uses the carbon dioxide For otosynthesis 1 1 trendylinnnen

Lower concentration of carbon dioxide in the intercellular air space of leaf and higher concentration of carbon dioxide in the atmosphere Carbon dioxide diffuse the leaf through the stomata into the intercellular air space Dissolve in the thin film of moisture and enter into the mesophyll cells Glucose is formed by photosynthesis and stored as starch in the leaf Caterpillar ingest