VS 2024 O Level Pure Biology P2 MS w Feedback

2024_6093 Biology Paper 1 Feedback for Paper 1 Qn No Ans Comments 5 B candidates were aware that glycogen is composed of glucose units but were unaware that glucose units can combine in other ways to produce cellulose. 6 B heating Benedict’s solution to 37 C for four minutes will not result in a positive result with glucose. 8 D These candidates either mis-identified the named blood vessels, did not understand liver functions or did not realise that maltose would not be present in the blood stream.

11 A When X (bicuspid) valve closes, the AV-valve on the right closes as well - what happens on one side of the heart, happens on the other side too. - eliminating D When AV valve closes, blood cannot flow from atria to ventricles, eliminating B. X closes when ventricular pressure exceeds atrial pressure during ventricular systole to prevent backflow of blood. Soon after, aortic valve open (not closes) during ventricular systole. - eliminating C Blood flows out of heart to lungs via pulmonary artery and to rest of body via aorta 14 A glucose is necessary for the alveolar cells to function. 16 A glucose will reduce while blood passes through the kidney. The kidney needs energy for the functions it performs, in particular for the reabsorption of substances from the glomerular filtrate. 18 B if the skin temperature reduces then less heat must be reaching the skin and so the blood flow must have been restricted. 28 D Arrow A: Carbon dioxide → plants → This is photosynthesis , where plants take in CO ₂ . This happens on a huge scale, so a lot of carbon moves here. Arrow B: Plants → herbivores → This is feeding (plants being eaten). Many herbivores eat plants, so again, a large amount of carbon is transferred. Arrow C: Herbivores → carnivores → This is also feeding (herbivores being eaten). Less energy and biomass pass on to carnivores compared to herbivores, so the carbon transferred here is smaller than A or B. Arrow D: Carnivores → decomposers → This is when carnivores die and decomposers break them down. But remember: there are far fewer carnivores than herbivores or plants, so the total carbon flowing here is very small .

32 B Meiosis does not occur in haploid cells. Haploid cells are produced from meiotic division. Meiosis, aka reductive division, results in halving of chromosome number in cells, forming haploid cells. When the haploid gametes fuse (during fertilisation), diploid number of chromosomes is restored 38 A Heterozygous - one dominant and one recessive allele. Based on the genetic cross of heterozygotes (individual 4 and 5), there’s a 50% chance that individual 7 is heterozygous. Each birth event is independent of the previous. Paper 2 Qn Answer Marks Remarks 1(a) Root hair cells are usually found underground where sunlight is absent ; Because of this, root hair cells, do not require chloroplasts to absorb light for photosynthesis to occur ; 1 1 Most candidates understood why root hair cells do not require chloroplasts. A significant proportion of candidates described the root hair cell as being ‘underground’ without reference to light. Weaker responses simply stated that the function of root hair cells is to absorb water and mineral ions.

1(b)(j) 1(b)(ii) Mitochondrion ; Organelle A is used to convert glucose into energy ; Which is released during respiration ; For protein synthesis which is required for cell growth and repair that helps with growth of plants ; OR Energy released is for active transport of stored manufactured food substances for translocation of substances from roots to leaves for cell growth during periods of absence of lights OR For active transport of ions into the root hair cells, which may be used for plant growth OR For active transport of ions into root hair cells, to lower the water potential in the root hair cells, for water to enter via osmosis and is 1 1 1 1 This question was answered correctly by almost all candidates. Take note of the singular form and not plural form. Many candidates recognised the role of mitochondria in the growth of plants and referred to energy in their answer. A common incorrect answer was to describe the uptake of water by active transport. Weaker responses indicated that energy could be used for photosynthesis or respiration. eventually used by leaves as a raw material for photosynthesis ; 1(b)(iii) Endoplasmic reticulum; Golgi body ; 1 1 A common incorrect response was ribosome instead of endoplasmic reticulum.

2(a) When the student looks away from the boat (far away object) and looks at the book (near object), his ciliary body in the eyes will contract ; This will cause the suspensory ligaments to slacken ; This reduces the tension on the lens causing the lens to be thicker and more convex ; As a result, focal length decreases, causing the light rays from the book to bend and focus sharply on the retina ; 1 1 1 1 Suspensory ligaments will relax is rejected as they are not muscles. Students have to remember that the question is testing on accommodation reflex and they have to take note of the keywords of what happens when the lens becomes thicker. Many candidates described the eye when the student was looking at the boat or the detail of nervous coordination to bring about the changes, which were not required. 2(b)(i) Percentage decrease = (5.8-2.5)/5.8 X 100 % = 56.9 % (3sf) 3 1 mark for correct working 1 mark for the correct calculation 1 mark for correct number of sf Since the question states calculate, if there is no calculation, students would not get the mark for this question and students may miss out the number of sf stated in the qn.

2(b)(ii) To allow less light to enter the eye preventing over-exposure to light that would cause damage to the retina. ; 1 Many candidates could correctly suggest why it is important for the pupil diameter to decrease in bright light. Weaker responses only referred to allowing less light to enter the eye. 2(b)(iii) Radial muscle of iris relaxes and circular muscle of iris contracts ; Constricting the pupil, reducing the amount of light entering the eye. ; 1 1 Students may use words like contracting pupil. However, pupil is a gap which can only dilate or constrict in size. Weaker responses referred to muscles constricting rather than contracting, referred to the radial muscle as the longitudinal muscle or referred to the circular muscle as the ciliary muscle. 3(a)(i) Differences in phenotypes or traits between individuals of the same species ; 1 Many responses needed more detail, often referring to differences without specifying between what. 3(a)(ii) Height, skin colour ; AVP 1 3(a)(iii) Blood type, presence of dimples, ability to roll tongue ; AVP 1 3(b)(i) P has