Question Section A
Answer all questions. Answers must be written within the answer boxes provided.
1. The land snail Cepaea nemoralis is very common in North America and in Europe.
The base colour of its shell varies between brown, pink and yellow, and also in its intensity. Some shells are unbanded, but most show one to five bands of different width on top of the shell base colour.
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In the early 1950s, scientists studied the proportion of colours and banding of C. nemoralis in woods and fields near Oxford, UK, which differed in the type of plants and background colour. Each data point on the graph represents the percentage of yellow base colour shells and unbanded shells in a sample from either one type of wood or field, although other snail colours were present.
Determine the maximum percentage of yellow base colour shells found in woods. [1]
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Suggest either one possible advantage or one disadvantage of having a banded shell,
stating whether it is an advantage or disadvantage. [1]
Using the data in the graph, distinguish between the distribution of C. nemoralis shells in woods and fields. [2]
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The population of C. nemoralis has been studied for many years in open fields in a similar area. In the graph, each data point represents the percentage of adults of a given base colour plotted against the percentage of juveniles of the same base colour collected each year.
P
Percentage of juveniles
Deduce from the data in the graph which shell base colours are on average most andleast frequent among adult snails. [2]
Most frequent:
Least frequent:
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Discuss whether there is evidence in the data that colour plays a role in the survival ofthe snails. [3]
Using the theory of natural selection, explain the differences shown in the graph between the three colours of snail. [3]
▶️Answer/Explanation
Ans: a .
78(%) Accept answers ranging between 77 and 80 %. 1.
b advantage: camouflage OR disadvantage: visibility 1.
c a. more yellow in fields (than in woods) / vice versa b. more unbanded in woods (than in fields) / vice versa c. more overlap within banding than within yellow colour OR yellow colour range greater than banding range
d. very little overlap between fields and woods / some outliers Do not acceptanswers with only numerical data. 1.
d a. brown most frequent b. pink least frequent 1.
e Evidence that colour plays a role: a. few yellow adults (relative to juveniles) means that yellow juveniles do not survive into adulthood b. frequent brown adults (relative to juveniles) means brown juveniles survive well into adulthood Evidence that colour does not play a role: c. similar numbers of adult and juvenile pink individuals means pink colour does not play a role d. all three colours show wide variation/considerable overlap therefore evidence is not strong 1.
f a. natural selection requires that snails become adults /live to reproduce their variations/undergo differential predation OWTTE b. higher adult frequency of brown shows selection c. but results for pink do not show selection d. more brown juveniles survive into adulthood showing that brown is selected for / vice versa against yellow e. not enough alone to support theory of natural selection but may be added evidence to similar observations in other organisms / OWTTE
Question
(a) (i) Distinguish between the structure of amylose and the structure of amylopectin. [1]
(ii) Suggest the reason for cellulose passing undigested through the human gut. [1]
(b), Draw an annotated diagralm to show how a peptide bond is formed. [3]
(c) State two structural features that differ between RNA and DNA. [2]
▶️Answer/Explanation
Ans: a i amylose unbranched/helical while amylopectin branched / vice versa 2.
a ii enzymes required to digest cellulose not present in the human gut / OWTTE OR undigested cellulose provides bulk/fibre 2.
b a. correct structure of two amino acids b. \(\mathrm{H}_2 \mathrm{O}\) lost \(\mathbf{c}\). C from \(\mathrm{COOH}\) of one links to \(\mathrm{N} \mathrm{of} \mathrm{NH}_2 / \mathrm{NH}_3+\) from the other d. correct labelling of the peptide bond
2. c a. number of strands OR] (usually) only one strand in RNA/two strands in DNA
b. base composition OR uracil only in RNA / thymine only in DNA
c. type of pentose OR ribose only in RNA / deoxyribose only in DNA
Question
(a) Using the Punnett grid, explain how two parents can have children with any of the different ABO blood groups.
(b) Distinguish between the structure of arteries and the structure of veins. [3]
(c) Explain how cuts in the skin are sealed by blood clotting. [2]
▶️Answer/Explanation
Ans: 3. a a. correct gametes of one parent as IA AND i in header line/column AND correct gametes of other parent as IB AND i in header column/line b. correct corresponding genotypes in inner squares as IAI B, IAi, IBi, ii c. corresponding phenotypes of children identified as AB, A, B and O d. ratio of phenotypes is 1:1:1:1 OWTTE 
b a. arteries have thicker (muscular) walls/layer/tunica (media) OR veins have thinner (muscular) walls/layer/tunica (media) b. arteries have no valves OR
veins have valves c. arteries have thicker elastic layer OR veins have thinner elastic layer d. arteries have a smaller lumen/bore OR veins have a larger lumen/bore Accept answers presented in a table. 3. c a. clotting factors released from platelets b. clotting process involves a cascade/series of reactions c. produces thrombin d. causes rapid conversion of fibrinogen into fibrin e. fibrin makes a mesh to seal the wound/OWTTE
Question
4. (a) (i) State one reason that viruses are not classified as living organisms. [1]
(ii) State the plant phylum which is characterised by the absence of vascular tissue. [1]
(b) C. nemoralis (pictured in question 1) is a mollusc. Identify two external features that distinguish this snail from an arthropod. [2]
(c) Outline the role of plant pigments in the process of photosynthesis.[3]
▶️Answer/Explanation
Ans: a i a. they do not have a metabolism/homeostasis/other specifically named life function b. cannot reproduce by themselves c. they are not cells/they need a host cell 4. a ii bryophyta 4. b a. unsegmented body (whereas arthropods are segmented) b. shell (versus exoskeleton in arthropods) c. muscular foot (which arthropods do not have) d. no (jointed) appendages/(jointed) legs (whereas arthropods have jointed
legs/appendages) e. slimy/mucus-covered / arthropod is not slimy Do not award marks for any answers after the first two given. 4. c a. pigments/chlorophyll absorb light b. red and blue/violet light absorbed c. absorption of light energy is necessary for photolysis/use of water in photosynthesis d. other pigments allow for wider action spectrum than the absorption spectrum of chlorophyll
QuestionSection B
Answer one question. Up to one additional mark is available for the construction of
your answer. Answers must be written within the answer boxes provided.
5. (a) Draw a labelled diagram to show the fluid mosaic model of the plasma membrane. [4]
(b) Unicellular and multicellular organisms share the same functions of life. Outline four functions of life. [4]
(c) The structure of organisms is based on organic molecules containing carbon.
Explain the cycling of carbon in an ecosystem. [7]
▶️Answer/Explanation
Ans: a Draw a labelled diagram to show the fluid mosaic model of the plasma membrane.
a. two correctly oriented layers of phospholipids/phospholipid bilayer shown with heads facing in opposite directions
b. phospholipids shown with two parts labelled hydrophilic/phosphate head AND hydrophobic/hydrocarbon tail
c. protein (any) shown as a globular structure embedded in one/both layers o phospholipid
d. peripheral protein, shown as globular structure at the surface of the membrane AND integral protein shown as embedded globular structures
e. glycoprotein shown as embedded globular structure with antenna-like carbohydrate protruding / carbohydrate shown as a branched/antenna-like structure either on a protein or on a phospholipid OR channel protein(s) shown with a pore passing through it OR pump protein shown as a transmembrane globular structure f. cholesterol shown in between adjacent phospholipids
b a. nutrition: process by which organisms take in and make use of food//nutrients OWTTE b. metabolism: conversion of organic molecules/chemical reactions in an organism
c. growth: increase in size/mass/number of cells within an organism
d. response/irritability/sensitivity: reactions/responsiveness to stimuli/factors
e. homeostasis: regulating/maintaining constant/stable interior environment
f. reproduction: production of similar cells/organisms from existing ones/offspring
g. excretion: elimination of (metabolic) wastes
5. c a. autotrophs/producers absorb carbon (dioxide} from atmosphere/air/water
b. autotrophs make carbohydrates/organic compounds / perform photosynthesis
c. carbon (compounds) pass along food chains/trophic levels (as consumers feed)
d. respiration releases carbon (dioxide) into atmosphere/water e. carbon (dioxide} is released from dead matter /by decomposition/respiration
f. methane is produced during anaerobic respiration of organic matter / by methanogens in cattle/herbivores
g. methane is oxidized into carbon dioxide in the atmosphere h. fossil fuels/peat were made from partially decomposed organic matter
i. combustion of fossil fuels/forest fires/biomass releases carbon (dioxide} into the atmosphere
j. volcanic eruptions may add large quantities of carbon (dioxide) into the atmosphere
k. limestone (from shells/reefs)/trees/permafrost are sinks of carbon
Question
6. (a) Outline the role of the parts of an alveolus in a human lung. [4]
(b) Explain how antibiotic resistance can evolve in bacteria, such as those causing
pneumonia. [4]
(c) Many diseases are caused by bacteria and other pathogens. Explain, using examples,
how other factors can lead to disease in humans. [7]
▶️Answer/Explanation
Ans: a a. the (spherical) wall of an alveolus maximizes/allows gas exchange
b. pneumocytes I (optimize) gas exchange
c. pneumocytes II produce surfactant
d. adjacent capillaries enclose alveolus for efficient gas exchange with blood
e. surfactant reduces surface tension/prevents collapse of alveolus f. (alveolar) macrophages/phagocytes help with defense/homeostasis/response to foreign substances
b a. antibiotic resistance exists as a genetic variation (within the population) b. (antibiotic resistance) may occur from transfer of genetic material OR (antibiotic resistance) may occur through mutation c. resistance is specific to one antibiotic d. only bacteria with resistance gene reproduce in the presence of antibiotic
e. frequency of resistant bacteria increases in population f. resistant population replaces non-resistant over time
c Since this question is open-ended here is how it may be marked: For any non-pathogenic disease being addressed, look for the following components
● name of disease/condition. ● factor/category e.
g.: genetic, lifestyle, environmental, psychological, multi-factoral. ● description/symptoms of disease. ● cause of disease. At least 2 of these qualities must be present to earn any marks for a disease or category/factor For this question use the unlettered tick. Award if only one condition is explained. Sample answers:
e.g. cystic fibrosis genetic multiple lung infections/sticky mucus allows opportunistic bacterial infections of lungs / patients lack lipases/cannot digest fat/do not “thrive” recessive (autosomal) allele / homozygous recessive subjects display cystic fibrosis phenotype / chloride channels are faulty
e.g. rickets environmental / lifestyle / nutritional bones are soft/do not calcify lack of vitamin D