GCE ASBiology

January 2008

Mark SchemesIssued: April 2008

iii

NORTHERN IRELAND GENERAL CERTIFICATE OF SECONDARY EDUCATION (GCSE) AND NORTHERN IRELAND GENERAL CERTIFICATE OF EDUCATION (GCE)

MARK SCHEMES (2008)

Foreword

Introduction

Mark Schemes are published to assist teachers and students in their preparation for examinations. Through the mark schemes teachers and students will be able to see what examiners are looking for in response to questions and exactly where the marks have been awarded. The publishing of the mark schemes may help to show that examiners are not concerned about fi nding out what a student does not know but rather with rewarding students for what they do know.

The Purpose of Mark Schemes

Examination papers are set and revised by teams of examiners and revisers appointed by the Council. The teams of examiners and revisers include experienced teachers who are familiar with the level and standards expected of 16- and 18-year-old students in schools and colleges. The job of the examiners is to set the questions and the mark schemes; and the job of the revisers is to review the questions and mark schemes commenting on a large range of issues about which they must be satisfi ed before the question papers and mark schemes are fi nalised.

The questions and the mark schemes are developed in association with each other so that the issues of differentiation and positive achievement can be addressed right from the start. Mark schemes therefore are regarded as a part of an integral process which begins with the setting of questions and ends with the marking of the examination.

The main purpose of the mark scheme is to provide a uniform basis for the marking process so that all the markers are following exactly the same instructions and making the same judgements in so far as this is possible. Before marking begins a standardising meeting is held where all the markers are briefed using the mark scheme and samples of the students’ work in the form of scripts. Consideration is also given at this stage to any comments on the operational papers received from teachers and their organisations. During this meeting, and up to and including the end of the marking, there is provision for amendments to be made to the mark scheme. What is published represents this fi nal form of the mark scheme.

It is important to recognise that in some cases there may well be other correct responses which are equally acceptable to those published: the mark scheme can only cover those responses which emerged in the examination. There may also be instances where certain judgements may have to be left to the experience of the examiner, for example, where there is no absolute correct response – all teachers will be familiar with making such judgements.

The Council hopes that the mark schemes will be viewed and used in a constructive way as a further support to the teaching and learning processes.

v

CONTENTS

Page

AS 1: Module 1 1

AS 2: Module 2 7

AS 3A: Module 3A 13

ADVANCED SUBSIDIARY (AS)General Certifi cate of Education

January 2008

MARKSCHEME

ASB1W8 3310.01

Biology

Assessment Unit AS 1assessing

Module 1: Cell Biology

[ASB11]

TUESDAY 15 JANUARY, AFTERNOON

1

AVAILABLEMARKS

2ASB1W8 3310.01

Section A

1 Interphase synthesis/S mitosis/karyokinesis metaphase cytokinesis [4] for fi ve, [3] for four, [2] for three, [1] for two [4] 4

2 (a) Facilitated diffusion involves protein carriers, while diffusion does not; both involve the movement of substances along the concentration gradient/passive/does not involve energy expenditure; [2]

(b) Ascorbic acid moves through the protein component of the membrane; since this contains a hydrophilic (water-soluble) core/either by active transport or facilitated diffusion; calciferol moves across the lipid component of the membrane; since it is soluble in lipid; [4] 6

3 (a) Nucleolus; nuclear envelope/membrane; nuclear pore; mitochondrion; [4]

(b) Any two from • membrane-bound organelles/example of membrane-bound organelles (nucleus/mitochondrion/chloroplast/endoplasmic reticulum/Golgi apparatus) are only found in eukaryotic cells • DNA in prokaryotic cells is naked i.e. is not associated with protein/ DNA in eukaryotic chromosomes is bounded by protein (histones) • prokaryotic cells may contain extrachromosomal DNA/plasmids • prokaryotic cells have smaller (70s) ribosomes/eukaryotic cells have larger (80s) ribosomes • prokaryotic cells have a cell wall (of peptidoglycan)/some eukaryotic cells (i.e. animal cells) lack a cell wall • prokaryotic cells are much smaller, rarely exceeding 2 μm in width/ eukaryotic cells are generally greater than 5 μm in size • other appropriate example or Two examples of membrane bound organelles (see list above); [2] 6

/ denotes alternative points ; denotes separate points Comments on mark values are given in bold

3ASB1W8 3310.01

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4 (a) Glycerol; [1]

(b) Hydrolysis; [1]

(c) A decrease in pH indicates an increase an acidity; due to the production of fatty acids; [2]

(d) 5 °C: relative inactivity is due to low kinetic energy of molecules in solution/ low collision rate of enzyme and substrate; 65 °C: inactivity is due to the denaturation/loss of tertiary structure of the enzyme; [2] 6

5 (a) Any three from • potato cylinder shortens in length • cylinder loses water osmotically • into solution which has a lower (more negative) water potential/ from solution of greater water potential • cells become plasmolysed/tissue becomes fl accid [3]

(b) –680 kPa; [1]

(c) At –400 kPa the increase is 115%; 115% of 80 is 92; [2] 6

6 (a) Phosphate; deoxyribose; [2]

(b) (i) 20 cytosine and guanine, 30 thymine; thymine has the same amount as adenine since they base pair; leaving 40 to be shared between cytosine and guanine (which also base pair); [3]

(ii) Even though the composition of bases may be the same the base order will be quite different; providing a different genetic code for the production of proteins/ determining different amino acid sequences; [2] 7

AVAILABLEMARKS

4ASB1W8 3310.01

7 (a) (i) Peptide; [1]

(ii) Folded shape/S – S (disulphide) bond; [1]

(b) 14 × 3 = 42 (addition of start and stop codons = 48); [1]

(c) Sticky ends make it easier to join with other sections of DNA (annealing); which have complementary sticky ends/base sequences; [2]

(d) A plasmid is opened with a restriction endonuclease; to leave complementary sticky ends; the DNA sections are joined (annealed) by DNA ligase; [3] 8

Section A 43

5ASB1W8 3310.01

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Section B

8 Ten points with a maximum of three in any one section

Chloroplast: • plant cells may possess chloroplasts surrounded by a double membrane/ envelope • contain an internal membrane system, lamellae/thylakoids/grana • and a matrix known as stroma • chlorophyll (and other pigments) are contained on the internal membranes (site of light-dependent reactions) • while light-independent reactions take place in the stroma

Cell wall: • plant cells possess a cellulose cell wall while animal cells lack a cell wall • cellulose fi brils are composed of chains (of β-glucose) linked by H-bonds • the cell wall prevents the cell lysing in hypotonic/high water potential conditions • since a wall pressure develops to negate the high turgor pressure

Plasmodesmata: • plant cells are connected via plasmodesmata/channels of interconnecting cytoplasm • allowing direct movement of molecules between cells Centrioles • animal cells possess centrioles/plant cells lack centrioles • centrioles are organelles containing microtubules • in animal cells centrioles produce the spindle • in plant cells the spindle is produced from “free” microtubules

Cytokinesis: • animal cells divide via a cleavage furrow • whereby the membrane is pulled in by microtubules along the equatorial plane • plant cells divide via the production of a cell plate/phragmoplast • from coalescing vesicles produced by Golgi bodies/dictyosomes Vacuoles: • plant cells normally possess vacuoles • the sap vacuole is surrounded by the tonoplast • it stores nutrients and excretory products

Lysosomes: • animal cells possess lysosomes • that contain powerful hydrolytic enzymes • involved in intracellular digestion/autolysis

Carbohydrate storage: • plant cells have starch grains while animal cells may have glycogen • any plant cell may contain starch, glycogen is confi ned to muscle/liver cells • starch consists of amylose and amylopectin/glycogen is more highly branched • other appropriate responses [10]

AVAILABLEMARKS

6ASB1W8 3310.01

Consider QWC:

2 marks: The candidate expresses ideas clearly and fl uently, through well-linked sentences and paragraphs. Arguments are generally relevant and well-structured. There are few errors of grammar, punctuation and spelling.

1 mark: The candidate expresses ideas clearly, if not always fl uently. Arguments may sometimes stray from the point. There are some errors of grammar, punctuation and spelling, but not such as to suggest a weakness in these areas.

0 marks: The candidate expresses ideas satisfactorily, but without precision. Arguments may be of doubtful relevance or obscurely presented. Errors in grammar, punctuation and spelling are suffi ciently intrusive to disrupt the understanding of the passage. [2] 12

Section B 12

Total 55

ADVANCED SUBSIDIARY (AS)General Certifi cate of Education

January 2008

MARKSCHEME

ASB2W8 3408.01

Biology

Assessment Unit AS 2assessing

Module 2: Physiology and Ecology

[ASB21]

TUESDAY 15 JANUARY, AFTERNOON

7

AVAILABLEMARKS

8ASB2W8 3408.01

Section A

1 (a) Myoglobin; [1]

(b) Fibrinogen; [1]

(c) Absorption spectrum; [1]

(d) Ecological niche/niche; [1] 4

2 (a) Blood passes through the heart twice in each complete circulation/there is a pulmonary circuit and a systemic circuit during each circulation; [1]

(b)

[12] each [4] 5

3 (a) A: mucosa B: muscularis mucosa C: muscularis externa Three for [2], two for [1] [2]

(b) Long length of ileum/folds in the ileum (folds of Kerkring)/microvilli [1]

(c) (i) Goblet cells; [1]

(ii) Increase diffusion distance of the products of digestion/may block access to active transport or facilitated diffusion carrier molecules/may hinder movement of villi and so prevent the maintenance of a concentration gradient from lumen to epithelial cell/reduces contact of digested products with villus/any other appropriate answer; [1] 5

/ denotes alternative points ; denotes separate points Comments on mark values are given in bold

Blood vesselDirection of blood fl ow

Origin Destination

Vena cavaBody organ(except lungs)/other veins

Right atriumof the heart

Pulmonary artery Right ventricle Lungs

Renal artery Aorta (dorsal) Kidney

Hepatic portal vein Small intestine/ileum Liver

9ASB2W8 3408.01

AVAILABLEMARKS

4 (a) A: palisade mesophyll layer [12]

B: spongy mesophyll layer [12] [1]

(b) Stomatal pores; facilitates diffusion of gases in and out of the leaf; or Leaf is thin; minimises diffusion distances of gases; or Sub-stomatal air spaces; facilitates diffusion of gas within leaf; [2]

(c) Clear cuticle; to allow passage of light to underlying mesophyll tissue; or Epidermal cells lack chloroplasts/epidermal cells are thin; to allow passage of light to underlying mesophyll tissue; or Chlorophyll/chloroplast gradient from top to bottom of leaf; most chlorophyll is concentrated where most light hits; or Palisade cells are packed closely together; allowing more chloroplasts to be held close to the upper surface; or Chloroplasts may be concentrated at the upper end of the palisade cells; concentrated where most light falls; [2]

(d) Any two from • larger surface area of leaf • greater concentration of chloroplasts within the palisade cells • greater concentration of chlorophyll within the chloroplasts • chloroplasts may contain more grana • leaves produced at an earlier time before the leaf canopy develops • reduced number of cells/lower compensation point [2] 7

5 (a) Any two from • pig respiration • excretion/urine • indigestible parts of the food consumed/egestion/faeces [2]

(b) Increase as 385 less 350 = 35; divided by 350 = 10%; [2]

(c) Any two from • less energy used in respiration • since less energy used in movement (confi ned conditions) • less energy used to maintain body temperature (since homoiothermic) [2]

(d) Animal welfare concerns (e.g. regarding crowding, stress etc.)/ environmental concerns (e.g. regarding disposal of organic waste)/issue concerned with the disposal of pig slurry/issue concerned with excessive use of antibiotics/other appropriate issue; [1] 7

AVAILABLEMARKS

10ASB2W8 3408.01

6 (a) 0.1 second; at that point the pressure in the ventricle exceeds that in the atrium; [2]

(b) 0.4 second; at that point the pressure in the aorta exceeds that in the ventricle; [2]

(c) Any two from • immediate increase in pressure as the bicuspid valve bulges into atrium (reducing volume) • atrial pressure drops as blood is forced out of the heart (ventricle)/ continued atrial diastole • atrial pressure increases (after 0.2 s) as blood is returned to the atrium (from veins) [2]

(d) Low pressure required in pulmonary circulation to prevent fl uid accumulating in the alveoli (and the individual drowning); high pressure required in the body circulation to ensure the formation of tissue fl uid (and ultrafi ltration in the kidneys); or Any two from • the left ventricle is much more muscular than the right ventricle • since it must pump blood to the body • while the right ventricle pumps blood to the neighbouring lungs [2] 8

7 (a) Any two from • it takes place between individuals of the same species/within the same population • there is a decreased contribution of individuals to the next generation/ all individuals “suffer” (it is a –\– interaction)/results in a negative effect on survivorship and/or fecundity • the resource for which individuals are competing is in limited supply • the effect of competition is greater at higher population densities [2]

(b) (i) The mean length of limpets is greater at low population densities/is lower at high population densities; [1]

The greater the density of limpets the greater is the total biomass per unit area (up to a critical level – approximately 400 limpets per square metre); at high limpet density, further increase in density does not increase the total biomass; [2]

(ii) Any two from • limpets are competing for food/algae which they graze on the rocks • at high densities, individuals have less food and so are smaller • at high densities, total biomass remains relatively constant since while more limpets are present they are individually smaller [2] 7

Section A 43

11ASB2W8 3408.01

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Section B

8 Ten points (with at least four from each section)

Phloem: • both tissues are forms of vascular tissue with phloem on the outside of the vascular bundle • phloem is the tissue responsible for the transport of sugars and other organic substances • the transport elements in phloem are the sieve tube elements • the end walls of which are perforated/form sieve plates • since sieve tube elements lie end-to-end (forming a tube) these facilitate transport • sieve tube elements have a thin lining of cytoplasm and no nucleus/tonoplast • next to each element is a companion cell, translocation relies on their metabolism • movement through the sieve tubes may take place by mass fl ow/from source to sink or example • movement is both up and down the plant • phloem also contains parenchyma/fi bres for support • phloem is a living tissue

Xylem: • xylem is the tissue responsible for the transport of water and mineral ions • the conducting cells in xylem are the vessels • which have a lignifi ed secondary wall • in mature xylem this is often pitted (or reticulate) to allow lateral movement of water into surrounding tissues • in protoxylem (in growing regions) lignifi cation is annular/spiral • to allow for extension in the region of growth • lignifi cation prevents the vessels from collapsing/waterproof • under the negative pressure generated by transpiration • this pulls water up the xylem/movement unidirectional • transport in vessels is also aided by forces of adhesion and cohesion/root pressure • xylem also contains parenchyma/fi bres/tracheids • dead tissue/hollow/no cell contents • no cross walls allows for a continuous column of water [10]

AVAILABLEMARKS

12ASB2W8 3408.01

Consider QWC:

2 marks: The candidate expresses ideas clearly and fl uently, through well-linked sentences and paragraphs. Arguments are generally relevant and well-structured. There are few errors of grammar, punctuation and spelling.

1 mark: The candidate expresses ideas clearly, if not always fl uently. Arguments may sometimes stray from the point. There are some errors of grammar, punctuation and spelling, but not such as to suggest a weakness in these areas.

0 marks: The candidate expresses ideas satisfactorily, but without precision. Arguments may be of doubtful relevance or obscurely presented. Errors in grammar, punctuation and spelling are suffi ciently intrusive to disrupt the understanding of the passage. [2] 12

Section B 12

Total 55

ADVANCED SUBSIDIARY (AS)General Certifi cate of Education

January 2008

MARKSCHEME

ASB3W8 3633.01

Biology

Assessment Unit AS 3Aassessing

Module 3A: Practical Processes

[ASB31]

WEDNESDAY 23 JANUARY, MORNING

13

AVAILABLEMARKS

14ASB3W8 3633.01

1 (a) (i) 24%; each small square represents 4% (× 6 squares); [2]

(ii) Diffi culty of identifying individual plants (clumping)/reference to vegetative reproduction/better estimate of overall abundance since plants may differ in size; [1]

(b) Any four from Belt transect: • mark line of transect down the slope • from dry to wet region of meadow • quadrats placed contiguously (end-to-end)/interrupted (say every two metres) • % cover measured in each quadrat • results displayed in kite diagrams/series of histograms or Random sampling: • quadrats placed randomly in dry and wet regions of the meadow • by throwing over shoulder/using random coordinates • approximately 30 quadrat sites • % cover measured in each quadrat • water content of soil sample measured in each quadrat • average % cover determined in each region/scattergram drawn to determine possible correlation [4] 7

2 Drawing skills: block diagram showing tissue layers; all tissue layers drawn (completeness of drawing to show the tissues obvious in the photograph); accurate representation of the photograph, i.e. a drawing rather than a diagram; accurate positioning and proportionality of the tissue layers; quality of drawing (e.g. clear – smooth and continuous – lines drawn, not sketchy); [5]

Identifi cation of fi ve of the following structures; cortex/parenchyma pith (parenchyma) epidermis collenchyma sclerenchyma (bundle sheath) xylem phloem cambium [4] Five for [4], four for [3], three for [2], two for [1] 9

/ denotes alternative points ; denotes separate points Comments on mark values are given in bold

15ASB3W8 3633.01

AVAILABLEMARKS

3 (a) Unlike blood cells an infl ux of water will not cause the cells to burst which would affect the accuracy of the count; [1]

(b) Any two from • culture mixed to create an even suspension • coverslip used is of a mass to ensure a constant distance over haemocytometer • place a drop of the yeast suspension onto the slide alongside the coverslip in the area between the grooves • the yeast suspension should be drawn under the coverslip by capillary action [2] (c) Dilute the yeast suspension remembering to take the dilution factor into account in the fi nal calculation; [1]

(d) (i) Randomly select the C squares/avoid cells containing clumped yeast cells; [1]

(ii) Count cells touching the top and left lines of the type C square, ignore cells touching the bottom and right lines of the type C square/use the North-West rule when counting; [1]

(iii) 9 yeast cells [consistent with procedure shown in (ii)]; [1]

(iv) 9 cells found in a volume of .00025 mm3 (.00252 × .1 mm); 36 000 per mm3 (9/.00025)/3.6 ×104 mm-3; Allow answer consequential to value in (iii) [2]

(e) Count yeast cells in more than one type C square to get a more representative average/repeat for several sample of the yeast population/make sure the yeast suspension is well agitated before being sampled to ensure no settling has taken place/avoid clumped yeast cells/agitate the yeast culture throughout the incubation period to reduce the risk of clumping; [1] 10

AVAILABLEMARKS

16ASB3W8 3633.01

4 (a) Caption; scaling of the graph (using the graph paper to maximal effect); dilution of seawater as the independent variable along the x-axis; axes labelled; line graph with points joined with short straight lines/bar chart with bars (correctly scaled); accurate plotting of data; [6]

(b) Water moves into the periwinkles; from high to low water potential/diluted seawater has a higher water potential; [2]

(c) There is no (negligible) response where the immersing solution is 80% seawater or more/in partially diluted seawater there is no withdrawal response/periwinkles only start to respond by withdrawing into their shells at dilutions below 80% seawater; the response increases where seawater is further diluted from 80% to 40% (when all periwinkles have withdrawn)/in very dilute solutions there is an appreciable withdrawal response; [2]

(d) Withdrawal behaviour would reduce water uptake; preventing osmotic damage to periwinkles/cells lysing; [2] 12

AVAILABLEMARKS

17

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17ASB3W8 3633.01

AVAILABLEMARKS

18ASB3W8 3633.01

5 (a) Concentration of hydrogen peroxide/volume of hydrogen peroxide; height of foam in measuring cylinder; [2]

(b) Any four from • dilute hydrogen peroxide with water to produce different concentrations • add the same volume of hydrogen peroxide (different concentrations) to measuring cylinders • grind portions of liver • add same amount of liver (by volume or mass) to different concentrations of hydrogen peroxide (in measuring cylinders) • leave for the same period of time • measure the height of the foam (above solution) in each measuring cylinder [4]

(c) Any two from • some other factor (temperature, pH) may differ • the liver portions may not all be the same mass [if not noted above] • need to determine the amount of foam relative to the mass of liver used [if not noted above] • the time between adding the liver and measuring the height of the foam must be the same in each case [if not noted above] • different portions of liver may contain different amounts of catalase/ catalase may not be evenly distributed throughout the liver • the height of foam may not be proportional to the amount of oxygen produced/not all the oxygen produced may produce foam • other appropriate suggestion [2]

(d) Concentration of hydrogen peroxide along the x-axis and height of foam (estimate of oxygen produced) on the y-axis; increase in height of foam as substrate concentration is increased/ saturating curve; [2] 10

19ASB3W8 3633.01

AVAILABLEMARKS

Consider QWC in questions 1(b) and 5(b) 2 marks: The candidate expresses ideas clearly and fl uently, through well-linked sentences and paragraphs. Arguments are generally relevant and well-structured. There are few errors of grammar, punctuation and spelling.

1 mark: The candidate expresses ideas clearly, if not always fl uently. Arguments may sometimes stray from the point. There are some errors of grammar, punctuation and spelling, but not such as to suggest a weakness in these areas.

0 marks: The candidate expresses ideas satisfactorily, but without precision. Arguments may be of doubtful relevance or obscurely presented. Errors in grammar, punctuation and spelling are suffi ciently intrusive to disrupt the understanding of the passage. [2] 2 Total 50