APW/Jan07/BYB1

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3 Differential centrifugation was used to isolate five components from leaf cells.

(a) The leaf tissue was first homogenised in ice-cold isotonic sucrose solution. Explainwhy an isotonic solution was used.

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(b) The homogenate was then centrifuged five times, each time at a higher speed. Thepellet formed at the bottom of the centrifuge tube after each centrifugation wasremoved. Each pellet contained a different cell component. The components were cellwalls, chloroplasts, mitochondria, nuclei and ribosomes.

(i) Complete the table to show the order in which the cell components were isolatedfrom the homogenate.

(2 marks)

(ii) Which of these cell components contains the most polysaccharide?

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(iii) Which of these cell components is the site of protein synthesis?

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Order in which pellets wereCell componentproduced

1

2

3 Chloroplasts

4

5

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(c) Complete the table to give two structural differences, other than size, between achloroplast and a mitochondrion.

(2 marks)

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8

Chloroplast Mitochondrion

Biology B - AQA GCE Mark Scheme 2007 January series

4

Question 3 (a) No net movement of water / no osmosis / no osmotic effects; Prevent organelles / named organelle changing shape / bursting; 2 (reject cells and cell components) (b) (i) 1 Cell walls 2 Nuclei 4 Mitochondria 5 Ribosomes; 2 (any 3 in correct order = 1 mark) (allow number if correctly corresponding to named part) (ii) (Cell) walls; 1 (iii) Ribosomes; 1 (c) Reference to: Cristae/folded inner membrane/detail of structure; Starch grains; Grana/detail of structure; 2 max (use list rules for marking) (shape neutral) (allow labelled diagrams) Total 8 Question 4 (a) (i) Condensation; 1 (ii) Box drawn around appropriate OH and H; 1 (iii) Peptide; 1 (b) (i) Hydrogen/ionic; 1 (ii) Cysteine; Contains sulphur; Required to form disulphide bonds / sulphide bridges / (S-S bonds); Bonds are strong / bonds are covalent (not broken by heat treatment); 2 max (if not cysteine, then max 1) Total 7

APW/Jun09/BYB1

2 Areas outsidethe box will

not be scannedfor marking

1 The diagram shows part of an epithelial cell from the small intestine as seen with an electronmicroscope.

1 (a) What is the function of the organelles labelled A and B?

A .........................................................................................................................................

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B .........................................................................................................................................

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Answer all questions in the spaces provided.

(02)

A

B

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not be scannedfor marking

1 (b) Name one organelle shown in the diagram that would be present in a prokaryotic cell.

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1 (c) The internal structure of organelle B can be seen using an electron microscope but notwith a light microscope. Explain why.

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(Extra space) ......................................................................................................................

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APW/Jun09/BYB1(03)

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Biology - AQA GCE Mark Scheme 2009 June series

3

Question Part Sub Part Marking Guidance Mark Comments

1 (a) A – modifies/packages/ proteins/enzymes / produce glycoproteins /vesicles

/lysosomes;

B – aerobic respiration/production of ATP/converts energy;

2

1 (b) Ribosome; 1

1 (c) Electron microscope uses (a beam of) electrons; Shorter wavelength than light; Greater resolution;

2 max Or description

APW/Jun08/BYA1 R

4 Areas outsidethe box will

not be scannedfor marking

2 (a) The table shows some features that may or may not be present in different cells.Complete the table with either a tick if the feature is present or a cross if it is notpresent.

(4 marks)

2 (b) Some of the cells in the pancreas make large amounts of enzymes. These cells containmany ribosomes and many mitochondria. Explain the importance of these cellscontaining

2 (b) (i) many ribosomes

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2 (b) (ii) many mitochondria.

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(04)

CellFeature

Red blood cell Leaf cell BacteriumEpithelial cellfrom alveolus

Nucleus

Plasma membranesurrounding cell

Cell wall

Biology Specification A - AQA GCE Mark Scheme 2008 June series

3

Question 1

(a) (i) Box drawn round appropriate H and OH; 1

(ii) Condensation; 1

Accept close versions such as condensing reaction or condensing.

(b) An H atom is at the bottom/an OH is at the top in ȕ glucose;

At the right-hand side of the molecule; 2

Note that this is the lowest acceptable answer. Better candidates might be expected to

refer to C1. Obviously such answers should gain credit. Reject polymerisation.

(c) Two marks for correct answer of 0.9/0.89 or expressed as fraction 8/9 /

.

0.8 ;;

One mark for incorrect answer such as 1.12(5) or 0.8 derived from correct values; One mark for 0.9 with no working; 2 max

(d) (i) Left hand side marked; 1

(ii) Separates amino acids/spots/B and C more; 1

Total 8

Question 2

(a)

Cell Feature

Red blood cell Leaf cell Bacterium Epithelial cell

from alveolus

Nucleus

X 9 X 9

Plasma membrane

surrounding cell

9 9 9 9

Cell wall

X 9 9 X

Allow one mark for each correct column;;;; 4

Do not accept hybrid tick/crosses or blank spaces.

If no crosses at all accept blank as equivalent to a cross

(b) (i) Site of enzyme/protein synthesis; 1

(ii) Release/transfer/make available energy/ATP/site of respiration;

For synthesising/making/secreting proteins/enzymes; 2

Ignore references to making/producing energy.

(c) Blue/blue-black/purple/black with iodine;

Reference to use of microscope; 2

Total 9

APW/Jan09/BYA1

6 Areas outsidethe box will

not be scannedfor marking

3 In the diagram, the circles represent three types of cell. The letters A to G represent featuresfound in these cells.

3 (a) In which space A to G would you put the following?

3 (a) (i) Nucleus

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3 (a) (ii) Cell wall

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3 (b) Name one organelle that should be put in

3 (b) (i) space D

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3 (b) (ii) space G.

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(06)

Prokaryotic cell White blood cell

Leaf cell

G

E FD

B CA

7 Areas outsidethe box will

not be scannedfor marking

3 (c) (i) Give one feature of a lysosome that could be seen with a transmission electronmicroscope.

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3 (c) (ii) The detailed structure of a lysosome can be seen with a transmission electronmicroscope. It cannot be seen with an optical microscope.

Explain why the detailed structure of a lysosome cannot be seen with an opticalmicroscope.

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3 (c) (iii) Immediately after giving birth, a woman’s uterus weighed approximately 2 kg.As soon as the baby was born, the tissues of her uterus were invaded by whiteblood cells. These white blood cells contain lysosomes. Nine days after givingbirth her uterus weighed about 50 g.

Explain the link between the lysosomes and the change in mass of the woman’suterus.

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APW/Jan09/BYA1

9

(07)

Biology Specification A - AQA GCE Mark Scheme 2009 January series

3

Question 1

(a) Nitrogen; 1

Q Do not accept N in the context of this question.

(b) (i) Heat with Benedict’s solution;

Green/yellow/orange/red (precipitate); 2

Q Do not accept unqualified references to placing in a water bath.

(ii) A; 1

(c) (i) Joining together/forming a bond/with removal of (a molecule of) water; 1

(ii) C; 1

(d) (i) D; 1

(ii) Maximum amount of hydrogen;

No double bonds/all carbon atoms attached to two hydrogen atoms;

In hydrocarbon chain between carbon atoms/other than in COOH group; 2 max

Total 9

Question 2

(a) Capillary endothelium/epithelium and alveolar epithelium;;

Capillary wall/wall of alveolus; 2

General principle for marking

One mark for correct identification of the layers involved. Two marks for correct

identification of layers involved and use of appropriate terminology.

(b) (i) Contracts/lowers/flattens;

Increases volume; 2

(ii) Air entering the lungs (during inspiration); 1

(c) Correct answer of 18.2/18.18/18;;

Incorrect answer correctly based on identifying duration of one complete breath

as 3.3 seconds; 2

Total 7

Question 3

(a) (i) F; 1

(ii) E; 1

(b) (i) Ribosome/ Accept plasma/cell (surface) membrane; 1

(ii) Chloroplast/ (Large) vacuole; 1

Biology Specification A - AQA GCE Mark Scheme 2009 January series

4

(c) (i) Membrane/Accept lumen/shape; 1

(ii) Uses light which has longer wavelength;

Optical microscope has low(er) resolution/resolving power; 2

Q The term resolution is essential for the second mark.

(iii) Contain/release/secrete enzymes;

Lysosomes/enzymes digest/break down/destroy proteins/cells/tissue (of uterus);

2

Total 9

Question 4

(a) (S=) C

H; 1

(b) (More) impulses along parasympathetic/vagus nerve/fewer/no impulses along

sympathetic/accelerator nerve;

SAN sends fewer impulses/waves if electrical activity/signals; 2

Q To gain first marking point, a reference must be made to impulses.

Do not credit such terms as messages.

(c) (i) 0.5 (cm3 g-1 minute-1); 1

(ii) (Allow comparison because) the organs/tissues are different sizes/

masses/weights; 1

(iii) Heart muscle contracts more/work harder/increase cardiac output;

More oxygen/respires faster/removes carbon dioxide; 2

Total 7

Question 5

(a) (i)

Valve J Valve K

Closes Opens;

1

(ii) Increases pressure (of blood)/in vein/between valves;

Higher pressure above than below valve (opens valve); 2

APW/Jun09/BYA1

2 Areas outsidethe box will

not be scannedfor marking

1 The diagram shows how some organelles may be distinguished from each other.

1 (a) (i) Name organelle B.

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1 (a) (ii) Describe the function of organelle B.

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Answer all questions in the spaces provided.

(02)

Organelle found in prokaryoticand eukaryotic cells.

Organelle A

Larger organelle surroundedby an envelope through whichthere are pores. Usually one

per cell.Organelle C

Smaller organelle surroundedby an outer membrane. Has an inner

membrane, folded to form cristae.Many in a cell.

Organelle D

Organelle found inanimal cells and in

plant cells. Does notcontain membranesarranged in stacks.

Organelle found inplant cells. Contains

inner membranesarranged in stacks.

Organelle B

Organelle found only in eukaryotic cells.

3 Areas outsidethe box will

not be scannedfor marking

1 (b) Which organelle A, B, C or D

1 (b) (i) is a ribosome?

(1 mark)

1 (b) (ii) contains most of the DNA found in a plant cell?

(1 mark)

1 (c) Some liver tissue was ground, filtered and centrifuged to make a suspension oforganelle D.

1 (c) (i) Explain why the solution in which the liver tissue was ground should be ice-cold.

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1 (c) (ii) The ground liver was centrifuged at low speed. The pellet that formed at thebottom of the centrifuge tube was thrown away and the supernatant centrifugedagain at higher speed. Explain why it was necessary to first centrifuge theground liver at low speed in order to obtain a suspension of organelle D.

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APW/Jun09/BYA1(03)

8

Biology Specification A - AQA GCE Mark Scheme 2009 June series

3

Question 1

(a) (i) Chloroplast; 1

(ii) Photosynthesis;

Uses light (energy);

To produce carbohydrates/starch/glucose/sugars/ATP/reduced NADP; 2 max

Note that candidates cannot be expected to have a detailed knowledge of

photosynthesis

(b) (i) A; 1

(ii) C; 1

(c) (i) Slows enzymes/prevents enzymes being denatured/prevents/

stops self-digestion; 1

Ignore references to bacteria. Reject enzymes not working

(ii) To remove organelle C/ nuclei;

Which are larger/heavier/more dense; 2

Total 8

Question 2

(a) (i) C and D; 1

(ii) Left ventricle with thicker wall/more muscle / (muscle in) left ventricle

contracts more forcefully/beats/pumps more strongly; 1

(b) Higher in atria/lower in ventricles;

Atrioventricular valves/valves between atria and ventricles open; 2

(Position of valves must be identified. Do not accept an unqualified reference to valves.

Assume pronouns refer to atria.)

(c) (i) Atrioventricular node/AVN; 1

(ii) Bundle of His/Purkyne tissue/; 1

Accept Purkinje tissue

(d) (i) Allows blood to pass into ventricles/from atria/so that atria can empty;

Before ventricles contract; 2

(ii) Ventricle contracts from base / upwards / all blood ejected; 1

Total 9

APW/Jan08/BYA1

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8 The table shows the percentages of different membranes in two animal cells.

(a) The main function of one of these cells is to make enzymes. Suggest which cell hasthis main function and explain the evidence for your answer.

Cell .....................................................................................................................................

Evidence .............................................................................................................................

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(b) (i) In both cells the figure for the inner membrane of the mitochondria is differentfrom the figure for the outer membrane. Explain this difference.

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(ii) The appearance of the mitochondria in Cell R is different from the appearance ofthe mitochondria in Cell S. Use the figures in the table to suggest how they aredifferent in appearance.

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Type of membrane Percentage of total membrane in

Cell R Cell S

Plasma membrane3 5

surrounding cell

Rough endoplasmic38 60

reticulum

Outer membrane of11 4

mitochondria

Inner membrane of34 17mitochondria

Lysosome membrane 3 3

Other membranes 11 11

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(c) Cell R is a eukaryotic cell. Describe two ways in which the distribution of membranesin cell R is different from the distribution of membranes in a prokaryotic cell.

1. ........................................................................................................................................

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2. ........................................................................................................................................

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Phenylalanine is an amino acid. Scientists investigated the rate of uptake of phenylalanineby a cell. They changed the concentration of phenylalanine outside the cell and measuredthe rate at which it entered the cell. The graph shows the results.

(d) The concentration of phenylalanine outside the cell affects the rate at which it entersthe cell. Describe how.

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(e) Phenylalanine enters the cell by facilitated diffusion. Increasing phenylalanineconcentration from 4 mmol dm–3 to 5 mmol dm–3 does not increase the rate at which itenters the cell. Explain why.

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Question 8 continues on the next pageTurn over !

APW/Jan08/BYA1

00 1 2

Concentration of phenylalanine outside cell / mmol dm–3

Rate of entryinto cell / arbitraryunits

3 4 5

20

40

60

80

100

APW/Jan08/BYA1

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(f) A centrifuge may be used to obtain a sample of chloroplasts from leaves.Starting with some lettuce leaves, describe how.

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END OF QUESTIONS

15

Biology / Biology (Human) - AQA GCE Mark Scheme 2008 January series

7

Question 8

(a) Cell S has more rough endoplasmic reticulum;

Ribosomes are site of protein/enzyme synthesis/

where enzymes are made; 2

(b) (i) Inner membrane folded/forms cristae; 1

(ii) Fewer folds/cristae in cell R; 1

Accept converse; unqualified descriptions refer to cell R.

(c) Only eukaryotic cells have membrane bound organelles;

Nucleus/nuclear envelope;

Endoplasmic reticulum;

Mitochondria;

Lysosomes;

Smaller percentage of membrane is plasma membrane;

Do not have mesosomes; 2

Accept converse; unqualified descriptions relate to cell R. Note that this is an

animal cell. Do not accept general statement about membrane-bound organelles

in addition to rough endoplasmic reticulum/mitochondria and lysosomes.

(d) Rate of uptake increases then levels out;

At approximately 3 (mmol dm-3 ); 2

(e) Limited by carrier molecules/ proteins/ carriers are saturated; 1

(f) 1 Homogenise/chop (or otherwise crudely break) leaves;

2 Suspend in/mix with buffer;

3 Cold and isotonic;

4 Filter and centrifuge filtrate;

5 At low speed;

6 Discard pellet/keep supernatant;

7 Centrifuge again at faster speed

8 Chloroplasts are in pellet (formed by second centrifugation); 6 max

Total 15