A Level Extended Response Questions

Unit 1

Unit 2

Unit 4

Unit 5

Microscopes

Prokaryotic cells

Cell fractionation

Scientists use optical microscopes and transmission electron microscopes (TEMs) to

investigate cell structure. Explain the advantages and the limitations of using a TEM

to investigate cell structure.

Advantages:

1 Small objects can be seen;

2 TEM has high resolution;

3 Wavelength of electrons shorter;

Limitations:

4 Cannot look at living cells;

5 Must be in a vacuum;

6 Must cut section / thin specimen;

7 Preparation may create artefact

8 Does not produce colour image;

The structure of a cholera bacterium is different from the structure of an epithelial cell from the small intestine. Describe how the structure of a cholera bacterium is

Different.

1 Cholera bacterium is prokaryote;

2 Does not have a nucleus/nuclear envelope/ has DNA free in cytoplasm/has loop of DNA;

3 and 4 Any two from

No membrane-bound organelles/no mitochondria / no golgi/

no endoplasmic reticulum/etc;

5 Small ribosomes only;


Capsule/flagellum/plasmid / cell wall/etc;

Measuring the size of an object under a microscope

Measure with an eyepiece graticule

Calibrate with the stage mcirometer (an object of a known size)

Repeat and calculate an average

Explain the advantages and limitations of using a transmission electron microscope to study cells.

1 TEM uses (beam of) electrons;

2 These have short wavelength;

3 Allow high resolution/greater resolution/Allow more detail tobe seen/greater useful magnification;

4 Electrons scattered (by molecules in air);

5 Vacuum established;

6 Cannot examine living cells;

7 Lots of preparation/procedures used in preparing specimens/ fixing/staining/sectioning;

8 May alter appearance/result in artefacts;

Starting with some lettuce leaves, describe how you would obtain a sample of undamaged chloroplasts. Use your knowledge of cell fractionation and ultracentrifugation to answer this question.

1. Chop up (accept any reference to crude breaking up); 2. Cold; (reduces enzyme activity)

3. Buffered solution; (prevents pH affecting enzymes)4. Isotonic / same water potential; (prevents osmosis and possible lysis or shrinkage of organelles)

5. Filter and centrifuge filtrate;6. Centrifuge supernatant;

7. At higher speed;

8. Chloroplasts in (second) pellet;

Prokaryotic cells and fractionation

The bacteria in the intestine are prokaryotic cells. The epithelial cells which line the small intestine are eukaryotic cells. Describe the ways in which prokaryotic cells and eukaryotic cells differ

1 Prokaryotic cells do not have a nucleus / have genetic material in cytoplasm;2 DNA in loop / ring;3 Not associated with proteins / do not have chromosomes / chromatin / do not divide by mitosis;4 Smaller ribosomes;5 No membrane-bound organelles;6 Such as mitochondria / lysosomes / endoplasmic reticulum / Golgi / chloroplasts;7 Prokaryotic cells may have mesosomes;8 Prokaryotic cells smaller;9 May be enclosed by capsule;

How prokaryotic cell is the same and different to a eukaryotic cell

cytoplasm;ribosomes;phospholipid membranes / cell membrane / semipermeablemembrane;2 max

(accept folded membrane for two marks)

(ii)(it = bacterium)cell wall;capsule;flagellum;mesosome;no nucleus / nuclear membrane / DNA free;no mitochondria;

(accept no membrane-bound organelles if neither nucleus normitochondria mark scored)

no microvilli;no Golgi;no ER;70S/smaller ribosomes;

Parts of the prokaryotic cell

cell (surface) membrane,regulates entry/exit/selectively permeable;

Bmesosome,respiration/cell division;

Ccell wall,(mechanical) protection/prevents (osmotic) lysis;

Dslime layer/capsule,protection (against e.g. antibiotics);

Eflagellum,movement of cell;

F DNA molecule/bacterial chromosome,genetic information;

Give two factors which affect the ability of bacteria to cause a disease.

pathogenicity / toxicity of products;site of infection;invasiveness;

Microscopes

Fractionation

Labelled antibodies and an electron microscope can be used to produce images locating proteins on the surface of organelles, but cannot be used to observe cross bridge cycling in muscle cells. Explain why.

1.e.m. gives high resolution;2.due to short wavelength of electrons;3.antibodies attach specifically to target proteins;4.gold particles are electron dense;5.electrons must pass through a vacuum;6.material must be dead / fixed for e.m.;7.cross-bridge cycling requires living cells / metabolism / namedaspect-e.g. ATP synthesis;

Starting with some lettuce leaves, describe how you would obtain a sample of undamaged chloroplasts. Use your knowledge of cell fractionation and ultracentrifugation to answer this question.

1. Chop up (accept any reference to crude breaking up);2. Cold;3. Buffer solution;4. Isotonic / same water potential;5. Filter and centrifuge filtrate;6. Centrifuge supernatant;7. At higher speed;8. Chloroplasts in (second) pellet;

Explain the advantages and the limitations of using a TEM to investigate cell structure.

Advantages:

1Small objects can be seen;

2TEM has high resolution;

Accept better

3Wavelength of electrons shorter;

Advantages: allow maximum of 3 marks.

Limitations:

4Cannot look at living cells;

5Must be in a vacuum;

6Must cut section / thin specimen;

7Preparation may create artefact

8Does not produce colour image;5 max

Limitations: allow maximum of 3 marks.

Describe the ways in which prokaryotic cells and eukaryotic cells differ

1 Prokaryotic cells do not have a nucleus / have genetic material in cytoplasm;2 DNA in loop / ring;3 Not associated with proteins / do not have chromosomes /chromatin / do not divide by mitosis;4 Smaller ribosomes;5No membrane-bound organelles;6 Such as mitochondria / lysosomes / endoplasmic reticulum / Golgi / chloroplasts;7 Prokaryotic cells may have mesosomes;8 Prokaryotic cells smaller;9 May be enclosed by capsule;

Prokaryotic cells and viruses and microscopes

Describe the ways in which prokaryotic cells and eukaryotic cells differ

Prokaryotic cells do not have a nucleus / have genetic materialin cytoplasm;DNA in loop / ring;Not associated with proteins / do not have chromosomes /chromatin / do not divide by mitosis;Smaller ribosomes;No membrane-bound organelles;Such as mitochondria / lysosomes / endoplasmic reticulum /Golgi / chloroplasts;Prokaryotic cells may have mesosomes;Prokaryotic cells smaller;May be enclosed by capsule;

Define resolving power and state why it is bteter for electron microscopes than light

(i)Ability to distinguish points (close together);1

(ii)Electrons have a shorter wavelength;

Explain how viruses cause damage to cells.

uses / breaks up / digests host nuclear / genetic material (allow referencesmade to DNA /RNA instead of nuclear /genetic);virus DNA / genetic material inserted into hosts DNA / chromosome/ genetic material;host cells amino acids are used to synthesize viral proteins;cell lysis;by enzyme (produced by expressing a virus gene);toxin production;

Cell membranes

Describe the fluid-mosaic structure of a cell surface membrane.(5)

Phospholipids and proteins;Phospholipid bilayer;Arrangement of phospholipid molecules Tails to tails;Floating(protein) molecules / molecules can move in membrane;Intrinsic proteins extend through bilayer;Extrinsic proteins in outer layer only;(Ref. to intrinsic and extrinsic, unqualified, gains 1 mark);Detail of channel proteins / protein shapes / glycoproteins;Presence of cholesterol.

Some substances pass through the plasma membrane of a milk-producing cell by diffusion. Describe the structure of a plasma membrane and explain how different substances are able to pass through the membrane by diffusion (6)

1 Phospholipids forming bilayer/two layers;2 Details of arrangement with heads on the outside;3 Two types of protein specified; e.g. passing right through or confined to one layer / extrinsic or intrinsic / channel proteins and carrier proteins / two functional types4 Reference to other molecule e.g. cholesterol or glycoprotein;5 Substances move down concentration gradient/from high to low concentration;Reject references to across or along a gradient6 Water/ions through channel proteins/pores;7 Small/lipid soluble molecules/examples pass between phospholipids/through phospholipid layer;8 Carrier proteins involved with facilitated diffusion;Ignore references to active transport.Credit information in diagrams.

Describe how proteins are arranged in a plasma membrane and the part they play in transporting substances into and out of cells.(6)

1 Some proteins pass right through membrane;

2 Some proteins associated with one layer;

3 Involved in facilitated diffusion;

4 Involved in active transport;

5 Proteins act as carriers;

6 Carrier changes shape / position;

7 Proteins form channels / pores;

8 Protein allows passage of water soluble molecules /charged particles / correct named example;

Explain how three features of a plasma membrane adapt it for its functions.

1. phospholipid bilayer (as a barrier);

2.forms a barrier to water soluble / charged substances / allows non-polar substances to pass

OR

maintains a different environment on each side / compartmentalisation;

3. bilayer is fluid;

4. can bend to take up different shapes for phagocytosis / form vesicles / self repair;

5. channel proteins (through the bilayer)/intrinsic protein;

6. let water soluble/charged substances through / facilitated diffusion;

7. carrier proteins (through the bilayer);

8. allow facilitated diffusion / active transport;

9 surface proteins / extrinsic proteins, glycoproteins / glycolipids;

10 cell recognition / act as antigens / receptors;

11cholesterol;

12 regulates fluidity / increases stability;

Cell membrane

Describe the structure of a cell membrane.

Double layer of phospholipid molecules;Detail of arrangement of phospholipids;Intrinsic proteins/protein molecules passing right through;Some with channels/pores;Extrinsic proteins/proteins only in one layer/on surface;Molecules can move in membrane/dynamic/membrane containscholesterol;Glycocalyx/carbohydrates attached to lipids/proteins;

Describe how the distribution of cell membranes in a prokaryotic cell such as a bacterium differs from that in a cell from a plant leaf.

Absence of nuclear envelope/membrane;Membrane bounded organelles;Such as mitochondria/chloroplast/vacuole/lysosome;and membrane systems/endoplasmic reticulum/Golgi;Mesosomes in prokaryotes;

Describe the part played by cell surface membranes in regulating the movement of substances into and out of cells.

Non-polar/lipid soluble molecules move through phospholipid layer/bilayer;Small molecules/water/gases move through phospholipid layer/bilayer;Ions/water soluble substances move through channels in proteins;Some proteins are gated;Reference to diffusion;Carriers identified as proteins;Carriers associated with facilitated diffusion;Carriers associated with active transport/transport with ATP/pumps;Different cells have different proteins;Correct reference to cytosis;

Describe the role of proteins in the transport of molecules and ions across cell surface membranes.

Allows passage of charged particles / ions;allows passage of water soluble / large molecules;

channel proteins / proteins with pores;specificity related to diameter / charge;

carrier proteins;specificity lined to shape of receptor sites;functions by changing shape / conformation;

facilitated diffusion with concentration gradient;active transport against concentration gradient;active transport requiring energy / ATP;

Cell membranes

Describe how proteins are arranged in a plasma membrane and the part they play in transporting substances into and out of cells.









Describe the structure of a plasma membrane and explain how different substances are able to pass through the membrane by diffusion.

1Phospholipids forming bilayer/two layers;2Details of arrangement with heads on the outside;3Two types of protein specified;e.g.passing right through or confined to one layer /extrinsic or intrinsic /channel proteins and carrier proteins /two functional types4Reference to other molecule e.g. cholesterol or glycoprotein;5Substances move down concentration gradient/from high to low concentration;Reject references to across or along a gradient6Water/ions through channel proteins/pores;7Small/lipid soluble molecules/examples pass between phospholipids/through phospholipid layer;8Carrier proteins involved with facilitated diffusion;

Suggest why this model is known as fluid mosaic.

Molecules within the membrane able to move;mixture of phospholipid and protein / arrangement of protein;

Explain how three features of a plasma membrane adapt it for its functions.

1. phospholipid bilayer (as a barrier);

2. forms a barrier to water soluble / charged substances / allows non-polar substances to pass

OR

maintains a different environment on each side / compartmentalisation;

3. bilayer is fluid;

4. can bend to take up different shapes for phagocytosis / form vesicles / self repair;

5. channel proteins (through the bilayer)/intrinsic protein;

6. let water soluble/charged substances through / facilitated diffusion;

7. carrier proteins (through the bilayer);

8. allow facilitated diffusion / active transport;

9 surface proteins / extrinsic proteins, glycoproteins / glycolipids;

10 cell recognition / act as antigens / receptors;

11 cholesterol;

12 regulates fluidity / increases stability;6 max

principle mark (only for 5, 6, 7, 8)

proteins transport material across the membrane

Cell membranes










Describe the structure of a phospholipid molecule and explain how phospholipids are arranged in a plasma membrane.

1 Phosholipid consists of glycerol;2 (To which are joined) two fatty acids;3 And phosphate;4 By condensation/elimination of water molecules;5 Arranged as bilayer in membrane;6 Head/phosphate hydrophilic/polar and tail/fatty acid hydrophobic/non-polar;7 Heads outside and tails attracted to each other/inside;










Describe the structure of a plasma membrane and explain how different substances are able to pass through the membrane by diffusion.

1Phospholipids forming bilayer/two layers;2Details of arrangement with heads on the outside;3Two types of protein specified;e.g.passing right through or confined to one layer /extrinsic or intrinsic /channel proteins and carrier proteins /two functional types4Reference to other molecule e.g. cholesterol or glycoprotein;5Substances move down concentration gradient/from high to low concentration;Reject references to across or along a gradient6Water/ions through channel proteins/pores;7Small/lipid soluble molecules/examples pass between phospholipids/through phospholipid layer;8Carrier proteins involved with facilitated diffusion;

Cell membranes


Some proteins pass right through membrane;

















Enzymes

Explain how pepsin is inactivated by the high pH in the small intestine.

High pH denatures enzyme/ alters charge on active site;

Breaks bonds;

Alters tertiary structure of enzyme molecule;

Changes shape of active site;

Active site can no longer bind with/ form ES complexes with/ is nolonger complementary to substrate;

Enzymes

In terms of your knowledge of the way in which enzymes work, explain why the rate of reaction would change if: temperature fell and pH changed dramatically

(i)Molecules would have less (kinetic) energy;move slower;fewer collisions / fewer ES complexes form;max 2

(ii)Change in pH alters charge / shape;distorts active site / tertiary structure of enzyme / denatures enzyme;substrate will no longer fit active site;

Amylase is an enzyme, found in saliva, which breaks down starch. It works best at a pHof 8. Explain why amylase does not function in the stomach where the pH isapproximately 3.

Tertiary structure changes / enzyme denatured / bonds broken;Will affect active site (of enzyme);Starch cannot bind / fit / form enzyme-substrate complex;

Explain how inhibitors affect the rate of enzyme-controlled reactions.

1 Statement about two types, competitive and non-competitive;Note. Award points 2 5 only in context of competitive andnon-competitive inhibitionCompetitive2 Similarity of shape of inhibitor and substrate;3 Inhibitor can enter/bind with active site (of enzyme);

Non-competitive4 Affect/bind to enzyme other than at active site;5 Distorts shape of active site;

Inhibitors6 Prevent entry of/binding of substrate to active site;7 Therefore fewer/no enzyme-substrate complexes formed;

Use your knowledge of protein structure to explain why enzymes are specific and may be affected by non-competitive inhibitors.

1 each enzyme/protein has specific primary structure / amino acid sequence;2 folds in a particular way/ has particular tertiary structure;3 active site with unique structure;4 shape of active site complementary to/ will only fit that of substrate;maximum of three marks for inhibition, points 5 85 inhibitor fits at site on the enzyme other than active site;6 determined by shape;7 distorts active site;8 so substrate will no longer fit / form enzyme-substrate complex;

Enzymes

Explain what happens to an enzyme molecule when it is denatured by high temperature.

Correctly named bonds broken / water removed;tertiary / globular shape of enzyme changed;shape of active site affected;

Temperature has a marked effect on blood pH. At 37 C blood plasma has a pH of 7.4 but at a temperature of 25 C, the pH is 6.9. In some surgical procedures the body is cooled by 10 C. Other than the direct effect that lowering the temperature will have, explain how this cooling will affect the reactions taking place in the body.

enzymes involved;formation of the enzyme-substrate complex reliant on the correct pH;pH affects the active site;by disrupting bonds/altering charge;lowering temperature will reduce pH;enzymes have optimum pH;pH change will slow the rates of reactions;

Describe how the condensation reaction can be catalysed by an enzyme.

enzyme has an active site;with a complementary shape to the substrate molecules;enzyme-substrate complex formed;lowering the (activation) energy for the reaction;glycosidic bond formed/bringing together hydroxyl groups/watermolecule removed;products leave the active site;enzyme unchanged;

Lysozyme breaks down bacterial cell walls but does not affect the walls of plant cells. Explain why.

Walls made of different materials / peptidoglycan or murein v. cellulose;specificity of active site / substrate does not fit.

Enzymes

Explain how a substrate is broken down by the enzyme.

Substrate enters active site;Complimentary shapes / Lock and Key;(Binding) to form enzyme-substrate complex;Lowering of activation energy;Conformational / shape change;Breaking of bonds in substrate;Products no longer fit active site and so are released;

Use your knowledge of the tertiary structure of enzymes to explain how a non competitive inhibitor could reduce the rate of an enzyme controlled reaction.

Inhibitor is a different shape to substrate;Binds at position other than active site/allosteric site;Alters shape of active site;Substrate cannot bind/enzyme-substrate complex not formed;

Describe and explain how an increase in temperature affects the rate of an enzyme controlled reaction.

TemperatureRate of reaction increases;Increasing temperature increases rate of movement of molecules/kinetic energy;Collide more often/substrate enters active site more often/moreenzyme-substrate complexes formed;Up to optimum;Rate of reaction decreases;High temperatures cause denaturation/loss of tertiary structure/3D structure;By breaking specified bonds (not peptide bond);Active site altered/substrate cannot bind/fit/

Many reactions take place in living cells at temperatures far lower than those required for the same reactions in a laboratory. Explain how enzymes enable this to happen.

lowers activation energy;relevant mechanism e. g. brings molecules close together / reaction in smallersteps / change in charge distribution / proton donation or acceptance / inducedfit ensuring substrates brought in correct sequence;including relevant reference to active site;

Enzymes

Explain how the shape of an enzyme molecule is related to its function.

specific 3D tertiary structure/shape;substrate complementary shape; (reject same shape)substrate (can bind) to active site/ can fit into each active site;

decreasing the pH affects carbohydrase activity.

(decrease in pH) increases H+ ions/protons;5 attach/attracted to amino acids;6 hydrogen/ionic bonds disrupted/broken;7 denatures enzyme / changes tertiary structure;8 changes shape/charge of active site;9 active site/enzyme unable to combine/fit with starch/enzyme-substratecomplex no longer able to form decreases rate of breakdown of starch/rate of reaction/carbohydrase activity;

Enzymes

Describe how molecular shape is important in explaining the way in which enzymes may be affected by inhibitors.

Active site (of enzyme) has particular shape;(Into which) substrate molecule fits / binds;Appropriate reference linking induced fit and shape;(Competitive inhibitor) has similar shape to substrate;Also fits active sites;Prevents substrate access;(Non-competitive inhibitor) fits at site other than active site;Distorting shape of active site / enzyme;Prevents substrate access; (award once only)Two types identified as competitive and non-competitive;





Enzymes

Describe how molecular shape is important in explaining the way in which enzymes may be affected by inhibitors.(6)

1 Active site (of enzyme) has particular shape;2 (Into which) substrate molecule fits / binds;3 Appropriate reference linking induced fit and shape;4 (Competitive inhibitor) has similar shape to substrate;5 Also fits active sites;6 Prevents substrate access;7 (Non-competitive inhibitor) fits at site other than active site;8 Distorting shape of active site / enzyme;6 Prevents substrate access; (award once only)9 Two types identified as competitive and non-competitive;

decreasing the pH affects carbohydrase activity.

(decrease in pH) increases H+ ions/protons;5 attach/attracted to amino acids;6 hydrogen/ionic bonds disrupted/broken;7 denatures enzyme / changes tertiary structure;8 changes shape/charge of active site;9 active site/enzyme unable to combine/fit withstarch/enzyme-substrate complex no longer able to form; decreases rate of breakdown of starch/rate of reaction/carbohydrase activity;

Explain how raising the temperature affects carbohydrase activity;

1 increase in temperature increases kinetic energy;2 increases collisions (between enzyme/active site and substrate) / increases formation of enzyme/substrate complexes;3 increases rate of breakdown of starch /rate ofreaction/carbohydrase activity;



Enzymes

Describe how the condensation reaction can be catalysed by an enzyme.

enzyme has an active site;with a complementary shape to the substrate molecules;enzyme-substrate complex formed;lowering the (activation) energy for the reaction;glycosidic bond formed/bringing together hydroxyl groups/watermolecule removed;products leave the active site;enzyme unchanged;

Explain how substrates are broken down by the enzyme.

Substrate enters active site;Complimentary shapes / Lock and Key;(Binding) to form enzyme-substrate complex;Lowering of activation energy;Conformational / shape change;Breaking of bonds in substrate;Products no longer fit active site and so are released;

Explain how amylase makes it possible for starch to be digested at body temperature.

Activation energy reduced;starch attached to active site / formation of enzyme-substrate complex;less energy required to bring (substrate) molecules together/ to break bonds;reaction occurs in small(er) steps;change in shape of enzyme molecule (induced fit) brings moleculestogether / allows bonds to break / causes overlapping of electronorbits of substrates.

Describe and explain how an increase in temperature affects the rate of an enzyme controlled reaction.

TemperatureRate of reaction increases;Increasing temperature increases rate of movement of molecules/kinetic energy;Collide more often/substrate enters active site more often/moreenzyme-substrate complexes formed;Up to optimum;Rate of reaction decreases;High temperatures cause denaturation/loss of tertiary structure/3D structure;By breaking specified bonds (not peptide bond);Active site altered/substrate cannot bind/fit/

Enzymes



Expalin how decreasing the pH affects carbohydrase activity.

(decrease in pH) increases H+ ions/protons;5 attach/attracted to amino acids;6 hydrogen/ionic bonds disrupted/broken;7 denatures enzyme / changes tertiary structure;8 changes shape/charge of active site;9 active site/enzyme unable to combine/fit withstarch/enzyme-substratecomplex no longer able to form;decreases rate of breakdown of starch/rate of reaction/carbohydrase activity;



Biological molecules

Describe a chemical test you could carry out to show that a piece of coconut contains lipids.(3)

(Crush in) ethanol / alcohol;Add (to) water (Order of adding is critical for this point);Emulsion / white colour

Describe how you would use a biochemical test to show that a sample contained reducing sugar.(2)

Benedicts and heat;Green / yellow / orange / red / brownDo not credit unqualified references to water baths

Describe how the sequence of amino acids in part of a protein from a persons Tears could enable this protein to act as an enzyme inhibitor.(6)

1 Sequence of amino acids gives shape;2 This is tertiary structure;3 Has similar shape to substrate;4 Fits / competes for active site;5 Fits at site other than active site;6 Distorting active site;7 Therefore substrate will not fit (active site);

Describe how you would use a biochemical test to show that a solution contained protein.

Biuret / alkali + copper sulphate;Lilac/purple/mauve/violet;

Explain what is meant by a polymer.

(Molecule) made up of many identical/similar molecules/monomers/subunits;

Explain how proteins are suited for their roles as receptor molecules.

Many different sorts of proteins;Different primary structures/sequences of amino acids;Tertiary structure;Shape; allowing formation of receptor/binding site/site into whichsubstance/substrate fits;

Lipid/protein carbs

With reference to named parts of the diagram, explain the difference between the terms:

triglyceride and phospholipid;

Phospholipid has (one) phosphate / Phosphoric acid;2replacing fatty acid;

saturated and unsaturated.

Saturated all valencies of C filled / saturated with hydrogen / all (CC)single bonds / no double bonds;fatty acid 1 is saturated/fatty acids 2 and 3 are unsaturated;

Describe how a saturated fatty acid differs in molecular structure from an unsaturated fatty acid.

absence of a double bond;in the (hydrocarbon) chain;unable to accept more hydrogen / saturated with hydrogen;

Explain how the structure of fibrous proteins is related to their functions.

Long chains of aa;Folding of chain into a coil / folds / helix / pleated sheet;

Association of several polypeptide chains together;Formation of fibres / sheets explained;2

H bonds / Disulphide bonding (In context);Fibres provide strength (and flexibility);Sheets provide flexibility;Example e.g. keratin in hair, collagen in bone; (MUST be in context)Insoluble because external R-groups are non-polar;

Explain how a change in the primary structure of a globular protein may result in a different three-dimensional structure.

sequence of amino acids changes;tertiary structure changes/folds in a different way;bonds form in different places;

Explain how proteins are suited for their roles as receptor molecules.

Many different sorts of proteins;Different primary structures/sequences of amino acids;Tertiary structure;Shape; allowing formation of receptor/binding site/site into whichsubstance/substrate fits;

Biological molecules

Describe the structure of an amino acid molecule and explain how amino acids link together.

1 Amino acid based on carbon with four groups attached;

2 Amino/ NH2 and carboxyl / COOH;

3 R-group/ side chain + hydrogen;

4 R-group differs from one amino acid to another;

5 Amino acids joined by condensation;

6 Bond formed between NH2 and COOH;

7 Involves removal of molecule of water;

8 H from NH2 and OH from COOH;

Explain how amino acid molecules may be linked to form a polypeptide chain which is folded into a specific tertiary shape.

Condensation;removal of water molecule;from amino and carboxyl groups;forming peptide bonds;same amino acids in same sequence;bonds form between R-groups/side chains;e.g. sulphur-containing amino acids / ionic bonds / hydrogen bonds;bonds form in same place;

Polypeptides such as spectrin are formed from amino acids. Describe the structure of an amino acid molecule and explain how amino acids link together.

1 Amino acid based on carbon with four groups attached;

2 Amino/ NH2 and carboxyl / COOH;

3 R-group/ side chain + hydrogen;

4 R-group differs from one amino acid to another;

5 Amino acids joined by condensation;

6 Bond formed between NH2 and COOH;

7 Involves removal of molecule of water;

8 H from NH2 and OH from COOH;



Biochemical tests

Describe how you could use Benedicts reagent to test a urine sample for the presence of glucose.

Add (Benedicts) reagent (to urine sample) and heat / heat the mixture;red/ brown/ orange/ green/ yellow;

describe a further biochemical test to find out if substance D is a non-reducing sugar.

heat with acid, then neutralise / hydrolyse using enzyme;(heat) with Benedicts (solution);

Describe how you would use a biochemical test to show that a solution contained protei

Biuret / alkali + copper sulphate;Lilac/purple/mauve/violet;

Describe a chemical test you could carry out to show that a piece of coconut contains lipids.

(Crush in) ethanol / alcohol;Add (to) water (Order of adding is critical for this point);Emulsion / white colour;

Describe how standard solutions could be used to estimate the concentration of reducing sugar in the samples.

Sugar solutions of known / specific concentrations;Test each concentration with Benedicts solution;use equal volumes of solutions / variables controlled;Method of comparison, e.g. compare colours, mass of precipitate.

Cholera

Explain how the effects of diarrhoea on the body can be treated.

oral rehydration therapy/ORT;replaces lost water and salts;ORdrinking large amounts of water;with salts/minerals;

Suggest why the cholera exotoxin is specific to the epithelial cells of the small intestine.

receptor / proteins on membrane;complementary shape of exotoxin;

Describe the difference between an endotoxin and an exotoxin.

endotoxins produced from the breakdown of bacteria (cell walls);(allow burst / lyse do not allow decompose)exotoxins secreted / released (from living cells) (not produced);endotoxins are lipopolysaccharides;exotoxins are protein;

Explain how an oral rehydration solution (ORS) replaces water lost by diarrhoea

Increases uptake of sodium ions/glucose/sugars / salts;

By co-transport channels/proteins;

Lowers water potential in cells/tissue;

Water moves out of intestine/into cells;

By osmosis;

Cholera

The structure of a cholera bacterium is different from the structure of an epithelial cell from the small intestine. Describe how the structure of a cholera bacterium is different.

Cholera bacterium is prokaryote;

Does not have a nucleus/nuclear envelope/ has DNA free incytoplasm/has loop of DNA;


No membrane-bound organelles/no mitochondria / no golgi/noendoplasmic reticulum/etc;

Maximum of 2 marks for points 3 and 4.

5Small ribosomes only;



Oral rehydration solutions (ORS) are used to treat diarrhoeal disease. What does an ORS consist of and how does it work?(5)

1. Contains glucose/starch/ carbohydrate / sugar;

2. Sodium/salt;

3. Co-transport / symport;

4. Sodium and glucose taken up (from lumen);

5. Lowers water potential in cells/ increases water potential gradient;

6. Water taken up by osmosis

Give two ways in which pathogens can cause disease when they enter the body of their host.

Damage/destruction of cells/tissues;Production of toxins;

Digestion

Describe the role of the enzymes of the digestive system in the complete breakdown of starch.

Amylase;

(Starch) to maltose:

Maltase;

Maltose to glucose;

Hydrolysis;

(Of) glycosidic bond;

Describe the processes involved in the absorption of the products of starch digestion.

Glucose moves in with sodium (into epithelial cell);

Via (carrier/channel) protein/symport;

Sodium removed (from epithelial cell) by active

transport/sodium-potassium pump;

Into blood;

Maintaining low concentration of sodium (in epithelial cell) /

maintaining sodium concentration gradient (between lumen

and epithelial cell);

Glucose moves into blood;

By (facilitated) diffusion;

Describe and explain the roles of diffusion, facilitated diffusion and active transport in the absorption of digested food by the ileum.

Diffusion

movement along / down concentration gradient;monoglycerides / micelles/fatty acids move into epithelial cells;monoglycerides move from epithelium into blood;chylomicrons move into lacteals / lymph;

facilitated diffusion

movement along / down concentration gradient;reference to carrier / channel proteins;monosaccharides or named / amino acids move into epithelial cells;

active transport

movement against concentration gradient;energy / ATP required;reference to carrier proteins;monosaccharides or named / amino acids moved into epithelial cells;reference to co-diffusion e.g. glucose and NaCl;monosaccharides or named / amino acids move into blood;

Describe how sugars are absorbed from the small intestine into the blood of a mammal.

Principles:diffusion into capillaries;active transport/facilitated diffusion involved;ATP used by active transport;Detail:disaccharidases/enzymes in cell surface membrane;glucose /monomers/monosaccharides actively transported into epithelial cells;via protein carriers/channels (in membranes);facilitated diffusion from epithelial cell / towards blood;

Digestion

Explain how the small intestine is adapted to its function in the absorption of the products of digestion.

Large surface area provided by villi / microvilli;long / folds increase surface area / time for absorption;thin epithelium;short diffusion pathway;capillary network absorbs amino acids / sugars;lacteal for absorption of digested fats;

Maintains a steep concentration gradientmitochondria supply ATP / energy for active transport;carrier proteins (in membranes);

Describe how carbohydrate eaten as starch is digested to produce glucose.

Starch digested to maltose by amylase;Found in saliva; Secreted by pancreas;Maltase converts maltose to glucose;Found in membranes of cells lining small intestine;Both reactions involve hydrolysis;

Describe how maltose in the small intestine is digested, absorbed and transported to the liver as glucose.

Hydrolysed by maltase;Maltase enzymes in membranes of epithelial cells of small intestine;

Glucose absorption involves diffusion;Associated with uptake of sodium ions;Involves active transport/energy dependent;Requires carrier molecules;Role of villi/microvilli in increasing surface area;

Transported in solution/in plasma;To liver via hepatic portal vein;

Describe how glucose is absorbed from the small intestine.

Glucose absorption involves diffusion;Associated with uptake of sodium ions;Requires carrier molecules; sodium glucose co-transport carrier and the sodium potassium pump

Involves active transport/energy dependent;

Where sodium is pumped out of the cell

Glucose leaves the cell by facilitated diffusion

Role of villi and microvilli in increasing surface area;Transport into capillaries/hepatic portal vein;

Digestion

Describe and explain the roles of diffusion, facilitated diffusion and active transport in the absorption of digested food by the ileum.

(allow general points provided correct molecule/particle involved)

diffusion

movement along / down concentration gradient;monoglycerides / micelles/fatty acids move into epithelial cells;monoglycerides move from epithelium into blood;chylomicrons move into lacteals / lymph;

facilitated diffusion

movement along / down concentration gradient;reference to carrier / channel proteins;monosaccharides or named / amino acids move into epithelial cells;

active transport

movement against concentration gradient;energy / ATP required;reference to carrier proteins;monosaccharides or named / amino acids moved into epithelial cells;reference to co-diffusion e.g. glucose and NaCl;monosaccharides or named / amino acids move into blood;

Describe the role of the enzymes of the digestive system in the complete breakdown of starch.

Amylase;

(Starch) to maltose:

Maltase;

Maltose to glucose;

Hydrolysis;

(Of) glycosidic bond;

Describe and explain how the small intestine is adapted to increase the rate of absorption

many / projecting villi (X) (no double penalty for microvilli);large surface area (for absorption);large/good blood supply / many capillaries/blood vessels;maintains concentration gradients / efficient removal of digested products;thin outer layer / blood vessels near to surface;short diffusion pathway;

Describe the processes involved in the absorption of the products of starch digestion.

Glucose moves in with sodium (into epithelial cell);

Via (carrier/channel) protein/symport;

Sodium removed (from epithelial cell) by active transport/sodium-potassium pump;

Into blood;

Maintaining low concentration of sodium (in epithelial cell) /maintaining sodium concentration gradient (between lumenand epithelial cell);

Glucose moves into blood/out of the epithelial cell;

By (facilitated) diffusion;

Digestion

How small intestine epithelia are adapted for absorption

1. Microvilli;

2. Large/increased surface area;

3. Many mitochondria;

4. (Mitochondria/respiration) produce ATP / release or provide energy (for active transport);

5. Carrier proteins for active transport;

6. Channel / carrier proteins for facilitated diffusion;

7. Co-transport of sodium (ions) and glucose or symport / carrier protein for sodium (ions) and glucose;

8. Membrane-bound enzymes digest disaccharides / produce glucose

Lifestyle and Disease

Describe how atheroma may form and lead to a myocardial infarction.(6)

1 fatty substance / foam cells / cholesterol in artery wall / under endothelium;2 formation of plaques / atherosclerosis / atheroma narrows lumen of artery;

3 atheroma creates turbulence / damage to lining of artery;4 (turbulence) increases risk of blood clot / embolus;5 blood clot / thrombus breaks off;6 (blood clot) lodges in coronary artery;7 reduced blood supply to heart muscle;8 reduced oxygen supply;9 leads to death of heart muscle;

Cigarette smoking and a diet high in saturated fat increase the risk of myocardial infarction. Explain how.(6)

Carbon monoxide combines with haemoglobin/causes lessoxygen to be transported;Decreases concentration of antioxidants in blood;Increases the damage done to artery walls;Blood clot may occur;*Blood pressure increased*Blocks flow of blood to heart/in carotid arteries;*(4 max)

Saturated fat associated with cholesterol;Cholesterol deposited in arteries;Atheroma formation;Blood clot may occur*;Blood pressure increased*Blocks flow of blood to heart/in carotid arteries*;(4 max)

*Allow reference to these points only once.

Cholesterol / blood clot causes constriction of coronary arteries;Less oxygen transported to heart muscle tissue;

Describe how an atheroma is formed and how it can lead to a myocardial infarction.(6)

1.fatty material/foam cells/cholesterol in artery wall/under endothelium;2.creates turbulence/damage to lining of artery;3.formation of plaques/atherosclerosis/narrows lumen of artery;4.(turbulence) increases risk of blood clot;5.blood clot breaks off;6.(blood clot) lodges in coronary artery;7.reduces blood supply to heart muscle;8.reduces oxygen supply;9.results in death of heart muscle;

Pulmonary tuberculosis is a disease of the lungs. Describe the transmission and course of infection of pulmonary tuberculosis.

1 (Bacteria transmitted in) droplets / aerosol;

2 (Bacteria) engulfed / ingested by phagocytes / macrophages;

3 (Bacteria) encased in named structure e.g. wall /

tubercle / granuloma / nodule;

4 (Bacteria) are dormant / not active / not replicating;

5 If immunosuppressed, bacteria activate / replicate / released;

6 Bacteria destroy alveoli / capillary / epithelial cells;

7 (Leads to) fibrosis / scar tissue / cavities /calcification;

8 (Damage) leads to less diffusion /less surface area / increases diffusion distance;

9 (Activation / damage allows bacteria) to enter blood / spreads (to other organs);


Emphysema is another disease of the lungs. People with emphysema may feel weak and tired. Explain why.

1 Alveoli break down / collapse / rupture / walls thicken;

2 Less surface area / increases diffusion distance / less diffusion;

3 Loss of elastin / elastic tissue / elastase involved;

4 (Alveoli / lungs) cannot recoil / spring back / have reduced elasticity / more difficult to expel air;

5 Reduced diffusion gradient / air not replenished / less air leaves lungs;

6 Less oxygen enters blood / tissues;

7 Less respiration / less energy released / less ATP produced;

What is atheroma and how may it cause myocardial infarction?

1. Cholesterol / plaque / lipoprotein / LDL / fatty

material / cells;

2. In artery wall / under lining / endothelium of artery /

blood vessel;

3. Atheroma linked to blood clot / thrombosis;

4. (Blocks) coronary artery / artery supplying heart

muscle / tissue / cells;

5. Reduces oxygen / glucose supply (to heart muscle /

tissues / cells);

6. (Heart muscle / tissue / cells) unable to respire /

dies;

The structure of a cholera bacterium is different from the structure of an epithelial cell from the small intestine. Describe how the structure of a cholera bacterium is

different.

1 Cholera bacterium is prokaryote;

2 Does not have a nucleus/nuclear envelope/ has DNA free in cytoplasm/has loop of DNA;


No membrane-bound organelles/no mitochondria / no golgi/

no endoplasmic reticulum/etc;

5 Small ribosomes only;



Cholera

Water borne infection Rod shaped organism

Ingested and enters the small intestine

Using flagella in cork screw motion through the mucus layer

Attaches to the cells

Releases toxin (only attaches in the upper region of the small intestine as here there are receptors that complement the shape of the toxin molecule)

Toxin causes chlorine channels in the membrane to open

Chlorine exits the cell into the intestinal lumen (also Na, K, bicarbonate)

Intestinal lumen has more negative water potential than the cell

Water leaves the cell by osmosis

Treated with ORT


Describe how altered DNA may lead to cancer.

1 (DNA altered by) mutation;2 (mutation) changes base sequence;3 of gene controlling cell growth / oncogene / that monitors cell division;4 of tumour suppressor gene;5 change protein structure / non-functional protein / protein not formed;6 (tumour suppressor genes) produce proteins that inhibit cell division;7 mitosis;8 uncontrolled / rapid / abnormal (cell division);9 malignant tumour;

Explain what is meant by malignant. (2)

(Cancer = ) mass of cells that divide continuously / uncontrolled / faster;(Malignant = ) can spread (to other body parts);

explain what is meant by a malignant tumour and describe how exposure to cigarette smoke may result in the formation of a malignant tumour. (6)

(Relative risk of) lung cancer decreases the longer it is sincegiving up smoking;

(Relative risk of) lung cancer increases with the number ofcigarettes smoked per day;2

Mass of abnormal cells;

Idea of spread/ metastasis;

Altered DNA/ biochemical differences;

Rapid rate of cell division/ uncontrolled cell division;

Cigarette smoke contains carcinogens/ mutagens/cancer-causing chemicals;

causes changes in DNA;

Of genes that control cell division;

Reference to oncogenes;

reference to tumour suppresser genes;

Explain the relationship between the risk of developing coronary heart disease and cholesterol and gender

(i)because formation of atheroma/deposition of fatty material inartery walls;which weakens the wall leading to aneurysm;or leads to narrowing increasing the chanceof a clot obstructing the artery;max 2

(ii)presence of oestrogen protects women against CHD;

Lifestyle and disease

Explain how emphysema reduces the efficiency of gas exchange in the lungs. And suggest two factors that could increase risk other than smoking

walls of alveoli broken down / fewer alveoli present;smaller surface for diffusion;

ORreduced elasticity;ventilation restricted;

ORscar tissue formed;less area for gas exchange / slower gas exchange;

infection eg (chronic) bronchitis;heredity;industrial pollution - must contain reference toinhalation of particles (dust);

Explain why atheroma may result in cardiovascular disease.

weaken blood vessels may burst / aneurysm;vessels narrow;blood pressure may rise;blood clot may occur which restricts or cuts off blood flow;in coronary artery this leads to myocardial infarction / heartattack / angina;in artery to brain this leads to stroke;

Explain why these factors increase the risk of developing cardiovascular disease.salt, smoking

Fatblood cholesterol level increases;LDLs transport cholesterol in the blood;LDLs deposit;cholesterol in arteries / atheroma formed;blood pressure increased;(*)

SaltIncreased salt concentration in blood;decreases water potential of the blood;water moves into the blood;blood pressure increased;(*)

Smokingdecreases conc. of antioxidants in blood;phagocytes release more free radicals;this increases the damage done to artery walls;raises the number of platelets in the blood;makes them more sticky;more blood clots are likely to form;increase cholesterol / fat concentration in blood;causes constriction of coronary arteries;carbon monoxide combines with haemoglobin so less available totransport oxygen;blood pressure increased;

Explain how, high blood pressure, smoking and cholesterol increase chances of CHD

(high blood cholesterol may lead to) fatty deposition in artery walls;detail e.g. in epithelial / fibrous layer;atheroma formed;blood pressure increased;lumen of coronary vessels narrowed;reduced blood supply to heart muscle;angina;

weakness of arterial wall increases chance of aneurysm;increased risk of blood clot blocking vessels;increased risk of heart attack; affected heart muscle dies;high blood pressure puts increased strain on heart;and greater risk of aneurysm rupturing;atheroma increases risk of blood clots forming;smoking increases risk of aneurysm;less antioxidants / more free radicals;smoking increases number/activation of plateletsleading to increased chance of clots;

Lifestyle and disease

Explain how these effects of nicotine increase the risk of cardiovascular disease.

noradrenaline produced by SNS;stimulates SAN;increase in heart rate/cardiac output;blood pressure increases;increased risk of cerebrovascular accident/stroke;increased risk of blood clot/thrombosis;

The diet of a person can increase the risk of coronary heart disease. Explain how.

1. Too much saturated fat/ cholesterol in diet;

2. Increase in LDL/ cholesterol in blood;

3. Atheroma/ fatty deposits/ plaques in artery walls;

4. Reduces diameter of / blocks coronary arteries;

5. Less oxygen/ glucose to heart muscle /tissue/ cells;

6. Increase in blood pressure;

7. (Increased risk of )clot / thrombosis / embolism/ aneurysm;

Heart

Describe the parts played by the sinoatrial node (SAN) and the atrioventricular node (AVN) in controlling the heart beat.

1SAN initiates / sends heart beat;2Myogenic / beats spontaneously / does not require nerve impulse;3Rate of beating influenced by nerves:4Wave of electrical activity / impulses / excitation passes overatrium;5Triggers contraction of atrium;6Electrical activity can only pass to ventricles / along bundle of His by way of AVN7Fibrous tissue prevents passage elsewhere;8 Delay at AVN;9 Allows blood to empty into ventricles / atria to empty;

Describe how the regular contraction of the atria and ventricles is initiated and coordinated by the heart itself.

(cardiac) muscle is myogenic;sinoatrial node/SAN;wave of depolarisation/impulses/electrical activity (across atria);initiates contraction of atriaatrioventricular node/AVN;bundle of His/purkyne tissue spreads impulse across ventricles;ventricles contract after atria/time delay enables ventricles to fill;

The heart rate of a sleeping person is low. Explain how nerves supplying the heart may produce a low heart rate in a sleeping person.

Impulses;Along parasympathetic/vagus;OR Fewer impulses;Along sympathetic/(cardiac)accelerator;Slows activity from SAN/pacemaker;3[Reject: decelerator nerve]

Describe the role of the nervous system in modifying the heart rate in response to an increase in blood pressure.

pressure receptors;in aorta/carotid artery/sinus;send impulses (award once only);to medulla;send impulses (award once only);along parasympathetic / vagus pathway;slows heart rate;

Heart

Explain how a rise in blood pressure results in a decrease in the rate of heartbeat.

1 pressure receptors / baroreceptors / stretch receptors;2 in aorta / carotid arteries / carotid sinus; (reject carotid body)3 send impulses; (reject signals / messages / electronic)4 to cardiovascular centre / medulla / cardio-inhibitory centre;5 send impulses;(once only)6 parasympathetic nerves / vagus; (accept inhibitory nerve)7 to SAN;8 release of ACh / inhibits SAN / decreases impulses from SAN;9 decreases impulses to AVN / decreased stimulation of AVN /

decreases impulses from AVN;

Increased intensity of exercise leads to an increased heart rate. Explain how.

1. (Oxygen/carbon dioxide) detected by chemoreceptors / (pressure) detected by baroreceptors;

2. Medulla/cardiac centre involved;

3. More impulses to SAN/along sympathetic nerve;

The heart controls and coordinates the regular contraction of the atria and ventricles. Describe how.

1. SAN AVN bundle of His /Purkyne fibres;

2. Impulses / electrical activity (over atria);

3. Atria contract;

4. Non-conducting tissue (between atria and ventricles);

5. Delay (at AVN) ensures atria empty/ ventricles fill before ventricles contract;

6. Ventricles contract from apex upwards;

1 mark for correct sequence

Diseases

Explain the effect of smoking on blood pressure; (2)

Because arteries cannot dilate / dilate less;Heart must work harder to force blood through;Increases blood pressure;

explain how smoking might lead to the formation of a blood clot. (3)

Higher blood pressure causes damage to blood vessel lining / endothelium/ collagen;Platelets stick together / form a plug / adhere to collagen fibres;Release of thromboplastin / thrombokinase;Fibrinogen converted to insoluble fibrin;Platelet plug trapped by fibrin mesh;

Explain how each of smoking, high blood pressure and cholesterol increases the risk of heart disease (6)

Plasma cholesterol:More laid down in lining of arteries;Walls of arteries damaged / weaken;Arteries are narrowed;Aneurysm forms;Clot forms;

High blood pressure:Increases rate at which cholesterol is laid down;Higher fibrinogen levels;Clots form (once only);

Smoking:Increases blood pressure:Muscle in artery becomes thicker / lumen narrower;

Explain why a blood clot in a coronary artery is likely to result in a heart attack. (3)

Region is deprived of (blood and therefore) oxygen;Cannot respire aerobically / must respire anaerobically;Lactate is formed;Muscle cannot contract / eq. ;Cell death / tissue death;

Explain how smoking and a high blood cholesterol concentration increase the risk of developing coronary heart disease. (6)

CHD = heart muscle receives inadequate amount of bloodor oxygen / (coronary) blood supply reduced;

Smoking:

Raises concentration of fibrinogen (in blood) / increased risk ofclotting;Increases viscosity of blood;(Nicotine) causes platelets to stick together / causes vasoconstriction;Carbon monoxide associated with plaque formation;Reduces ability of arteries to dilate / reduces elasticity;

Cholesterol:

Fatty streaks / deposits adhere to wall of arteries;

Atheroma / atherosclerosis / plaque;

Narrows lumen of artery;

Damages endothelium;

Can lead to formation of thrombus / blood clot;

Clots need to be in context

Disease

What is atheroma? (2)

Plaque/ fatty material/ cholesterol/ foam cells/ lipoprotein build up;

In artery/ blood vessel wall;

Describe how atheroma can lead to an aneurysm. (2)

Weakens artery wall;

So that it swells/ bursts;

Describe and explain how atheroma can lead to myocardial infarction.3

Atheroma/fatty material deposited in wall of artery;Causes turbulence/damage to endothelium/raises blood pressure;Blood clot formation;Atheroma/blood clot lodges in narrowed blood vessel/coronary artery;Reduces oxygen (supply) to (region of) heart muscle/heart cells;

Describe how atheroma may form and lead to a myocardial infarction.(6)

1 fatty substance / foam cells / cholesterol in artery wall / under endothelium;2 atheroma creates turbulence / damage to lining of artery;3 formation of plaques / atherosclerosis / narrows lumen of artery;4 (turbulence) increases risk of blood clot / embolus;5 blood clot / thrombus breaks off;6 (blood clot) lodges in coronary artery;7 reduced blood supply to heart muscle;8 reduced oxygen supply;9 leads to death of heart muscle;

Describe how an atheroma is formed and how it can lead to a myocardial infarction. (6)

1.fatty material/foam cells/cholesterol in artery wall/under endothelium;2.creates turbulence/damage to lining of artery;3.formation of plaques/atherosclerosis/narrows lumen of artery;4.(turbulence) increases risk of blood clot;5.blood clot breaks off;6.(blood clot) lodges in coronary artery;7.reduces blood supply to heart muscle;8.reduces oxygen supply;9.results in death of heart muscle;

Diseases

Describe how atheroma is caused and how it may result in a myocardial infarction. (6)

1. High fat diet/high salt diet/lack of exercise/age/gender;

TWO risk factors for one markNot hypertension as this is given later

2. Atheroma forms under endothelium/in artery wall;

3. Atheroma may narrow lumen of artery;

4. Atheroma increases blood pressure;

5. Atheroma promotes clotting;

6. Details of effect of atheroma on clotting;

7. Blood clot lodges in coronary artery;

8. Reduced blood supply to heart muscle;

9. Reduced oxygen/glucose supply leading to cell death;

Cigarette smoking and a diet high in saturated fat increase the risk of myocardial infarction. Explain how.(6)

Carbon monoxide combines with haemoglobin/causes lessoxygen to be transported;Decreases concentration of antioxidants in blood;Increases the damage done to artery walls;Blood clot may occur;*Blood pressure increased*Blocks flow of blood to heart/in carotid arteries;*(4 max)

Saturated fat associated with cholesterol;Cholesterol deposited in arteries;Atheroma formation;Blood clot may occur*;Blood pressure increased*Blocks flow of blood to heart/in carotid arteries*;(4 max)

*Allow reference to these points only once.

Cholesterol / blood clot causes constriction of coronary arteries;Less oxygen transported to heart muscle tissue;

What is atheroma? (2)

Cholesterol/ lipoprotein/ fatty material/cells;

Reject fatty acid

In the artery wall/under lining/endothelium of artery/blood vessel;

Explain the link between atheroma and the increased risk of aneurism. (4)

Fatty material within walls of arteries;Vessels narrow;Blood pressure rises;Weakened blood vessels may burst;

Atheroma makes it more likely that a blood clot will form. Describe how a blood clot may lead to a myocardial infarction. (3)

(Trapped in) coronary artery/artery supplying heart muscle/ tissue/cells;

i.e. material of heart wall

Prevents oxygen;

Reaching (heart muscle/tissue);

(Heart muscle) dies/stops respiring;

Breathing

Describe how muscles in the thorax (chest) cause air to enter the lungs during breathing.

Diaphragm/intercostal muscles contract;Increases volume of thorax/chest/lungs;Negative/lower pressure in lungs;

In normal breathing, describe the part played by the intercostal muscles

Contract;ribs move upwards/out;increasing volume/decreasing pressure in chest/thorax/lungs;

Describe how the structure of the lungs and the red blood cells enable efficient diffusion and transport of oxygen.

1 Large surface area produced by many alveoli;2 Single layer of epithelial cells / very thin epithelium / squamous / pavement;3 Capillary walls one cell thick;4 Giving short diffusion pathway;5 RBC thin / flattened / disc-shaped so large surface area;6 No nucleus / mitochondria;7 Haemoglobin for transport of oxygen;8 Red cell close to capillary wall;

Describe the difference in the composition of gases in inhaled and exhaled air. Explain how these differences are caused.

1 inhaled air contains more oxygen than exhaled air;2 inhaled air contains less carbon dioxide than exhaled air;3 inhaled air contains less water (vapour);4 relative amount/percentage of nitrogen also changes;5 respiration results in lower blood oxygen / higher blood carbon dioxide;6 oxygen enters blood / carbon dioxide leaves blood in alveoli;7 by diffusion;8 water vapour diffuses from moist surface;

Breathing

Describe how the medulla in the brain and the stretch receptors in the lungs maintain the breathing rate when the body is at rest.

Respiratory centre in medulla;Impulses from inspiratory centre / medulla / respiratory centre;Causes contraction of muscles;Lungs inflate, stretch receptors stimulated;Send impulses to expiratory / inspiratory centre;Fewer impulses to respiratory muscles / inspiration inhibited /expiration occurs;

Describe how the rate of breathing is increased during exercise.

Chemoreceptors;In medulla / carotid body / aortic bodies;Detect increase in carbon dioxide;Impulses to medulla / respiratory centre / inspiratory centre;Impulses transmitted to respiratory muscles;

Immunity

Phagocytes and lysosomes are involved in destroying microorganisms. Describe how.

Phagocytes engulf pathogens/microorganisms;

Enclosed in a vacuole / vesicle/ phagosome;

Lysosomes have enzymes;

That digest/hydrolyse molecules/proteins/lipids/microorganism;

An antigen in a vaccine leads to the production of antibodies. Describe the part played by B lymphocytes in this process.(5)

1 macrophages present antigens to B lymphocytes;2 antigen binds to/is complementary to receptors on lymphocyte;3 binds to a specific lymphocyte;4 lymphocytes become competent/sensitised;5 (B) lymphocytes reproduce by mitosis /(B) lymphocytes cloned;6 plasma cells secrete antibodies;

Describe how these antibodies are produced in response to foreign antigens.

antigens attach to macrophages / antigen presenting;T lymphocytes activated by antigens;helper T lymphocytes activate;B lymphocytes;specific cells (activated);divide (by mitosis) / clone;plasma cells / lymphocytes secrete antibodies;(accept T cells/ B cells as alternatives throughout)

Antibodies are protein molecules. Explain why protein molecules are particularly well suited to carry out the role of antibodies.

large variety of different molecules;range of shapes;

tertiary shape;locks onto / complements specific antigen;

Immunity

Vaccines protect people against disease. Explain how.(5)

1. Vaccines contain antigens / antigens are injected;

2. Dead pathogens / weakened pathogens;

3. Memory cells made;

4. On second exposure memory cells produce antibodies / become active / recognise pathogens;

5. Rapidly produce antibodies / produces more antibodies;

6. Antibodies destroy pathogens;

7. Herd effect / fewer people to pass on disease;

What is an antibody?(2)

protein/immunoglobulin;specific to antigen;idea of fit/complementary shape;

What is a monoclonal antibody? (2)

Reference to hybrid cell from tumour / cancer andB-lymphocyte/hybridoma;antibodies all the same / from one type of plasma cell;specific to / complementary to / fits only one antigen;

Describe how antibodies are produced in the body following a viral infection. (6)

1.virus contains antigen;2.virus engulfed by phagocyte/macrophage;3presents antigen to B-cell;4memory cells/B-cell becomes activated;5(divides to) form clones;6by mitosis;7plasma cells produce antibodies;8antibodies specific to antigen;9correct reference to T-cells/ cytokines;

What is an antigen? (2)

Molecule/part of molecule/protein/glycoprotein;[Allow: polysaccharide]Stimulates immune response;

Immunity

Describe how B-lymphocytes respond when antigens stimulate them.

Divide by mitosis / form clones;produce plasma cells; (plasma cells) make antibodies;(plasma cells) produce memory cells;

Divide by mitosis / form clones; produce plasma cells; (plasma cells) make antibodies;(plasma cells) produce memory cells;

Immunisation programmes may use either attenuated or dead microorganisms. Suggest why there might be problems for the patient when using these vaccines.

Process of killing organisms might not be 100% efficient;live organisms might give rise to full-blown disease;attenuated organisms are non-virulent;but might mutate to virulent forms;immunity can decline - booster injections required;named side effects, eg allergies;less effective due to changed antigens;

Explain the role of B-lymphocytes and T-lymphocytes in the defence of the body against a virus infection.

B lymphocytes produce antibodies/involved in humoral response;T lymphocytes involved in cell mediated immunity;Macrophages present antigens;(specific) B lymphocytes recognise/bind to antigen;increase in numbers by mitosis;produce plasma cells (which make antibodies);antibodies bind to and clump/ agglutinate virus;memory cells produced by 1st exposure/cloned on 2nd exposure;T lymphocytes(helpers) produce lymphokines/chemicals;which aid B lymphocyte cloning;encourages phagocytes to engulf clumped virus;killer T cells kill virus infected cells;

Vaccines protect against disease by stimulating the production of memory cells. Describe how memory cells protect the body from disease.

On further exposure to same microorganism;Antigen recognised;Faster response;Greater production of antibodies;

Immunity

Give two ways in which passive immunity differs from active immunity.

Antibodies not produced by body;No memory cells;Short-term / not lifelong;Antibodies (or context established) donated by mother /across placenta / in milk;

What is vaccination?

Injection of antigens/toxoids;

(Antigen from) attenuated microorganism/non-virulent microorganisms/dead

microorganisms/isolated from microorganism;

Stimulates the formation of memory cells;

Give two other methods used to prepare vaccines.

killed microorganism;modified toxin;attenuated/heat treated/UV treated microorganism;genetically engineered antigens;isolated antigen;

Describe how the scientists could use Kochs postulates to show that the disease is caused by this bacterium.

Show that bacterium is not present in any animal without the disease;Isolate bacterium (from infected animal) and grow in (pure) culture;When cultured bacterium introduced to healthy animals,the disease should develop;Re-isolate bacterium;

Bacterium (always found) in diseased organism and not inhealthy organism;Bacterium (can be) cultivated / cultured / isolated;(Pure) cultures of the bacterium must cause the same disease / symptomswhen introduced into (susceptible) other organisms;Can be re-isolated (from the other experimentally infected animals);

Explain how skin, tears, cilia and phagocytes protect against disease

barrier to microorganisms/bacteria/pathogens;layer of dead cells;impregnated with keratin/cornified;fatty acids in sebum inhibit growth of microorganisms;commensal bacteria compete with other microorganisms;max 2

contain lysozyme/enzyme;capable of digesting bacterial cell walls/killing bacteria;physical washing away;max 2

transport mucus;mucus contains trapped bacteria/microorganisms;microorganisms are moved up the respiratory tract and are swallowed;killed by acid in the stomach;max 2

engulf microorganisms;digested/destroyed by enzymes;released from lysosomes;role of macrophages in the immune response;max 2

[8]

Immunity

Explain why protein molecules are particularly well suited to carry out the role of antibodies.

large variety of different molecules;range of shapes;

ORtertiary shape;locks onto / complements specific antigen;

Explain how the respiratory system stops pathogens getting and the stomach reduces numbers

(a)mucus traps pathogens;lysozyme breaks down bacterial cell walls;cilia moves pathogens to pharynx;where they are either swallowed or removed;max. 3

(b)enzyme;in saliva or gastric juice;acid in stomach;disrupts bacterial membrane / wall;

Explain how a host is made less susceptible by the use of vaccination.

nature of vaccine e.g. attenuated strain;vaccine introduces antigen;stimulate / sensitise lymphocytes;memory cells produced;if host meets pathogen (following vaccination);production of same (B/T) lymphocytes;large number / rapid production of plasma cells / antibodies / T killer cells;pathogen destroyed before it can affect host;

Explain how the defence mechanisms of the body reduce the chance of entry by a pathogen.

Epidermis of skin is dead / keratinised so pathogens cannot penetrate;mucus in respiratory system is trapping sticky pathogens;cilia move fluid / mucus removing pathogens;tears / saliva / mucus contain lysozyme breaking down bacterial cell wall;stomach contains hydrochloric acid which destroys bacteria;blood clot prevents entry;fluid nature of tears wash away bacteria;vaginal acid destroys bacteria;commensal bacteria on skin compete with pathogen;sebum (fatty acid) inhibits bacterial growth;

Immunity

Explain how the body responds both generally and specifically to pathogens that enter the blood.

action of phagocytes;Interferon production;body temperature increased;ref to B or T lymphocytes;activated by non-self antigen;either clone / divide by mitosis;T helper cells role;B plasma cells produced;which produces antibodies;any specific effect (e.g. immobilise /agglutinate / lysis /coat for recognition /neutralise toxins);T killer / cytotoxic cell;perform produced;memory cell produced;

Suggest two reasons why parents may decide against vaccination for their children.

consider vaccines to be unsafe / have side effects / damage immune system;consider natural immunity to be more effective; allow in (a) if not herereligious / ethical objections qualified e.g. objections to use of fetal /animal tissue;consider low risk of disease when high percentage of population alreadyvaccinated/Ref. to Head Effect

Explain how vaccination protects against developing a disease.

T lymphocytes / cells recognize antigen in vaccine;T cells attach to antigens / destroy antigens;B lymphocytes / cells clone;Produce Plasma Cellsproduce antibodies (which kill microbe);memory cells; rapidly produce of these antibodies on re-infection

Many elderly people are vaccinated against influenza.Explain why it is necessary to vaccinate these people every year.

influenza virus mutates;different strains / different - shaped antigen;mutant forms will not be recognised by lymphocytes memory cellsimmune system; accept elderly have weaker immune system

Immunity

Suggest how cloning results in the production of B-lymphocytes that all have the same antibody-producing capability

Mitosis;Identical genetic material/DNA passed to daughter cells;(ignorereference to chromosomes)DNA/gene codes for protein;Antibody is a protein;

Explain how antibodies are produced more quickly if the same type of antigen gets into the blood on a second occasion.

memory (T) cells / lymphocytes;activate B cells / lymphocytes quickly; ormemory (B) cells / lymphocytes;in (large) numbers; (do not allow antibodies produced quickly)

A person who is rhesus negative will produce rhesus antibodies if rhesus antigens get into the blood. Describe how

antigens attach to macrophages / antigen presenting;T lymphocytes activated by antigens;helper T lymphocytes activate;B lymphocytes;specific cells (activated);divide (by mitosis) / clone;plasma cells / lymphocytes secrete antibodies;(accept T cells/ B cells as alternatives throughout)

Describe how macrophages help to prevent the spread of microorganisms that enter the bloodand other tissues.

move to site of infection;phagocytosis/engulf bacteria;

(digest neutral)

stimulate (T)-lymphocytes/B cells/T cells;

Immunity

An antigen in a vaccine leads to the production of antibodies. Describe the part played by B lymphocytes in this process.

1 macrophages present antigens to B lymphocytes;2 antigen binds to/is complementary to receptors on lymphocyte;3 binds to a specific lymphocyte;4 lymphocytes become competent/sensitised;5 (B) lymphocytes reproduce by mitosis /(B) lymphocytes cloned;6 plasma cells secrete antibodies;

When a pathogen enters the body it may be destroyed by phagocytosis. Describe how.

1. Phagocyte attracted by a substance/ recognises (foreign) antigen;

2. (Pathogen)engulfed/ ingested;

3. Enclosed in vacuole/ vesicle/ phagosome;

4. (Vacuole) fuses/joins with lysosome;

5. Lysosome contains enzymes;

6. Pathogen digested/ molecules hydrolysed;

Phagocytes and lysosomes are involved in destroying microorganisms. Describe how.

Phagocytes engulf pathogens/microorganisms;

Enclosed in a vacuole / vesicle/ phagosome;

Lysosomes have enzymes;

That digest/hydrolyse molecules/proteins/lipids/microorganism;

Microfold cells take up the antigens and transport them to cells of the immune system. Explain how vaccines that make use of microfold cells would lead to a person developing immunity to a pathogen.

1. (Vaccine contains) antigen/attenuated/dead pathogen;

2. Microfold cells take up/bind and present/transport antigen (to immune system/lymphocytes/T-cells);

3. T-cells activate B-cells;

4. B-cells divide/form clone/undergo mitosis;

5. B-cells produce antibodies;

6. Memory cells produced;

7. More antibodies/antibodies produced faster in secondary response/on reinfection;

DNA structure for function

Explain how the structure of DNA is related to its function.(6)

sugar - phosphate backbone gives strength;(coiling gives) compact shape;sequence of bases allows information to be stored;long molecule stores large amount of information;information can be replicated / complementary base pairing;(double helix protects) weak hydrogen bonds / double helix makesmolecule stable prevents code being corrupted;chains held together by weak hydrogen bonds;chains can split for replication / transcription

Give three ways in which the structure of the DNA molecule enables it to carry out its functions.(6)

Sugar phosphate backbone gives strength;Coiling gives compact shape;Sequence of bases allows information to be stored;Long molecule / coiling stores large amount of information;Complementary base pairing enables information to be replicated /transcribed;Double helix protects weak hydrogen bonds / double helix makesmolecule stable;Many hydrogen bonds together give molecule stability;Prevents code being corrupted;Hydrogen bonding allows chains to split for replication / transcription ORmolecule unzips easily for replication / transcription.

Describe two features of DNA which make it a stable molecule.

two strands with specific base pairing;large number of hydrogen bonds (between strands);helix/coiling reduces chance of molecular damage / protects H bonds;strong sugar-phosphate backbone;(reject strong bonds between nucleotides)

Explain how DNA replicates.(5)

hydrogen bonds broken;semi-conservative replication / both strands used (as templates);nucleotides line up;complementary / specific base pairing / A and T / C and G;DNA polymerase;

DNA structure for function

Describe and explain how the structure of DNA results in accurate replication.(6)

1 two strands therefore semi-conservative replication (possible);

2 base pairing/hydrogen bonds holds strands together

3 hydrogen bonds weak/easily broken, allow strands to separate;

4 bases (sequence) (exposed so) act as template /can be copied;

5 A with T, C with G / complementary copy;

6 DNA one parent and one new strand;

Describe the molecular structure of DNA and explain how a sequence of DNA is replicated in the bacteria.(9)

nucleotideas;composition of a nucleotide,4 bases named;sugar-phosphate backbone;two (polynucleotide) strands;specific base-pairing;example e.g. AT / CG;hydrogen bonding;uncoiling / unzipping;semi-conservative replication;DNA polymerase;new complementary strands form / identical DNA molecule produced;DNA inserted into plasmids;which are self-replicating;

Describe the molecular structure of DNA and explain how a sequence of DNA is replicated in the bacteria. (9)

nucleotides;composition of a nucleotide,4 bases named;sugar-phosphate backbone;two (polynucleotide) strands;specific base-pairing;example e.g. AT / CG;hydrogen bonding;uncoiling / unzipping;semi-conservative replication;DNA polymerase;new complementary strands form / identical DNA molecule produced;DNA inserted into plasmids;which are self-replicating;

Describe and explain how the structure of DNA results in accurate replication.

1 two strands therefore semi-conservative replication (possible);

2 base pairing/hydrogen bonds holds strands together

3 hydrogen bonds weak/easily broken, allow strands to separate;

4 bases (sequence) (exposed so) act as template /can be copied;

5 A with T, C with G / complementary copy;

6 DNA one parent and one new strand;

DNA structure and function

Explain why DNA replication is described as semi-conservative.

each strand copied/acts as a template;2(daughter) DNA one new strand and one original/parent strand;

Explain how DNA replicates.

hydrogen bonds broken;semi-conservative replication / both strands used (as templates);nucleotides line up;complementary / specific base pairing / A and T / C and G;DNA polymerase;

Explain how the structure of DNA is related to its function.

sugar - phosphate backbone gives strength;(coiling gives) compact shape;sequence of bases allows information to be stored;long molecule stores large amount of information;information can be replicated / complementary base pairing;(double helix protects) weak hydrogen bonds / double helix makesmolecule stable prevents code being corrupted;chains held together by weak hydrogen bonds;chains can split for replication / transcription

Mitosis

Describe the behaviour of chromosomes during mitosis and explain how this results in the production of two genetically identical cells. (7)

1 chromosomes shorten/thicken/supercoiling;

2 chromosomes (each) two identical chromatids/strands/copies (due to replication);

3 chromosomes/chromatids move to equator/middle of the spindle/cell;

4 attach to individual spindle fibres;

5 spindle fibres contract / centromeres divide / repel;

6 (sister) chromatids/chromosomes (separate) move to opposite poles/ends of the spindle;

7 each pole/end receives all genetic information/identical copies of each chromosome;

8 nuclear envelope forms around each group of chromosomes/ chromatids/at each pole;

Describe what happens to the chromosomes during each of the following stages of mitosis. Prophase, Metaphase, Anaphase, Telophase.

prophase coil up/spiralise/condense;(allow shorter/contract/become visible)metaphase move to equator or centre of cell / attach to spindle;(reject if reference to pairing)anaphase chromatids separate/centromeres divide;(reject chromosomes move to poles without further explanation)telophase uncoil; (allow lengthen/becomes less visible)4(allow labelled diagrams)

Describe the features which would help you to recognise when a cell is in metaphase of mitosis; in anaphase of mitosis

(i)Chromosomes or chromatids on equator / in middle of cell;Of spindle (once);No nuclear membrane (once only).

(ii)Chromatids moving towards poles / centrioles;of spindle (once);Two centromeres per chromosome/ centromeres are being pulled;No nuclear membrane (once only).

Compare meiosis and mitosis

Mitosis

Describe the role of the spindle in mitosis.

Attachment of centromeres;Separation of (daughter) chromatids;

Mitosis is important in the life of an organism. Give two reasons why.

1. Growth / increase in cell number;

2. Replace cells / repair tissue / organs /body;

3. Genetically identical cells;

4. Asexual reproduction /cloning;

Describe the features which would help you to recognise when a cell is in metaphase and anaphase

Chromosomes or chromatids on equator / in middle of cell;Of spindle (once);No nuclear membrane (once only).

(ii) Chromatids moving towards poles / centrioles;of spindle (once);Two centromeres per chromosome/ centromeres are being pulled;No nuclear membrane (once only).

Describe two events which occur during interphase.

Increased in volume of cell / amount of cytoplasm / increase in mass /cell bigger;Increase in number of organelles;Protein synthesis / specific example;DNA replication / chromosomes become chromatids / chromosomes copy;I references to G1, G2 and S phases)

Increase in volume of cell/volume of cytoplasm / increase in mass / cell bigger; increase in number of organelles;synthesis of protein/named protein;DNA replication/increase / chromosomes copied;ATP synthesis / respiration;

Describe what happens to the chromosomes during each of the following stages of mitosis. Prophase, metaphase, anaphase telophase

prophase coil up/spiralise/condense;(allow shorter/contract/become visible)metaphase move to equator or centre of cell / attach to spindle;(reject if reference to pairing)anaphase chromatids separate/centromeres divide;(reject chromosomes move to poles without further explanation)telophase uncoil; (allow lengthen/becomes less visible)4(allow labelled diagrams)

Meiosis

Describe what happens to chromosomes in meiosis.(6)

1. Chromosomes shorten/thicken/condense;2. Chromosomes associate in homologous/(described) pairs / formation of bivalents / tetrads;3. Crossing-over / chiasma formation;4. Join to spindle (fibres) / moved by spindle;(*)5. (At) equator/middle of cell;(*)6. (join via) centromere / kinetochore;(*)7. (Homologous) chromosomes move to opposite poles / chromosomes separate/move apart; (ALLOW are pulled apart)8. (Pairs of) chromatids separated in 2nd division;max 6(*) OR independent assortment unqualified = 1 mark

Explain how crossing over can contribute to genetic variation.

sections of chromatids exchanged;sections have different alleles;new combinations of (linked) alleles;

Meiosis results in genetic variation in the gametes which leads to variation in the offspring formed by sexual reproduction. Describe how meiosis causes this variation and explain the advantage of variation to the species.(5)

1. Crossing-over; [IGNORE any wrong ref. to timing]2. Independent/random assortment/orientation/segregation of (homologous) chromosomes in meiosis I;3. Independent/random assortment/orientation/segregation of chromatids in meiosis II;

Any three from:4. Different adaptations / some better adapted;5. Some survive / example described;6. To reproduce;7. Pass on gene/allele;8. Allows for changing environment/different environment/example described;

Explain why the gametes produced by meiosis from a single cell contain different alleles.

A gene (may) have more than one type of allele;Different chromosomes in a homologous / pair have different alleles;Homologous / pairs of chromosomes separate in meiosis;One chromosome from each pair goes to each daughter cell;

Meiosis

Explain the importance of meiosis in the life cycle of a sexually reproducing organism.

Meiosis halves the number of chromosomes;Restoration of diploid number at fertilisation;Introduces variation;Correct reference to natural selection / survival;

Explain why the sperms produced by a man are genetically different from each other.

produced by meiosis;crossing over;independent assortment of chromosomes;

Give two ways in which meiosis results in genetic variation in the gametes produced.

crossing over;random assortment of chromosomes;

Explain the importance of genetic va

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A Level Extended Response Questions