Unit One Common Questions

Question 1

Explain how a substrate is broken down by the enzyme

Answer 1

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

Question 1

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

Answer 1

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;

Question 2

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

Answer 2

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

Question 2

Describe the part played by cell surface membranes in regulating the movement of substances into and out of cells. (6)

Answer 2

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

Question 3

Describe the structure and function of the RER

Answer 3

Endoplasmic Reticulum (ER). This is a series of interconnected membrane channels involved in synthesising and transporting materials. Rough Endoplasmic Reticulum (RER) is studded with numerous ribosomes, which give it its rough appearance. The ribosomes synthesise proteins, which are processed in the RER (e.g. by enzymatically modifying the polypeptide chain, or adding carbohydrates), before being exported from the cell via the Golgi Body

Question 3

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

Answer 3

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 gradient mitochondria supply ATP / energy for active transport; carrier proteins (in membranes);

Question 3

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

Answer 3

Large variety of different molecules; range of shapes; Tertiary shape; locks onto / complements specific antigen

Question 4

Describe the structure and function of the Golgi

Answer 4

Golgi Body (or Golgi Apparatus). Another series of flattened stacks of membrane vesicles, formed from the endoplasmic reticulum. Its job is to transport proteins from the RER to the cell membrane for export.

Question 4

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

Answer 4

Temperature Rate of reaction increases; Increasing temperature increases rate of movement of molecules/ kinetic energy; Collide more often/substrate enters active site more often/more enzyme-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

Question 4

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

Answer 4

Carbon monoxide combines with haemoglobin/causes less oxygen 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;* 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*; *Allow reference to these points only once.

Question 5

Explain how inhibitors affect the rate of enzyme-controlled reactions

Answer 5

1 Statement about two types, competitive and non-competitive; Note. Award points 2 –5 only in context of competitive and non-competitive inhibition Competitive 2 Similarity of shape of inhibitor and substrate; 3 Inhibitor can enter/bind with active site (of enzyme); Non-competitive 4 Affect/bind to enzyme other than at active site; 5 Distorts shape of active site; Inhibitors 6 Prevent entry of/binding of substrate to active site; 7 Therefore fewer/no enzyme-substrate complexes formed

Question 6

What is a monoclonal antibody? (2)

Answer 6

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

Question 7

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

Answer 7

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/out of the epithelial cell; By (facilitated) diffusion;

Question 8

What is an antigen?

Answer 8

Molecule/part of molecule/protein/glycoprotein; Stimulates immune response

Question 9

Give 2 ways in which pathogens can cause disease when they enter the body of their host

Answer 9

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

Question 9

Explain how a change in pH affects enzymes activity

Answer 9

( this answer is for a decrease in pH) increases H+ ions/protons; attach/attracted to amino acids; hydrogen/ionic bonds disrupted/broken; denatures enzyme / changes tertiary structure; changes shape/charge of active site; active site/enzyme unable to combine/fit with starch/enzyme-substrate complex no longer able to form decreases rate of breakdown of substrate

Question 9

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

Answer 9

Phagocytes engulf pathogens/microorganisms; Enclosed in a vacuole / vesicle/ phagosome; Fuses with lysosome to form a phagolysosome Lysosomes have enzymes; That digest/hydrolyse molecules/proteins/lipids/microorganism

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

1 Phospholipid 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

Question 14

Describe the structure and function of the Lysosomes

Answer 14

These are small membrane-bound vesicles formed from the RER containing a cocktail of hydrolytic enzymes. They are used to break down unwanted chemicals, toxins, organelles or even whole cells, so that the materials may be recycled

Question 16

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

Answer 16

Biuret / Sodium Hyrdroxide + copper sulphate; Lilac/purple/mauve/violet;

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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)

Question 18

What is atheroma? (2)

Answer 18

Plaque/ fatty material/ cholesterol/ foam cells/ lipoprotein build up; In artery/ blood vessel wall;

Question 19

What is Heart Rate?

Answer 19

The heart rate can be calculated from the pressure graph by measuring the time taken for one cardiac cycle and using the formula: Heart rate (beats per minute) =60 ÷cycle time (s)

Question 20

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

Answer 20

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

Question 21

What is Cardiac Output?

Answer 21

Cardiac Output is the amount of blood flowing through the heart each minute. It is calculated as the product of the heart rate and the stroke volume. Cardiac output = heart rate x stroke volume

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

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

Answer 25

Long chains of amino acids will; Fold 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

Question 27

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

Answer 27

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

Question 28

Describe the structure and function of the Mitochondria

Answer 28

This is a sausage-shaped organelle (8Vm long), and is where aerobic respiration takes place in all eukaryotic cells (anaerobic respiration takes place in the cytoplasm). Mitochondria release energy (in the form ATP) from carbohydrates, lipids and other energy rich molecules. Cells that use a lot of energy (like muscle cells) have many mitochondria.

Question 29

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

Answer 29

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

Question 30

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

Answer 30

Weakens artery wall; So that it swells/ bursts

Question 32

How V.cholerae causes Diarrhoea

Answer 32

1. The cholera bacterium adheres to the epithelium and secretes the cholera toxin CT. CT enters the epithelial cells and activates a chloride ion channel in the cell membrane. 2. This causes chloride ions to diffuse out of the cells into the lumen. 3. This lowers the water potential in the lumen of the gut. 4. So water is lost from cells to the lumen by osmosis, producing diarrhoea and dehydration.

Question 33

Describe the parts played by the sinoatrial node (SAN) and the atrioventricular node (AVN) in controlling the heartbeat

Answer 33

1 SAN initiates / sends heart beat; 2 Myogenic / beats spontaneously / does not require nerve impulse; 3 Rate of beating influenced by nerves: 4 Wave of electrical activity / impulses / excitation passes over atrium; 5 Triggers contraction of atrium; 6 Electrical activity can only pass to ventricles / along bundle of His by way of AVN 7 Fibrous tissue prevents passage elsewhere; 8 Delay at AVN; 9 Allows blood to empty into ventricles / atria to empty

Question 35

Describe the structure and function of the Ribosomes

Answer 35

These are the smallest and most numerous of the cell organelles, and are the sites of protein synthesis. Ribosomes are either found free in the cytoplasm, where they make proteins for the cell’s own use, or they are found attached to the rough endoplasmic reticulum, where they make proteins for export from the cell

Question 36

Describe the structure and function of the Nucleus

Answer 36

This is the largest organelle. It is surrounded by a nuclear envelope, which is a double membrane with nuclear pores – large holes containing proteins that control the exit of substances from the nucleus. The interior is called the nucleoplasm, which is full of chromatin – the DNA/protein complex (see unit 2).

Question 38

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.

Answer 38

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

Question 39

Describe the structure and function of the Chloroplast

Answer 39

Membranes arrangement and disc shape provides large surface for light absorption; layering of membrane allows a lot of pigment; Permeable membrane allows diffusion of gases /carbon dioxide; membranes provide surface for attachment of electron / hydrogen acceptors; Contains chlorophyll for light absorption; Contains different pigments to absorb different wavelengths; Stacking / arrangement of grana/thylakoids maximises light catchment;

Question 40

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

Answer 40

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;

Question 41

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

Answer 41

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, e.g. allergies; less effective due to changed antigens

Question 43

What is Facilitated Diffusion? What substances pass through cell membranes by facilitated diffusion?

Answer 43

Net movement from a high conc to a low conc (down a conc gradient) with the assistance of channel proteins or carrier proteins (different structures). Large polar molecules and water soluble molecules

Question 44

Suggest why the model of the membrane is described as a fluid mosaic

Answer 44

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

Question 45

What is resolution and why is it better in Electron Microscopes than in light

Answer 45

Ability to distinguish points (close together), Electrons have a shorter wavelength;

Question 47

Explain what is meant by a polymer

Answer 47

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

Question 48

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

Answer 48

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; 6 and 7 Any two from Capsule/flagellum/plasmid / cell wall/etc.

Question 49

What is Diffusion? What substances pass through cell membranes by diffusion?

Answer 49

Net movement from a high conc to a low conc (down a conc gradient): Lipid soluble non polar molecules

Question 50

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

Answer 50

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

Question 51

What is active transport?

Answer 51

Movement against concentration gradient and requires ATP

Question 52

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

Answer 52

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; (can be expressed as a diagram)