Revision:AQA-A-Biology- Module 1

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This contains suggestions has to how you might approach essay questions on topics which could appear in module 1.

Selectivity of enzymes

• Only these substances have the right shape/structure (complementary Ξ shape); To fit/bind with active site/form ES complex with active site;

• Only trypsin has right-shaped active site; To bind/fit with substrate/ to form ES complex;

Difference between lock and key and induced fit

1. Active site not totally complementary/does not match exactly it wraps round substrate/ Enzyme changes shape;.

Specific shape of enzymes and 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 - 8

1. inhibitor fits at site on the enzyme other than active site;
2. determined by shape;
3. distorts active site;
4. so substrate will no longer fit / form enzyme-substrate complex;

Why adding enzyme speeds up reaction

• Lowers activation energy (of reaction);
• More molecules able to react;
• By splitting the reaction into stages;
• Allows E-S complex to be formed;
• Provide a surface/place for reaction;

How a diameter could be estimated

1. Measure diameter of field with ruler/other appropriate device; Find proportion taken up by granulocyte;
2. (Measure length) with (eyepiece) graticule/eyepiece scale; Calibrate with stage micrometer/something of known length/red blood cell;

Transmission electron microscope

1. TEM uses (beam of) electrons;
2. These have short wavelength;
3. Allow high resolution/greater resolution/Allow more detail to be 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;

Benedicts test

• Heat/warm with Benedicts solution;
• Turns green/yellow/orange/red;

Emulsion test

• Mix with ethanol/alcohol/meths then water;
• Milky/white (emulsion)/ emulsion produced;
• Do not accept unqualified reference to cloudy
• Ignore incorrect references to precipitate etc.

• Do the emulsion test. gets mark for result.

Water vapour is higher in alveolus

• (Lining of) alveoli moist/surface film of fluid/water;
• Evaporates; Due to warm body temperature;

Tissue

• (Group of) cells which have a common origin/ similar;
• Ignore references to function

Organ

• made of (different) tissues/specified tissues; Made up of several layers of tissue/tissues;

Protein denatured

1. Breaks bonds (holding tertiary structure/shape);
2. Such as hydrogen bonds/disulphide bonds;
3. Protein loses shape/tertiary structure;
4. Active site (of enzymes) affected;
5. Substrate no longer able to fit/bind/form ES complex;
6. Receptor/binding sites on carrier proteins lose shape/affected;
7. Therefore unable to move substances by active transport;
8. And facilitated diffusion;
9. (Ion) channel distorted/change shape;

Adaptations of red blood cell

1. Contains no nucleus/ mitochondria/ organelles;
2. Haemoglobin;
3. Biconcave shape/small size; Allow description
4. Large surface area to volume;
5. For diffusion;
6. Disc means short distance to .centre. of cell/ no point far from surface;
7. Approx same size/diameter as capillary;
8. Only pass down in .single file./ slow passage down capillary gives time for diffusion/uptake;
9. (Surface pressed against capillary wall therefore) short distance for oxygen to travel;

Nerves increasing heart rate

1. increase in number of impulses;
2. reject faster or larger in sympathetic/accelerator nerve;
3. more impulses/signals from SAN;
4. less parasympathetic activity

Composition of gases in inhaled/exhaled air

• maximum of three marks for description, points 1 to 4

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; by diffusion;
7. water vapour diffuses from moist surface;

Structure of cellulose

1. made from β-glucose;
2. joined by condensation/removing molecule of water/glycosidic bond;
3. 1 : 4 link specified or described;
4. "flipping over" of alternate molecules;
5. hydrogen bonds linking chains/long straight chains;
6. cellulose makes cell walls strong/cellulose fibres are strong;
7. can resist turgor pressure/osmotic pressure/pulling forces;
8. bond difficult to break;
9. resists digestion/action of microorganisms/enzymes; 6 max

• allow maximum of 4 marks for structural features

Structure of starch

1. Formed from α glucose;
2. Joined by condensation/ by the removal of a water molecule/ glycosidic bonds;
3. Between (carbons) 1 and 4 (and 1 and 6);
4. Coiled chain; )
5. (Allows) storage of large amount in a small space; )
6. Insoluble so has no effect on osmosis/water potential;
7. Branches; )
8. (Allows) rapid breakdown/release of glucose / hydrolysis) 6 max

• Accept information shown clearly in a diagram
• Reject easily/readily broken down

Veins in leg return to heart

1. Muscles (surrounding veins) contract;
2. Press on (walls of) vein;
3. Squeezes blood along veins;
4. Valves prevent backflow/ensure flow in one direction;
5. Systole/contraction of heart pumps blood (through arteries) into veins/residual arterial pressure;
6. Negative pressure in chest due to inspiration;
7. Recoil of heart muscle during diastole/after contraction;
8. Draws blood from veins into atria; Accept sucks
9. Wide lumen little resistance/friction

Polymer

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

Centrifugation

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;

Structure of artery/ vein

1. Thick wall of artery;
2. Allowing it to withstand (higher) pressure;
3. Thin wall of vein;
4. Does not .need. to withstand pressure;
5. Both have endothelium/epithelium;
6. Consisting of squamous/flat cells;
7. Reduces friction with blood / allows smooth flow of blood;
8. Muscle which may contract and alter vessel diameter / divert blood;
9. Elastin smoothes out pressure / stretches and recoils;
10. Valves in veins;
11. Prevent backflow of blood;