W3 2(c) Biological molecules

Fill in the blanks. (10 marks)

• M1: oxygen / O₂

• M2: cellulose;

• M3: insoluble / does not dissolve;

• M4: iodine / I₂ / KI/ iodide

• M5: brown / reddish brown / yellow / orange;

• M6: blue / black / blue black; (Ignore red / brick red)

• M7: glycogen;

• M8: liver;

• M9: insulin;

• M10: pancreas;

Describe the test for glucose. (3 marks)

• M1: Benedict’s;

• M2: heat / water bath;

• M3: green / yellow / orange / red / brick red;

Describe the test for protein. (2 marks)

• M1: Biuret / add NaOH and CuSO₄ / albustix / eq;

• M2: lilac / purple / pink; (Accept: uristicks / colour change to blue or green for 1 mark)

Describe the test for starch. (2 marks)

• M1: iodine (1);

• M2: blue black / blue / black / eq (1); (Allow: purple)

Describe the test for a lipid. (2 marks)

• M1: mix the food in ethanol and pour into water (1); (Accept: add water and ethanol and mix)

• M2: white emulsion forms (1); (Accept: white precipitate / goes cloudy / emulsion test)

Describe the role of enzymes in cells. (2 marks)

• M1: catalyse / speed up / increase rate / lower activation energy / eq;

• M2: (chemical) reactions / (metabolic) reactions;

Describe the location and function of amylase, protease, restriction, and ligase enzymes. (4 marks)

• amylase

• protease

• restriction

• ligase

• M1 (Amylase): salivary gland / digest or breakdown starch; (Turns starch into maltose)

• M2 (Protease): stomach / pancreas / allow small intestine / digest or breakdown proteins / peptides;

• M3 (Restriction): bacteria / cutting DNA at certain points;

• M4 (Ligase): cell nucleus / joining DNA / genes / eq;

Describe the effect of EXCESS temperature on enzyme activity. (3 marks)

• M1: increased temperature causes vibrations / breaks bonds (1);

• M2: causes change in shape of active site (1);

• M3: enzyme denatures (1);

• M4: substrate can no longer fit in / bind with enzyme (1); (Reject: reference to enzyme being killed)

Describe how changes in temperature LOW and HIGH affect enzyme activity. (3 marks)

• M1: less (kinetic) energy at low temperatures;

• M2: fewer collisions / less movement at low temperatures / eq;

• M3: enzyme denatures; (Reject if linked to low temperature)

• M4: changes active site / eq;

• M5: substrate can no longer bind / eq;

Describe the effect of temperature on metabolic activity / growth of an organism. (4 marks)

• M1: higher temperatures produce more growth / faster growth / eq (1);

• M2: enzymes (1);

• M3: more kinetic energy (1);

• M4: more frequent collisions / enzyme substrate complexes form faster / eq (1);

• M5: faster respiration (1);

Describe the consequence of pH 8.5 on urease. (3 marks)

• M1: (rate of reaction) lower / eq (1);

• M2: denatured / change in shape of active site / eq (1);

• M3: urea does not bind (into active site) / fewer E/S complexes / eq (1);

Describe how a student could investigate the effect of pH on the rate of an enzyme-controlled reaction. (5 marks)

• M1: use a named enzyme and substrate (e.g., amylase and starch / catalase and hydrogen peroxide);

• M2: use a range of at least 3 different pH solutions (e.g., using buffer solutions);

• M3: control the temperature using a water bath;

• M4: measure the time taken for the substrate to disappear / product to form;

• M5: Repeat the experiment at each pH to calculate an average / increase reliability (OR: calculate the rate using 1/time.

Describe the structure of a DNA molecule. (3 marks)

• M1: (it consists of) two strands;

• M2: (coiled together to form a) double helix;

• M3: (the strands are) held together by paired bases / A-T and C-G;