biological molecules exam Questions with Verified Answers

Describe how the structure of glycogen is related to its function. (4 marks) AS paper 1 Nov 2021 - ANSWERS1. Helix/coiled/branched so compact; 2. Polymer of glucose so easily hydrolysed; 3. Branched so more ends for faster hydrolysis; 4. Glucose (polymer) so provides respiratory substrate for energy (release); 5. Insoluble so not (easily) lost (from cell) OR Insoluble so does not affect water potential/osmosis; The general structure of a fatty acid is RCOOH. Name the group represented by COOH. (1 mark) AS paper 2 Nov 2021 - ANSWERScarboxyl Describe how you would test for the presence of a lipid in a liquid sample of food. (2 marks) AS paper 2 Nov 2021 - ANSWERS1. Add ethanol/alcohol then add water and shake/mix OR Add ethanol/alcohol and shake/mix then pour into/add water; 2. White/milky (emulsion) OR (emulsion) test turns white/milky; In 1935, scientists suggested a model for the chemical structure of a cell-surface membrane. Figure 2 shows the membrane structure the scientists suggested. Give one similarity and two differences between the membrane structure shown in Figure 2 and the fluid-mosaic model of membrane structure. (3 marks) AS paper 2 Nov 2021 - ANSWERS(Similarity) 1. Both have a phospholipid bilayer OR Both have fatty acid/hydrophobic tails pointing in/face each other OR Both have phosphate/polar/hydrophilic heads pointing out OR Both have protein; (Differences) 2. No channel/carrier proteins, whereas fluid mosaic does OR Protein layer outside (phospholipids), fluid mosaic is 'dotted'; 3. Cholesterol is not present whereas it is present in fluid mosaic; 4. Glycoprotein is not present whereas it is present in fluid mosaic; 5. Glycolipid is not present whereas it is present in fluid mosaic; A student investigated the activity of the enzyme amylase. He cut three identical wells box (D, E and F) in starch-agar in a Petri dish. He added 0.2 cm3 of: • amylase solution to well D • boiled amylase solution to well E • water to well F. After 60 minutes, he covered the starch-agar with iodine solution. Figure 7 shows his results. Explain the appearance of the agar in the clear area surrounding well D. (2 marks) AS paper 2 Nov 2021 - ANSWERS1. Amylase hydrolyses starch; 2. (To) maltose; What can you conclude about the activity of amylase from the appearance of the agar surrounding well E and well F in Figure 7? (2 marks) AS paper 2 Nov 2021 - ANSWERS1. (E) Amylase/enzyme is denatured; 2. (F) amylase is needed for/causes starch hydrolysis/breakdown/digestion OR (F) water (alone) does not (cause starch) hydrolysis/breakdown/digestion; The student cut out a piece of agar from the clear area surrounding well D. He obtained a solution of the substances contained in this piece of agar. Describe a different biochemical test the student could use with this solution to confirm that amylase had affected the starch in the clear area surrounding well D. [2 marks] AS paper 2 Nov 2021 - ANSWERS1. Heat in Benedict's (solution); 2. Red/green/orange (precipitate/colour) (shows maltose/reducing sugar); The fruit fly is a species of small insect. The fruit fly has a gene that codes for an enzyme called alcohol dehydrogenase (AD). AD catalyses the breakdown of alcohol when alcohol is in the insects' food. The gene coding for AD has two alleles, ADF and ADS. The enzyme encoded by the ADF allele catalyses the breakdown of alcohol faster than the enzyme encoded by the ADS allele. Suggest why. (3 marks) AS paper 2 Nov 2021 - ANSWERS1. Different primary structure/amino acid sequence; 2. Different tertiary structure/shape of active site; 3. Enzyme-substrate complexes more likely (with enzyme from ADF allele); Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3 marks) A level paper 1 Nov 2020 - ANSWERS1. Substrate binds to the active site/enzyme OR Enzyme-substrate complex forms; 2. Active site changes shape (slightly) so it is complementary to substrate OR Active site changes shape (slightly) so distorting/breaking/forming bonds in the substrate; 3. Reduces activation energy;