Topic 4 Practice Paper: Biological molecules and enzymes — question paper

Section A: Multiple-choice questions[10 marks]

Choose one answer for each question. Each question is worth 1 mark.

1. 1

   Which elements does a protein contain that a carbohydrate does not?

   1. AIron
   2. BNitrogen
   3. CPhosphorus
   4. DSodium
   ( )
2. 2

   Which reagent gives a brick-red colour when heated with its target nutrient?

   1. AIodine solution
   2. BBiuret solution
   3. CBenedict’s solution
   4. DDCPIP
   ( )
3. 3

   Fats and oils are built from

   1. Afatty acids and glycerol
   2. Bamino acids
   3. Cglucose and oxygen
   4. Dnucleotides
   ( )
4. 4

   Which statement about DNA is correct?

   1. AIt is a single straight strand
   2. BA pairs with C
   3. CIt is made of amino acids
   4. DIt is a double helix with A pairing with T
   ( )
5. 5

   Enzymes are

   1. Afats that store energy
   2. Bcarbohydrates that provide energy
   3. Cproteins that catalyse metabolic reactions
   4. Dnucleic acids that store information
   ( )
6. 6

   The shape of an enzyme’s active site is

   1. Acomplementary to the substrate
   2. Bidentical to the substrate
   3. Cthe same for all enzymes
   4. Dchanged by every reaction
   ( )
7. 7

   A very low pH stops an enzyme working because it

   1. Adissolves the substrate
   2. Bfreezes the active site
   3. Cremoves the enzyme’s nitrogen
   4. Ddenatures the enzyme’s active site
   ( )
8. 8

   An enzyme works fastest at 35 °C. At 60 °C its activity is close to zero mainly because

   1. Athe substrate has all been used
   2. Bthe enzyme is denatured
   3. Cthe reaction has reached equilibrium
   4. Dthe active site has shrunk into the nucleus
   ( )
9. 9

   A food sample produces a cloudy white layer in the ethanol emulsion test and a purple colour in the biuret test. What does it contain?

   1. AProtein and vitamin C
   2. BStarch and sugar
   3. CFat and protein
   4. DStarch and fat
   ( )
10. 10

    As temperature rises from 10 °C to an enzyme’s optimum at 40 °C, activity increases because

    1. Amolecules gain kinetic energy, so collisions are more frequent and effective
    2. Bthe active site grows larger
    3. Cthe pH rises towards the optimum
    4. Dthe substrate concentration rises
    ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided.

1. 11

   An unknown food solution is tested in the laboratory.

   Nutrient tested	Name of test	Positive result
   Starch
   Protein

   1. (a)

      Complete the table with the name of each test and the result that would show the nutrient is present.

      [4]
   2. (b)

      The solution turns Benedict’s solution orange when heated. State the nutrient present and one further result needed to confirm there is no fat.

      [2]
2. 12

   The activity of an enzyme was measured at different temperatures by recording the time taken for a fixed amount of substrate to be used up.

   Temperature / °C	10	20	30	40	50	60
   Time / s	120	60	30	20	60	300

   1. (a)

      Work out the reaction rate at 20 °C (1 ÷ time), giving your answer to 3 decimal places.

      rate =s⁻¹[2]
   2. (b)

      State the optimum temperature from these data.

      [1]
   3. (c)

      Explain the shape of the graph of rate against temperature between 30 °C and 60 °C.

      [4]
3. 13

   A strand of DNA has the base sequence G–A–T–T–A–C. (Supplement)

   1. (a)

      Name the shape formed by the two strands of a DNA molecule, and state the two base-pairing rules.

      [3]
   2. (b)

      Give the base sequence of the strand that pairs with this one.

      [2]
   3. (c)

      In a different DNA sample, 22% of bases are cytosine. Calculate the percentage of guanine, explaining your reasoning.

      [2]