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ZIMSEC A Level · 9190/4 · N2003

Biology Paper 4 November 2003

Questions
26
Total marks
60
Time allowed
150 min
Syllabus code
9190/4

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Questions
26
Pass mark
16
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Answer every question in the printed order, get marked at the end, then see the answers.

The questions

Question 101

[1 marks]Enzymes: effect of pH on catalase activity (practical)
In this investigation catalase activity was measured by timing how long it took manometer fluid to rise 5 cm in a boiling tube containing potato discs, buffer and hydrogen peroxide. After adding the hydrogen peroxide and replacing the bung, the tube was shaken gently. State the reason the tube was shaken.

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Question 102

[1 marks]Enzymes: effect of pH on catalase activity (practical)
In this investigation, catalase activity was tested in buffer solutions at pH3, 4, 5, 6, 7 and 8, so that the rate of the reaction could be compared across the different pH values. State why buffer solutions, rather than plain solutions of acid or alkali, were necessary for this investigation.

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Question 103

[1 marks]Enzymes: effect of pH on catalase activity (practical)
Catalase activity was measured over the pH range 3 to 8. As the pH rises from pH3 towards pH7, the rate of the reaction increases. What happens to the ionisable groups of catalase's active site as the pH rises over this range?
  1. AThey are destroyed permanently and cannot recover
  2. BThey are completely unaffected by the pH change
  3. CThey are progressively modified
  4. DThey stop being ionisable altogether

Question 104

[1 marks]Enzymes: effect of pH on catalase activity (practical)
As the ionisable groups of catalase's active site are modified between pH3 and pH7, what specifically is disrupted, allowing the reaction rate to rise?
  1. AThe ionic bonding (or hydrogen bonding) that helps maintain the enzyme's specific shape
  2. BThe disulfide bonds linking two entirely separate catalase polypeptide chains together permanently
  3. CThe covalent peptide bonds that make up the primary structure of the enzyme's backbone
  4. DThe covalent bonds holding together the hydrogen peroxide substrate molecule itself

Question 105

[1 marks]Enzymes: effect of pH on catalase activity (practical)
Between pH3 and pH7, disruption of the ionic bonding that maintains catalase's shape is linked to a rising reaction rate, without yet denaturing the enzyme. What effect does this disruption have on the active site over this range?
  1. ASubstrate binding to the active site becomes permanently irreversible, trapping the substrate in place forever
  2. BThe active site becomes completely unable to bind any substrate at all, stopping the reaction
  3. CThe active site becomes more efficient at binding substrate, so more enzyme-substrate (ES) complexes form
  4. DThe active site permanently changes shape and begins binding an entirely different substrate

Question 106

[1 marks]Enzymes: effect of pH on catalase activity (practical)
Above pH7 (towards pH8), the rate of the catalase reaction falls. What happens to catalase's ability to form enzyme-substrate (ES) complexes over this range?
  1. ACatalase progressively loses its ability to form ES complexes as its ionic bonds are further disrupted
  2. BCatalase's ability to form ES complexes continues to increase steadily as the pH keeps rising
  3. CCatalase stops requiring substrate binding altogether and begins catalysing a completely unrelated reaction instead
  4. DThe ES complexes formed become permanently stable and accumulate without ever breaking down again

Question 107

[1 marks]Enzymes: effect of pH on catalase activity (practical)
Between pH7 and pH8, the concentration of hydroxide ions (OH-) in the reaction mixture increases. What effect does this have on catalase?
  1. AIt has no effect on the enzyme's structure or activity at any pH value tested
  2. BIt increases the enzyme's affinity for its substrate, making the reaction proceed even faster
  3. CIt converts catalase into a completely different enzyme with an entirely new active site
  4. DIt alters the ionic charge of the basic groups on the enzyme, denaturing it

Question 201

[1 marks]Biochemical tests: ascorbic acid (DCPIP) and glucose (Benedict's) determination
In this investigation, the number of drops of each ascorbic acid standard needed to decolourise DCPIP was counted by eye and recorded. Which change to the way the ascorbic acid solution is added would make the volume measurement more accurate than counting drops?
  1. ACooling the DCPIP solution in ice before starting each test to slow the reaction
  2. BUsing a burette or other appropriate titration apparatus to measure the volume added
  3. CIncreasing the volume of DCPIP used in each test to make the colour change last longer
  4. DUsing a much wider test tube to hold the DCPIP solution during each test

Question 202

[1 marks]Biochemical tests: ascorbic acid (DCPIP) and glucose (Benedict's) determination
Only four standard ascorbic acid concentrations (0.5, 1.0, 2.0 and 4.0 mg cm-3) were tested to decolourise DCPIP. Which change to the standards used would improve the accuracy of the ascorbic acid concentration estimated for the orange juice?
  1. ATesting the orange juice sample before testing any of the ascorbic acid standards prepared
  2. BReducing the number of standard concentrations tested to save time and materials
  3. CUsing only the highest concentration standard for every single comparison made
  4. DPreparing a wider range of standard concentrations, for example by serial dilution

Question 203

[1 marks]Biochemical tests: ascorbic acid (DCPIP) and glucose (Benedict's) determination
In this investigation, each ascorbic acid standard and the orange juice sample were tested only once for the number of drops needed to decolourise DCPIP. Which change to the procedure would improve the reliability of these results?
  1. AUsing a narrower syringe for the ascorbic acid solution
  2. BTesting the orange juice sample several times but each standard only once
  3. CStopping the stirring of the DCPIP solution during each test
  4. DRepeating each test (using replicates) and taking an average

Question 204

[1 marks]Biochemical tests: ascorbic acid (DCPIP) and glucose (Benedict's) determination
In the glucose test, orange juice and glucose standards from 0.1% to 4% were tested with Benedict's solution and the colour/turbidity produced was matched by eye against the standards. What difficulty does matching colour by eye create for this quantitative test?
  1. AIt cannot detect any reducing sugar present in the orange juice sample
  2. BIt uses far more Benedict's solution than a titration method would need
  3. CIt is difficult to match colours or turbidity accurately by eye
  4. DIt cannot be carried out at room temperature without a water bath

Question 205

[1 marks]Biochemical tests: ascorbic acid (DCPIP) and glucose (Benedict's) determination
Which instrument would overcome the difficulty of matching Benedict's test colours by eye when estimating glucose concentration?
  1. AA pH meter, which measures acidity rather than colour
  2. BA colorimeter or spectrophotometer, which measures colour
  3. CA manometer, which measures gas pressure rather than colour
  4. DA hand lens, which magnifies rather than measures colour

Question 206

[1 marks]Biochemical tests: ascorbic acid (DCPIP) and glucose (Benedict's) determination
The glucose test used only five standard concentrations spread across the range 0.1% to 4%, each compared with Benedict's solution by eye. What limitation of the Benedict's test itself does this expose when trying to estimate the orange juice's glucose concentration precisely?
  1. ABenedict's solution reacts specifically with ascorbic acid rather than with reducing sugars present
  2. BBenedict's test is not sensitive enough to distinguish closely spaced concentrations reliably
  3. CBenedict's solution decolourises instead of changing colour when heated with any sugar
  4. DThe 0.1% to 4% range chosen for the standards is too wide ever to be useful

Question 207

[1 marks]Biochemical tests: ascorbic acid (DCPIP) and glucose (Benedict's) determination
How could the set of standard glucose concentrations be adjusted to improve the precision of the glucose estimate obtained from the Benedict's test?
  1. AIncrease the number of intermediate glucose concentration values within the 0.1% to 4% range
  2. BTest only the highest and lowest glucose concentrations and ignore all the values between
  3. CRemove the intermediate glucose concentrations entirely to save time and Benedict's solution
  4. DUse only whole-number percentage values for every one of the standard glucose concentrations

Question 301

[1 marks]Organism observation: Annelida external features and vein histology
Z1 is an animal belonging to the phylum Annelida, examined with a hand lens. Its body is visibly divided into many similar repeating units along its length. State the term for this visible feature.

Answer this when you sit the paper.

Question 302

[1 marks]Organism observation: Annelida external features and vein histology
Z1 is an animal belonging to the phylum Annelida, examined with a hand lens. Along each segment are small hair-like structures that can be felt gripping the surface it is placed on. State the name of these structures.

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Question 303

[1 marks]Organism observation: Annelida external features and vein histology
Z1 is an animal belonging to the phylum Annelida, examined with a hand lens. Its body surface appears shiny. State the term for the outer covering that produces this shiny appearance.

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Question 304

[1 marks]Organism observation: Annelida external features and vein histology
Z1 is an animal belonging to the phylum Annelida, examined with a hand lens. A distinct, unsegmented, thickened band, associated with reproduction, is visible around part of its body. State the term for this structure.

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Question 305

[1 marks]Organism observation: Annelida external features and vein histology
Z1 is an animal from the phylum Annelida whose body is divided into many similar repeating segments. State the main function this segmentation gives the animal.

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Question 306

[1 marks]Organism observation: Annelida external features and vein histology
Z1 is an animal from the phylum Annelida with small hair-like chaetae (setae) on each segment. State the function of the chaetae.

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Question 307

[1 marks]Organism observation: Annelida external features and vein histology
Z1, an animal from the phylum Annelida, lives in soil and feeds on dead organic matter. State the term for an organism with this feeding role in its habitat.

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Question 308

[1 marks]Organism observation: Annelida external features and vein histology
Z1, an animal from the phylum Annelida, burrows through soil, mixing organic and inorganic material as it moves. State one way this burrowing activity benefits the soil in its habitat.

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Question 309

[1 marks]Organism observation: Annelida external features and vein histology
Z1 was examined with a hand lens and found to be segmented, with a shiny cuticle, chaetae arranged segmentally and a clitellum. Identify the phylum to which Z1 belongs.

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Question 310

[1 marks]Organism observation: Annelida external features and vein histology
Z2 is a transverse section through a tubular structure from the body of a mammal, examined under the microscope. It has a wide lumen. State how this feature relates to the structure's function.

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Question 311

[1 marks]Organism observation: Annelida external features and vein histology
Z2 is a transverse section through a tubular structure from the body of a mammal, examined under the microscope. Its wall is thin. State how this feature relates to the structure's function.

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Question 312

[1 marks]Organism observation: Annelida external features and vein histology
Slide Z2 is a transverse section through a tubular structure found in the body of a mammal. It has a wide lumen and a thin wall containing elastic fibres. Identify Z2.

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