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MYP 4 & 5 · Biology

B2 - Biological molecules and enzymes

20 questions across 5 sub-topics

Use the Sub-Topic filter above to focus on one.

B2.1 - Carbohydrates, lipids, proteins and nucleic acids B2.2 - Food tests and interpreting observations B2.3 - Enzyme action and specificity B2.4 - Effects of temperature, pH and concentration on enzymes B2.5 - Planning and evaluating enzyme investigations

B2.1 - Carbohydrates, lipids, proteins and nucleic acids 4 questions

QUESTION 1 6 marks Criterion A
Medium

Roles of biological molecules

Match molecular structure to biological function.

a. Explain why glycogen is suitable for energy storage.
[2]
b. Explain why phospholipids form membranes.
[2]
c. Explain why protein function depends on amino-acid sequence.
[2]
Show complete worked solution
(a)
It is a compact insoluble polymer of glucose and is highly branched, allowing rapid release of glucose without strongly changing cell water potential.
(b)
Their hydrophilic heads interact with water while hydrophobic tails avoid water, so they self-assemble into bilayers.
(c)
The sequence determines folding and the three-dimensional shape, including binding and active sites.
QUESTION 2 9 marks Criterion B
Hard

Comparing macromolecule energy

Plan a safe calorimetry comparison of equal masses of carbohydrate-rich and lipid-rich foods.

a. State the dependent quantity.
[2]
b. Describe a controlled method.
[5]
c. State two limitations.
[2]
Show complete worked solution
(a)
Estimate energy transferred per gram from the temperature rise of a known water mass.
(b)
Dry and weigh equal food masses, ignite each beneath the same insulated calorimeter containing equal water mass at the same starting temperature, keep flame distance and stirring constant, record maximum temperature and mass actually burned, calculate \(q=mc\Delta T\) per gram, and repeat.
(c)
Heat loss and incomplete combustion underestimate chemical energy; foods also contain mixtures and water.
QUESTION 3 6 marks Criterion C
Hard

Food-energy data

A sample transfers 8.36 kJ to 50.0 g water and loses 0.420 g by burning. Label energy is 25.0 kJ g?¹.

a. Calculate measured energy per gram.
[2]
b. Calculate percentage of label value recovered.
[2]
c. Explain the shortfall.
[2]
Show complete worked solution
(a)
\[\frac{8.36}{0.420}=19.9\,\mathrm{kJ\,g^{-1}}\]
(b)
\[\frac{19.9}{25.0}\times100=79.6\%\]
(c)
Some heat warms the apparatus or escapes, and combustion may be incomplete, so not all released energy reaches the water.
QUESTION 4 6 marks Criterion D
Hard

DNA data ownership

A nutrition service offers diet advice from a saliva DNA sample and retains customers’ sequence data for research.

a. State one biological promise and limitation.
[2]
b. Evaluate responsible use.
[4]
Show complete worked solution
(a)
Variants can be associated with metabolism or disease risk, but diet outcomes are also shaped by many genes, environment and behavior, so predictions may be weak.
(b)
Require evidence of predictive validity, informed and withdrawable consent, clear data retention, security, limits on third-party access, ancestry-aware uncertainty and access to qualified advice. Research use should be separately consented and independently governed.

B2.2 - Food tests and interpreting observations 4 questions

QUESTION 1 6 marks Criterion A
Medium

Interpreting food tests

A sample gives Benedict’s orange after heating, iodine remains brown, biuret turns purple and ethanol emulsion is clear.

a. Identify nutrients present and absent.
[4]
b. State why a negative result does not prove absence.
[2]
Show complete worked solution
(a)
Reducing sugar and protein are present. Starch and lipid are not detected.
(b)
The nutrient may be below the detection limit, extraction may be incomplete or reagents may fail; a known positive control is needed.
QUESTION 2 8 marks Criterion B
Hard

Validating food-test reagents

Design controls to validate Benedict’s, iodine, biuret and emulsion tests.

a. Describe positive controls.
[3]
b. Describe negative controls.
[2]
c. Explain how sample comparison is standardized.
[3]
Show complete worked solution
(a)
Test known glucose, starch, protein and lipid standards with their corresponding reagents to confirm expected changes.
(b)
Use distilled water or a matrix lacking the nutrient to show the reagent does not change without the target.
(c)
Use equal sample and reagent volumes, fixed concentrations, identical heating time and temperature where needed, consistent mixing and a defined color scale or colorimeter.
QUESTION 3 6 marks Criterion C
Hard

Quantitative Benedict’s test

Glucose standards give absorbance: 0 mmol dm?³ 0.02, 2 0.18, 4 0.34, 6 0.50, 8 0.66. An unknown gives 0.42.

a. Estimate glucose concentration.
[3]
b. Explain why visual color categories are less precise.
[2]
c. State one calibration check.
[1]
Show complete worked solution
(a)
0.42 lies halfway between absorbance 0.34 at 4 and 0.50 at 6, so concentration is approximately \(5.0\,\mathrm{mmol\,dm^{-3}}\).
(b)
Human judgment and lighting vary, and broad categories lose continuous intensity information.
(c)
Include a blank, replicate standards and ensure the unknown lies within the standard range.
QUESTION 4 6 marks Criterion D
Medium

Claims on “sugar-free” food

A snack labeled “sugar-free” gives a weak positive Benedict’s result after extraction.

a. Give two possible scientific explanations.
[2]
b. Recommend how the claim should be assessed.
[4]
Show complete worked solution
(a)
A small amount of reducing sugar may be present, another reducing substance may interfere, contamination may occur, or “sugar-free” may use a legal threshold rather than absolute zero.
(b)
Repeat with controls and a quantitative calibrated method, test multiple batches, review the legal definition and ingredient processing, and report detection limit and uncertainty before alleging mislabeling.

B2.3 - Enzyme action and specificity 4 questions

QUESTION 1 7 marks Criterion A
Medium
enzyme + substrateenzyme–substrate complexenzyme + products

Enzyme specificity model

Use the enzyme diagram.

a. Explain specificity.
[2]
b. Explain how products form and the enzyme is reused.
[3]
c. State one limitation of a rigid lock-and-key picture.
[2]
Show complete worked solution
(a)
Only substrates with complementary shape and chemical properties bind effectively at the active site.
(b)
Binding forms an enzyme–substrate complex, lowers the reaction’s activation energy, converts substrate to products, and releases products while the enzyme remains available.
(c)
Real active sites are dynamic; binding can induce shape changes and depends on charge and chemical interactions, not outline alone.
QUESTION 2 8 marks Criterion B
Hard

Comparing enzyme substrates

Plan an experiment to compare how rapidly lactase acts on lactose, sucrose and starch.

a. Define the response.
[2]
b. Describe controls and method.
[5]
c. State the expected result.
[1]
Show complete worked solution
(a)
Measure glucose production rate with calibrated glucose strips or a sensor.
(b)
Use equal substrate molar concentrations and volumes, equal lactase concentration, fixed pH and temperature. Sample at short fixed times, stop reaction or read promptly, include no-enzyme and known-glucose controls, repeat and calculate initial gradients.
(c)
Lactose should produce glucose fastest; little or none should form from sucrose or starch because they do not fit lactase appropriately.
QUESTION 3 7 marks Criterion C
Medium

Specificity evidence

Initial rates with enzyme E are: substrate P 4.8, Q 0.2, R 0.0, P plus inhibitor 1.5 mmol min?¹.

a. Identify the likely substrate.
[1]
b. Interpret the Q result cautiously.
[2]
c. Calculate inhibition of P.
[2]
d. State what additional data distinguish competitive inhibition.
[2]
Show complete worked solution
(a)
P is the likely substrate because it gives by far the highest rate.
(b)
Q may react very slowly, contain P contamination, or be near background signal; a no-enzyme blank and repeats are required.
(c)
\[\frac{4.8-1.5}{4.8}\times100=68.8\%\]
(d)
Measure rate across increasing P concentration with and without inhibitor; competitive inhibition is increasingly overcome by high substrate concentration.
QUESTION 4 6 marks Criterion D
Hard

Enzymes in detergent

A detergent adds protease and lipase but may enter rivers after use.

a. Explain the cleaning benefit.
[2]
b. Evaluate environmental responsibility.
[4]
Show complete worked solution
(a)
Protease hydrolyzes protein stains and lipase hydrolyzes fats into smaller, more soluble products at moderate wash temperatures.
(b)
Lower wash temperature can save energy, but enzyme manufacture, aquatic toxicity of the full formulation, biodegradation, dosing and wastewater removal must be assessed. Use concentrated low-dose products, clear allergy guidance and independently measured life-cycle data.

B2.4 - Effects of temperature, pH and concentration on enzymes 4 questions

QUESTION 1 6 marks Criterion A
Hard
temperature / °Cinitial rate / arbitrary unitsoptimum

Temperature-rate curve

Use the graph of enzyme rate against temperature.

a. Explain the rising section.
[2]
b. Explain the rapid fall above the optimum.
[3]
c. Predict the effect of cooling from below the optimum.
[1]
Show complete worked solution
(a)
Higher temperature raises kinetic energy and collision frequency, increasing successful enzyme–substrate interactions.
(b)
Heat disrupts bonds maintaining the enzyme’s tertiary structure, changing the active site so fewer substrates bind; denaturation can be irreversible.
(c)
Rate decreases reversibly because molecular movement and collision frequency fall, but the enzyme is not necessarily denatured.
QUESTION 2 8 marks Criterion B
Hard

Separating pH and temperature

Design an investigation of pH effect on amylase without confounding temperature.

a. Describe the method.
[5]
b. State why buffers are used.
[2]
c. Explain why enzyme and substrate are pre-equilibrated.
[1]
Show complete worked solution
(a)
Use buffer solutions across a pH range, identical starch and amylase concentrations, equal volumes and a constant-temperature water bath. Mix after equilibration, sample at fixed intervals into iodine and determine time until starch is no longer detected. Repeat.
(b)
They maintain the chosen pH despite reaction mixture components.
(c)
The reaction begins at the intended temperature rather than warming during timing.
QUESTION 3 6 marks Criterion C
Hard

Substrate-concentration data

Substrate concentrations 1, 2, 4, 8, 16 mmol dm?³ give rates 0.9, 1.7, 2.9, 4.0, 4.2 units.

a. Describe the relationship.
[2]
b. Explain the plateau.
[2]
c. Predict a change that raises the plateau.
[2]
Show complete worked solution
(a)
Rate increases strongly at low concentration and approaches a plateau between 8 and 16 mmol dm?³.
(b)
Most active sites are occupied most of the time, so enzyme concentration limits rate.
(c)
Increase enzyme concentration while keeping other conditions constant; more active sites allow a higher maximum rate.
QUESTION 4 6 marks Criterion D
Medium

Temperature advice for medicines

A liquid enzyme medicine is stored above its recommended temperature for six hours but still looks normal.

a. Explain why appearance is insufficient.
[2]
b. Recommend a response.
[4]
Show complete worked solution
(a)
Enzyme activity can fall through structural change without a visible color, odor or texture change.
(b)
Use manufacturer stability data for the exact time-temperature exposure and consult a pharmacist rather than testing by sight. Record the excursion and replace the medicine if stability cannot be confirmed; do not generalize from other enzymes.

B2.5 - Planning and evaluating enzyme investigations 4 questions

QUESTION 1 7 marks Criterion A
Medium

Evaluating an enzyme method

A student changes pH by adding different volumes of acid but does not keep total volume constant.

a. Explain the confounding variable.
[2]
b. Give two corrections.
[3]
c. Explain why repeats matter.
[2]
Show complete worked solution
(a)
Adding different acid volumes also changes enzyme and substrate concentrations, so rate differences cannot be attributed only to pH.
(b)
Use equal-volume buffers of known pH and keep final volume constant; verify pH after mixing.
(c)
They reveal random variation and anomalies and permit a mean and uncertainty estimate.
QUESTION 2 8 marks Criterion B
Hard

Designing an immobilized-enzyme test

Plan to compare free lactase with lactase immobilized in alginate beads.

a. Define a fair basis for enzyme amount.
[2]
b. Describe method and response.
[4]
c. Test reusability.
[2]
Show complete worked solution
(a)
Use equal estimated enzyme activity or enzyme mass in both conditions, with an enzyme-free bead control.
(b)
Pass equal lactose solution volumes at fixed concentration, pH, temperature and contact time through each system, measure glucose produced with calibration, repeat and express rate per enzyme amount.
(c)
Run repeated equal batches through recovered beads, wash consistently and plot retained activity by cycle; free enzyme would require a matched fresh or recovery comparison.
QUESTION 3 6 marks Criterion C
Hard

Replicate and anomaly analysis

Rates at pH 7 are 4.8, 4.9, 1.2 and 5.0 units. At pH 5 they are 2.5, 2.7, 2.6 and 2.5.

a. Identify and handle the likely anomaly.
[2]
b. Calculate provisional means excluding the anomaly.
[2]
c. State a justified conclusion.
[2]
Show complete worked solution
(a)
1.2 at pH 7 is inconsistent with the other three. Investigate procedural records and repeat; do not remove it silently.
(b)
\[\bar r_{pH7}=\frac{4.8+4.9+5.0}{3}=4.90\] \[\bar r_{pH5}=\frac{2.5+2.7+2.6+2.5}{4}=2.58\]
(c)
The enzyme is faster at pH 7 in these conditions, but more pH values are required to locate the optimum.
QUESTION 4 6 marks Criterion D
Hard

Industrial enzyme decision

A factory can use free enzyme once or immobilized enzyme repeatedly. Immobilization lowers the initial rate by 20% but allows ten cycles.

a. Explain one biological reason for the lower rate.
[2]
b. Evaluate adoption.
[4]
Show complete worked solution
(a)
Some active sites may be inaccessible or diffusion through the matrix limits substrate contact.
(b)
Repeated use and easier product separation may reduce enzyme input and contamination, despite a slower initial rate. Pilot total product per enzyme mass, retained activity, flow energy, bead manufacture, leakage and product quality across cycles before comparing cost and waste per product unit.