O Level Biology Practical 2020 Answers [verified]

The 2020 Singapore-Cambridge O-Level Pure Biology (6093/03) practical exam primarily focused on food tests for glucose in "urine" samples and biological drawings of citrus fruits. Question 1: Glucose Concentration in "Urine"

In this experiment, candidates used Benedict's solution to determine the glucose concentration in five unknown "urine" samples (A–E). Key Results:

Sample B: Contained the highest glucose concentration (~0.95 ), showing the fastest time to change colour (approx. 26s). Sample D: Contained no glucose ( ), remaining blue even after 120s of heating. Samples A & E: Had identical concentrations (~0.62 ) and similar reaction times (approx. 34s). Accuracy Improvements:

Use a thermostatically controlled water bath to maintain a constant temperature, as cooling water affects reaction rates.

Ensure constant volumes of Benedict's solution and urine sample across all tubes. Read syringes at eye level to avoid parallax error. Question 2: Biological Drawing & Measurement

Candidates were required to observe and draw a transverse section (T.S.) of a lime fruit. Drawing Criteria:

Proportion: Must show the relative thickness of the green fruit skin (exocarp) vs. the white tissue (mesocarp).

Details: Include at least one sector showing the "juicy pulp" (juice sacs). o level biology practical 2020 answers

Quality: Use clean, continuous, free-hand lines (no shading or sketching). Magnification Calculation: Measure the diameter of the drawing ( ) and the actual specimen ( Formula: Marking Tips for Practical Papers

Table Formatting: The Independent Variable (e.g., Urine Sample) must be in the leftmost column. Headers must include units (e.g., /s or /g dm-3d m to the negative 3 power ) after a solidus.

Graphing: Points should be marked with a small 'x'. The line of best fit should be a smooth curve or a series of straight lines joining the points, depending on the trend.

Answering "Explain" Questions: Always link biological observations to concepts like enzyme-substrate complexes or active site denaturation if temperature or pH is involved.

2020 O-Level Biology Practical Guide | PDF | Flowers - Scribd

The 2020 O Level Biology Practical (Syllabus 5090 and 6093) centered on testing students' ability to execute experimental procedures, record precise observations, and interpret biological data. Key experiments included investigating glucose concentration in "urine" samples and analyzing the transverse section of a lime fruit. 2020 Practical Paper Highlights & Answers

The examination was divided into investigative tasks that required both manual dexterity and theoretical application. Question 1: Glucose Concentration Analysis 2020 Follow-up Question (Control experiment)

In this experiment, students were tasked with estimating the concentration of glucose in five different samples (labeled A-E) representing "urine."

Methodology: Students used the Benedict’s test, recording the time taken for the first color change to occur. Sample Results:

Sample B typically showed the shortest time (e.g., 26 seconds), indicating the highest glucose concentration (approx.

Sample D often remained blue or took over 120 seconds, representing a concentration of

Key Table Requirements: Answers had to include correct headings (e.g., "Time taken for color change / s") and consistent units. Question 2: Biological Drawing and Magnification

This section focused on the Transverse Section (T.S.) of a lime fruit.

Drawing Criteria: Successful diagrams occupied at least half the provided space, used clean, continuous lines (no shading), and correctly detailed the juicy pulp and sectors. What control would you use to prove the

Calculation: Students calculated the magnification using the formula:

Magnification=Length of drawingLength of actual specimenMagnification equals the fraction with numerator Length of drawing and denominator Length of actual specimen end-fraction Answers were expected to be given to 2 significant figures.

2020 O-Level Biology Practical Guide | PDF | Flowers - Scribd

2020 Follow-up Question (Control experiment)

What control would you use to prove the reaction is due to the enzyme?

Model answer: Use boiled potato extract (or water instead of potato). No bubbles → confirms enzyme was denatured.

8. Pedagogical Recommendations (Actionable)

Curriculum-aligned practical program: Weekly short practicals plus termly full practical assessments mirroring exam formats.
Standardized skill checklists: Instrument use, observation recording, graphing, microscopy, and safety.
Mark scheme workshops: Regular student practice with official mark-scheme rubrics and annotated exemplar answers.
Emphasize replication and uncertainty: Teach taking repeats, calculating averages, and briefly discussing sources of error.
Low-stakes timed practice: Simulate exam timing for drawing, calculation, and explanation tasks to build fluency.
Concept-practice integration: Pair conceptual mini-quizzes with each lab to address misconceptions revealed by practicals.

Typical Data (2020 style)

| Sucrose (M) | Final length (mm) | Change (mm) | | :--- | :--- | :--- | | 0.0 | +3 | Increase | | 0.2 | +1 | Increase | | 0.4 | 0 | No change | | 0.6 | -2 | Decrease | | 0.8 | -4 | Decrease |

Expected Answer (Marking Grid – 6 points):

Critical 2020 note: Simply writing "repeat to get average" without stating what you average (bubble count) lost a mark. Be specific.

7. Equity and Accessibility Considerations

Some tasks favor students with prior hands-on exposure or access to lab equipment outside school.
Time pressure: practical questions that require detailed diagrams or calculations under timed conditions disadvantage slower writers.
Recommendation: ensure equitable access to practice equipment and teach time-management strategies for exams.