o level biology practical 2020 answers

O Level Biology Practical 2020 Answers [top] May 2026

For the 2020 O Level Biology Practical (Paper 3/6093), the exam focused on testing core skills like food tests, enzyme activity, and biological drawings. While specific data depends on the exact specimen you were given in the lab, the following breakdown covers the key questions and expected answers. 1. Investigation of Enzyme Activity (Catalase)

Candidates typically investigated the breakdown of hydrogen peroxide by the enzyme catalase, often using potato extract or yeast.

Key Observation: Effervescence (bubbling) occurs as oxygen is released. Why catalase only breaks down

: Enzymes are specific; the active site of catalase is complementary in shape only to the hydrogen peroxide substrate.

Improving Accuracy: To count bubbles accurately at high concentrations, one could use a gas syringe to measure the exact volume of gas instead of counting by eye.

Planning Question: For a setup testing the effect of pH, you would need to use buffer solutions to maintain specific pH levels while keeping temperature and substrate concentration constant. 2. Food Tests & Glucose Concentration

In some versions of the 2020 paper, students tested "urine" samples for glucose concentration using the Benedict’s test. Time to color change (s) Final Color Estimated Glucose Concentration A Red precipitate High (e.g., 0.62 B Red precipitate Highest (e.g., 0.95 D

Inference: Sample B had the shortest time to change color, indicating the highest concentration of reducing sugar. Common Error: Failing to include units (e.g., ) in table headers. 3. Biological Drawings & Magnification

A drawing task typically involved specimens like flies or testis tubules.

Drawing Standards: Use sharp, continuous lines (no shading). Labels must be on one side with straight leader lines. Magnification Formula:

Magnification=Size of DrawingActual Size of SpecimenMagnification equals the fraction with numerator Size of Drawing and denominator Actual Size of Specimen end-fraction o level biology practical 2020 answers

Calculation Tip: If your drawing measures 30 mm and the actual specimen is 10 mm, the magnification is ×3cross 3 4. Sources of Error and Improvements

Examiners frequently ask for limitations of the experiment performed.

Error: It is difficult to judge the exact moment color changes (subjective).

Improvement: Use a colorimeter for more objective measurement.

Error: Contamination between samples if syringes are not washed.

Improvement: Use separate syringes for each sample or rinse thoroughly with distilled water. Key Skills Checklist

Tables: Ensure the independent variable is in the first column.

Graphs: Use at least 50% of the grid, label axes with units, and mark points with a neat '

Observation: Record what you see (e.g., "blue-black color formed"), not what you know (e.g., "starch is present").

[O Level] 6093/03 Pure Biology Practical Megathread : r/SGExams For the 2020 O Level Biology Practical (Paper

The 2020 O Level Biology Practical (6093/3) focused on food tests, including Benedict’s solution, biological drawings, and comparative studies of flower adaptations. Key experiments involved calculating glucose concentrations and investigating the impact of temperature on membrane permeability in beetroot. For comprehensive recommended answers, visit 2020 O' Levels 6093/3 - Recommended Answers | PDF - Scribd

This exam focused on enzyme activity and food tests, specifically using the Benedict’s test to identify unknown glucose concentrations. Glucose Concentration Investigation:

Procedure: You were required to perform serial dilutions and record the time taken for Benedict's solution to change from blue to a "first sign" of color (e.g., green, yellow, or brick-red).

Data Analysis: Faster color changes indicated higher glucose concentrations. For example, a sample that changed color in 26 seconds was estimated at 0.95 g/dm³, while one taking 42 seconds was lower at 0.45 g/dm³.

Graphing: Expected graphs plotted "Time taken for color change" against "Concentration of glucose". Drawing & Identification:

Specimen Drawing: A transverse section of a lime fruit. Marks were awarded for clear, continuous lines, occupying at least half the provided space, and realistic details like the juicy pulp and green skin.

Magnification: Calculations required measuring the realistic length of the specimen and including proper units (cm/mm). 2. 5090 Alternative to Practical (Paper 6)

Common topics in the 5090 series included the effects of temperature on pigments and plant tissue reactions.

Beetroot Pigment Investigation: You investigated how temperature affects the release of red pigment from beetroot cells. Higher temperatures generally cause more cell membrane damage, leading to a darker red color in the surrounding water.

Enzyme Reactions in Fruits: One version featured banana slices to observe browning caused by enzymes reacting with oxygen when exposed to air. 3. Key Practical Skills & Tips Typical Data (2020 style) | Sucrose (M) |

Independent vs. Dependent Variables: In the 2020 papers, the independent variable was often temperature or concentration, while the dependent variable was time (e.g., time for color change).

Accuracy: Always record time to the nearest second and use a measuring cylinder for precise volumes.

Table Construction: Ensure your table has clear headings with units separated by a slash (e.g., Time / s) and that the independent variable is in the first column.

To refine your study, you can download official mark schemes and examiner reports from platforms like PapaCambridge or Save My Exams.

Note for the author: Because exam boards (Cambridge, Edexcel, OCR, etc.) do not publicly release official mark schemes for all variants of 2020 practicals (and many papers were cancelled/modified due to COVID-19), this post focuses on model answers, common core skills, and data interpretation—which is what students actually need to learn.

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 |

4. Microscopy & Drawing (e.g., onion epidermal cells or leaf cross-section)

2020 marking scheme expectations:

  • Drawing rules: Single, clear outline; no shading; label lines with ruler; title and magnification.
  • Typical labels: Cell wall, nucleus, cytoplasm, vacuole (onion). For leaf: cuticle, palisade mesophyll, stomata, guard cells.

Calculation of magnification:
[ \textMagnification = \frac\textDrawn length\textActual length ] (e.g., if actual cell = 0.1 mm and drawing = 20 mm → magnification = ×200)

Section A: Food Tests (Likely Q1)

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.