O Level Biology Practical 2020 Answers

The 2020 O Level Biology practical assessments (specifically for the Cambridge 5090 syllabus) focused on two main experimental areas: pigment release from beetroot growth of seedlings in different light conditions.

Below is a summary of the core practical findings and answers based on the official Mark Schemes Examiner Reports for that year. Paper 31 & 32 (Practical Test) 1. Pigment Release Experiment (Beetroot)

Candidates investigated how temperature affects the leakage of red pigment through the cell membranes of beetroot cylinders. Observation

: As temperature increases, the surrounding water becomes a darker red. Conclusion

: Higher temperatures damage the cell membrane (denaturing membrane proteins), making it more permeable and allowing more pigment to leak out. Controlled Variables

: Volume of water, surface area/length of beetroot cylinders (e.g., 30 mm), and time of immersion. PastPapers.Co 2. Seedling Growth in Light vs. Dark

This task required observing 15 seedlings grown in light and 15 grown in the dark. Stem Length

: Seedlings grown in the dark were typically longer (etiolation) as they "stretch" to find a light source. Leaf Appearance Light-grown : Large, green leaves (due to chlorophyll development). Dark-grown : Small, yellowish/pale leaves. Paper 61 & 62 (Alternative to Practical)

Since many students could not take physical exams in June 2020 due to the pandemic, Paper 6 focused on analyzing data and planning. TeachifyMe Enzyme Activity

: Analyzing catalase activity by counting oxygen bubbles from hydrogen peroxide. Improvement

: Use a gas syringe or a graduated cylinder to measure volume for better accuracy than counting bubbles. Genetic Diagrams

: Expected results for F2 generation fly crosses, often involving phenotypic ratios like 3:1 for dominant/recessive traits. Magnification Calculations

: A common requirement was to calculate the actual size of a specimen (e.g., a testis tubule or leaf) using the formula: Summary of Results for Singapore SEAB 6093/03

For students following the Singapore SEAB O Level (6093) syllabus, the 2020 practical included: Urine Glucose Testing

: Using Benedict's solution to identify glucose concentrations in "urine" samples. Citrus Fruit Analysis

: Making a transverse section drawing of a lime fruit and identifying differences between 2020 O' Levels 6093/3 - Recommended Answers | PDF - 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

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. o level biology practical 2020 answers

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

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

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 The 2020 O Level Biology practical assessments (specifically

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

The 2020 O Level Biology Practical (Syllabus 6093/03 for Singapore and 5090/31 for Cambridge) featured experiments focused on enzyme activity, nutrient testing, and observational drawing. 2020 Pure Biology (6093/03) Practical Key Topics & Answers

According to the 6093/03 Practical Megathread, the paper focused on glucose concentration in "urine" samples and catalase activity in fruit. Question 1: Glucose Testing (Benedict’s Test)

Goal: Determine the concentration of glucose in five "urine" samples (A–E).

Observations: Final colours typically ranged from blue (Sample D, 0 g/dm³) to brick-red (Sample B, highest concentration/shortest time).

Data Presentation: Candidates were required to draw a table with clear headings (e.g., Urine sample, Time taken for colour change / s, Final colour) and plot a bar graph of concentration against sample.

Experimental Variables: The independent variable was the urine sample/glucose concentration; the dependent variable was the time taken for the first colour change. Question 2: Catalase Activity & Fruit Observations

Goal: Compare catalase enzyme activity in different fruits (e.g., banana, pineapple) and perform biological drawings.

Key Takeaways: Results generally showed that pineapple had the highest enzyme activity (most bubbles), while banana had little to no activity.

Drawing: Candidates were asked to provide a line drawing of 5 tubules of a testes and calculate actual diameter using magnification. 2020 Cambridge O Level (5090/31) Practical Key Topics

The 5090/31 May/June 2020 Question Paper focused on cell membrane permeability and temperature.

Beetroot Experiment: Candidates investigated the effect of temperature on the release of red pigment from beetroot tissue.

Method: Placing beetroot cylinders in water baths at 40°C, 60°C, and 80°C.

Expected Results: Higher temperatures damage cell membranes more extensively, leading to a darker red solution as more pigment leaks out. General Practical Guidelines

Drawing: Always use a sharp HB pencil. Drawings must be larger than half the provided space with no shading.

Tables: Ensure all raw data is recorded to the same degree of precision (e.g., all times to the nearest second).

Safety & Improvements: Common improvements include using a thermostatically controlled water bath for better temperature control.

Detailed mark schemes for these papers are available on platforms like Save My Exams and Scribd. 2020 O' Levels 6093/3 - Recommended Answers | PDF - Scribd

Practical 1: Measurement of the Growth of Radish Seeds

Aim: To investigate the effect of light on the growth of radish seeds.

Materials:

• Radish seeds
• Soil
• Containers with lids (e.g., petri dishes or pots)
• Ruler
• Pencil
• Light source (e.g., lamp or sunlight)

Procedure:

1. Fill the containers with soil, leaving about 1 cm at the top for watering.
2. Plant 5-6 radish seeds about 1-2 mm deep in each container.
3. Water the seeds gently.
4. Place one container in a light source (e.g., under a lamp or in sunlight) and another container in a dark place (e.g., covered with a lid or in a cupboard).
5. Measure and record the initial length of the seedlings (or the distance from the soil surface to the tip of the seedling).
6. Measure and record the length of the seedlings at regular intervals (e.g., daily) for 5-7 days.
7. Plot a graph of seedling length against time for both light and dark conditions.

Results:

| Day | Light Condition | Seedling Length (mm) | Dark Condition | Seedling Length (mm) | | --- | --- | --- | --- | --- | | 0 | Light | 0 | Dark | 0 | | 1 | Light | 2 | Dark | 1 | | 2 | Light | 5 | Dark | 2 | | 3 | Light | 8 | Dark | 3 | | 4 | Light | 12 | Dark | 5 | | 5 | Light | 15 | Dark | 7 | | 6 | Light | 18 | Dark | 9 | Radish seeds Soil Containers with lids (e

Discussion:

• The seedlings in the light condition grew faster and longer than those in the dark condition.
• This is because light is essential for photosynthesis, which provides energy for growth and development.
• In the absence of light, seedlings undergo etiolated growth, characterized by weak and spindly stems.

Conclusion:

• Light is essential for the growth and development of radish seeds.

Practical 2: Investigation of the Effect of pH on the Activity of Amylase

Aim: To investigate the effect of pH on the activity of amylase.

Materials:

• Amylase powder
• Starch solution (1%)
• pH buffer solutions (e.g., pH 4, 5, 6, 7, 8)
• Iodine solution
• Benedict's solution
• Boiling water bath

Procedure:

1. Prepare 5-6 test tubes with different pH buffer solutions (e.g., pH 4, 5, 6, 7, 8).
2. Add 1-2 drops of amylase powder to each test tube.
3. Add 1-2 ml of starch solution to each test tube.
4. Incubate the test tubes in a boiling water bath for 5-10 minutes.
5. Add 1-2 drops of iodine solution to each test tube.
6. Observe the color change and record the results.

Results:

| pH | Color Change | Amylase Activity | | --- | --- | --- | | 4 | Blue-black | Low | | 5 | Purple | Moderate | | 6 | Brown | High | | 7 | Yellow-brick red | Very high | | 8 | Yellow-brick red | Very high |

Discussion:

• The optimal pH for amylase activity is around pH 7.
• Amylase activity decreases at lower and higher pH values.

Conclusion:

• Amylase activity is pH-dependent, with optimal activity at pH 7.

Practical 3: Observation of Mitosis in Root Tips

Aim: To observe mitosis in root tips.

Materials:

• Root tips (e.g., from onion or garlic)
• Aceto-orcein stain
• Microscope
• Slides and coverslips

Procedure:

1. Prepare the root tips by cutting them into small pieces.
2. Stain the root tips with aceto-orcein stain.
3. Place a stained root tip on a slide and cover with a coverslip.
4. Observe the root tip cells under a microscope.
5. Identify and record the different stages of mitosis.

Results:

• Different stages of mitosis can be observed, including:
  • Interphase
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

Discussion:

• Mitosis is the process of cell division that results in two daughter cells with the same number of chromosomes as the parent cell.
• The different stages of mitosis can be observed in root tip cells.

Conclusion:

• Mitosis can be observed in root tip cells using aceto-orcein stain and a microscope.

These write-ups are just a sample and may not reflect the exact questions and experiments in your O-Level Biology Practical 2020. However, they should give you an idea of how to approach and answer practical questions. Make sure to follow the instructions and guidelines provided by your teacher or the exam board. Good luck with your 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.

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Part 6: Common Errors Students Made in the 2020 Paper

Based on examiner feedback, here are the top 3 errors that lost marks:

1. Mixing up reagents: Writing "add iodine to test for protein." This is the #1 memory slip.
2. Unlabeled axes: On graph questions, missing "Time (s)" on X-axis or "Mass change (g)" on Y-axis.
3. Table construction: For results tables, the independent variable must go in the first column (left), and repeated trials/mean in subsequent columns. Many wrote it sideways.

Part 2: Osmosis & Plasmolysis (Variant 32 & 34 – 2020)

One of the most common 2020 practicals involved placing onion epidermal cells or potato strips into salt/sugar solutions of varying concentrations.

Expected Answers for Spotting Tests:

Question Example: Describe the procedure and result for testing solution B for reducing sugar.

Model Answer (4-5 marks):

1. Add 2 cm³ of Benedict’s solution to 2 cm³ of solution B.
2. Shake the mixture.
3. Place the test tube in a boiling water bath for 5 minutes.
4. Positive result: A brick-red/orange precipitate forms.
5. Negative result: Solution remains blue.

Examiner’s trap in 2020: Many wrote "turns blue-black." That is for starch (iodine). No points were awarded for "turns yellow" – that is for non-reducing sugars after hydrolysis.

Common Drawing Question

“Make a large, labelled drawing of the region indicated.”

2020 Mark scheme keywords:

• Large – at least half the space provided.
• Clear single lines (no sketching or double lines).
• Proportions – relative sizes of tissues must be realistic.
• Labels with leader lines touching the structure (no arrows crossing).
• Title (e.g., “T.S. of dicot stem – low power”).

Question 1: Microscopy

• Describe the procedure for preparing and observing cells under a microscope:
  1. Prepare a slide with a sample of cells (e.g., onion epidermal cells).
  2. Focus the microscope and observe the cells at different magnifications.
  3. Record observations and draw diagrams.