Welcome to Your Practical Guide!
In your Pearson Edexcel International GCSE Science (Single Award) course, you won't just read about science—you will see how it works through prescribed practical investigations. Even though there isn't a separate practical exam, about 20% of the marks in your written papers come from questions about these experiments. This guide breaks down every investigation you need to know for Biology, Chemistry, and Physics. Don't worry if you haven't done all of these in a lab yet; we will walk through them step-by-step!
Note: For more on how to design an experiment from scratch or how to handle data, check out our other chapters on "Experimental design" and "Measurement and graphs."
1. Biology: Investigating Life
Food Tests (Investigating Biological Molecules)
To find out what is in a piece of food, we use specific chemical tests. You need to know these four:
1. Glucose: Add Benedict’s solution and heat in a water bath. If glucose is present, the blue liquid turns brick-red.
2. Starch: Add Iodine solution. If starch is present, the orange-brown liquid turns blue-black.
3. Protein: Add Biuret solution. It turns from blue to purple/violet if protein is there.
4. Fat (Lipids): Mix the food with ethanol, shake it, then pour it into water. A milky-white emulsion shows fat is present.
Enzymes and Temperature
Enzymes are biological catalysts. We investigate how fast they work by changing the temperature.
The Setup: We usually measure how long it takes for an enzyme (like amylase) to break down a substrate (like starch) at different temperatures.
Key Tip: Always use a water bath to keep the temperature steady. If the temperature is too high, the enzyme's active site changes shape—we say it is denatured.
Photosynthesis Investigations
We can prove plants are photosynthesizing by checking for oxygen or starch:
1. Oxygen Evolution: Place a water plant (like Elodea) in water and count the bubbles of oxygen released, or measure the volume of gas collected.
2. Starch Production: We test a leaf for starch to show it has been photosynthesizing. We must first boil the leaf in ethanol to remove the green chlorophyll so we can see the color change when we add iodine.
3. Requirements: By covering part of a leaf (blocking light) or using a variegated leaf (areas without chlorophyll), we can prove that light and chlorophyll are needed for photosynthesis.
Populations in the Wild
How many daisies are in a field? We can't count them all, so we use a quadrat (a square frame).
The Method: Place the quadrat randomly in two different areas. Count the organisms in the quadrat. Repeat this many times to get an average. This makes your results more reliable.
Yeast and Respiration
Yeast can respire without oxygen (anaerobic respiration), producing carbon dioxide and ethanol.
The Investigation: Mix yeast with a sugar solution in a test tube. Use a layer of oil on top to block out oxygen. Connect this to a tube of limewater. The faster the limewater turns cloudy, the faster the yeast is respiring. You can change the temperature or the type of sugar to see how it affects the rate.
Biology Takeaway: Focus on the color changes in food tests and the bubbles in photosynthesis!
2. Chemistry: Investigating Matter
Paper Chromatography
This technique separates mixtures like ink or food coloring.
Important Steps: Draw the baseline in pencil (so the ink doesn't smudge!). Place a spot of the mixture on the line. Dip the bottom of the paper in a solvent (like water), but keep the solvent below the pencil line.
The Calculation: You might be asked to calculate the \(R_f\) value:
\(R_f = \frac{\text{distance moved by the spot}}{\text{distance moved by the solvent front}}\)
Percentage of Oxygen in the Air
Did you know air is about \(21\%\) oxygen? We can prove this by reacting a known volume of air with copper or phosphorus.
How it works: As the metal reacts with oxygen to form an oxide, the oxygen is "used up." The volume of air decreases. By measuring the starting volume and the final volume, you can calculate the percentage of oxygen that was removed.
Energetics: Temperature Changes
Some reactions get hot (exothermic) and some get cold (endothermic).
The Investigation: Mix two substances (like an acid and an alkali for neutralisation, or a salt in water) in a polystyrene cup. The cup acts as an insulator to keep the heat in. Measure the temperature change with a thermometer.
Common Error: Forgetting to put a lid on the cup! The lid stops heat escaping to the air.
Rates of Reaction
How fast does a reaction go? We often use marble chips (calcium carbonate) and hydrochloric acid.
1. Surface Area: Compare large marble chips to small crushed pieces. Smaller pieces have a larger surface area and react faster.
2. Concentration: Use stronger acid to see the rate increase.
Measurement: You can measure how fast gas is produced using a gas syringe or by placing the flask on a mass balance and watching the mass drop as the gas escapes.
Chemistry Takeaway: Remember that \(R_f\) values are always a decimal less than 1. If you get a number bigger than 1, you've flipped the fraction!
3. Physics: Investigating Forces and Waves
Motion of Everyday Objects
To find the speed of a toy car or a tennis ball, you need two things: distance and time.
The Formula: \(\text{average speed} = \frac{\text{distance moved}}{\text{time taken}}\)
The Method: Use a meter ruler for distance and a stopwatch for time. To make it more accurate, use light gates—these remove human reaction time when starting and stopping the clock.
Refraction of Light
When light travels from air into a glass block, it slows down and bends. This is refraction.
The Investigation: Use a ray box to shine a thin beam of light into rectangular blocks, semi-circular blocks, or prisms. Trace the path of the light on paper. Always draw a normal line (a dotted line at \(90^{\circ}\) to the surface) to measure your angle of incidence and angle of refraction.
Magnetic Fields
Magnetic fields are invisible, but we can map them!
1. Iron Filings: Sprinkle them around a bar magnet to see the overall shape of the field.
2. Plotting Compasses: Place a small compass near the magnet, mark the direction it points, and move it along. Joining the marks creates magnetic field lines.
Important: Field lines always go from North to South!
Penetration of Radiation
Different types of radiation can be blocked by different materials. We use a Geiger-Muller (GM) tube to measure the count rate.
1. Alpha (\(\alpha\)): Stopped by a thin sheet of paper.
2. Beta (\(\beta\)): Passes through paper but stopped by a few millimeters of aluminium.
3. Gamma (\(\gamma\)): Most penetrating; reduced by thick lead or concrete.
Safety First: Always handle radioactive sources with tongs and keep them in a lead-lined box when not in use.
Physics Takeaway: In any experiment involving timing, doing repeats and finding an average helps to spot "anomalies" (weird results) and makes your data more reliable.
Quick Review: The "Investigation Checklist"
When you see a question about a practical in the exam, ask yourself:
• Variables: What am I changing (Independent)? What am I measuring (Dependent)? What must I keep the same (Control)?
• Safety: Do I need goggles? Tongs? A heat-proof mat?
• Accuracy: Can I use a more precise tool (like a syringe instead of a measuring cylinder)?
• Reliability: Have I repeated the experiment at least three times?