IGCSE Biology practicals guide (0610)
The food test results and the standard investigations in one place: what you do, what you change, what you measure, and the wording that earns the marks. Use it alongside the Biology revision notes.
Food tests
Learn the positive and the negative result for every test. A negative result is not a failed test. For solid foods, crush the food and mix it with water first. Notes: Biological Molecules.
| Test | Detects | Positive result | Negative result |
|---|---|---|---|
| Iodine solution | Starch | Yellow-brown to blue-black | Stays yellow-brown |
| Benedict’s solution (heat in a hot water bath) | Reducing sugar | Blue through green, yellow and orange to brick-red | Stays blue |
| Biuret solution | Protein | Blue to purple (mauve) | Stays blue |
| Ethanol emulsion (dissolve in ethanol, then pour into water) | Fat or oil | Cloudy white emulsion | Stays clear |
| DCPIP (add the sample drop by drop) | Vitamin C | Blue goes colourless | Stays blue |
- Sucrose (table sugar) is not a reducing sugar. It stays blue with Benedict’s unless it is first broken down.
- For the ethanol emulsion test, the cloudy white emulsion appears only after the water is added.
- For DCPIP, write “decolourised” or “goes colourless”. The fewer drops of juice needed to decolourise it, the more vitamin C the juice contains.
Enzyme activity: amylase and catalase
Notes: Enzymes
Method
- Amylase and starch: warm the amylase and the starch solution separately in a water bath at a set temperature, then mix them.
- Every 30 seconds, put a drop of the mixture on a spotting tile and add a drop of iodine solution. While starch remains the drop turns blue-black.
- Record the time at which the iodine stops turning blue-black and stays yellow-brown: the starch has been broken down.
- Catalase and hydrogen peroxide: add catalase (for example from liver or potato) to hydrogen peroxide. Measure the volume of oxygen collected in a set time, or the height of foam formed if a drop of washing-up liquid is added.
Variables
| Change (independent) | Temperature, using water baths at different temperatures (or pH, using buffer solutions) |
|---|---|
| Measure (dependent) | Time for starch to disappear (amylase) or volume of oxygen (catalase) |
| Keep the same | Volume and concentration of enzyme and substrate; pH when temperature is changed, temperature when pH is changed |
Exam tips
- Name the variable you change, the variable you measure, and at least two you keep the same. Examiners look for all three.
- Repeat each condition and calculate a mean.
- A boiled-enzyme control gives no reaction because the enzyme is denatured. This shows the change is caused by the working enzyme.
- Quote values from the table or graph when describing a trend, with units. “It goes up then down” is not enough.
Diffusion
Notes: Movement into and out of Cells
Method
- To test temperature, drop the same amount of coloured dye into equal volumes of water at different temperatures.
- Time how long the colour takes to spread through the water.
- To test surface area or distance, use agar cubes of different sizes that contain an indicator, and time how long the colour change takes to reach the middle.
Variables
| Change (independent) | Temperature (or the size of the agar cube) |
|---|---|
| Measure (dependent) | Time for the colour to spread or reach the middle |
| Keep the same | Volume of water and amount of dye |
Exam tips
- Repeat to check results.
- Give the factor, the direction of change and the reason: a higher temperature speeds diffusion because the particles have more kinetic energy and move faster.
Osmosis in potato chips
Notes: Movement into and out of Cells
Method
- Cut equal potato chips and weigh each one.
- Place one chip in each of several sugar solutions, including pure water.
- After a set time, blot each chip dry and weigh it again.
- A chip that gains mass has taken water in by osmosis. A chip that loses mass has lost water to a more concentrated solution.
Variables
| Change (independent) | Concentration of the sugar solution |
|---|---|
| Measure (dependent) | Change in mass of the chip |
| Keep the same | Size of the chips and the time left in the solution |
Exam tips
- Percentage change in mass = (final mass − starting mass) ÷ starting mass × 100. A negative value means a loss in mass.
- Quote the data: write the starting and finishing values, not just “it went up”.
- On a graph of change in mass against concentration, the line crosses zero where the solution is about as concentrated as the cell contents, so there is no net movement of water.
- Osmosis is the movement of water only. Writing that “sugar moves” or “the solution moves” loses the mark.
Photosynthesis: the starch test and the rate of photosynthesis
Notes: Plant Nutrition
Method
- Testing a leaf for starch: leave the plant in the dark for a day or two so its leaves use up their starch. After the experiment, test a leaf.
- Boil the leaf in water to kill it.
- Warm it in ethanol in a hot water bath to remove the chlorophyll.
- Rinse it in water, then add iodine solution. Blue-black shows that starch is present.
- Rate of photosynthesis: place pondweed in water containing a little sodium hydrogencarbonate under a funnel, with a lamp at a measured distance. Count the bubbles of oxygen released in a set time.
Variables
| Change (independent) | Lamp distance (light intensity) |
|---|---|
| Measure (dependent) | Number of oxygen bubbles in a set time |
| Keep the same | The other factors, such as temperature and the amount of sodium hydrogencarbonate |
Exam tips
- Repeat each condition and calculate a mean.
- Extended: while light is the limiting factor the rate rises as light increases. When the line levels off, light is no longer limiting, and carbon dioxide or temperature is.
Transport in plants: the stain and the rate of transpiration
Notes: Transport in Plants
Method
- Pathway of water: stand a stem, such as celery or a white flower, in water containing a coloured stain and leave it for some hours.
- Cut across the stem, or along it, and look at the cut surface. The stain appears only in the xylem, and in the veins of the leaves.
- Rate of transpiration: fix a leafy shoot into the potometer and note the position of the bubble. After a set time measure how far it has moved.
- To test temperature, repeat in places at different air temperatures. To test wind speed, put a fan at different distances.
Variables
| Change (independent) | Air temperature or wind speed |
|---|---|
| Measure (dependent) | Distance the bubble moves in a set time |
| Keep the same | The other factors, and the time |
Exam tips
- Higher temperature and faster wind speed increase the rate of transpiration. Higher humidity decreases it.
- Say “water vapour”, not “water”: transpiration is loss as a gas.
- The stain shows where the water travels, but only the xylem becomes coloured.
Exercise: breathing rate, heart rate and limewater
Notes: Gas Exchange in Humans
Method
- Breathing: count the number of breaths in one minute at rest, and estimate the depth of each breath, for example by the chest movement.
- Take exercise for a set time, then count again straight afterwards and at regular intervals until the rate returns to its resting value.
- Heart rate: count the pulse for a set time at rest. Take exercise, such as stepping or jogging, for a fixed time, then count the pulse straight afterwards and at regular intervals until it returns to the resting value.
- Limewater: breathe in through one tube and out through another, each leading into limewater. The limewater through which expired air passes turns milky quickly. With inspired air it stays clear for much longer.
Variables
| Change (independent) | Rest or exercise |
|---|---|
| Measure (dependent) | Breaths or pulse beats per minute; how quickly limewater turns milky |
| Keep the same | The person, the time and the type of exercise in each trial |
Exam tips
- Repeat to find a mean.
- Heart rate increases during exercise and takes time to recover.
- Limewater is a test for carbon dioxide. Expired air has more carbon dioxide than inspired air.
Tropisms
Notes: Hormones, Homeostasis and Tropisms
Method
- Phototropism: grow identical seedlings in a box with light coming from one side only, and compare them with seedlings that receive light from all sides.
- Gravitropism: place seedlings on their side in the dark, so that light cannot affect them.
- Record the direction of growth of the shoots and roots after a few days.
Variables
| Change (independent) | The direction of the light (or gravity, with light removed) |
|---|---|
| Measure (dependent) | Direction of growth of shoots and roots |
| Keep the same | The seedlings, which must be identical |
Exam tips
- Keeping the seedlings in the dark removes light as a second stimulus, so any bending is due to gravity.
Questions
What practical work is in IGCSE Biology 0610?
This guide covers the standard investigations in the Glide Biology notes: food tests, enzyme activity, diffusion, osmosis, photosynthesis, transport in plants, exercise and tropisms. Check your own syllabus for the full list your teacher expects you to know.
How do I describe a food test in an exam?
Give the reagent, any step needed (such as heating Benedict’s solution in a hot water bath), and both colours: the starting colour and the colour at the end. “It changes colour” earns nothing.
What makes an investigation a fair test?
Change one factor only and keep the others the same. If two things change, you cannot tell which caused the result.
Practise on real questions: every Biology past paper comes with its mark scheme. For how to word your answers, see the command words guide.
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