Question 1 Medium
Three reaction times are 0.20 s, 0.24 s and 0.22 s. Calculate the mean.
Show answer
Answer: 0.22 s
- Add: 0.20 + 0.24 + 0.22 = 0.66.
- 0.66 ÷ 3 = 0.22 s.
Required practicals and working scientifically in biology: GCSE Combined Science Biology practice questions
A second set of questions on required practicals and working scientifically in biology. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
More questions
Question 2 Medium
In the amylase practical the iodine stays orange-brown. What does this show about the starch?
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Answer: it has all been broken down
- Iodine only goes blue-black with starch.
- So there is no starch left.
Question 3 Hard
A pondweed gives off 12 bubbles a minute with the lamp 10 cm away. The lamp is moved to 20 cm. By what factor does the light intensity fall?
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Answer: 4
- Intensity is proportional to 1 ÷ d².
- Doubling the distance makes the light intensity one quarter.
Question 4 Hard
Why is a water bath placed between the lamp and the pondweed?
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Answer: to keep the temperature constant
- The lamp gives out heat as well as light.
- The water bath stops the temperature changing.
Question 5 Hard
Why is soda lime used in a respirometer?
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Answer: it absorbs carbon dioxide
- Seeds release carbon dioxide as well as using oxygen.
- Soda lime absorbs the carbon dioxide so that only the oxygen use changes the volume.
Question 6 Hard
In the DNA extraction from fruit, what is the job of the detergent?
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Answer: to break open the cell membranes
- DNA is inside the nucleus inside the cell.
- The detergent breaks open the membranes.
Question 7 Hard
A cell is 0.2 mm long. A drawing of it is 40 mm long. Calculate the magnification.
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Answer: 200
- Magnification = image size ÷ real size.
- 40 ÷ 0.2 = 200.
Question 8 Hard
Convert 0.2 mm to micrometres (µm).
Show answer
Answer: 200 µm
- 1 mm = 1000 µm.
- 0.2 × 1000 = 200 µm.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is the independent variable?
Show answer
The variable you change.
Check 2
What is the dependent variable?
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The variable you measure.
Check 3
What do you do with an anomalous result?
Show answer
Leave it out when you work out the mean.
Check 4
What is the test for starch?
Show answer
Add iodine solution. It turns from orange-brown to blue-black.
Check 5
What is the test for reducing sugars?
Show answer
Add Benedict's solution and heat. Blue changes to green, yellow, orange or brick-red.
Check 6
What is the test for protein?
Show answer
Add Biuret reagent. Blue changes to purple.
Check 7
What is the test for lipids?
Show answer
Shake with ethanol and add water. A cloudy white emulsion forms. Sudan III stains the lipid layer red.
Check 8
How do you stop air bubbles under a coverslip?
Show answer
Lower the coverslip at an angle with a mounted needle.
Check 9
Which objective lens do you start with on a microscope?
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The lowest power lens.
Check 10
What is the formula for magnification?
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Magnification = image size ÷ real size.
Check 11
What are the rules for a biological drawing?
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Sharp pencil, clear single lines, no shading, label lines that do not cross, a title and the magnification.
Check 12
In the amylase practical, what does iodine tell you?
Show answer
Blue-black means starch is still present. Orange-brown means it has all gone.
Check 13
How do you calculate the rate in the amylase practical?
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Rate = 1000 ÷ time in seconds.
Check 14
Why do you use buffer solutions in the amylase practical?
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To keep the pH fixed at a known value.
Check 15
Why are potato cylinders blotted dry before weighing?
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Surface water would add to the mass.
Check 16
What is the formula for percentage change?
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(final − initial) ÷ initial × 100.
Check 17
What does a potato cylinder gaining mass show?
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Water moved into it by osmosis, because the solution was more dilute than the potato.
Check 18
What does the point where the osmosis graph crosses zero show?
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There is no net water movement, so the solution matches the potato cell contents.
Check 19
Why is sodium hydrogencarbonate added to the pondweed water?
Show answer
It supplies carbon dioxide for photosynthesis.
Check 20
Why is a water bath placed between the lamp and the pondweed?
Show answer
To stop the heat from the lamp changing the temperature.
Check 21
How is light intensity related to distance?
Show answer
It is proportional to 1 ÷ distance², so it falls quickly as the distance grows.
Check 22
Why is soda lime used in a respirometer?
Show answer
It absorbs carbon dioxide, so the volume change is due to the oxygen used.
Check 23
What control is used in a respirometer?
Show answer
A tube with dead (boiled) seeds.
Check 24
What are the steps for extracting DNA from fruit?
Show answer
Mash, add detergent and salt, filter, then add ice-cold ethanol so DNA forms white strands.
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