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5.3.7Unit 5: Respiration, Internal Environment, Coordination and Gene Technology

Core Practical 12: Effect of Temperature on Development — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 6 parts Lesson 31 of 36 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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Part 1 of 5Seedling Method

1
Plant seeds of the same variety in pots or trays of compost, and grow them under identical conditions until germination.
2
Measure the initial height of each seedling, using the same method each time.
3
Place the trays in incubators at different temperatures for the same period, for example five days.
4
Keep soil moisture, pH and light intensity the same in every tray.
5
Measure final heights and calculate the mean growth rate: mean increase in height ÷ number of days.

Part 2 of 5Brine Shrimp Method

Brine Shrimp Method
Set-up
  • Set-up Place an equal number of eggs, for example 40, in non-chlorinated salt water in water baths at different temperatures.
Controls
  • Controls Keep the age of eggs, salt concentration, volume of water and oxygen supply the same in every water bath.
Recording
  • Recording Count the number of eggs that have hatched at regular intervals, such as every 12 hours.
Rate
  • Rate Hatching rate = number hatched ÷ time in hours.

Part 3 of 5Reliability, Safety and Ethics

Repeats
  • Repeats Repeat each temperature several times and calculate a mean to reduce the effect of anomalies.
Typical result
  • Typical result Rate often rises with temperature to an optimum and then falls, probably because enzymes denature.
Welfare
  • Welfare Handle shrimps gently, return them to a suitable habitat afterwards, and avoid dangerously high temperatures.
Lamp
  • Lamp Any lamp used to see hatchlings should be switched off when not needed, to avoid heating the water.

Part 4 of 5Worked Example

Question

  • Seedlings at 25 °C had a mean height of 2.4 cm at the start and 7.8 cm after 5 days.
  • Calculate the mean growth rate.

  1. Find the increase7.8 − 2.4 = 5.4 cm.
  2. Divide by the time5.4 ÷ 5 days.
  3. Give the unit as cm per day.

Answer 1.08 cm per day.

Part 5 of 5Exam Checklist & Tips

5.3.7 – Key Points for the Exam

  • Independent variable The factor deliberately changed by the investigator.
  • Dependent variable The factor that is measured as a result.
  • Control variable A factor kept constant so that it does not affect the result.
  • Germination The start of growth of a seed into a seedling.

Common Mistakes

  • Allowing light or water to vary between trays, which means temperature is not the only difference.
  • Stating hatching as a total rather than as a rate, which makes different time periods impossible to compare.
  • Using only one sample at each temperature, so that one unusual result cannot be recognised.
  • Forgetting animal welfare when using living organisms, such as returning shrimps to suitable water.

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