Practical: Conditions for Germination (Edexcel IGCSE Biology: Double Science)

• Germination marks the beginning of seed growth
• Three key factors are needed for successful germination:
  • Water: swells the seed, breaks the seed coat, and activates enzymes for growth
  • Oxygen: necessary for respiration to provide energy
  • Warmth: boosts enzyme activity and improves germination until a certain temperature
• Carbon dioxide has no effect on germination

Apparatus

• Test tubes
• Test tube holder
• Cress seeds
• Cotton wool
• Fridge

Method

• Prepare 4 test tubes with 10 cress seeds on cotton wool, labeled A, B, C, and D
  • Tube A: Keep the cotton wool dry
  • Tube B: Moisten the cotton wool with water
  • Tube C: Cover the seeds and cotton wool with water and add a layer of oil on top
  • Tube D: Moisten the cotton wool and place the tube in a fridge (~4°C)
• Keep tubes A, B, and C at room temperature or around 20°C
• After 3-5 days, ensure the cotton wool in tubes B and D stays moist
• Compare the number of germinated seeds in each tube

Conditions required for germination: how to set up the experiment

Results and Analysis

• The test tubes are set up to test the necessity of water, oxygen, and warmth for germination by removing each factor in turn:

  • Tube A: Water is absent
  • Tube B: Control, all factors present
  • Tube C: Oxygen is blocked by oil and water layers
  • Tube D: Warmth is removed by refrigeration
• As germination requires all three factors, only the seeds in the control tube (B) are expected to germinate

Conditions required for germination: Example results table

Applying CORMS to practical work

• When working with practical investigations, remember to consider your CORMS evaluation

CORMS evaluation

• In this investigation, your evaluation should look something like this:
  • C - We are changing the abiotic conditions in which the seeds are germinating
  • O - The cress seeds will all be taken from the same parent plant (or at least from the same species of cress plant)
  • R - We will repeat the investigation several times to ensure our results are reliable
  • M1 - We will record how many seeds in each test tube germinate
  • M2 - ...after a set time period (e.g. 3 days)
  • S - We will control the temperature for tubes A, B and C. We will also control the type of water used (i.e. sterile water, which is made by first boiling then cooling water)