Practical: Conditions for Germination (Edexcel IGCSE Biology): Revision Note

Practical: Conditions for Germination

• 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: increases enzyme activity and improves germination until a certain temperature

Apparatus

• Test tubes

• Test tube holder

• Cress seeds

• Cotton wool

• Fridge

Method

• Prepare four 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

• The CORMS prompt can be applied when designing a germination investigation

The CORMS prompt

• The CORMS for the above investigation would look something like this:

  • C - 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 - repeat the investigation several times to ensure our results are reliable

  • M1 - measure how many seeds in each test tube germinate

  • M2 - ...after a set time period (eg. 3 days)

  • S - control the temperature for tubes A, B and C, the type of water used (ie. sterile water, which is made by first boiling then cooling water)