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: 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)