Biology - 11 Hormonal Coordination - Required Practical 8: Plant Responses

Aims:

  • investigate the effect of light or gravity on the growth of newly germinated seedlings

Risk Assessment:

Safety:

Equipment:

Light:

  • 3 petri dishes

  • 30 seeds (mustard or cress)

  • cotton wool

  • water

  • ruler

Gravity:

  • petri dish

  • 4 seeds (mustard or cress)

  • cotton wool

  • water

Control variables:

Light:

  • volume of water in cotton wool at start

  • volume of water added per day

  • type of seed

  • number of seeds placed in petri dish

  • number of seedlings at beginning of experiment

  • how long each set of seedlings is left

  • the surrounding temperature of each petri dish

Gravity:

  • volume of water in cotton wool at start

  • type of seed

  • light intensity on seed

Independent variable:

Light:

  • light intensity of seedlings

Gravity:

  • vertical orientation of seedlings

Dependent variable:

Light:

  • mean height of seedlings

Gravity:

  • direction of shoots and roots

Method:

Light:

  1. Prepare 3 petri dishes by adding a layer of cotton wool to each and soaking with the same volume of water. Add, to each, 10 seeds, evenly spaced, and allow to germinate in a warm place for 2 days, watering each with the same volume of water each day

  2. Remove excess seedlings from dishes so that each dish has the same number as the dish with the least

  3. Using a ruler, measure and record the height of each seedling (and find a mean for each dish)

  4. Place the seedlings each in different conditions:

    1. In full sunlight

    2. In partial light

    3. In full darkness

  5. Using a ruler, measure and record the height of each seedling each day for at least 5 days (and find a mean each day for each dish)

Gravity:

  1. Prepare a petri dish by adding a layer of cotton wool and soaking with water. Add 4 seeds, each in a different orientation:

    1. Upside down

    2. Right side up

    3. On left

    4. On right

  2. Cover with a lid, leaving space for air flow. Stand the petri dish up on its side and leave in a sunlit area for 3-5 days

  3. Observe the direction of growth of roots and shoots for each seed

Calculations/graphing: