5.4.5

Required Practical - Light or Gravity on Seedlings

Test yourself

Investigating The Effect of Light or Gravity on Seedling Growth

The aim of this experiment is to explore how environmental factors such as light or gravity influence the direction and rate of growth in newly germinated seedlings.

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Apparatus and materials

  • 3 Petri dishes
  • Cotton wool
  • Pipette or dropper
  • Ruler (millimetre scale)
  • 30 seeds (mustard or cress work well)
  • Forceps
  • Labels or a marker pen
  • Warm, safe place for incubation
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Independent and dependent variables

  • Independent variable:
    • Light conditions (full light, partial light, complete darkness).
  • Dependent variable:
    • Average (mean) height of seedlings after several days.
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Control variables

  • Control variables:
    • Number of seeds per dish
    • Temperature
    • Volume of water
    • Type and thickness of cotton wool
    • Spacing between seeds
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Method (before germination)

  • Line each Petri dish with cotton wool and moisten it using the same volume of water.
  • Place the same number of seeds across the surface of each dish.
  • Leave the dishes in a warm area where they will not be disturbed.
  • Check daily and add more water if the cotton wool begins to dry out.
  • When germination begins (after about 2–3 days), make sure each dish contains the same number of healthy seedlings.
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Method (after germination)

  • Assign each Petri dish to one of the following conditions:
    • Dish A: Placed in full light.
    • Dish B: Kept in the dark.
    • Dish C: Placed in partial light (a shaded area).
  • Over five to seven days, measure the height of every seedling. Write down the results in a table.
  • Calculate the mean height for each dish daily.
  • Compare the growth patterns to identify how light (or gravity) affects the direction and rate of growth.
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Recording Results

  • Create a results table with columns for each day and condition.
  • Draw labelled biological diagrams showing the direction of seedling growth.
  • Note differences between the treatments (for example, seedlings in darkness may grow taller but paler as they search for light).
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Results

  • Light conditions: Seedlings bend towards the light source (positive phototropism).
  • Darkness: Seedlings grow taller but weaker and lack chlorophyll.
  • Gravity test: Roots grow downward (positive gravitropism), while shoots grow upward (negative gravitropism).

Jump to other topics

1Cell Biology

1.1What's in Cells?

1.2Cell Division

1.3Transport in Cells

2Organisation

2.1Principles of Organisation

2.2Enzymes

2.3Circulatory System

2.4Non-Communicable Diseases

2.5Plant Tissues, Organs & Systems

3Infection & Response

4Bioenergetics

5Homeostasis & Response

5.1Homeostasis

5.2The Human Nervous System

5.3Hormonal Coordination in Humans

5.4Plant Hormones

6Inheritance, Variation & Evolution

6.1Reproduction

6.2Variation & Evolution

6.3Genetics & Evolution

6.4Classification

7Ecology

7.1Adaptations & Interdependence

7.2Organisation of Ecosystems

7.3Biodiversity

7.4Trophic Levels

7.5Food Production

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