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Investigating light and gravity in seedlings

Homeostasis and response • Plant hormones (biology only)

Key concepts

What you'll likely be quizzed about

  • Seeds are placed on moist cotton wool in shallow containers.
  • Using various covers, light can be restricted, allowed from the top, or from the side, ensuring that the only variable is the direction of incoming light.
  • Observations occur after several days, comparing shoot direction across treatments to identify the effect of light direction.
  • For gravity experiments, seedlings are grown vertically and then reoriented; the curvature of roots and shoots indicates their gravitropic responses.

Flashcards

Test your knowledge with interactive flashcards

Dependent variable examples in the practical

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Shoot curvature direction, curvature angle, root direction, and growth rate.

Key notes

Important points to keep in mind

Phototropism: shoots bend toward light because the shaded side elongates more.

Gravitropism: roots grow down due to differential elongation that drives curvature relative to gravity.

Auxin from shoot tips diffuses to other cells and controls growth direction.

Maintain constant variables except the tested factor to clarify cause and effect.

Use replicates and document both qualitative sketches and quantitative angles.

Low temperature or poor seed quality limits observable responses.

An impermeable barrier tests if a chemical signal diffuses from the tip.

Measure angles with a protractor and present means and ranges for comparison.

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