Stimulus & Response in Plants

Stimulus & Response in Plants

Tropisms

• Tropism = plant's growth response toward or away from a stimulus

  • Positive tropism

  • Negative tropism

• Tropism = plant’s growth response toward or away from a stimulus

  • Positive tropism = plant grows toward a stimulus

  • Negative tropism = plant grows away from a stimulus

Hydrotropism

• Hydrotropism = a plant's roots grow toward water

Phototropism

• Plants grow toward a source of light

• Uni-directional light

• Phototropism in mung bean seedling: the shoot is positively phototropic.

Thigmotropism

• A plant grows toward or away from pressure

  • Positive turns toward pressure

  • Negative turns away from pressure

Geotropism / Gravitropism

• A plant grows with or against gravity

• Negative: A plant’s stems or trunk grow up, against the pull of gravity.

• Positive: A plant’s roots grow down, with the pull of gravity

• Regardless of the slope of the land, the tree grows up against gravity.

• Regardless of the position a seed is planted in, the roots grow down with gravity and the stem up against gravity.

Working Together

• Plant tropisms work together to maintain homeostasis within the plant

  • + geotropism + phototropism

  • - geotropism + hydrotropism