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Plant Responses to Environmental Stimuli

Explore how plants react to external and internal stimuli, including tropisms like geotropism, phototropism, and thigmotropism. Learn about positive and negative plant responses, such as growth towards or away from stimuli, and the role of turgor pressure in plant rigidity.

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Plant Responses to Environmental Stimuli

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  1. Response to Change

  2. Stimulus • A change in an organism’s surroundings that causes the organism to react.

  3. 2 Types of Stimulus • External Stimulus • Stimulus occurring on the outside • Example: sun causes you to squint your eyes • Internal Stimulus • Stimulus occurring on the inside • Example: you get goose bumps because you are cold

  4. Response • a reaction to a stimulus

  5. Tropism • A plant’s response to a stimulus Three types of Tropisms are: • Geotropism • Phototropism • Thigmotropism

  6. Geotropism • the way a plant grows or bend in response to the Earth (or gravity).

  7. Phototropism • the way a plant grows or bend in response to light.

  8. Thigmotropism • the way a plant grows or bend in response to touch

  9. Hydrotropism • A plant’s response to water

  10. Responses can be positive or negative. A Positive response is when the plant moves toward the stimulus A Negative response is when a plant moves away from the stimulus

  11. Examples of a positive response • Roots respond positively to gravity by growing down into the soil • Trunk and branches respond positively to light by growing toward the light

  12. Example of a negative response: • Trunk and branches respond negatively to gravity by growing up toward the sky

  13. Turgor Pressure • The pressure of the cell contents against the cell wall • A force is exerted on the cell wall that keeps the plant rigid

  14. Examples No Turgor Pressure Turgor Pressure

  15. Inside a Cell

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