Responses to the Environment
Introduced| English | Meaning |
|---|---|
| stimulus/ˈstɪmjʊləs/ | A change in the internal or external environment that can be detected and produce a response. |
| response/rɪˈspɒns/ | A change in an organism or cell resulting from a detected stimulus. |
| tropism/ˈtrəʊpɪzəm/ | A directional growth response to a stimulus. |
| taxis/ˈtæksiz/ | Directed movement toward or away from a stimulus, such as toward light. |
Living things react
- Poke an animal and it moves; shine light on a plant and it grows toward it.
- Every organism senses its surroundings and responds.
- Responding to the world is a basic feature of being alive.
- It keeps an organism safe, fed, and in good conditions.
Stimulus and response
- A stimulus 刺激 is a change an organism can detect — light, heat, touch, a smell.
- The reaction it produces is the response 响应.
- Sense the stimulus, then react: this is the basic pattern.
- Good responses keep an organism alive and well.
Sunflowers face the light: organisms detect and respond to environmental stimuli
A stimulus is…
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A stimulus is a change in the environment (like light or heat) that triggers a response.
Plant responses: tropisms
- Plants respond mostly by growing, slowly and in a direction.
- A tropism 向性 is a directional growth response to a stimulus.
- A shoot growing toward light is phototropism.
- Roots growing downward, toward gravity, is gravitropism.
A plant shoot bending toward light is an example of a…
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A tropism is a directional growth response — here, growth toward light (phototropism).
An animal moving toward or away from a stimulus is showing a ____.
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A taxis is a directed movement of an animal toward or away from a stimulus.
Animal responses: taxis and reflexes
- Animals can respond by moving — quickly.
- A taxis 趋性 is movement toward or away from a stimulus, like a woodlouse heading for damp shade.
- A reflex is a fast, automatic response, like pulling your hand from a hot pan.
- These quick reactions protect the animal from harm.
Sort the responses
Sort each behaviour by the kind of response it is - a plant growth response, an animal movement, or a fast reflex.
Plants respond to their environment too, usually by slow growth.
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Plants respond by growing (tropisms) — slower than animals, but still a real response.
Select all true statements about responses.
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Plants respond too, just more slowly. The other three are correct.
Do not think only animals respond. Plants respond too — just slowly, by growing. A sunflower turning to follow the sun and a root growing downward are both real responses, even though there is no movement you can watch in real time.
A seedling reaching for light:
- A young shoot detects light coming from one side (the stimulus).
- It grows faster on the shaded side, so it bends toward the light.
- This phototropism brings its leaves into the sun — a growth response that aids survival.
Organisms detect a stimulus and produce a response. Plants respond by directional growth — a tropism (like phototropism toward light). Animals respond by directed movement — a taxis — or by fast reflexes. Responding to the environment helps every organism survive.
Write from positive phototropism
- A shoot tip is lit from one side.
- The shoot bends toward the light. Auxin is involved.
What response is this?
Tropisms are growth responses. Photo means light.
What is growth of a shoot toward light?
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Toward the stimulus is positive. Growth makes it a tropism.