This is a draft cheat sheet. It is a work in progress and is not finished yet.
Types of Receptors
Photoreceptors |
Detects light, colour not important. detection of movement and shapes essential |
Thermoreceptors |
Infra-red detected, receptors not in eyes |
Mechanoreceptors |
Detects: touch, pressure, movement, gravity, stretch. important for co-ordination |
Proprioreceptors |
responds to tension in muscles and joints |
Chemoreceptors |
Smell (olfaction), taste(gustation) |
Auditory Receptors |
Detects sound waves |
Electrical Fields |
Fish use to detect disturbances nearby |
Magnetic Fields |
Homing in pigeons |
Tropism
Tropisms are a plant growth response to stimuli. This response can be positive (towards) or negative (away from). |
Types of Tropism
Stimulus |
Root |
Shoot |
Advantage |
Phototropism |
- |
+ |
More light for shoot. Better anchorage+water+minerals for root |
Geotropism |
+ |
- |
Same as above |
5 Major Plant Hormones
Name |
Stimulus |
Produced |
Effect |
Auxin |
Light in shoot, Gravity in roots |
Apical Meristem |
Cell elongation promoted in shoots and inhibited in roots |
Gibberellins |
|
Apical Meristem |
Breaks dormancy, elongation of stems |
Ethylene |
|
Senesing leaf |
Stimulates sugar production from starch |
Cytokinins |
|
Apical Meristem |
Cell division in presence of auxin. |
Abscisic Acid (ABA) |
Response to water stress |
Leaves, Fruit, Stem, Root cap |
Controls dormancy, promotes abscission, inhibits seed growth |
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Phototropism
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What causes Phototropism? Auxin (IAA)
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Where is it produced? Apical meristem
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What does it do? Promotes cell elongation in shoot, inhibits in root
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Where does it go? Moves down plant from shoot to root
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Why does it only affect one side? Moves laterally across to the shaded side
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What is the result of elongation? Shoot grows towards light, root grows away.
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What is the benefit? More light for photosynthesis in shoots. roots grow away into soil where there is more minerals and water for photosynthesis.
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Geotropism
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What is it? Plant growth response to gravity
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How is it detected? Starch grains called Statoliths settle at bottom of root cap cells
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What is th response? Leads to redistribution of auxin at roots causing the root to grow towards gravity.
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Does it affect shoots? Yes, in the absence of light shoots exhibit negative geotropism, they grow away from gravity
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Nastic Responses
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What is it? Movement of a plant part in response to stimuli
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How fast does it occur? Slow, but faster than tropisms
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How responded? Uniform response, regardless of direction of stimuli
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Examples of responses Venus flytrap responding to chemicals.
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