Why plants respond to the environment

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What is a plant's response when the stimulus is predation from herbivores?
Rapid growth, spines & thorns, toxins in tissues
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What is a plant's response when the stimulus is favourable conditions?
Extra nutrient storage
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What is a plant's response when the stimulus is competition from other plants?
Growth to create shade, production of inhibiting chemicals
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What is a plant's response when the stimulus is water shortage or low temperature?
Arrested growth or dormancy
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Define: Tropism
A directional growth response in which the direction of the response is determined by the direction of the external stimulus
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What is the tropism for light?
Phototropism (eg. shoots are positive, roots are negative)
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What is the tropism for gravity?
Geotropism (eg. shoots are negative, roots are positive)
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What is the tropism for water?
Hydrotropism (eg roots are positive)
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What is the tropism for a chemical stimulus?
Chemotropism (eg. pollen tubes are positive)
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What is the tropism for touch/solid surfaces?
Thigmostropism (eg. shoots of climbing plants, such as ivy)
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What is a nastic response?
Also referred to as nasties, non-directional responses to environmental stimuli
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What is an example of a nastic response?
Mimosa pudica - a thigmonastic response where the plant's leaves suddenly droop when touched
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What is the role of plant hormones?
Also referred to as plant growth factors, they are chemical messengers that act on target cells/ tissues
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What are the effects of Auxins?
Promote cell elongation, inhibit the growth of side shoots, inhibit leaf abscission and are involved in phototropism
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What are the effects of Giberellins?
Promote seed germination and growth of stems
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What are the effects of Cytokinins?
Promote cell division
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What are the effects of Ethene?
Promote fruit ripening and leaf abscission
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What are the effects of Abscissic acid (ABA)?
Inhibit seed germination and growth, and causes stomatal closure when the plant is stressed by low water availability
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What are the similarities between plant and animal hormones?
They are; chemical messengers, act on target cells/tissues, can only bind to specific receptors on cell surface membrane with complementary shapes
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What are the differences between plant and animal hormones?
They are; produced in a variety of tissues (not endocrine glands), transported by mass flow in phloem or in xylem vessels (as opposed to blood)
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What is synergy?
Where some plant hormones amplify the effect of others
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What is antagonsim?
Where some plant hormones cancel out the effect of others
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Card 2

Front

What is a plant's response when the stimulus is favourable conditions?

Back

Extra nutrient storage

Card 3

Front

What is a plant's response when the stimulus is competition from other plants?

Back

Preview of the front of card 3

Card 4

Front

What is a plant's response when the stimulus is water shortage or low temperature?

Back

Preview of the front of card 4

Card 5

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Define: Tropism

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