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55 Cards in this Set
- Front
- Back
What are three common plant hormone responses?
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Auxin, gibberellins, ethylene
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What are three types of plant movements?
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Tropisms, nastic movements, and phytochrome-mediated responses
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What is the definition of a plant hormone?
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an organic compound produced at one site that regulates function at another site
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What are the five categories of plant hormones?
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auxin
gibberellins cytokinins abscisic acid ethylene |
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Know that there five characteristics of hormones make them difficult to study.
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-small conc.s make detection difficult
-effects vary from plant to plant -slight changes in conc. cause different responses -hormones interact with each other -hormones activate genes |
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What was the first identified hormone?
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Auxin was the first identified hormone, by Fritz Went
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Auxin causes ________ by _______.
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Auxin causes bending toward light by differential transport of chemicals from lighted side of plant to shaded side.
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What is the structure of auxin?
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an organic acid, IAA, or indole-3acetic acid
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How many forms of auxin are there?
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There are two synthetic auxins (2,4-D, NAA) and only one known naturally occurring auxin
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What kind of transport do auxins have?
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unidirectional (polar) in parenchyma, down shoots, up roots,
and nonpolar transport in phloem |
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What is phototropism?
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a positive response to unidirectional light
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What happens when a leaf or fruit undergoes abscission due to a change in auxin?
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Normal leaves have high levels auxins which inhibits the abscission zone, a damaged leave has lowered auxin synthesis, and short days and cool nights cause ethylene production which blocks auxin synthesis.
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What does auxin do in regard to roots?
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auxin causes induction of adventitious roots
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What does very high concentrations of auxin (as an herbicide) cause?
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stimulates ethylene synthesis which can cause: epinastic growth (leaf curling and bending of shoot tips, eventual abscission of leaves and death of plant)
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What does epinasty mean? What causes it?
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epinasty is the downward curvature of a leaf, leaf part, or stem resulting from more rapid growth on the upper side of a petiole than the lower side in reaction to ethylene
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What does auxin do to some fruits?
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causes parthenocarpic(seedless) fruits in tomatoes, cucumbers, eggplant, strawberries
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What is auxin used for in tissue culture?
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root induction
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What are the sites of synthesis of gibberellins?
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young. actively dividing tissues, seeds
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Where are gibberellins in?
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both x and p
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What are four effects of gibberellins?
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1) hyperelongation of some plants (by both cell division and enlargment)
2) normal growth of dwarf varieties 3) regulates production of hydrolytic enzymes in seeds of cereals- initiates germination 4) parthenocarpic fruits (grapes, mandarin oranges, peaches and other plants not affected by IAA) |
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What is cytokinesis?
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cell division
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What do cytokinins stimulate?
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cell division and shoot development in plant tissue cultures
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What is the site of synthesis of cytokinins?
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primarily root tips
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How are cytokinins transported?
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x (roots to shoots)
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What are the four effects of cytokinins?
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1) promotes cell division
2) shoot development in undifferentiated callus tissues 3) delays leaf senescence 4) counteracts inhibitory effects of IAA in apical dominance |
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What is abscission?
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the process by which a plant intentionally drops one or more of its parts, such as a leaf, fruit, flower or seed
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What are the sites of synthesis for Abscisic acid?
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mature leaves, seeds
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How is abscisic acid transported?
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from leaves in P; from roots in X
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What are the two affects of abscisic acid?
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1) induction and maintenance of dormancy in seeds and buds
2) stomate closure |
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What is ethylene's structure?
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a hydrocarbon gas
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What is the site of synthesis of ethylene?
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in any tissues experiencing physiological stress; ripening fruit
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How is ethylene transported?
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by diffusion from site of synthesis
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What is the effect of ethylene?
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fruit ripening, induces senescence and abscission
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What does endogenous mean?
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produced, originating or growing from within
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Is a plant's circadian response endogenous or a environmental response?
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endogenous ( not under external control but rather controlled by an internal clock that can be adjusted or "set" by external stimulii)
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What are tropisms?
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responses to environmental stimuli in which the direction of the response depends on the direction from which the stimulus is detected
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What are mastic movements?
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responses which are independent of the direction from which stimulus comes
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What is phototropism and what is its mechanism?
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movement of shoot apices toward lights; IAA is transported away from lighted side in response to blue light
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What is gravitropism?
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response to the pull of gravity- roots have a positive response and shoots have a negative response
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How does gravitropism work?
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occurs in root and shoot apices
special starch-containing plastids called amyloplasts (pr statolithes) may be involved, and IAA is thought to be involved |
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What is thigmotropism?
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response to touch, usually +
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What hormones are involved in thigmotropism?
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IAA and ethylene
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What are thigmonastic movements?
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responses to touch but not in the direction towards or away from the touch; direction of movement always the same
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What are nyctinastic movements?
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sleep movements, nightly movements of leaves in many plants, esp. legumes
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What are photoperiodic responses?
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responses to changes in light-dark cycles
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What is the importance of photoperiodic responses?
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they enable plants to respond to seasonal environments
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What is an example of photoperiodic responses?
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flowering
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What are the three kinds of 'day' plants and their needs for flowering?
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Long-day plants: require lengthening days to flower
Short-day plants: require shortening days to flower Day-neutral plants: flower whenever they mature regardless of the season |
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The basic response to photoperiod is regulated by a receptor called _______.
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phytochrome
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T/F: plants that respond to daylength are not influenced with other factors (temp., state of development, etc.)
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F. frequent daylength is coupled with other factors
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Where are phytochromes found?
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not localized at site of flowering but found in all plant tissues (including roots)
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Which factor is more critical: length of light period or length of dark period?
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length of dark period
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What is the wavelength (color) required to cause a photoperiodic response?
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red, but any response stimulated by red light is inhibited by a subsequent exposure to far-red light- suggesting the existence of a reversible switch that depends on the wavelength striking it last
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What are the two forms of the photochrome receptor?
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Pr, which is sensitive to red light and Pfr that is sensitive to far-red light
these are convertible Pfr causes red light responses Pfr also convert back to Pr in the dark (which allows plant to tell the length of the dark period) |
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What is the structure of phytochromes and how do they work?
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both forms of phytochrome are a molecule that consists of a light-absorbing chromophore attached to a large protein
the chromophore changes structurally when it absorbs light energy |