Unit 5: Feedback and Response Flashcards Preview

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Flashcards in Unit 5: Feedback and Response Deck (46):
1

regulator

an animal who, for a particular environmental variable, uses internal mechanisms to control internal change in the face of external fluctuation

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conformor

for an environmental variable, the organisms internal condition changes with the environment

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homeostasis

animals maintenance of internal balance and a relatively constant internal environment even when the external environment changes significantly

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set point

a particular, healthy value of a variable that is maintained for an animal to achieve homeostasis

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stimulus

fluctuations in a variable away from the set point which are detected by a sensor

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sensor

detects stimulus, sends signal to control center which generates an output that triggers a response

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response

a physiological activity that helps return the variable to the set point

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negative feedback

a control mechanism that reduces a stimulus, products of a chain inhibit a previous enzyme

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positive feedback

a control mechanism that amplifies, rather than reduces the stimulus
-does not play a major role in homeostasis but help drive processes (such as childbirth) to completion

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regulated changes

normal changes in homeostasis that are necessary for normal bodily functions
ex- change in hormones during puberty

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circadian rhythm

a set of physiological changes that occur roughly every 24 hours
-ex body temp and melatonin

12

acclimatization

the gradual process by which an animal adjusts to changes in its external environment
-temporary changes during an animal's life
-may cause normal range of homeostasis to change

13

plant hormone

a signaling molecule that is produced in tiny amounts by one part of an organism's body and transported to other parts, where it binds to a specific receptor and triggers responses in target cells and tissue.
-generally control plant growth and development by affecting the division, elongation, and differentiation of cells

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tropism

any growth response that results in plant organs curving toward or away from stimuli

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phototropism

plant growth toward or away from light

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auxin properties

-synthesized in plant tips and young leaves
-developing seeds and fruit contain high levels
-moves only from tip to base

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Major Functions of Auxin

-stimulates cell elongation withing developing shoots
-rapidly alters gene expression and stimulates sustained growth response in region of elongation
- plays a role in pattern formation (flow of auxin controls development of branches)
-local peaks of auxin determine the site of leaf formation
- polar transport from leaf margin directs the pattern of leaf veins
- controls activity of vascular cambium which produces woody tissues

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pattern formation

the spatial organization of a developing plant,
-Auxin plays a major role in it

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Properties of Cytokinins

-synthesized in roots and actively growing tissues
- most common is zeatin
-only have an effect when auxin is present

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Major Functions Cytokinins

-regulate cell division in shoots and roots
-plays a role in apical dominance
- slows aging in plants by inhibiting protein breakdown, stimulating RNA and protein synthesis, and mobilizing nutrients from surrounding tissues
-slows progress of apoptosis

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Properties of Gibberellins

-produced in young roots and leaves
- embryo of seed is a rich source

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Apical Dominance

the ability of the apical bud (bud at tip of stem) to suppress the development of auxiliary buds
-cytokinins, auxins, and strigolactones interact in its control
-polar flow of auxin down the shoot triggers the synthesis of strigolactones, which repress bud growth

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Major Functions of Gibberelins

-stimulate stem and leaf growth by enhancing cell elongation and cell division
-in many plants, must be present along with auxin for fruit to develop
- release of gibberellins, after water is imbibed, from embryo signals seed to germinate

24

Brassinosteroids

-produced in all plant tissues
-induce cell elongation and division in stem segments and seedlings
-slow leaf drop
-promote xylem differentiation

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photomorphogenesis

the effects of light on plant morphology
-plants detect the direction, intensity, and wavelength of light
-red and blue light are most importent

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Blue-light photoreceptors

-initiates phototropism, light-induced opening of stomata, and slowing of hypocotyl elongating in seedlings
-three pigments involved
cryptochromes
phototrophin
zeaxanthing

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cryptochromes

blue light pigments that are involved in the inhibition of stem cell elongation

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phototrophin

-involved in mediating phototrophic curvatures

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zeaxanthing

involved in opening of the stomata

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Phytocromes and Seed Germination

-a seed may germinate only when light is optimal
-reverts back and forth between two isomers depending on color of light
-Pr form absorbs red light maximally (increased germination)
-Pfr absorbs far red light (inhibits germination, also triggers many of plants developmental response to light
-ratio of Pfr to Pf increases in sunglight triggering seeds to germinate

31

Phytocromes and Shade Avoidance

Pr-Pfr eventually reaches a dynamic equilibrium, with the ratio of each form indicating the relative amounts of red and far-red light
-shade increases Pr ratio, stimulating a tree to grow taller
-direct sunlight increases proportion of Pfr, stimulating branching and inhibiting vertical growth

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circadian rhythms

cycles with a frequency of 24 hours which are not directly controlled by any environmental variable
-if an organism is kept in a constant environment, its circadian rhythm can vary from 21-27 hours
-24 period may arise from negative-feedback loops involving the transcription of a few central "clock" genes

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Effect of Light on Biological Clock

-light is the factor that entrains the biological clock to precisely 24 hours every day
-in darkness Pr formation is favored but as light increases Pr is suddenly converted Pfr
-increase in Pfr at dawn resets biological clock

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Photoperiodism

a physiological response to photoperiod (the relative lengths of night and day)

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short day plant

a plant that requires a light period shorter than a critical length to flow
-usually blooms late summer - winter

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long-day plants

flower only when light period is longer than a certain length
-flower in late spring and early summer

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day-neutral plants

unaffected by photoperiod and flower when they reach a certain stage of maturity

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Critical Night Length

flowering responses are actually controlled by night length
-flowering of a short day plant can be stopped if the dark time is interrupted by a flash of light
-red light is the most effective at interrupting
-

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vemalization

the use of pretreatment with cold to induce flowering

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florigen

hypothetical signaling molecule for flowering
-macromolecule

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phyllotaxy

the arrangement of leaves on a stem

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meristem

plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth

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abscisic acid (ABA)

-present in all tissues
-slows growth
-play a role in all tissues ( high levels in maturing seeds inhibit germination and increase production of proteins that help seeds withstand dehydration)
- drought tolerance; ABA accumulates in leaves, causing stomata to close

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properties of strigolactones

- produced in roots
-upwardly mobile

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Major Functions of Strigolactones

-stimulate seed germination
-help establish mycorrhizal associations
-help control apical dominance

46

Ethylene

-produced in response to stress
-plays a part in triple response
- burst of ethylene associated with apoptosis of cells during senescence
-plays role in leaf abscission
-a burst often triggers fruit ripening process