Unit 5: Feedback and Response Flashcards
regulator
an animal who, for a particular environmental variable, uses internal mechanisms to control internal change in the face of external fluctuation
conformor
for an environmental variable, the organisms internal condition changes with the environment
homeostasis
animals maintenance of internal balance and a relatively constant internal environment even when the external environment changes significantly
set point
a particular, healthy value of a variable that is maintained for an animal to achieve homeostasis
stimulus
fluctuations in a variable away from the set point which are detected by a sensor
sensor
detects stimulus, sends signal to control center which generates an output that triggers a response
response
a physiological activity that helps return the variable to the set point
negative feedback
a control mechanism that reduces a stimulus, products of a chain inhibit a previous enzyme
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
regulated changes
normal changes in homeostasis that are necessary for normal bodily functions
ex- change in hormones during puberty
circadian rhythm
a set of physiological changes that occur roughly every 24 hours
-ex body temp and melatonin
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
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
tropism
any growth response that results in plant organs curving toward or away from stimuli
phototropism
plant growth toward or away from light
auxin properties
- synthesized in plant tips and young leaves
- developing seeds and fruit contain high levels
- moves only from tip to base
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
pattern formation
the spatial organization of a developing plant,
-Auxin plays a major role in it
Properties of Cytokinins
- synthesized in roots and actively growing tissues
- most common is zeatin
- only have an effect when auxin is present
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
Properties of Gibberellins
- produced in young roots and leaves
- embryo of seed is a rich source
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
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
Brassinosteroids
- produced in all plant tissues
- induce cell elongation and division in stem segments and seedlings
- slow leaf drop
- promote xylem differentiation
photomorphogenesis
the effects of light on plant morphology
- plants detect the direction, intensity, and wavelength of light
- red and blue light are most importent
Blue-light photoreceptors
-initiates phototropism, light-induced opening of stomata, and slowing of hypocotyl elongating in seedlings
-three pigments involved
cryptochromes
phototrophin
zeaxanthing
cryptochromes
blue light pigments that are involved in the inhibition of stem cell elongation
phototrophin
-involved in mediating phototrophic curvatures
zeaxanthing
involved in opening of the stomata
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
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
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
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
Photoperiodism
a physiological response to photoperiod (the relative lengths of night and day)
short day plant
a plant that requires a light period shorter than a critical length to flow
-usually blooms late summer - winter
long-day plants
flower only when light period is longer than a certain length
-flower in late spring and early summer
day-neutral plants
unaffected by photoperiod and flower when they reach a certain stage of maturity
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
-
vemalization
the use of pretreatment with cold to induce flowering
florigen
hypothetical signaling molecule for flowering
-macromolecule
phyllotaxy
the arrangement of leaves on a stem
meristem
plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth
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
properties of strigolactones
- produced in roots
- upwardly mobile
Major Functions of Strigolactones
- stimulate seed germination
- help establish mycorrhizal associations
- help control apical dominance
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
