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plant dev & hormones
biol 1210
| Question | Answer |
|---|---|
| describe the capabilities of a plant's sensory system | plants can sense & respond to info abt light, gravity, pressure & wounds. Have a sense of smell that can perceive airborne molecules & a sense of taste since their roots detect nutrients in the soil |
| describe how plants gather, process & respond to stimuli | using sensory cells & target cells: Sensory cells receive an external signal -> change into intracellular signal -> send a signal to target cells in another part of plant -> target cells receive signal -> change activity in appropriate response |
| characteristics of a plant hormone | usually transported to target cells, causing physiological response. Can be hydrophobic or hydrophilic, gases, amino-acid derivatives or peptides. Plant cells can receive several hormones at once and they often interact w each other |
| how are hormones transported in plants? | by specialized transport proteins in cell membranes, in xylem sap, phloem sap or by simple diffusion |
| how do hormones control plant growth & development ? | affect certain cellular processes incl. cell division, cell elongation, cell differentiation & cell death. They r produced in very low concentrations, so small changes to concentration can greatly affect plant |
| describe tropism & name types of tropism | a growth response that results in a curvature of organs toward or away from a stimulus. Positive tropism = growth towards stimulus, negative tropism = growth away from stimulus & categories phototropism, gravitropism, thigmotropism |
| describe each type of tropism & whether (+) or (-) | phototropism - response to light, usually (+). Gravitropism - response to gravity, stem (-), roots (+). Thigmotropism - response to mechanical disturbance (+) or (-) |
| describe 6 other responses observed in plants | dormancy: inhibition of plant growth incl. germination.Germination: plant growth from seed/spore.Flowering: make flowers.Fruit ripening: fruits palatable & fall from stem. Senescence: programmed cell/organ death. Leaf abscission: process of leaves falling |
| what are cytokinins? | plant hormones that stimulate cytokinesis = cell division that divides the cytoplasm of a parental cell into 2 daughter cells |
| describe the control of cell growth & differentiation | cytokinins produced in actively growing tissues (roots, embryos, fruits) regulate growth by activating genes that keep cell cycle going -> cell division. Work together w auxin to control cell division & differentiation - cytokinins alone have no effect! |
| describe example of position-based cell differentiation | gene inhibiting root hair growth: if epidermal cell borders cortical cell -> gene expressed -> hairless. If epidermal cell borders 2 cortical cells -> gene NOT expressed -> cell develops root hairs. This sparses the root hairs & differs root cells |
| describe the control of apical dominance by hormones | cytokinins, auxins & other factors control apical dominance = a terminal/apical bud's ability to suppress the growth of axillary/lateral buds so plant grows vertically. If terminal bud removed, plant grows laterally (bushier) |
| describe the growth of branches by hormones | branch growth is inhibited by auxin from the apical bud & stimulated by cytokinins from the root. |
| list 5 main plant hormones | auxins, cytokinins, gibberellins, abscisic acid, ethylene, florigens |
| what is auxin? | refers to class of plant hormones that promote cell elongation in stem & roots |
| describe the acid growth hypothesis | auxin stimulates proton pumps in cell membrane that pump H+ into cell wall, increasing acidity & loosening cellulose (expanisns break H bonds btwn fibres), cell absorbs more water & vacuole swells-> hydrostatic pressure elongates cell thru loose cellulose |
| describe direction of cell elongation | the direction in which cellulose microfibrils r oriented in the cell wall restricts the direction of cell elongation; cell expands primarily along plant's main axis & not in all directions |
| how do new seedlings grow tall so rapidly? | plants r able to grow rapidly & cheapy by intake & storage of water in vacuoles -> this puts more energy towards cell division and nutrient processing while allowing young plant to extend stem/roots quickly |
| besides cell elongation, what other processes is auxin involved in? | root formation & branching, affecting secondary growth (by inducing cell division in vascular cambium & inducing differentiation of secondary xylem), & gravitropism and phototropism |
| describe Darwin-Darwin experiment with phototropism | learned that the phototropic response only occurs when tip is illuminated by removing or covering tip with opaque then transparent cap - only transparent cap resulted in stem curvature |
| describe Boysen-Jensen experiment with phototropism | learned that the phototropic response only occurs when tip is separated by a permeable barrier, not impermeable one -> proves that something diffuses/transports from tip to site of curvature on stem |
| describe Went experiment with phototropism | learned that the dark side of a stem has a higher concentration of growth-promoting substance (auxin) by using an agar cube - hormones diffuse into cube, then transplant the cube -> growth hormone offset, causes curvature |
| describe conclusion of the first experiments with phototropism | when the tip of the plant receives light, auxin is transported to shaded side of the seedling where it stimulates cell elongation |
| describe anti-aging effects & which hormone(s) affects it | delay aging of some plant organs by inhibiting protein breakdown, simulating RNA & protein synthesis & assembling nutrients from surrounding tissues. Slows deterioration of leaves - dipped in cytokinins -> stay green longer |
| describe stem elongation & which hormone(s) affects it | gibberellins stimulate growth of leaves & stems (by stimulating cell elongation & cell division) |
| describe fruit growth & which hormone(s) affects it | in many plants, both auxin & gibberellins need to be present for fruit to form |
| describe germination & which hormone(s) affects it | after imbibition, embryo releases gibberellin to aleurone -> secretes alpha-amylase to hydrolyze sugars in endosperm -> sugars absorbed by scutellum, initiating embryo to grow |
| define imbibition, aleurone & scutellum in seed germination | imbibition = water taken up by a dry seed. Aleurone = outer layer of the seed coat. Scutellum = cotyledon, the first leaves that emerge from a seed |
| describe seed dormancy & which hormone(s) affects it | abscisic acid (ABA) inhibits plant growth & seed gemination; adding ABA to aleurone decreases alpha-amylase levels. In some seeds, dormancy is broken when ABA is removed by rain/light/cold |
| describe drought tolerance & which hormone(s) affects it | drought stress causes ABA to accumulate in plant -> travels to leaves & rapidly closes stomata = reduces transpiration & prevents further water loss. ABA also increases transcription of proteins to stabilize non-drought resistant proteins |
| describe ethylene in plants | plant hormone in form of gas that is released from plant tissues -> antagonistic to plant growth hormones. Produced in response to stresses (drought, flooding, mechanical pressure, injury, infection). Related to fruit ripening & leaf death |
| describe fruit ripening & which hormone(s) affects it | burst of ethylene triggers ripening = breakdown of cell wall, softening fruit, conversion of starch/acids to sugars to make fruit sweeter. |
| describe senescence & which hormone(s) affects it | programmed death of plant cells/organs/entire plant, aka apoptosis, associated w burst of ethylene. |
| describe leaf abscission & which hormone(s) affects it | process associated w autumn & the falling of leaves. Controlled by regulation of ethylene & auxin levels in leaf - normally high [auxin]:[ethylene], when balance shifts to ethylene -> trigger senescence & leaf abscission |
| describe the triple response in plants & which hormone(s) affects it | in response to dark & mechanical stress, ethylene induces triple response to allow a growing shoot to avoid obstacles: slowing of stem elongation + stem thickening + horizontal growth (curvature towards light). |
| describe photoperiodism & which hormone(s) affects it | physiological response to relative length of day & night, such as flowering - controlled by florigens |
| contrast short-day and long-day plants | short-day/long-night: flowers when photoperiod is short, light needs to be constant to trigger flowering. Long-day/short-night: flowers when photoperiod is long, flash of light increases length of photoperiod & can cause flowering. |
Created by:
AntBanana
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