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TAMS, Dr. Ayre, Biology, Ch. 40


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What is photomorphogenesis? What are phototropisms?
Nondirectional, light-triggered development. Directional, light-triggered development.
What pigment is responsible for absorbing red light? What are it's two states?
Phytochrome. Pr (inactive) and Pfr (active).
What color of light is cheifly involved in phototropisms?
Stems are ___________ phototropic and roots are ___________ phototropic. (positively/negatively/not)
Positively. Not.
What is gravitropism? What are the four steps of gravitropism?
Response of a plant to a gravitational field. 1. Gravity is perceived by the cell. 2. Signals form in the cell. 3. The signals are transduced. 4. Cells elongate according to the signals.
Where are gravity sensing cells in the shoots? In the roots?
The endodermis. The root caps.
What are thigmotropism and thigmonasty? What is the difference between them?
Plant responses to touch. Thigmonastic responses do not depend on the direction of the signal.
What are some other tropisms besides thigmotropisms, gravitropisms, and phototropisms?
Electrotropism, Chemotropism, Traumotropism (response to wounds), Thermotropism, Aerotropism (response to oxygen), Skototropism (response to dark), Geomagnetotropism, and Hydrotropism.
What is turgor?
The pressure within a living cell resulting from water diffusion.
What are pulvini?
Multicellular swellings at the base of the leaf/leaflet that respond to touch by turgor changes.
What are circadian rhythms? What are teh four characteristics of a circadian rhythm?
Internal daily clocks that tell plants when to "sleep". 1. It runs in the abscense of external inputs. 2. It must be about 24 hours in duration. 3. It can be reset or entrained. 4. It can compensate for temperature.
What do heat shock proteins do? When are they produced?
They stabilize other proteins, preventing their denaturation. When the temperature suddenly rises by several degrees.
What is a difference between hormone production in animals and hormone production in plants?
Hormone production in plants usually occurs not in specialized tissues, but in tissues that carry out addition functions.
What are the seven major kinds of plant hormones?
Auxin, Cytokinins, gibberellins, Brassinosteroids, Oligosaccharins, Ethylene, and Abscisic Acid.
What does auxin do? What does it seem to be inhibited by?
It softens cell walls and promotes elongation of stems. Light.
What scientists were involved in the discovery of auxin?
Charles Darwin, Peter Boysen-Jensen, Arpad Paal, and Frits Went.
What does the acid growth hypothesis state?
Auxin plays a part in thickening plant cell walls by lower pH within the cell, activiating certain enzymes.
What do cytokinins do?
They, in combination with auxin, cause cell division and differentiation.
How are different parts of the plant differentiated?
The relative amounts of auxin and cytokinins cause the development of different specialized tissues.
What do gibberellins/gibberellic acids (GAs) do?
They trigger growth and development.
What do brassinosteroids do?
They perform a wide variety of functions including: elongation, division, bending, tissue development, membrane polarization, and delayed senescence.
What are oligosaccharins? What do they do?
Complex carbohydrates that occur in plant cell walls that can be released and function like hormones. They can signal defense responses.
What is ethylene? What does it do?
A gaseous, hydrocarbon plant hormone. It suppresses elongation and stimulates fruit development.
What does abscisic acid do?
It induces winter bud formation and counteracts some effects of gibberellins and auxin.
Abscisic acid helps control the opening and closing of stomata and prevents vivipary. What is vivipary?
Premature germination.

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