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Marieb anatomy and physiology essay questions and activities

Space-filling model of the chlorophyll molecule. Anthocyanin gives these pansies their dark purple pigmentation. Biological pigment Among the most important molecules for plant function are the pigments. Plant pigments include a variety of different kinds of molecules, including porphyrinscarotenoidsand anthocyanins. All biological pigments selectively absorb certain wavelengths of light while reflecting others.

The light that is absorbed may be used by the plant to power chemical reactionswhile the reflected wavelengths of light determine the color the pigment appears to the eye. Chlorophyll is the primary pigment in plants; it is a porphyrin that absorbs red and blue wavelengths of light while reflecting green.

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It is the presence and relative abundance of chlorophyll that gives plants their green color. All land plants and green algae possess two forms of this pigment: Kelpsdiatomsand other photosynthetic heterokonts contain chlorophyll c instead of b, red algae possess chlorophyll a. All chlorophylls serve as the primary means plants use to intercept light to fuel photosynthesis.

Carotenoids are red, orange, or yellow tetraterpenoids.

  1. All land plants and green algae possess two forms of this pigment.
  2. Most are spread from one person to another by sexual contact.
  3. Humans, like other organisms, pass certain characteristics of themselves to the next generation through their genes , the special carriers of human traits.

They function as accessory pigments in plants, helping to fuel photosynthesis by gathering wavelengths of light not readily absorbed by chlorophyll.

The most familiar carotenoids are carotene an orange pigment found in carrotslutein a yellow pigment found in fruits and vegetablesand lycopene the red pigment responsible for the color of tomatoes. Carotenoids have been shown to act as antioxidants and to promote healthy eyesight in humans.

Anthocyanins literally "flower blue" are water-soluble flavonoid pigments that appear red to blue, according to pH. They occur in all tissues of higher plants, providing color in leavesstemsrootsflowersand fruitsthough not always in sufficient quantities to be noticeable.

In these plants, the anthocyanin catches light that has passed through the leaf and reflects it back towards regions bearing chlorophyll, in order to maximize the use of available light Betalains are red or yellow pigments. Like anthocyanins they are water-soluble, but unlike anthocyanins they are indole -derived compounds synthesized from tyrosine.

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This class of pigments is found only in the Caryophyllales including cactus and amaranthand never co-occur in plants with anthocyanins. Betalains are responsible for the deep red color of beetsand are used commercially as food-coloring agents. Plant physiologists are uncertain of the function that betalains have in plants which possess them, but there is some preliminary evidence that they may have fungicidal properties. They also produce compounds such as phytochrome that are sensitive to light and which serve to trigger growth or development in response to environmental signals.

Plant hormone Plant hormonesknown as plant growth regulators PGRs or phytohormones, are chemicals that regulate a plant's growth. According to a standard animal definition, hormones are signal molecules produced at specific locations, that occur in very low concentrations, and cause altered processes in target cells at other locations. Unlike animals, plants lack specific hormone-producing tissues or organs. Plant hormones are often not transported to other parts of the plant and production is not limited to specific locations.

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Plant hormones are chemicals that in small amounts promote and influence the growthdevelopment and differentiation of cells and tissues. Hormones are vital to plant growth; affecting processes in plants from flowering to seed development, dormancyand germination.

They regulate which tissues grow upwards and which grow downwards, leaf formation and stem growth, fruit development and ripening, as well as leaf abscission and even plant death. The most important plant hormones are abscissic acid ABAauxinsethylenegibberellinsand cytokininsthough there are many other substances that serve to regulate plant physiology.

Photomorphogenesis While most people know that light is important for photosynthesis in plants, few realize that plant sensitivity to light plays a role in the control of plant structural development morphogenesis. The use of light to control structural development is called photomorphogenesisand is dependent upon the presence of specialized photoreceptorswhich are chemical pigments capable of absorbing specific wavelengths of light.

Plants use four kinds of photoreceptors: The first two of these, phytochrome and cryptochrome, are photoreceptor proteinscomplex molecular structures formed by joining a protein with a light-sensitive pigment. Cryptochrome is also known as the UV-A photoreceptor, because it absorbs ultraviolet light in the long wave "A" region.

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The UV-B receptor is one or more compounds not yet identified with certainty, though some evidence suggests carotene or riboflavin as candidates.

The most studied of the photoreceptors in plants is phytochrome. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night photoperiodism and to set circadian rhythms. It also regulates other responses including the germination of seeds, elongation of seedlings, the size, shape and number of leaves, the synthesis of chlorophyll, and the straightening of the epicotyl or hypocotyl hook of dicot seedlings.