Anonymous
Anonymous asked in Science & MathematicsBotany · 1 decade ago

how do different wavelengths of light affect photosynthesis?

green and red plants reflect different colours, so why do they?

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  • 1 decade ago
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    Pigments are only capable of absorbing a limited range of wavelengths for photosynthesis the rest is reflected. Plants that have more chlorophyll & accessory carotene pigments absorb in both flanking wavelengths but reflect the green gap. The green gap reflects most over the span between 470 & 650nm and this is the light that reaches our eyes so plants appear green.

    The red leaf coloration is due to the chromoplasts in the leaves. Chromoplasts contain pigments, just like chloroplasts, but are not photosynthetic. Their abundant pigments overwhelm the light reflected from the chloroplasts, however if you look at a leaf in the shade that red colouration thins out, and you can see the green chlorophyll showing through.

    Plants that appear red are those with anthocyanins in addition to more carotenoids. These chromoplasts pigments are active in protecting plants as antioxidants and as UV sunblock.

    The green leaved sugar maple is more sensitive to limited nutrient stresses associated with low pH soils than the red maple Acer rubrum. An increase in chromoplast content can mediate the negative effects of nutrient imbalances on maples by relieving UV & oxidative stress. Red maples can out compete other maples for nutrient poor acidic soils by having more chromoplasts. http://www.ingentaconnect.com/content/bsc/pce/2005...

    Anthocyanins reflect red, blue, purple, or magenta colors and are in the chemical class of flavonoids. These pigments protect leaves from UV damage by attenuating the light (absorbing the high energy blue spectra reflecting the purple - red) thus preventing DNA damage. Many are antioxidants binding free radicals. Anthocyanins, found throughout the plant in leaves, stems, and roots as well as flowers & fruit, are found predominantly in outer cell layers where their protective function is most effective.

    Carotenoids reflect yellow, orange, or red and absorb blue light. There are over 600 known carotenoids just as there are some 500 anthocyanins all doing different jobs in the plants. Carotenoids collect light in wavelengths chlorophyll can’t then transfer it to chlorophyll in the photosynthesis reaction center. Other carotenes absorb excess light energy and dissipate it in order to avoid damage in what is termed the Xanthophyll Cycle. Xanthophylls are a common but sub class of the carotenoid group. Lutein, the yellow pigment found in marigold petals, is a xanthophyll. Carotenes appear to have a role in sensing blue light, which is involved in opening stomata and in phototropism to move the plant towards sunlight. The breakdown products of carotenoids are even fragrant, producing the key odour-contributing compounds in some flowers, and fruit. They contribute to fragrances found in roses, red wine, black tea, tobacco, and many yellow or red fruit.

    http://www.leffingwell.com/caroten.htm

  • Anonymous
    5 years ago

    The intensity of light speeds up the rate of photosynthesis. These chemicals that speed up the rate of reactions are called enzymes.

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