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Capturing Light Energy and the Electromagnetic Spectrum

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Capturing Light Energy and the Electromagnetic Spectrum – PowerPoint PPT presentation

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Title: Capturing Light Energy and the Electromagnetic Spectrum


1
Capturing Light Energy and the Electromagnetic
Spectrum
2
The Big Picture The Conversion
of Light Energy
  • Light Reactions of Photosynthesis convert light
    energy (from the sun) into chemical energy (ATP
    and NADPH)
  • Chloroplasts in plant cells act as chemical
    factories powered by the sun
  • The thylakoids in the chloroplast convert the
    light energy into chemical energy
  • To understand the conversion we are going to
    take a look at some important properties of
    light!

3
Sunlight (Contains Visible Light)
  • Sunlight is a form of electromagnetic energy!
  • Photosynthesis transforms (converts)
    electromagnetic energy into chemical energy of
    organic molecules (sugars)
  • Sunlight is part of the electromagnetic spectrum.

4
Sunlight Contains Visible Light
  • Sunlight (contains Visible Light) is a form of
    electromagnetic energy.
  • Electromagnetic energy travels as a wave, but is
    composed of particle-like bundles of energy.
  • Sunlight travels as a wave and contains bundles
    of energy known as photons.

5
Sunlight Wave Behavior
  • Wave Theory
  • Light travels through space as a wave
  • Waves have the following characteristics
  • Wavelength- the distance between the crests of
    electromagnetic waves
  • Energy- shorter the wavelength the greater the
    energy of each photon
  • Frequency- a measure of the number of wavelengths
    in a given amount of time

6
Sunlight Light Particle behavior
  • Light behaves as though it consists of particles
    called photons
  • Each photon has a fixed quantity of energy
  • Amount of energy is inversely related to the
    wavelength of light
  • The shorter the wavelength the greater the
    energy of each photon of that light
  • Ex photon of violet light packs almost twice as
    much energy as a photon of red light

7
Sunlight and The Electromagnetic Spectrum
  • Electromagnetic Spectrum the entire range of

    radiation.
  • Visible Light the segment most important to
    life
  • the narrow band from about 380nm to 750nm in
    wavelength
  • it is detected as various colors by the human eye
  • The sun radiates the full spectrum of
    electromagnetic energy, but atmosphere is
    selective and allows only visible light to pass
    through.

Visible light part of the spectrum we can see
drives photosynthesis
8
The Electromagnetic Spectrum
White light is a mixture of all wavelengths of
visible light. A prism can sort
white light into its component colors.
9
(No Transcript)
10
Pigments
  • Light may be either
  • reflected, transmitted, or absorbed.
  • Pigments- substances that absorb visible light.
  • The color we see an object to be is the color
    most reflected or transmitted by the pigment.
  • EX Leaves look green because the main pigment in
    them (chlorophyll) absorbs violet-blue and red
    light while it transmits/reflects green light.

11
Absorption Spectrum
  • Absorption Spectrum is a graph that plots a
    pigments light absorption versus wavelength of
    light.

12
The three pigments shown below differ in the
colors of light they absorb.
13
Absorption Spectrum
  • The three pigments shown in the prior graph
    differ in the colors of light they absorb.
  • Where a curve has a peak is where much of the
    light at that wavelength is absorbed
  • Where there is a trough, much of the light at
    that wavelength is reflected or transmitted.
    (what we see)

14
Reexamine the Absorption Spectrum
15
Light and Pigments
  • Pigments- compounds that absorb light/ most
    absorb certain colors more strongly than others.
  • Several pigments are located in the membrane of
    the thylakoid
  • Chlorophyll a
  • Chlorophyll b
  • Carotenoids

16
Chlorophyll a
  • Absorbs violet-blue and red light
  • Allows green light to be reflected/transmitted
  • Is the main pigment within the photosystems.
  • Directly involved in the light reactions of
    photosynthesis

17
Accessory Pigments
  • Pigments with different absorption spectra than
    chlorophyll a.
  • Are clustered with chlorophyll a within
    photosystems.
  • Help the leaves to capture the maximum amount of
    light energy
  • Chlorophyll b
  • Carotenoids

18
Chlorophyll b
  • An accessory pigment
  • Assists chlorophyll a in capturing light energy
  • Almost identical to chlorophyll a but there is a
    slight structural difference
  • Absorbs blue light

19
Carotenoids
  • Yellow, orange, and brown
  • Accessory pigments
  • Absorbs colors that chlorophyll a cannot
    enables plant to capture more energy
  • In fall when plants lose chlorophylls their
    leaves take on the rich hues of the carotenoids

20
When Pigments Absorb Light
  • Colors corresponding to the absorbed wavelengths
    disappear from the spectrum
  • When a molecule absorbs a photon of light, one of
    the molecules electrons is elevated (excited) to
    where it has more potential energy
  • Each pigment absorbs only photons corresponding
    to specific wavelengths, which is why each
    pigment has a unique absorption spectrum
  • Excited state is unstable so the excited
    electrons drop back down releasing their excess
    energy.
  • As excited electrons drop back down, energy is
    given off.

21
Photosystems
  • Cluster of pigments and proteins embedded within
    the thylakoid membrane.
  • Contain accessory pigments that surround
    chlorophyll a, the main pigment of
    photosynthesis.
  • Are able to absorb the maximum amount of light
    possible due to the accessory pigments and
    chlorophyll a.

22
Photosystems
  • Photosystems are found embedded within the
    thylakoid membrane of the chloroplast.

23
Photosystems Are embedded in the Thylaoid
Membrane of the Chloroplast.
24
Next time Photosystems and Chloroplasts!!!
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