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Light energy and photosynthetic pigments

Light energy and photosynthetic pigments. Section 3.2 Pg. 147. Photosynthesis takes place in the chloroplasts. Three stages:. “The light reactions”. Light Energy. Light. A form of electromagnetic radiation Speed = 3.00 x 10 8 m/s. The Photon Model of Light.

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Light energy and photosynthetic pigments

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  1. Light energy and photosynthetic pigments Section 3.2 Pg. 147

  2. Photosynthesis takes place in the chloroplasts. Three stages: “The light reactions”

  3. Light Energy

  4. Light • A form of electromagnetic radiation • Speed = 3.00 x 108 m/s

  5. The Photon Model of Light • Light travels in packets called “photons”. • Each photon has a characteristic wavelength, and energy content

  6. The electromagnetic spectrum

  7. Wavelengths of light within the visible range are seen as different colours • White light radiated by the Sun is composed of a mixture of all these different photons

  8. Chlorophylls a and b have maximal absorption in the blue-violet range and the red range. This is the absorption spectrum of chlorophyll.

  9. Why is chlorophyll green?? Blue-violet, and Red light is absorbed by the pigment Green photons are reflected and transmitted – these reach our eyes

  10. Photosynthesis occurs most when chlorophyll is exposed to blue-violet light, or red light. This is the action spectrum of chlorophyll. Pg. 151 – Engelmann experiment

  11. Compare the spectra – what does it mean? Most of the wavelengths absorbed are used in photosynthesis.

  12. Photosystems

  13. Thylakoid membrane: • Photosynthetic pigments are clustered into photosystems

  14. The Light Reactions (stages 1&2) • The photosystems absorb certain photons. • The light energy is used for: • ATP formation • NADP+  NADPH (reduction) Electrons for reducing NADP+ come from H2O from the stroma

  15. Components of a Photosystem Antenna complex • web of chlorophyll and other pigments Reaction centre • A transmembrane protein complex containing chlorophyll a

  16. Only chlorophyll a can transfer light energy to the other reactions of photosynthesis. Accessory pigments: Absorb other wavelengths, and transfer that energy to chlorophyll a. Examples: • chlorophyllb – green • carotenoids (e.g. beta carotene) – yellow-orange • xanthophylls – yellow • anthocyanins* – red, violet, & blue(*FOUND IN VACUOLES – NOT CHLOROPLASTS)

  17. Absorption spectra of all the pigments together covers almost the entire visible spectrum.

  18. Autumn: The leaves change... • Chlorophyll is the most abundant pigment  Leaves look green. • In cooler temperatures, plants stop producing chlorophyll • Allows the other pigments to become visible

  19. Homework • Pg. 154# 1-3, 6, 7

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