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PHOTOSYNTHESIS. 9 th grade – Biology Miss Alexandra Martínez GCI 2012-2013. Using the Energy in Sunlight. Plants, algae and some bacteria capture about 1\% of the energy in sunlight that reaches Earth and convert it to “chemical energy” through

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9th grade – Biology

Miss Alexandra Martínez

GCI 2012-2013

using the energy in sunlight
Using the Energy in Sunlight
  • Plants, algae and some bacteria capture
  • about 1% of the energy in sunlight that reaches
  • Earth and convert it to “chemical energy” through
  • the process of PHOTOSYNTHESIS
  • Directly or indirectly, photosynthesis nourishes (feeds) almost the entire world.
  • Photosynthesis happen in 3 stages
three stages of photosynthesis
Three Stages of Photosynthesis
  • STAGE 1: Energy is captured from sunlight
  • STAGE 2: Light energy is converted to chemical
  • energy which is temporarily stored in ATP and
  • STAGE 3: The chemical energy stored in ATP and NADPH powers the formation of organic compounds, using carbon dioxide. It is called the Carbon Fixation Stage
stage 1 absorption of light energy
Stage 1: Absorption of Light Energy
  • Plants absorb energy from the sun by the use
  • of pigments (light absorbing substances)
  • Pigments absorb only certain wavelengths of light
  • and reflect all the others.
  • Plants use chlorophyll (a & b), which absorb red and blue, and reflect green and yellow
  • Plants use carotenoids, which absorb green and blue, and reflect yellow, orange, red.
  • Having both pigments enables plants to absorb more light energy
stage 1 absorption of light energy1
Stage 1: Absorption of Light Energy
  • Photosynthesis occurs in chloroplasts, where
  • clusters of pigments are embedded in the mem-
  • brane of disk-shaped structures called Thylakoids.
  • When light strikes a Thylakoid, energy is transferred to electrons in chlorophyll causing electrons to be “energized” and be able to capture the energy of sunlight
  • These “energized” electrons jump to the thylakoid membrane where they are used to power the second stage of photosynthesis
  • When electrons hit the thylakoid membrane, an enzyme splits water molecules, leaving H+, and the remaining oxygen atoms combine to form oxygen gas, which leaves the membrane as a waste product.
stage 2 conversion of light energy
Stage 2: Conversion of Light Energy
  • Excited electrons that leave chlorophyll are
  • used to produce new molecules, including ATP
  • and NADPH.
  • The electrons are passed through a series of molecules along the thylakoid membrane, which is the Electron Transport Chain
  • Excited electrons loose some of their energy as they pass through this chain, through the enzymes embedded there.
  • The energy lost by the electrons is used to pump H+ inside the thylakoid membrane. They help in the breaking down of water molecules, keeping the H+ inside and generating a concentration gradient, so they have a tendency to diffuse back out.
stage 2 conversion of light energy1
Stage 2: Conversion of Light Energy
  • These H+ are pumped out the membrane
  • through a specialized protein called ATP Synthase,
  • to produce ATP.
  • ADP + H+ ATP
  • Other H+ are used to produce NADPH, which provides
  • high energy electrons needed to make carbon-hydrogen bonds in
  • the 3rd stage.
  • NADP+ + H+ NADPH
  • Lets checkout some videos.
  • Pigments in the thylakoid of chloroplasts
  • absorb light energy
  • Electrons are excited and move through the electron transport chain
  • Water molecules breakdown by an enzyme creating oxygen gas as a waste product and H+
  • The H+ accumulate inside the thylakoid, setting a concentration gradient that provide energy to make ATP and NADPH