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PHOTOSYNTHESIS

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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PHOTOSYNTHESIS

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  1. PHOTOSYNTHESIS 9th grade – Biology Miss Alexandra Martínez GCI 2012-2013

  2. 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

  3. 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 • NADPH • 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

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. SUMMARY • 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

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