Photosynthesis
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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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Photosynthesis
PHOTOSYNTHESIS

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

  • 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


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.


Summary
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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