Download Photosynthesis - Lake Stevens School District

Chapter 10
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Autotrophs vs. Heterotrophs
Photosynthesis: conversion of light energy into
chemical energy (sugar)
◦ carbon dioxide + water + light ---> sugar +
oxygen
◦ Energy converting process...not primary ATP
producer for autotrophs
◦ Two reactions...
 Light reactions and Calvin cycle
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Chloroplasts.
◦ concentrated in leaves
◦ found in mesophyll
◦ within chloroplast are thylakoids, which
increase surface area for reactions
 this is where the light reactions of
photosynthesis take place
◦ Fluid surrounding thylakoids in chloroplast
is Stroma.
 this is where Calvin cycle takes place
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Sunlight.
◦ electromagnetic energy that travels in waves.
Visible spectrum most important to life.
◦ light organized into photons (particle with
fixed quantity of energy)
 short wavelength = more energy
 long wavelength = less energy
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Photosynthetic pigments.
◦ substances that absorb visible light
◦ color we see is wavelength of light that is
reflected and not absorbed.
 plants appear green because the pigments
absorb red and violet-blue light and reflect
green
◦ each pigment absorbs a slightly different
wavelength, increasing the spectrum of colors
to drive photosynthesis
 chlorophyll a
 chlorophyll b
 carotenoids
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Occurs in the thylakoid membrane and thylakoid
space.
Reactions are organized into two photosystems
(protein complexes that absorb energy from sunlight)
◦ photosystem II and photosystem I
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In general...
◦ Use water and sunlight to produce oxygen and ATP
◦ transfer electrons from light energy to electron
carriers.
 NADP+ (nicotinamide adenine dinucleotide
phosphate) converted to NADPH
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How light reactions work...
◦ absorption of light excites electrons in
chlorophylls (pigment)
◦ Photosystems transfer these electrons through
ETC
 creates H+ gradient, ATP synthesized
◦ electrons are also used to create NADPH,
carrying electrons to Calvin Cycle
http://highered.mheducation.com/olc/dl/1200
72/bio13.swf
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Anabolic process. Builds carbohydrates and
consumes energy.
Occurs in the stroma of the chloroplast
◦ Takes carbon dioxide and produces a
carbohydrate
 reaction catalyzed by enzyme rubisco
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only works with NADPH and ATP produced
from the light reactions
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With photosynthesis,
some water is lost via
the stomata (where gas
exchange takes place)
◦ On hot days, stomata
close to prevent excess
water loss…but it also
limits gas exchange and
photosynthetic activity
◦ C3 plants (normal photosynthesis)
 Produce less sugar on hot, dry days (rice, wheat)
◦ C4 plants (alternate photosynthesis)
 Unique leaf anatomy that allows for alternate
pathway-able to synthesize CO2
 Still able to produce sugar on hot, dry days (corn,
sugarcane)
◦ CAM Plants (succulents)
 Open stomata at night…close during day
 Two steps of photosynthesis occur at different times
 CO2 is stored in other parts of plant (as organic
compounds)
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Organisms that have the ability to
synthesize organic compounds without
sunlight or oxygen
◦ Take CO2 or CH4 with H2S and produce carbon
compounds for energy
◦ Mostly these organisms are found on the ocean
floor (bacteria)
Carbon dioxide + water + hydrogen sulfide  sugar +
sulfuric acid (sulfur compound)