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8.2 Photosynthesis Overview
Photosynthesis-plants use energy
to change water and carbon
dioxide into sugars and oxygen
(waste product)
Transpiration

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Loss of water through leaves
Lost water replaced by xylem
What factors can increase this?
Gas exchange

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Occur in spongy mesophyll
Stomata (openings in leaves)-not left
open; too much water lost
Only open to get enough
photosynthesis
Stomata respond to pressure changes


High pressure-open
low pressure-close
Open-day closed-night
Adaptations to leaves

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Thorns-no photosynthesis/stems carry it
out
Pine-narrow leaves with waxy epidermis
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Sunken stomata-reduce water loss
Rock plants-few stomata, dry conditions
Thick cuticles-prevent water loss
Pitcher plants-attract prey/insects give
nutrition
I. History of Photosynthesis

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Jan van Helmont-found that most of the
gain in mass of plants had come from
water
Joe Priestley-realized a candle burned
out when oxygen was not present.

Then realized the candle could be relit if a
plant was placed in the jar

Plant produced oxygen

Jan Ingenhousz-showed light was
needed in order for Priestley’s
experiment to work
II. The Photosynthesis
Equation
Sunlight+ 6CO2 + 6H20 ---->
C6H12O6 + 6 02
-plants use C6H12O6 (glucose) to
make more complex carbohydrates
like starch
-includes two stages-Light dependent
reaction and Calvin Cycle