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8.2 Photosynthesis Overview
Photosynthesis-plants use energy
to change water and carbon
dioxide into sugars and oxygen
(waste product)
Loss of water through leaves
Lost water replaced by xylem
What factors can increase this?
Gas exchange
Occur in spongy mesophyll
Stomata (openings in leaves)-not left
open; too much water lost
Only open to get enough
Stomata respond to pressure changes
High pressure-open
low pressure-close
Open-day closed-night
Adaptations to leaves
Thorns-no photosynthesis/stems carry it
Pine-narrow leaves with waxy epidermis
Sunken stomata-reduce water loss
Rock plants-few stomata, dry conditions
Thick cuticles-prevent water loss
Pitcher plants-attract prey/insects give
I. History of Photosynthesis
Jan van Helmont-found that most of the
gain in mass of plants had come from
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
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