Chapter 4
Is the Earth Warming?
Photosynthesis
Copyright © 2007 Pearson Prentice Hall, Inc.
Photosynthesis
• Photosynthesis
– Removes carbon
dioxide from the air
and turns it into sugar
(food)
6 CO2 + 6 H2O + light energy 
C6H12O6 + 6 O2
carbon dioxide + water + light
glucose + oxygen +energy
•
In photosynthesis, plants use light
energy to rearrange the atoms of
CO2 and H2O into carbohydrates
Photosynthesis
• Plants are not the only organisms that can
photosynthesize
• Algae
• Photosynthetic bacteria can photosynthesize without
chloroplasts
Transpiration
Xylem sap (water and
dissolved minerals from soil)
travel up inside a plant
Water vapor is lost from leaves
When water evaporates, the forces of cohesion
and adhesion create tension
Tension causes water molecules from the xylem
to be drawn out into the leaf to replace the water
that has evaporated
This, in turn, increases tension on the water
molecules immediately below them in the
xylem
This causes water to move towards the leaves,
and so on
•
Transpiration relies on
– The sun to cause evaporation
– Hydrogen bonding
•
Plants can modify the rate of transpiration
by regulating stomata size
http://www.youtube.com/watch?v=At1BJJD
cXhk
• Chloroplasts are structures in plant cells
that allow them to carry out photosynthesis
• Pigment molecules called chlorophyll are on the surface
of the thylakoid membrane
• Chlorophyll molecules absorb and capture light energy
from the sun
• Chlorophyll gives plants their green color
• The electromagnetic spectrum is made up of
several types of light, each having a different
energy level and wavelength
http://academic.kellogg.edu/herbr
andsonc/bio111/animations/0053.
swf
The Light Reactions
and Calvin Cycle
• Step 1: photo– Light reactions
• Light energy is
harvested
•
Step 2: -synthesis
– Calvin cycle
• Sugar is made
Light Reaction**Occurs in
thylakoid
http://dendro.cnre.vt.edu/forestbiology/photosynthesis.swf\
Uses Water and light
Produces Oxygen, ATP, and
NADPH
http://www.science.smith.edu/depart
ments/Biology/Bio231/ltrxn.html
“Calvin cycle”
**Occurs in stroma
Uses CO2 ,
ATP, & NADPH
s,,
Produces
Sugar
http://highered.mc
grawhill.com/sites/9834
092339/student_vi
ew0/chapter39/cal
vin_cycle.html
http://www.science.smith.edu/dep
artments/Biology/Bio231/calvin.ht
ml
C3, C4, and CAM Plants
• Stomatal openings
through which plant
cells bring CO2 into
leaves are surrounded
by guard cells that
open and close
• Water can also move
through the stomatal
openings in
transpiration
• Photorespiration
involves the closing of
stomatal openings to
prevent water loss
C3, C4, and CAM Plants
• C3 plants – normal
photosynthesis
• C4 plants – live in hot
climates; need to
conserve water; can
make sugar, but this
takes more ATP than
normal
Sugarcane
crabgrass
• CAM plants –stored as
acid until daytime
houseplants