Figure 6.3

1
chlorophyll in chloroplasts
Figure 6.3
2
Photorespiration with O2 to 2-C to CO2
Rubisco fixes C
sugar rubisco
3-C molecules
(18)
Calvin-Benson Cycle or C3 cycle
Fig. 6.1 (EFB)
3
Efficiency of this process is relatively low Of
all light striking a plant, only 38 is
absorbed More energy lost in conversion
processes during photosynthesis Amount of
chemical energy ultimately stored by plant
is only 0.01 to 3.0 of light energy absorbed
4

• Respiration releasing energy stored in
  glucose
• to complete cellular functions
• Aerobic respiration
• C6H12O6 6O2 ---------- 6CO2 6H2O ATP
• Uses O2, many steps, but net gain is 21-36 ATP
  
• per glucose molecule, efficiency 25 - 43
• 2. Anaerobic respiration (glycolysis)
• C6H12O6 2ATP ----------- 2C2H6O 2CO2 4ATP
• Net gain of only 2 ATP, efficiency only 2.4

5
Figure 6.6 (EFB)
6

• Role of Water in Plants
• Photosynthesis
• Turgor Pressure
• Transport nutrients

Figure 7.12 (EFB)
7
Osmosis movement of water across a concentration
gradient
The higher the concentration of water on one side
of the membrane,the higher the osmotic potential
8
Water Potential The force or pull of osmosis
-15 bars maximum in most environments permanent
wilting point Measured as - bars as pure water
is at 0 pressure
9
C4 Pathway
Figure 6.10
10
C3
C4
Figure 6.3 (EFB)
11
If C4 plants are more efficient than C3, then why
arent all plants C4?
Ability of C4 plants to concentrate CO2 in bundle
sheath cells saves water and increases efficiency
of Rubisco and C3 cycle in fixing CO2
Production of PEP requires more energy and is
less efficient under certain conditions
12
C4 plants most efficient at 30-45 C,
water-stressed environments, and high light
intensity
C3 plants most efficient at 10-25 C, wetter
and more temperate regions
13
(No Transcript)
14
Under ideal conditions, C3 plants range from 0.01
to 3.0 efficiency in converting light energy to
chemical energy
For C4 plants, that level goes up to 8,
mainly due to Rubisco working more efficiently at
higher temperatures
15
Most plants (95) are C3 e.g., trees, shrubs,
tropical to tundra species C4 plants include
many grasses, plants in water-stressed
environments It is rare to find a species that
can use both pathways, but tobacco and a marine
diatom have been found to do so
16
CAM Pathway
Figure 6.11