1. Plant Metabolism

2. Outline
Photosynthesis
Major Steps of Photosynthesis
Light-Dependent Reactions
Light-Independent Reactions
C4 Photosynthesis
CAM Photosynthesis
Respiration
Glycolysis
Electron Transport Chain

3. Enzymes and Energy Transfer
Enzymes regulate most metabolic activities.
Anabolism - Storing Energy.
Photosynthesis reactions
Catabolism - Consuming Stored Energy.
Respiration reactions
Oxidation-Reduction Reactions
Oxidation - Loss of electron(s).
Reduction - Gain of electron(s)
Usually coupled

4. 6CO2+12H2O + light  C6H12O6+6O2+6H2O
Photosynthesis
Energy for most cellular activity involves adenosine triphosphate (ATP).
Plants make ATP using light as an energy source.
Take place in cholorpolasts and in cells in which chlorophyll is embedded.
6CO2+12H2O + light  C6H12O6+6O2+6H2O

5. Carbon Dioxide
Carbon dioxide (0.037% of air) reaches cholorplasts in the mesophyll cells by diffusing through the stomata into the leaf interior.
Use of fossil fuels, deforestation, and other human activities have added excess carbon dioxide to the atmosphere.
May enhance photosynthesis.
Plants may counter-balance by developing fewer stomata.

6. Water
Less than 1% of all the water absorbed by plants is used in photosynthesis.
Most of the remainder is transpired or incorporated into cytoplasm, vacuoles, and other plant materials.
If water is in short supply, stomata usually close and thus reduce the supply of carbon dioxide available for photosynthesis.

7. Light
About 40% of the radiant energy received on earth is in the form of visible light.
Leaves commonly absorb about 80% of the visible light reaching them.
Light intensity varies with time of day, season, altitude, latitude, and atmospheric composition.
Considerable variation in the light intensities necessary for optimal photosynthetic rates.

8. Light Wavelengths

9. Effects of Light and Temperature on Photosynthesis

10. Chlorophyll Several different types of chlorophyll.
Most plants contain both chlorophyll a (blue-green) and chlorophyll b (yellow-green).
Other pigments include carotenoids (yellow and orange) phycobilins (blue or red found in cyanobacteria and red algae), and several other types of chlorophyll (chlorophylls c, d, and e in algae and photosynthetic bacteria).
About pigment molecules group as a photosynthetic unit.

11. Fig. 10.4

12. Major Steps of Photosynthesis
Light Dependent Reactions
Water molecules split apart releasing electrons and hydrogen ions (H+), and O2.
Electrons from splitting water passed along an electron transport chain.
ATP produced.
NADPH is produced.

13. Major Steps of Photosynthesis
Light Independent Reactions
Calvin Cycle
- Takes place in the stroma of chloroplasts.
- Carbon dioxide combines with RuBP and then the resulting molecule enters the Calvin cycle and is converted to sugars (Glucose) .
Energy is furnished by ATP and NADPH produced from the Light-Dependent Reactions.

14. Fig. 10.5

15. Fig. 10.6

16. Light Dependent Reactions - In Depth
Each pigment has its own distinctive pattern of light absorption.

17. Light Dependent Reactions - In Depth
Two types of photosynthetic units present in most chloroplasts make up photosystems.
Photosystems I and II
Both can produce ATP.
Only organisms with both photosystem I and photosystem II can produce NADPH and oxygen as a consequence of electron flow.

18. Photosystems

19. Fig. 10.8

20. Noncyclic photophosphorylation: The unidirectional flow of electrons from water through photosystem I (PS I) then photosystem II (PS II) and finally to NADP to produce NADPH. H+ are used to produce ATP via ATP synthase. Oxygen gas, produced from splitting water, is a byproduct of noncyclic photophosphorylation.
Cyclic photophosphorylation: Only PS I is involved. Electrons boosted from PS I are shunted back into the reaction center via the electron transport system. ATP is produced from ADP and P, but no NADPH or oxygen is produced.

21. Fig. 10.9

22. Light Independent Reactions - In Depth
Calvin Cycle
Six molecules of CO2 combine with six molecules of RuBP with the aid of rubisco (RuBP carboxylase/oxygenase).
Resulting complexes split into twelve 3PGA molecules.
NADPH and ATP (from light dependent reactions) supply energy and electrons that reduce the twelve 3PGA to 12 GA3P.
Ten of the twelve GA3P molecules are restructured into six RuBP molecules using another 6 ATPs. The remaining two GA3P are used in making glucose, starch and other cellular products (lipids & amino acids).
This is known as the C3 pathway (C3 plants).

23. The Calvin Cycle

24. Photorespiration Stomata usually close on hot, dry days.
Closed stomata prevent carbon dioxide from entering the leaf.
When carbon dioxide levels drop below about 50 parts per million, photorespiration is initiated.
Rubisco fixes oxygen instead of carbon dioxide allowing C3 plants to survive under hot, dry conditions. This helps to dissipate ATP and accumulated electrons from the light reactions thereby preventing photooxidative damage.

25. Light Independent Reactions - In Depth
4-Carbon Pathway
Plants have Kranz Anatomy.
Large chloroplast with few to no grana in the bundle sheath cells surrounding the veins.
Smaller chloroplasts with well-developed grana in the mesophyll cells.

26. Corn (Zea Mays) Cross-Section

27. 4-Carbon Pathway
Plants w (has high affinity to CO2 and is not sensitive to oxygen).ith Kranz Anatomy produce oxaloacetic acid (4-carbon compound).
Phosphoenolpyruvate (PEP) and carbon dioxide are combined in mesophyll cells with the aid of PEP carboxylase.
PEP carboxylase has high affinity to CO2 and is not sensitive to oxygen thus provides a major reduction in photorespiration.
Plants with Kranz anatomy are called C4 plants
C4 plants have two advantages:
- high concentration of PEP carboxylase (with high affinity to CO2) in mesophyll cells thus converts CO2 at a lower concentration than Rubisco.
- Optimum temperatures for C4 photosynthesis are much higher than C3 photosynthesis allowing C4 plants to thrive under temperatures that would adversely affect C3 plants.

28. CAM Photosynthesis
Similar to C4 photosynthesis in that 4-carbon compounds are produced during the light-independent reactions.
However, in CAM, the organic acids accumulate at night and break down during the day, releasing carbon dioxide.
Allows plants to function well under limited water supplies, as well as high light intensity.

29. CAM Photosynthesis

30. Respiration
Respiration is essentially the release of energy from glucose molecules that are broken down to individual carbon dioxide molecules.
Aerobic respiration:
C6H12O6 + 6O2 6CO2 + 6H2O + energy

31. Respiration Fermentation C6H12O6 2C2H5OH + 2CO2 + ATP
C6H12O6 2C3H6O3 + ATP
Anaerobic respiration and fermentation
Release less than 6% of the energy released
from a molecule of glucose by aerobic
Respiration.

32. Factors Affecting the Rate of Respiration
Temperature
Water
Oxygen

33. Major Steps of Respiration
Glycolysis
Occurs in the cytoplasm.
Glucose molecule becomes a fructose molecule carrying two phosphates.
Fructose molecule is split into two GA3P molecules.
Some hydrogen, energy, and water are removed, leaving pyruvic acid.

34. Major Steps of Respiration
Aerobic Respiration
Citric Acid (Krebs) Cycle
Occurs in the mitochondria
O.A. + acetyl CoA + ADP+P+3NAD + FAD 
O.A. + CoA+ATP+3NADH+H+ + FADH2+2CO2
Electron Transport
Oxidative Phosphorylation
Chemiosmosis

36. Energy (ATP) resulting from aerobic respiration of a glucose molecule
Glycolysis (cytoplasm) ATP -2 +4
2 NADH (ea = 2 ATP when moved into mitoch.) +4
Pyruvic acid to acetyl CoA (mitoch. matrix)
2 NADH (ea = 3 ATP) +6
Citric Acid Cycle (mitoch. matrix)
6 NADH (ea = 3 ATP)
2 FADH2 (ea = 2 ATP) +4 +2
TOTAL

37. Efficiency of aerobic respiration:
The 36 ATP molecules produced represent 39% of the energy harnessed in the glucose molecule. The remaining 61% of the energy in glucose is lost as heat or is unavailable.
Aerobic respiration is still 18 times more efficient than anaerobic respiration.

38. Assimilation and Digestion
Assimilation is the process of using organic matter produced through photosynthesis to build protoplasm and cell walls.
Digestion is the conversion of starch and other insoluble carbohydrates to soluble forms.
Nearly always hydrolysis.

39. Review
Photosynthesis
Major Steps of Photosynthesis
Light-Dependent Reactions
Light-Independent Reactions
C4 Photosynthesis
CAM Photosynthesis
Respiration
Glycolysis
Electron Transport Chain

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