Photosynthesis and Carbon Dioxide Essay

Lecture 6.8: Photosynthesis, Respiration, and Photorespiration
Respiration
The controlled breakdown of sugar to release energy (ATP and NADPH) stored as sugar. (Requires sugar and oxygen; happens in every cell of the plant)
High activity of respiration in sinks.
C6H12O6 [sugar] +O2=CO2 [byproduct] +H2O [byproduct] +Energy
Occurs in the mitochondria of the cell (an organelle in the cell)
Photorespiration
Rubisco (the enzyme used in the Calvin Cycle to attach the carbon in CO2 to a 5C [carboxylase] molecule to make sugar) makes a “mistake”: it binds O2 with the 5C instead of carbon dioxide [oxygenase]
In what process is rubisco important? Rubisco is used in the Calvin cycle to bind carbon in CO2 to a 5C molecule to make sugar
What’s the “problem”? Rubisco is not a “perfect” enzyme
It can add carbon [good] or oxygen gas [bad] during the Calvin Cycle
If rubisco binds an O2 molecule what happens during the Calvin Cycle?
1. Energy [ATP and NADPH] is used up pointlessly
2. Makes less sugar and causes a loss of efficiency
When does Photorespiration Occur?
When the stomatal pores close
Why would they close?: To reduce the amount of water loss caused by drought stress and high heat
How does the stomatal pores closing affect the amount of:
Water: The reason stomata close
Oxygen: Increases
Carbon dioxide: Decreases
The result: A buildup of oxygen gas occurs and photorespiration is more likely to happen decreasing the efficiency of photosynthesis in the plant
Alternative methods of carbon fixation: C4 and CAM Photosynthesis
C4 and CAM plants
Carbon dioxide is converted into a 4-C compound when it first enter the leaf
Carbon dioxide is released either WHERE or WHEN oxygen gas is not present
C4 Photosynthesis
The Calvin cycle is conducted in cells WHERE oxygen gas is excluded
Common in grasses
Locational
Advantages: Better results at high temperatures in comparison to C3, also less likely for photorespiration
Disadvantages: Roundabout way to get carbon dioxide to the Calvin cycle; Less energy produced at lower temperature.
PEP Carboxylase: the enzyme responsible for the fixation of carbon dioxide to the C3 molecule [this occurs in the mesophyll cells]
Bundle sheath cell has waxy coating to prevent molecular transfusion (carbon dioxide, oxygen gas, and water)
Benefit: no oxygen gas can get in to react with rubisco
Negative: carbon dioxide can only get in through as a big molecule [C4]
CAM Photosynthesis
The Calvin cycle only occurs WHEN oxygen gas uptake does not occur
During the day
Stomata are closed - no carbon dioxide uptake
At night
Stomata are open - carbon dioxide uptake
Common in plants in dry conditions
Night: oxygen produced from light reactions during the day is released out of the leaf; stomata is open at night when least amount of water loss happens
Day: 4 carbon compound diffuse from vacuole
Occur in chloroplasts in chlorenchyma cell
Plant function well in high light intensity and limited water

Lecture 7: Water, Nutrient, and Sugar Movement
Water
Properties of water
Diffusion: no energy is expended in the movement of water because it moves from areas of high concentration to areas of low concentration
Water Tension:
Cohesion: water binds with other water molecules
Adhesion: water molecules can bind to the cell walls of the xylem, therefore helping it fight gravity
Cohesion-tension theory
A chain of events
Pulls water up the xylem
Water is able to move through plants because:
1. Transpiration- the driving force; diffusion; passive; water evaporates through stomatal chamber/pore; High to low = stomatal to outside
2. Then water moves through the cells of xylem through cohesion and adhesion; bulk flow
SO…
1. Diffusion
2. Cohesion and Adhesion
3. Diffusion (in root hairs)
The movement of water is COMPLETELY passive
Factors that affect transpiration
Influenced by the environment
Temperature: high temperature means a high rate of transpiration; you need to know if the stomata are open or not
Humidity: high humidity levels mean a

Show More