Introduction
What Are C3 Photosynthetic Mechanisms?:
C3 photosynthesis is the process of a plant converting atmospheric CO2 into carbohydrates, known as the Calvin Cycle or Calvin-Benson Cycle. In this process, atmospheric CO2 into 6 3-phosphoglycerate molecules using rubisco, then 6 1,3-biphosphoglycerate molecules using ATP. Next, it is converted into 6 Glyceraldehyde-3- phosphate molecules with the help of NADPH. 1 of these 6 molecules leaves the cycle to be made into glucose after 5 more cycles are completed, and finally one whole glucose molecule is formed. The byproducts and leftovers are then reused in the cycle again.
What are C4 Photosynthetic Mechanisms?:
C4 photosynthesis is also the process of converting atmospheric CO2 into usable carbohydrates for the plant, but it is slightly different than C3 systems. This process fixes rubisco's tendency to uselessly fix oxygen rather than CO2 during photorespiration, by making sure rubisco does the fixation in a low oxygen, high CO2 environment. These plants have mesophyll cells, which take in lots of CO2 using PEP carboxylase to produce oxaloetic acid, and then pass it onto bundle-sheath cells with malate or aspartate. The malate is then decarboxylated, releasing the CO2 into the designated bundle-sheath cell. These extra steps cost the plant more ATP, making it less efficient than C3 photosynthesis in regular conditions (C4 excels in survival in droughts, high temperatures, or limited CO2 or N2 supplies).
Task
Where are C3 plants typically found?:
C3 plants are usually found in temperate climates, which is pretty much the space between the equator and arctic regions. This means that most of Canada and the US are completely littered with C3 plants, but there are still C4 plants around too.
Where are the C4s?:
C4 plants are typically in tropical or semi-tropical, light intense, high temperature, drought conditions. This pretty much covers the equator and the area around it up to the temperate climates, but like C3 plants, this isn't the only place you'll find them. For example, your lawn is most likely comprised of C3 and C4 grass.
Process
CO3 Diagram: C4 Diagram:
Evaluation
What are some plants that use C3?
Peanuts, cotton, sugar beets, tobacco, spinach, soybeans, most grass, and most trees are all pretty common plants that you've most likely seen, grown, or consumed (with the exception of tobacco, most likely). C3 plants are pretty much anywhere you go, especially in places like Canada where "normal" conditions for photosynthesis are present (high CO2, temps not too high, etc.)
Okay, but then what are some plants that use C4 photosynthesis?:
I'm glad you asked. Maize (corn), sugar cane, about 46% of grasses, cactus, orchids, pineapples, and agave are all quite common plants that also use C4 photosynthesis. The grasses account for about 61% of C4 species.
Conclusion
These plants seem pretty similar and common in many ways, so how do they compare?:
| Similarities: | Differences: C3 Plants: | C4 Plants: |
| Both systems involve the Calvin Cycle, and do not require light in the production of glucose directly (but do need it for the light-dependant reactions that produce energy and chemicals used in C3 and C4 photosynthesis). | More efficient | Require more ATP |
| Both C3 and C4 systems are used for the production of glucose | Work best in temperate climates, away from too much sun and heat | Work best in tropical and subtropical (hot and sunny) conditions. |
| C3 and C4 plants open their stomata in the day, closing them at night. | Use CO2 directly, in the leaf tissue | Require the CO2 to be transferred to a chamber in the form of an acid, before releasing it into the Calvin Cycle. |
| Both these systems use 6 carbon dioxide and 12 water molecules to produce a single glucose molecule. | Start with a 3-carbon molecule | Start with a 4-carbon molecule |