What is RUBISCO and why is it important?

RUBISCO is an enzyme that is important for fixing CO2 to RuBP.  RUBISCO can act as a carboxylase and as an oxygenase. It is a slow enzyme and plants produce huge amounts of it probably compensating for the lack of speed. 

  What is photorespiration and what are its effects in plants?

Photorespiration is when RUBISCO is acting as on oxygenase and only form one PGA instead of two. It also produces a molecule called phosphoglycoate. Phosphoglycoate can be transformed back into PGA, but is energy expensive requiring 2 ATP and CO2 is not fixed, but is instead released.

-The reaction sequence resembles respiration because it consumes oxygen and produces carbon dioxide. 

 Why might RUBISCO have both carboxylase and oxygenase activity?   

It could be part of a past evolutionary event when RUBISCO evolved it had both parts and it never lost its ability to react with oxygen. It has large chain and small chain and cant function without both parts. Photorespiration occurs when the CO2 levels inside a leaf become low. This happens on hot dry days when a plant is forced to close its stomata to prevent excess water loss. If the plant continues to attempt to fix CO2 when its stomata are closed, the CO2 will get used up and the O2 ratio in the leaf will increase relative to CO2 concentrations. 

Be able to clearly describe the differences in C3 and C4 photosynthesis, including the first

produce formed, where CO2 fixation from the atmosphere occurs, where CO2 fixation by

RUBISCO occurs, and differences in the anatomy of 

In C3 plants the first product in the Calvin Benson cycle is PGA. CO2 fixation takes place within mesophyll cells. Rubisco is found within the mesophyll cells and the bundle sheath cells are small compared to C4 plants. In C4 plants the first product formed is a 4 carbon molecule. C4 plants use PEP carboxylase to take CO2 out of the atmosphere. Malate transports the CO2 to the large bundle sheath cells where RUBISCO is used to complete the Calving Benson cycle. Bundle sheath cells in C4 plants have impenetrable layer, so no photorespiration can take place. 

What is the function of Krantz anatomy in C4 leaves?

It has been thought that a specialized leaf anatomy, composed of two, distinctive photosynthetic cell types (Kranz anatomy), is required for C4photosynthesis. Just enlarged bundle sheath cells in C4 plants. 

You don’t have to worry about photorespiration (undoing photosynthesis) by keeping CO2 concentration high in the leaves the plant makes photosynthesis more efficient. There is also a smaller amount of water loss because the stomates do not have to open as often.  In C4 plants CO2 concentration does not affect photosynthesis they are only limited by RuBP.

The cost of being a C4 plant is that it takes more energy to maintain. 

In hotter environments because of CO2 and O2 solubility at high temperatures. 

C4 and CAM plants would probably start making a shift because as the earth’s temperature increases they will be more efficient at preforming photosynthesis, so essential that might be able to exploit a niche created by a warming earth.