5.5.1 Photorespiration Flashcards
1
Q
photorespiration
A
- the process by which oxygen (O2) is consumed by rubisco and added into the Calvin cycle instead
of carbon dioxide (CO2). This process produces no ATP.
• Photorespiration is possibly an evolutionary remnant from a time when the atmosphere contained a much higher level of CO2 and less O2 than today
2
Q
guard cells
A
- of a plant leaf are usually open during the day. During dry hot conditions the guard cells close during the day so as not to lose too much water from evaporation.
The closing of the guard cells during the day can pose a problem for photosynthesis - The problem is that rubisco, the enzyme that fixes carbon dioxide (CO2) to RuBP in the Calvin cycle, will put oxygen (O2) into the Calvin cycle instead of CO2. When the guard cells are closed, O2 builds up from the light reactions.
- When rubisco incorporates O2 into the Calvin cycle rather than CO2, a five-carbon molecule results. This five-carbon molecule splits into a two-carbon molecule and a three-carbon molecule. The three-carbon molecule gets recycled back into the Calvin cycle. The two-carbon molecule leaves the chloroplast and is broken down to form CO2 in the peroxisome and mitochondria.
- Photorespiration is counterproductive to plants b because no ATP is made, and carbon is directed out of the Calvin cycle.
3
Q
The Calvin cycle is light independent but typically occurs during the day. Why?
A
- The Calvin cycle depends on products of the light reactions
4
Q
During photorespiration
A
- a two-carbon molecule leaves the chloroplast for every oxygen molecule that binds to RuBP
5
Q
Why is it difficult for most plants to carry out photosynthesis during hot, dry conditions?
A
- Oxygen builds up and carbon dioxide levels get too low because of the closing of the stomata
6
Q
True or false?
Rubisco binds to both oxygen and carbon dioxide.
A
- true
7
Q
Which statement about rubisco is true?
A
- It uses carbon dioxide as a substrate
