U3A2: 5B rubisco in C3, C4 and CAM photosynthesis

Question 1

role of rubisco

Answer 1

• initiates Calvin cycle, by binding carbon dioxide and fixing the carbon into 3-PGA.
• may use oxygen as a substrate instead of carbon dioxide, causing photorespiration.

Question 2

photorespiration

Answer 2

when rubisco binds to oxygen instead of carbon dioxide. this process is wasteful and unwanting as less glucose is produced and energy is wasted.

Question 3

why might photorespiration occur

Answer 3

• SUBSTRATE CONCENTRATION: the more substrate is present the greater chance it can enhance the enzyme and undergo a reaction. plants want to expose rubisco to a high carbon dioxide concentration and a low oxygen concentration.
• TEMPERATURE: photorespiration occurs in hot and dry weather when rubisco has a greater affinity for oxygen and conditions have caused the stomata to close.

Question 4

C3 plants

Answer 4

• do not limit photorespiration
• do not seperate initial carbon fixation and remainder of calvin cycle
• stomata is open during the day
• don’t comsume extra energy
• susceptible to photorespiration
• best adapted to moderate, cool, wet environments
• eg. most plants

Question 5

C4 plants

Answer 5

• limit photorespiration
• seperate initial carbon fixation and remainder of calvin cycle between cells (mesophyll, bundle-sheath cell respectively)
• stomata open during day
• minimises photorespiration
• consumes extra energy
• best adapted to hot, sunny habitats
• eg. corn, sugarcane

Question 6

CAM plants

Answer 6

• limit photorespiration
• seperate initial carbon fixation and remainder of calvin cycle between cells (at night CAM plants open stomata to bring in carbon dioxide, during day CAM plants close stomata to prevent water loss)
• stomata open during night
• minimises photorespiration and reduces water loss
• consumes extra energy
• best adapted to very dry, hot habitats
• eg. cacti, pineapples, orchids