Photosynthesis - Calvin Cycle, Photorespiration, & Plant Adaptations

what is the function of the Calvin Cycle?

To produce CO2, ATP, and NADPH to build sugars (reducing carbon into glucose)

What molecules does the Calvin Cycle require?

CO2, ATP, & NADPH

Where does the Calvin Cycle get CO2, ATP, & NADPH?

CO2 from the air; ATP & NADPH from the light reactions

Where in the cell does the Calvin Cycle occur?

The stroma of the chloroplast

What enzyme performs carbon fixation in the Calvin Cycle?

rubisco

What is photorespiration?

When O2 binds to Rubisco instead of CO2, causing the plant to waste energy and carbon

Why does photorespiration happen?

Because Rubisco can’t perfectly tell O2 and CO2 apart— especially when CO2 is low or O2 is high

Is photorespiration harmful? Why?

Yes. It wastes up to 40% of energy and carbon because the plant must fix the error

What do C3 plants do in respiration?

Nothing—they just tolerate it

What environments favor C3 plants?

Cool, wet, or mild climates where stomata can stay open (eg, forests, swamps)

What is the C4 strategy to reduce photorespiration?

Separate CO2 capture and Rubisco space—Rubisco stays in bundle sheath cells

What enzyme do C4 plants use to take initially capture CO2?

PEP Carboxylase

What environments favor C4 plants?

Hot, sunny, and dry environments (eg, grasslands)

Why don’t C4 plants grow well in cold climates?

PEP Carboxylase doesn’t work well at low temperatures

What do CAM plants do at night?

Open stomata, take in CO2, store it as a 4-carbon acid

What do CAM plants do during the day?

Close stomata and release stored CO2 for the Calvin Cycle

What environments favor CAM plants?

Very hot, very dry deserts (eg, cacti, aloe)

What conditions increase photorespiration?

High O2, low CO2, closed stomata, hot temperatures

What conditions decrease photorespiration?

High CO2, low O2, cool temperatures, open stomata

Why is photorespiration more likely when stomata are closed?

CO2 levels drop, O2 builds up inside the leaf

Why do C4 and CAM plants evolve in harsh climates?

They reduce photorespiration and converse water better than C3 plants

what is the CAM plant strategy?

Separate CO2 capture and Rubisco in time (night vs day)