C3, C4, and CAM plants

25/10/24

C₃ plants

• located in generally cool, moist environment

• wheat

• soybean

• oat

• barley

• sunflower

• Alfalfa

why are C₃ plants called C₃ plants

• first organic product in calvin cycle is 3-PGA

• 3-PGA has 3 carbons

• it follows the C₃ pathway

photorespiration

• occurs when stomata closes and gas cannot move in and out of plant

• common in hot and dry weather

• CO₂ is not low or not available

• rubisco fixes oxygen to RuBP instead

• does not produce ATP, NADPH, or G3P 

• plant is unable to make its own food

• RuBP + O2 → 2-PG + 3-PGA

does rubisco only fix CO₂

no, can fix other molecules, does not have a specific one

temperature and gas differences in calvin cycle and photorespiration

• calvin cycle: low temperature, high CO2 to O2 ratio

• photorespiration: high temperature, low CO2 to O2 ratio

why does the stomata close in a plant

• especially in hot and dry environments 

• to prevent water loss 

carbon fixation vs photorespiration main products

• carbon fixation: CO₂ + RuBP → two G3P

• photorespiration: O₂ + RuBP → phosphoglycolate + 3-phosphoglycerate 

chemical difference between photorespiration and carbon fixation

• lack of third carbon from CO2

• leads to different molecule

C₄ plants

• tropical grasses, corn, sugarcane

• present in hot and dry environments

• adapted to environment

• not as efficient as C₃ plants

• has unique anatomy: bundle sheath and mesophyll cells 

difference in anatomy of C₃ vs. C₄ plant

• vascular bundle in center of C₃ and C₄ plant

• C₄ plant has tightly packed palisade mesophyll

• bundle sheath surrounds vein/vascular bundle

• allows for separation of photorespiration 

• CAM plants have large vacuoles to store CO2 until night

first product of photorespiration after carbon fixation gives a 4 carbon compund is

oxaloacetate

photosynthetic cells of C₄ plant

• mesophyll cell: tightly backs around bundle sheath

• bundle sheath: surrounds vein

how does C₄ carbon fixation work?

• PEP fixes CO2 in mesophyll cells

• forms oxaloacetate

• forms malate

• also forms pyruvate

• CO2 leaves pyruvate by decarboxylation for calvin cycle

• pyruvate forms atp

• forms PEP

CAM plants

• located in desserts, hot and dry weather

• succulents, agave, aloe vera, cacti, pineapple

• same anatomy as C₄ plant

• fixes Carbon only at night to organic molecules

• Usually opens stomata for day and closes at night to avoid water loss

• materials held in mesophyll cells until night

• separates anatomy and time of reaction

fixation in each type of plant

• C₃ plant: regular CO₂ fixation to RuBP

• C₄ plant: uses PEP to fix CO₂ to RuBP

• CAM: uses PEP to fix CO₂ to RuBP only at night time

PEP

• enzyme used in C₄ carbon fixation

• only fixes CO₂ and not O₂

• helps plants limit photorespiration 

CAM plants are best for

water conservation, loses least water out of CAM, C₃ and C₄

how do C₃ plants lose water?

photorespiration

Which type of plant (C3 , C4 , or CAM) would you expect to grow most efficiently in each environment? Explain your reasoning. A hot, wet tropical environment

C₄ plants as they are adapted to hot environments and do not prioritize water conservation like CAM plants

Which type of plant (C3 , C4 , or CAM) would you expect to grow most efficiently in each environment? Explain your reasoning. Environment extremely hot days but cool night

CAM Plants as they conserve water best and can thrive in extremely hot environments by completing the calvin cycle at night

Which type of plant (C3 , C4 , or CAM) would you expect to grow most efficiently in each environment? Explain your reasoning. – Cool, damp environment

C₃ plants as they are native and used to this environment

Which type of plant (C3 , C4 , or CAM) would you expect to grow most efficiently in each environment? Explain your reasoning.– Moderate climate but nutrient poor soil

C₃ plant as C₄ and CAM as especially adapted to certain hotter environmemts