CAM Pathway

Summary

This video explains the CAM (Crassulacean Acid Metabolism) pathway, a unique process of carbon dioxide fixation in plants like cacti, which occurs in two stages: at night and during the day. At night, stomata open to fix CO₂ in mesophyll cells, storing it as malate. During the day, stomata close, and the stored malate releases CO₂ for use in the Calvin cycle to produce sugars. The CAM pathway allows plants to conserve water in hot, dry environments. This process is compared to C3 and C4 pathways, highlighting the temporal separation of steps in CAM plants.

Takeaways

• 😀 CAM pathway allows carbon dioxide fixation to occur at night, which is crucial for water conservation in arid environments.
• 🌙 During the night, stomata open to allow carbon dioxide to enter mesophyll cells, where it is fixed by PEP carboxylase.
• 🌱 The first carbon dioxide fixation in CAM plants involves the conversion of phosphoenolpyruvate (PEP) into oxaloacetate, which is then reduced to malate.
• 💧 Malate is stored in the vacuole overnight and acts as a carbon dioxide reservoir for later use in the daytime.
• ☀️ During the day, stomata close to reduce water loss, and malate is released from the vacuole to undergo decarboxylation, releasing carbon dioxide.
• 🔄 The released carbon dioxide enters the Calvin cycle, where Rubisco fixes it onto ribulose bisphosphate (RuBP) to form 3-phosphoglycerate (3-PGA).
• 🔋 Pyruvate is produced from malate after decarboxylation and is then converted back into PEP with the use of ATP.
• 🌵 CAM plants (e.g., cactus) carry out carbon fixation at night, and the Calvin cycle occurs during the day, providing an efficient mechanism for water use.
• 🌾 C4 plants, such as sugarcane and corn, also separate carbon fixation and the Calvin cycle but do so spatially (in different cells) rather than temporally like CAM.
• 🧬 CAM is an adaptation to dry environments, reducing water loss while maintaining efficient photosynthesis by temporally separating key metabolic steps.

Q & A

What is the main function of the CAM pathway in plants?

The main function of the CAM (Crassulacean Acid Metabolism) pathway is to fix carbon dioxide during the night and store it as malate, allowing plants to conserve water by keeping stomata closed during the day.

How does the CAM pathway differ from the C4 pathway?

The CAM pathway differs from the C4 pathway in timing. While both pathways fix carbon dioxide in mesophyll cells, the CAM pathway fixes carbon dioxide at night and processes it during the day, whereas the C4 pathway operates in both day and night but uses a spatial separation of steps.

What happens to the stomata in CAM plants during the night?

During the night, the stomata of CAM plants open to allow carbon dioxide to enter the mesophyll cells for fixation.

Which enzyme is responsible for fixing carbon dioxide in the CAM pathway?

PEP carboxylase is the enzyme responsible for fixing carbon dioxide in the CAM pathway. It attaches carbon dioxide to phosphoenolpyruvate (PEP), a 3-carbon molecule.

What is the role of malate in the CAM pathway?

Malate, or malic acid, is formed when oxaloacetate is reduced during the night in the CAM pathway. It stores carbon dioxide and is kept in vacuoles until the daytime, when it undergoes decarboxylation to release carbon dioxide for the Calvin cycle.

Why do CAM plants keep their stomata closed during the day?

CAM plants close their stomata during the day to minimize water loss. This is particularly important in arid environments where water conservation is crucial.

What happens to malate during the day in CAM plants?

During the day, malate is released from the vacuoles and undergoes decarboxylation, releasing carbon dioxide that enters the Calvin cycle for sugar production.

How does the CAM pathway help prevent photorespiration?

The CAM pathway helps prevent photorespiration by maintaining a high concentration of carbon dioxide during the day, which allows the Calvin cycle to function efficiently and reduces the risk of oxygen competing with carbon dioxide at the RuBisCO enzyme.

What are some examples of CAM plants?

Examples of CAM plants include cacti, succulents, and certain types of orchids.

How is phosphoenolpyruvate (PEP) regenerated in the CAM pathway?

Phosphoenolpyruvate (PEP) is regenerated from pyruvate during the day in the CAM pathway. This process requires ATP and ensures that the plant can continue fixing carbon dioxide during the night.