Tag: cam cycle

Crassulacean acid metabolism is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide. The $CO _2$ is stored as the four-carbon acid malate and then used during photosynthesis during the day. As photosynthesis occurs during night, the concentration of organic acid, which is the product of photosynthesis increases during night. Thus, option C is correct answer.

Ranson and Thomas coined the term CAM (Crassulacean Acid Metabolism)  in 1940. CAM pathway is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide.

C- Plants using PEP carboxylase have a ring of specialised cells, called bundle sheath cells, around the vascular bundles (veins) in their leaves. PEP carboxylase forms part of a carbon dioxide pumping mechanism. Oxaloacetate can be converted to malate in the leaf mesophyll cells and transferred to the bundle sheath cells. Here 4 carbon malate is converted to 3 carbon pyruvate, yielding carbon dioxide and reducing NADP to NADPH for use in the C3 carbon fixing cycle.

In CAM plants, organic acid content increases during the night because the stomata remain open at the night and close during the daytime to conserve water. When stomata are open during the night, carbon dioxide is fixed by the action of phosphoenolpyruvate carboxylase to malic acid, this is called as acidification. During daytime, when the stomata are closed, malic acid is converted to pyruvic acid and carbon dioxide, this is called as deacidification. Hence acid concentration increases at night and decreases at daytime. So, the correct answer is 'Increases during night'.

CAM stands for crassulacean acid metabolism because it was first studied in members of the plant family Crassulaceae (Bryophyllum). CAM is the fixation of carbon dioxide by plants in arid condition. In normal conditions, the opening of the stomata is always connected with the large losses of water. To inhibit this loss during intense sunlight, CAM plants have developed a mechanism which allows the uptake of carbon dioxide during the night. They are more common than C$ _4$ plants and include cacti and a wide variety of other succulent plants. So, the correct answer is 'Crassulaceae'.

A) Phanerogams are seed bearing plants like Gymnosperms and Angiosperms. They have prominent stomata.

A) Stomata are open both during the day and night in ${ C } _{ 4 }$ plants, but open only at night in CAM plants.

Crassulacean acid metabolism is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide.

• $C _4$ photosynthesis incorporates novel leaf anatomy, metabolic specializations, and modified gene expression.
• Plants that utilize this pathway typically possess a distinctive Kranz leaf anatomy, consisting of two photosynthetic cell types.
• Their vascular bundles are surrounded by two rings of cells; the inner ring, called bundle sheath cells, contains starch-rich chloroplasts lacking grana, which differ from those in mesophyll cells present as the outer ring.
• This structural framework allows for the compartmentalization and functional separation of two sets of carboxylation and decarboxylation reactions.
  Hence, the correct answer is C.