7. (4) In hot and dry climates, plants face extra challenges... when their stoma

Question

7. (4) In hot and dry climates, plants face extra challenges... when their stomata are open, plants can do the gas exchange they need for photosynthesis, but they also lose water. However, closing stomata to prevent water loss causes the internal levels of CO2 to fall. and this presents a problem because when plants run out of CO2, the enzyme RuBisCO will bind oxygen instead in a process called photorespiration. Define photorespiration and explain the two main strategies plants use to prevent it (they are called C4 plants and CAM plants).

Explanation / Answer

Photorespiration refers to a process where the enzyme RuBisCO oxygenates RuBP.

It is a tyical process that occurs during certain conditions such as high light intensity, dryness or heat (often resulting in the closure of stomata thet stops the entry of carbon di oxide and accumulation of oxygen that competes for common active sites and inhibits the process of photosynthesis)

this process results in the oxidation of glycolic acid and release of carbon dioxide and results in wastage of some energy produced during photosynthesis'

Photorespiration is also called as Oxidative photosynthetic carbon cycle or C 2 photosynthesis.

SOME PLANTS AVOID PHOTORESPIRATION for effective photosynthesis.

plants increase local carbon dioxide concentration through a process called C4 cycle. Phosph enolpyruvate (PEP)carboxyle enzyme play a key role in this process.this enzyme binds CO2 in the form of bicarbonate with PEP to generate Oxalo acetate in mesophyll tissue.The oxaloacetate is converted to malate and released into the bundle sheath cells (the sites of carbon dioxide fixation by RuBisCO) where oxygen concentration is low to avoid photorespiration.

The presence of PEP Carboxylase in C4 plants reduces photorespiration by separating initial CO2 fixation and calvin cycle(Photosynthesis) in space, and performing these two processess in different cell types. C4 plants include sugar cane, maize, and sorghum.

Crassulacean acid metabolism (CAM) plants minimize photorespiration and save water by separating these two processess (C4 and Calvin cycles) in time, between night and day.

At night, CAM plants open their stomata, allowing CO2 to diffuse into the leaves. ThisCO2 is fixed into oxaloacetate by PEP carboxylase (same as in the case of C4 plants), then converted to malate.The organic acid is stored inside vacuoles until the next day. In the daylight, the CAM plants do not open their stomata, but they can still photosynthesis. That's because the organic acids are transported out of the vacuole and broken down to release CO2 which enters the Calvin cycle. This controlled release maintains a high concentration of CO2 around rubisco.

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