Question
Answers

PEPc is associated with
(a) ${ C }_{ 3 }$
(b) CAM Plants
(c) ${ C }_{ 4 }$
(d) Both (b) and (c)

Answer
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Hint: PEPc is an enzyme that is characteristic of particular plants that have different leaf anatomy and biochemistry than the most common plants. These plants grow in areas with tropical climates and with a lack of water.

Complete answer:
- PEPc is phosphoenolpyruvate carboxylase, an enzyme that catalyzes the addition of bicarbonate (${ HCO }_{ 3 }^{ - }$) to phosphoenolpyruvate (PEP) to form the four-carbon compound oxaloacetate and inorganic phosphate.
- The enzyme carries out carbon fixation in CAM and ${ C }_{ 4 }$ plants.
- ${ C }_{ 4 }$ and CAM metabolism is similar in their function. Both pathways concentrate ${ CO }_{ 2 }$ around the RuBisCO enzyme.
- ${ C }_{ 4 }$ plants have the pathway to adapt to growth in tropical areas as it minimizes photorespiration. The leaf of the plant contains different anatomy than ${ C }_{ 3 }$ plants. Carbon fixation is carried by both the bundle sheath cells and mesophyll cells.
- In CAM plants, carbon fixation is carried out at night, not the day time. During the day, the stomata in the leaves are closed to prevent transpiration by evaporation of water.
- In ${ C }_{ 4 }$ plants, carbon dioxide is converted into bicarbonate in the mesophyll cells and is added to phosphoenolpyruvate through the PEPc enzyme. In CAM, after carbon dioxide is fixed at night, it is stored as the four-carbon compound malate. Carbon dioxide is released during daylight when the light-dependent reactions of photosynthesis take place. During the night, carbon dioxide enters through the open stomata and is fixed by PEPc as oxaloacetate. This is again converted to malate which accumulates in cell vacuoles.

Additional information:
- ${ C }_{ 4 }$ pathway is named after the observed plants showed the 4C compound malate as the storage molecule. The first stable carbon compound in the pathway is the 4C oxaloacetic acid.
- CAM pathway stands for Crassulacean Acid Metabolism as it was first observed in the Crassulaceae plants.
- Examples of ${ C }_{ 4 }$ plants are maize, sugarcane, sorghum, etc. Examples of CAM plants are aloe, agave, pineapple, etc.
So, the correct answer is ‘(d) Both (b) and (c)'.

Note:
- ${ C }_{ 4 }$ has more efficiency than CAM as they produce more 3-Phosphoglyceric acid.
- ${ C }_{ 4 }$ pathway is also known as the Hatch-Slack pathway.