Question

Describe the Hatch-Slack cycle and write its significance.

Answer 1

Hint: In most of the plants we know, the first $CO_2$ Fixation product is the Oxaloacetic acid with a 3 carbon containing compound. As the first product of $CO_2$ fixation which is a 4 carbon compound in some plants also makes use of Phospho- enol pyruvate (PEP). The complete path of carbon in these plants has been worked out by Hatch and Slack in the year 1966.

Complete answer:
There are many plants who make the use of phospho-enol pyruvate (PEP) as the first product of $CO_2$ fixation is called as PEP is a 4 carbon containing compound. The Hatch Slack pathway is also known as the C4 pathway. At this pathway, we will take a look step by step:
First, in the Mesophyll cells, under the influence of the enzyme PEP carboxylase, phospho-enol pyruvate(PEP) present in the mesophyll cells accepts $CO_2$. In the form of the mesophyll cell itself, after accepting the $CO_2$, Malic acid or the aspartic acid which are then transported to bundle sheath cells. In order to release $CO_2$and a 3 carbon molecule, in bundle sheath cells these acids are broken down. This 3 carbon containing molecule, is then transported back to mesophyll cells where it again forms and hence one turn of the cycle is completed. In bundle sheath cells, the $CO_2$ which was released participates in the regular C3 pathway as these cells are rich in RubisCo enzyme but they lack PEP carboxylase.
Significance: TheC4 plant’s structure peculiarity: An interesting type of leave anatomy is present in C4. Two types of cells participate in the photosynthesis- the mesophyll cells and the bundle sheath cells. The bundle sheath cells have large sized chloroplasts and the mesophyll cells have small sized chloroplasts. Malic acid is passed from the mesophyll cells to the bundle sheath parenchyma.

Note:
An interesting type of leave anatomy is present in C4. Two types of cells participate in photosynthesis- mesophyll and bundle sheath cells. The bundle sheath cells are large sized chloroplasts and the mesophyll cells are small sized chloroplasts. Malic acid is passed from mesophyll cells to the bundle sheath cells parenchyma.