Question

The alternate \[C{O_2}\] fixation mechanism was found in some tropical species of grass family by Hatch and Slack. Where were they from?
a) England
b) USA
c) Australia
d) New Zealand

Answer 1

Hint: The ATP and NADPH formed in the light reaction are used in biosynthetic (dark) phase, where the \[C{O_2}\] fixation occurs i.e., the \[C{O_2}\] and \[{H_2}O\] combines to form glucose by the expenditure of energy. It was the work of Melvin Calvin, that described that the first \[C{O_2}\] fixation product is a \[3\]- Carbon compound and gave the biosynthetic pathway, named as, the Calvin cycle or \[{C_3}\] Cycle. Later an alternative method of \[C{O_2}\] fixation was discovered, which has the first stable product as \[4\]-Carbon compound. This pathway was named as the Hatch and Slack pathway or \[{C_4}\] Cycle.

Complete answer:
They did not belong to England.
Option (a) is incorrect.
Neither did they belong to the USA.
Option (b) is incorrect.
Hatch and Slack were from this country, Australia.
Option (c) is correct.
They were not from New Zealand.
Option (d) is incorrect.

So the correct answer is option (c).

Additional Information:
In \[{C_3}\] plants the \[{C_3}\] cycle occurs in Mesophyll cells and has RuBP \[\left( {5C} \right)\] primary \[C{O_2}\] acceptor and forms phosphoglyceric acid \[\left( {PGA - 3C} \right)\] as first stable product.
In C4 plants the primary \[C{O_2}\] acceptor is PEP \[\left( {3C} \right)\] and the first stable product formed is oxaloacetic acid \[\left( {OAA - 4C} \right)\] in mesophyll cells. The decarboxylation of this \[{C_4}\] acid occurs in bundle sheath cells where \[C{O_2}\] is released which enters the \[{C_3}\] cycle that takes place here.
One of the main benefits of having the \[{C_4}\] pathway is that it neglects the process of ‘Photorespiration’ that occurs in \[{C_3}\] plants. This process neither does synthesis of sugar nor of ATP rather it results in release of \[C{O_2}\] and utilization of ATP. This is because the primary acceptor RuBisCO in \[{C_3}\] has both carboxylase and oxygenase activity and when the concentration of \[{O_2}\] increases it binds with oxygen and hence leads to decrease in \[C{O_2}\] fixation.

Note:
\[{C_3}\] Cycle occurs in all plants independent of the plant being a \[{C_3}\] or \[{C_4}\] plant but \[{C_4}\] cycle occurs only in \[{C_4}\] plants. They show a ‘Kranz anatomy’, and have large bundle sheath cells that form several layers around the vascular bundle. They are characterized by- large number of chloroplasts, thick walls, and no intercellular spaces. The plants adapted to the dry tropical region, ex. maize, sorghum, sugarcane, etc. show this pathway.