Question

The organism in which the Krebs cycle does occur in mitochondria is
A. Yeast
B. Man
C. Ulothrix
D. Moulds

Answer 1

Hint: Krebs's cycle takes place in all the aerobic organisms (organisms that use oxygen for respiration) to release the stored energy in the form of ATP. In eukaryotic and prokaryotic cells, it takes place in different locations in the cell. This cycle takes place in the eight steps just after glycolysis to release energy.

Complete answer: The Krebs's cycle is also specified as the tricarboxylic acid cycle or citric acid cycle. This cycle takes place after the glycolysis that is the breakdown of glucose into the pyruvate or EMP pathway. As the name suggests the citric acid is used in the process and it is regenerated after the cycle is completed. For the conversion of the molecules into energy, some specific enzymes are required. In the eukaryotic cells, the enzymes for respiration are present in the matrix of the mitochondria and hence it takes place there. In prokaryotic cells, the cells do not have mitochondria and hence the Krebs's cycle takes place in the cytoplasm of the cell.
Now let us match this with the given options:
-Yeast: In yeast respiration, starts with glycolysis. Krebs cycle in yeast only takes place in the cytoplasm and when oxygen is available. In most of the case, respiration takes place in absence of oxygen so product form will be ethanol.
-Man: Man is an example of mammals, an example of eukaryotic organisms that possess a well-defined nucleus and organelles. So, in man, the kerb’s cycle will take place in mitochondria.
-Ulothrix: It is an example of algae. Ulothrix respires normally by glycolysis. Krebs cycle may or may not occur in them. It is not always necessary that Krebs
-Moulds: It is a kind of fungi. Fungi usually do extracellular respiration that is outside the cell in order to complete their respiration. So, they do not follow the Krebs cycle. The glucose that is formed will be used in respiration.
Hence, the correct answer is Option B

Note: This Krebs's cycle not only releases energy but also produces the precursors of the amino acid along with the NADH. These are used in the other reactions for the further conversion of the products. The NADH released in Krebs's cycle is used in the electron transport pathway.