Question

With the help of a schematic flowchart, show the breakdown of glucose in a cell to provide energy:
(i) In the presence of oxygen
(ii) In the absence of oxygen
(iii) When there is a lack of oxygen

Answer 1

Hint: Respiration is a process of energy production. Living organisms use environmental oxygen to oxidise complex organic substances (glucose) to release energy while carbon dioxide as an end product.

Complete solution:
i) Breakdown of glucose in the presence of oxygen
Such a process involving breakdown of glucose is called aerobic respiration. In this process, glucose breaks down into carbon dioxide and water. In this process, a Glucose molecule is converted into 3 carbon molecules also called pyruvate. This pyruvate further breaks down to form water and carbon dioxide as end products. This kind of respiration takes place in mitochondria for extracting energy from food. This is the most common type of respiration.
ii) Breakdown of glucose in the absence of oxygen
Such a process involving breakdown of glucose is called anaerobic respiration. This process is triggered as a substitute to aerobic respiration in case of absence of oxygen. In this process, breakdown of the stored sugar takes place in the cytoplasm to produce energy.
iii) Breakdown of Glucose in lack of oxygen
Lack of oxygen is a situation in which the body fails to maintain pace with the activity in terms of energy supply as a result of which the level of oxygen reduces in the body. It leads to a condition called oxygen debt in which the first body starts anaerobic respiration to continue the flow of energy in the body which is sooner followed aerobic respiration with restoration of oxygen level is restored. This process creates lactic acid. It is common to be observed in case of intense exercise.

Note:
When respiration takes place in absence or lack of oxygen then the amount of energy yield (in terms of ATP, the energy currency of the body) is in a lesser amount, therefore, it is less efficient in comparison to aerobic respiration. The waste or end products of this process includes alcohol or lactic acid. This process commonly takes place in bacteria.