Respiration and Gas Transport

Carbon monoxide reduces the oxygen-carrying capacity of the blood.

The principle of counter current exchange can be illustrated using fish gills. In the gills, oxygen diffuses from an area of high concentration, the water, into an area of lower concentration, the fish’s bloodstream. First, consider what would happen under same or concurrent exchange. If oxygen-rich water and oxygen-deficient blood flow in the same direction, diffusion occurs into the bloodstream until equilibrium is reached. Thus, the maximum amount of oxygen that can enter the blood at any given time is only 50% of the total oxygen. On the other hand, if oxygen-rich water and oxygen-deficient blood flow in opposite directions, oxygen diffusion is continuous. This is because even though the oxygen concentration may decrease, the amount of oxygen in the water is always slightly greater than that in the blood, allowing diffusion to continue, and equilibrium to be avoided. In this case, the maximum amount of oxygen that can enter the blood is 90%, much greater than the amount which entered via concurrent exchange. 

The respiratory quotient (R.Q) is the ratio of $CO _2$ produced to $O _2$ consumed, while food is being metabolized.
RQ = $CO _2$ eliminated / $O _2$ consumed
R.Q for proteins is less than 1 since, amount of $CO _2$ evolved is lesser than amount of $O _2$ consumed.
When organic acids are broken down as respiratory substrates under aerobic conditions the R.Q is more than one. Organic acids contain more oxygen than carbohydrates and therefore require less oxygen for their oxidation.
R.Q is equal to zero for CAM plants at night time since, no $CO _2$ is evolved and $O _2$ is continuously consumed.
Thus, option D is correct.

During aerobic respiration, $O _2$ is consumed and $CO _2$ is released. The ratio of the volume of $CO _2$ evolved to the volume of $O _2$ consumed in respiration is called the respiratory quotient  (RQ) or respiratory ratio. The respiratory quotient depends upon the type of respiratory substrate used during respiration. When carbohydrates are used as substrate and are completely oxidised, the RQ will be 1, because equal amounts of $CO _2$ and $O _2$ are evolved and consumed, respectively. When fats are used in respiration, the RQ is less than 1. When proteins are respiratory substrates the ratio would be about 0.9.

R.Q. is the ratio of carbon dioxide evolved and the oxygen consumed during the process of respiration.

Respiratory quotient is defined as the volume of carbon dioxide released to the volume of oxygen consumed during the respiration process. Its value is one for oxidation of carbohydrates and less than one for oxidation of fats and proteins. The value is more than one for oxidation of organic acids.

R.Q stands for respiratory quotient or respiratory ratio. It is the volume of CO$ _2$evolved to the volume of O$ _2$ consumed. It depends upon the type of respiratory substrate used during respiration. When carbohydrates are used as a substrate and are oxidized completely the RQ is 1.  For fats, it is less than 1 and for proteins, it is 0.9.

The respiratory quotient depends on the type of respiratory substrate which is to release energy for the synthesis of ATP. If the respiratory substrate is a lipid, it consists carbon-hydrogen bonds mean more ATP is produced from them in respiration. This also means more oxygen is required to break them down, so has an RQ of less than one and if the substrate is glucose the RQ is 1.

Organic acids have more volume of $CO _2$ liberated during respiration than the volume of $O _2$ used. Therefore, the R.Q. value will be greater than one. E.g., R.Q of oxalic acid is 4.

RQ slightly more than unity is found when organic acids are broken down as respiratory substrates under aerobic conditions, e.g. for the breakdown of oxalic acid liberation of $CO _2$ is more than $O _2$.
$RQ=\frac{4{CO} _{2}}{{O} _{2}}=4.0$.

When the RQ value is less than one for fats,  as fats consume more oxygen for respiration than carbohydrates.

The respiratory quotient (RQ) is the ratio of CO$ _{2}$ produced to O$ _{2}$ consumed while food is being metabolized.
RQ = CO$ _{2}$ eliminated/O$ _{2}$ consumed.
The respiratory quotient for carbohydrate metabolism can be demonstrated by the chemical equation for oxidation of glucose.
C$ _{6}$H$ _{12}$O$ _{6}$ + 6 O$ _{2}$ 6 CO$ _{2}$+ 6 H$ _{2}$O
Because the gas exchange in this reaction is equal, the respiratory quotient for carbohydrates is: RQ = 6 CO2 / 6 O2 = 1. Thus, option A is wrong.
The chemical composition of fats differs from that of carbohydrates in that fats contain considerably fewer oxygen atoms in proportion to atoms of carbon and hydrogen. The substrate utilization of palmitic acid is:
C$ _{16}$H$ _{32}$O$ _{2}$ + 23 O$ _{2}$ 16 CO$ _{2}$ + 16 H$ _{2}$O
Thus, the RQ for palmitic acid is approximately 0.7. RQ = 16 CO$ _{2}$ / 23 O$ _{2}$ = 0.696. Thus, option B is wrong.
The respiratory quotient for protein metabolism can be demonstrated by the chemical equation for oxidation of albumin:
C$ _{72}$H$ _{11}$2N$ _{18}$O$ _{2}$S + 77 O$ _{2}$ 63 CO$ _{2}$ + 38 H$ _{2}$O + SO$ _{3}$ + 9 CO(NH$ _{2}$)2
The RQ for protein is approximately 0.8. RQ = 63 CO$ _{2}$/ 77O$ _{2}$ = 0.8. Thus, option C is wrong.
In case of organic fats, volume of CO$ _{2}$ given out during respiration is more than the volume of O$ _{2}$ used. Thus, option D is correct.

The utilization of oxygen is nill in anaerobic respiration. Hence the R.Q. value is infinity.