Respiration and Gas Exchange

Although frogs have lungs, they perform much of their respiration through their skin, bypassing their lungs completely. Their moist skin is specially designed with tiny blood vessels near the surface to help diffuse oxygen in and carbon dioxide out, even when the frogs are hibernating or underwater. When a frog breathes through his skin, it's called as cutaneous gas exchange. This means he's exchanging oxygen for carbon dioxide, similar to the way your lungs exchange the gases. The gases pass through the skin by diffusion. Frog breathes through lungs when on land. Fish and earthworms can not breath through lungs as they dont have. 

Frog are amphibians and they can survive on land and water both. In water they breathe through gills while on land they have fully developed lungs to breathe. During hibernation, when they are not active they take oxygen from the moist skin by the process of diffusion. 

Frog are amphibians and they can survive on land and water both. In water they breathe through gills while on land they have fully developed lungs to breathe. It undergoes hibernation as it is cold blooded and the body temperature fluctuates with the surrounding. During hibernation the diffused oxygen is taken from moist skin.  

While both the tadpole and the frog like other organisms need to take in oxygen from the environment, the respiratory mechanisms differ. The tadpoles make use of gills and the mature frogs respire need to take in oxygen from their environment, and the way they respire also changes as they develop. Tadpoles use gills, while mature frogs have three types of respiration- skin, buccal pumping and lungs

Animal P always breathes through gills - fish; animal Q breathes both through moist skin and lungs - frog; animal R breathes only through its moist skin - earthworm; animal S breathes through its cell membrane - amoeba. Oxygen diffuses in and carbon dioxide diffuses out of its cell membrane.

In frogs the process of respiration takes place through three respiratory surfaces - skin, lungs and lining of the mouth. However, when submerged in water, the frog respires through its cutaneous membranes on the skin as it is quite permeable to water and contains a large network of blood vessels. The cutaneous membrane allows the respiratory gases to readily diffuse directly. Even when out of water, mucus glands present in the skin help in the cutaneous respiration.

Respiration of aquatic animals is a process wherein they obtain the oxygen from the water. The large aquatic animals have well developed gills which helps them in their respiratory function. 

Respiration in frogs is both through lungs and skin. However, during hibernation, frogs make use of the skin to breathe. However, there are exceptions such as the wood frog which stops to breathe completely during its hibernating period. During hibernation most of these amphibians receive their necessary oxygen through their skin referred to as cutaneous gas exchange. Their skins soaks in the oxygen required by their bodies require.

The mucus glands present in the skin of the frog helps to absorb dissolved oxygen from the air. However, the frogs have three respiratory surfaces and exchange of gases with the surroundings through the skin is a continuous process.
Therefore, the correct answer is option D.

Gills are the respiratory organs of large aquatic animals. These organs are specifically adapted to their function. In Osteichthyes, the gills have four gill arches, Chondrichthyes have two, fish has 7 gill baskets with a long bony cover for the gills which is used to push water. 

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. Because, amount of $O _2$ consumed is higher than amount of $CO _2$ eliminated. So, protein rich pulses have R.Q less than 1. Thus, option C is correct and other options are incorrect.

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 (R.Q) 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 the volume of carbon dioxide evolved and oxygen consumed in respiration.

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. Thus the following expression is used to calculate the value of RQ.
RQ= volume of $CO _2$ evolved/ volume of $O _2$ consumed.
At compensation point there is no net evolution of carbon dioxide. Hence, numerator in above expression is zero, giving the value of RQ as zero.

Respiratory quotient (RQ) is defined as volume of carbon dioxide released to volume of oxygen absorbed during the process of aerobic respiration of a substrate.