Glucose oxidation and energy production :
This stage of internal respiration occurs in two steps.
2. Kreb's cycle
Glycolysis: This process occurs in the cytoplasm of the cell. At this stageoxygen is required. At this time one molecule of glucose breaks into two molecules of pyruvic acid.
1 Molecule of glucose = 2 molecules of pyruvic acid.
Kreb's cycle: This process occurs in the mitochondria of the cell. The entingprocess is completed by certain steps and in the presence of some specific enzymes. At this stage oxidation occurs in the presence of oxygen. As a reesult carbon-dioxide, water and energy are produced.
Transportation of carbon dioxide: The transportation of carbon-dioxideexactly the reverse process of oxygen transportation. That is, carbon-dioxide enriched blood is transported from the body cells towards the respiratory organs.
Carbon-dioxide transportation happens in 3 ways.
a) In the form of carbonic acid: A part of the carbon dioxide is mixed withthe water and is transported as carbonic acid.
b) In the form of bi-carbonate: Blood plasma carries carbon dioxide in theform of sodium bi-carbonate, and the red blood corpuscles in the form of potassium bi-carbonate.
c) In the form of carbamino compound: Blood plasma and red bloodcorpuscles transport carbon-dioxide in the form of carbamino compound.
4. Gill respiration : The larva of toad is called tadpole. Tadpole lives in water.
They have no lungs, so they respire with the help of gills like the fishes. In each gill there are numerous blood vessels. The dissolved oxygen of water
comes in contact with the smaller blood vessels of the gills and exchangcs oxygen and carbon-dioxide easily occurs.