The conditions essential for effective respiration are:
1. Presence of thin and permeable respiratory surface thin and permeable respiratory surfaces.
2. Rich supply of blood to the respiratory surface.
3. Passage for bringing oxygen to the respiratory surface and removing CO2 through the same passage.
4. Moist respiratory surface.
5. Presence of a circulatory system.
6. Presence of a respiratory pigment to carry out the respiratory gases (CO2 and O2) .