1. External Respiration -
It takes place outside cell.
It includes -
(1) In take of O2 upto respiratory organ.
(2) Transport of O2 from respiratory organ to cells.
(3) Transport of CO2 from cells to respiratory organ.
(4) Give out of CO2 from lungs.
2. Internal Respiration or Tissue Respiration or Cellular Respiration -
It includes glycolysis, kreb's cycle and ETS.
Respiratory organ is characterized by -
(1) More surface area
(2) Thin membrane like
(3) Highly vascular
(4) Surface is wet