Transportation in animals and plants of Class 7
Blood contains three different kinds of cells or corpuscles present in a liquid matrix called plasma.
- Red blood cells or erythrocytes (RBCs)
- White blood cells or leucocytes (WBCs)
- Platelets or thrombocytes
Red blood cell
- They are minute circular discs having no nuclei at maturity. In their cytoplasm is present a red pigment, haemoglobin, which is a protein with iron in its molecule.
- It has an affinity for oxygen and readily combines with it in conditions of high oxygen concentration. It forms an unstable compound called oxyhaemoglobin which, however, in conditions of low oxygen concentration readily breaks down and releases oxygen.
- This property makes it most efficient in transporting oxygen from the lungs to the tissues. There are about five-and-a-half million RBCs in a cubic millimetre of blood.
- A red blood cell lasts for about four months, after which it breaks down and is disintegrated in the liver or spleen.
- About 3 million RBCs are destroyed each day and about four times of this number are formed every day. RBCs are produced in the bone marrow.