If we observe a drop of blood under a microscope, we will see the following three types of cells:
1) RBC: It contains a protein haemoglobin which absorbs oxygen and transports it to all cells of the body.
2) WBC: It kills harmful bacteria and other foreign particles and protects our body from diseases.
3) Platelet: It helps in clotting of blood whenever there is wound in the body and prevents blood loss.