Blood group of Koushik is `O^(+ve)` and Pranavi is `B^(+ve)`. Whom can they donate blood and why?

Rh blood group was discovered by

Why do sponges and hydra not have blood

Given below are four statements (i-iv) regarding human blood circulatory system i) Arteries are thick-walled and have narrow lumen as compared to veins ii) Angina is acute chest pain when the blood circulation to the brain is reduced iii)Persons with blood group AB can donate blood to any person with any blood group under ABO system iv)Calcium ions play a very important role in blood clotting

The blood group in which A and B antigens are absent

Why is blood red in colour?

Why the blood is red in colour?

The genotype of blood group O is

Universal donor blood group is