General Science: Human Blood & Circulation

Blood is a fluid connective tissue that circulates in the body, delivering nutrients and oxygen to cells. An average adult has about 5 to 6 litres of blood.

Composition of Blood

• Plasma: The liquid part (55%), containing water, proteins, and salts.
• RBCs (Erythrocytes): Contain Hemoglobin for oxygen transport; lifespan of ~120 days.
• WBCs (Leukocytes): Act as the body’s defense system against infections.
• Platelets (Thrombocytes): Essential for blood clotting (coagulation).

Blood Groups & Types

• ABO System: Discovered by Karl Landsteiner. Blood groups are A, B, AB, and O.
• Universal Donor: Blood group O negative (O-) can be given to anyone.
• Universal Recipient: Blood group AB positive (AB+) can receive from anyone.
• Blood pH: Human blood is slightly basic with a pH of approximately 7.4.

Question for you: Which vitamin is primarily responsible for helping blood to clot properly after an injury?

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