All Free Biology MCQs with Answers

1381. Blood vessels which carry deoxygenated blood are called__________?

• A. Arteries
• B. Veins
• C. Capillaries
• D. None of these

Explanation: Veins generally carry blood toward the heart and commonly transport deoxygenated blood from body tissues. Students may choose arteries because they often associate them with oxygen-rich blood, but the defining difference is direction of flow, since the pulmonary artery carries deoxygenated blood.

1382. Carotid artery location in human body?

• A. Neck
• B. Wrist
• C. Elbow
• D. Brain

Explanation: The carotid arteries run through the neck and supply oxygenated blood to the head and brain. Students may choose the brain because these arteries supply it, but the arteries themselves are located in the neck before entering the skull.

1383. If the radius of blood vessels of a person decreases his/her blood pressure will__________?

• A. Decrease
• B. Increase
• C. Remain Same
• D. Becomes zero

Explanation: For a given blood flow, reducing vessel radius greatly increases resistance because resistance varies inversely with the fourth power of radius, R ∝ 1/r^4. The heart must therefore generate greater pressure, so blood pressure tends to increase; students may choose decrease by assuming a narrower vessel carries less pressure rather than offering more resistance.

1384. The blood vessel carrying blood from the lungs to the heart is_______?

• A. Hepatic artery
• B. Pulmonary artery
• C. Pulmonary vein
• D. Renal artery

Explanation: The pulmonary veins carry oxygenated blood from the lungs to the left atrium of the heart. Students may choose the pulmonary artery because it is also connected to the lungs, but it carries deoxygenated blood from the right ventricle to the lungs, not blood toward the heart.

1385. Serum differs from blood in________?

• A. Lacking globulins
• B. Lacking albumins
• C. Lacking clotting factors
• D. Lacking antibodies

Explanation: Serum is the liquid left after blood has clotted, so it lacks fibrinogen and other clotting components that were used or removed during coagulation. Students may choose lacking antibodies because serum has no cells, but antibodies remain dissolved in serum.

1386. Human blood is a viscous fluid due to_________?

• A. Platelets in plasma
• B. Proteins in blood
• C. RBC and WBC in blood
• D. Sodium in serum

Explanation: Plasma proteins, especially fibrinogen and globulins, increase the internal friction of blood and therefore contribute substantially to its viscosity. Students may choose RBCs and WBCs because blood cells also affect flow resistance, but the standard answer for the viscous nature of plasma is its dissolved proteins.

1387. Haemoglobin is dissolved in the blood of:___________?

• A. Earthworm
• B. Cockroach
• C. Hydra
• D. Sponges

Explanation: In earthworms, haemoglobin is dissolved directly in the plasma rather than enclosed in red blood cells, and it transports oxygen through the closed circulatory system. Students may choose cockroach because it has haemolymph, but cockroach respiratory tubes deliver oxygen directly and its haemolymph generally does not use haemoglobin for oxygen transport.

1388. Accurate name given to blood is ___________ ?

• A. Red fluid
• B. Hemoglobin
• C. Fluid tissue
• D. Plasma

Explanation: Blood is classified as a fluid connective tissue because its plasma matrix transports cells and dissolved substances throughout the body. Students may choose plasma because it is the fluid part of blood, but plasma alone is not the whole tissue; blood also contains formed elements such as RBCs, WBCs, and platelets.

1389. The normal pH of human blood is____________?

• A. 6.4
• B. 7.0
• C. 7.4
• D. 7.5

Explanation: Normal arterial blood is slightly alkaline, with a tightly regulated pH of about 7.35 to 7.45, commonly given as 7.4. A value of 7.0 represents neutral pH and may be chosen by students who overlook the buffering effect of blood and the need for slight alkalinity.

1390. It has been estimated that in a normal person plasma constitutes about ________ by volume of blood.

• A. 35%
• B. 45%
• C. 55%
• D. 75%

Explanation: Blood is composed of about 55% plasma and about 45% formed elements such as red blood cells, white blood cells and platelets. Plasma is the liquid part that transports cells, nutrients, hormones and wastes. Students may choose 45% because they confuse plasma with the packed cellular portion of blood.