Pakistan MCQs

Capillaries are the main exchange vessels. Damage limits diffusion of oxygen, nutrients, wastes, and signaling molecules between blood and tissues.

Large animals have cells far from the external environment. Circulatory systems transport gases, nutrients, wastes, hormones, and immune components efficiently.

Leukocytes or white blood cells participate in immune defense, including phagocytosis, antibody production, and cell-mediated responses.

Cardiac output is the volume of blood pumped per minute and equals heart rate times stroke volume. It is a core determinant of blood flow.

Earthworms have a closed circulatory system with major vessels that direct blood flow. This supports exchange and transport through the segmented body.

Small or flat animals may exchange materials effectively by diffusion because cells are close to the external environment. Large animals require transport systems.

Platelets are essential for normal clot formation. Low platelet count can lead to prolonged bleeding or easy bruising.

Vasodilation increases vessel diameter, reducing resistance and often increasing blood flow to a tissue.

Hemoglobin binding is crucial for oxygen transport. Impaired binding reduces oxygen delivery, causing tissue hypoxia.

Hemoglobin binds oxygen reversibly in red blood cells, allowing blood to carry far more oxygen than plasma alone.

Invertebrate clotting responses help seal wounds and trap pathogens. This is part of innate defense and fluid balance.

Arteriole constriction reduces local perfusion. Less warm blood reaches the tissue, making it cooler and paler.