All MCQs

Veins operate at low pressure, especially in limbs. Valves and skeletal muscle contractions help push blood back toward the heart and reduce pooling.

Heart valves prevent backflow during the cardiac cycle. They maintain directional flow from veins to atria, ventricles, and arteries.

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

Valve incompetence permits blood to flow backward, reducing pumping efficiency and increasing workload on the heart.

Inflammation increases blood flow and vessel permeability, allowing immune cells and molecules to reach the site. This helps contain pathogens and begin repair.

Stomach acid kills many swallowed microbes and is a chemical innate defense. It acts nonspecifically before pathogens enter tissues.

Amphibian skin is thin, moist, and richly supplied with blood vessels, making cutaneous gas exchange possible. Fish rely mainly on gills, while frog skin can supplement respiration.

In arthropods, the exoskeleton forms the body wall and provides internal attachment points for muscles. This arrangement allows jointed appendage movement and body support.

Closed systems maintain blood within vessels, allowing higher pressure and more precise distribution to active tissues. This supports greater activity in many animals.

Lymph is derived from interstitial fluid and usually contains fewer proteins and lacks red blood cells. It contains lymphocytes and other immune components.

Without circulation, internal transport depends on diffusion, which becomes inefficient over long distances. This limits body size and activity.

Blood and lymph carry leukocytes, antibodies, complement, and signaling molecules. This allows defense responses to reach damaged or infected tissues.