Pakistan MCQs

Dehydration lowers plasma volume, which can reduce venous return and blood pressure. Circulatory regulation attempts to compensate.

Hemocyanin is a copper-containing respiratory pigment found in many arthropods and molluscs. Oxygenated hemocyanin is often bluish.

Lymph nodes filter lymph and contain immune cells. Swelling often reflects immune activation during infection.

Large capillary surface area and short diffusion distance maximize exchange of gases, nutrients, and wastes between blood and cells.

Lacteals are lymphatic vessels in intestinal villi that absorb dietary fats and transport them as chyle into lymphatic circulation.

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.

Open circulation can be adequate for animals with lower metabolic demands. Many bivalves are less active and do not require high-pressure delivery systems.

Lymph flows under low pressure and depends on muscle movement and valves. Valves prevent backflow and support return to the bloodstream.

Different animal groups use body fluids for transport of nutrients, wastes, gases, hormones, or immune components. The exact composition and pathways vary.