AHL Transport in Multicellular Organisms

Flashcards reviewing key concepts in transport mechanisms in multicellular organisms, including tissue fluid exchange, circulation, cardiac cycle, xylem and pholem adaptations.

How is tissue fluid formed and reabsorbed in capillaries?

Tissue fluid is formed by pressure filtration of plasma in capillaries, promoted by higher pressure from arterioles. Lower pressure in venules allows tissue fluid to drain back in.

What is the composition of plasma and tissue fluid?

Blood cells are suspended in plasma, which consists of water, glucose, amino acids, ions, vitamins, hormones, and proteins. Tissue fluid forms as the liquid part of the plasma leaks through the fenestrations and basement membrane of the capillaries.

How does the lymphatic system drain excess tissue fluid?

Lymphatic vessels have permeable walls and valves to prevent backflow. Lymph flows into wider vessels, merging into veins and returning to the blood system.

What is the primary difference between single and double circulation?

In single circulation (bony fish), blood passes through the heart once per circuit. In double circulation (mammals), blood passes through the heart twice per circuit.

Name three key adaptations of the mammalian heart and their functions.

The sinoatrial node (pacemaker) initiates the heartbeat. Atria receive blood, ventricles pump blood. Atrioventricular and semilunar valves ensure unidirectional blood flow. The septum separates the heart chambers, and coronary vessels supply the heart muscle with blood.

What are the main stages in the cardiac cycle?

Blood enters atria via veins, passively filling ventricles. Atrial contraction forces remaining blood into ventricles. Ventricular contraction increases pressure, closing AV valves and opening semilunar valves to eject blood into pulmonary/systemic circuits.

What are systole and diastole?

Systole is the contraction phase; diastole is the relaxation phase.

How is root pressure generated in xylem vessels?

Water enters roots by osmosis and is drawn into xylem vessels, and root pressure helps to generate water movement in roots and stems. It's created by the active transport of mineral ions.

What is translocation, and what are sources and sinks in plants?

Translocation is the process where phloem vessels transport sap from sugar sources to sugar sinks. Sources are where sugars are produced (e.g., leaves), and sinks are where sugars needed (e.g., growing tissues).

What are adaptations of phloem sieve tubes and companion cells for translocation?

Sieve plates are porous membranes, between adjacent sieve tube cells. Reduced cytoplasm and no nucleus in sieve tube elements ease sap flow. Companion cells have many mitochondria for ATP production to actively load sugars into sieve tubes.