B3.2 Transport

• Capillaries are narrow, highly branched, and close to cells

• One-cell-thick endothelial walls reduce diffusion distance

• Fenestrations in some capillaries allow rapid exchange and tissue fluid formation

• Arteries and veins have endothelium, smooth muscle, elastic tissue, and collagen

• Arteries have thicker walls and smaller lumens to withstand high pressure

• Veins have wider lumens and thinner walls for low-pressure return

• Thick artery walls and collagen prevent rupture under high pressure

• Elastic fibres stretch and recoil to even out pulse pressure and maintain flow

• Smooth muscle in arteries and arterioles regulates blood distribution

• Ventricular contraction creates a pressure wave felt as a pulse

• Pulse rate can be measured at radial or carotid arteries

• Counting for a full minute is most accurate; shorter counts can be scaled

• Veins have valves that prevent backflow toward capillaries

• Thin flexible walls allow surrounding muscles to compress veins

• Large lumens reduce friction during low-pressure blood return

• Atherosclerosis forms plaques beneath damaged coronary artery endothelium

• Plaque rupture can trigger thrombosis and occlude coronary arteries

• Reduced oxygen supply can kill cardiac muscle and cause myocardial infarction

• Transpiration from leaf mesophyll creates tension in xylem water columns

• Cohesion between water molecules transmits tension from leaves to roots

• Adhesion to xylem walls helps maintain an unbroken transpiration stream

• Mature xylem vessels are dead, hollow tubes with absent or perforated end walls

• Lignified walls resist collapse under negative pressure and waterproof the vessel

• Pits allow lateral movement of water between vessels and surrounding tissues

• Dicot stems have epidermis, cortex, pith, and vascular bundles in a ring

• Each vascular bundle contains xylem, phloem, cambium, and supporting fibres

• Plan diagrams show tissue positions without drawing individual cells

• Dicot roots have epidermis with root hairs, cortex, endodermis, and central vascular tissue

• Xylem forms a central cross with phloem between its arms

• The Casparian strip blocks apoplast flow and forces selective symplast entry to xylem