Water Transport in Plants

Water can travel through roots into xylem by:

Symplast Pathway - goes through living parts of cells (cytoplasm). Cytoplasm of neighbouring cells connect through plasmodesmata.

Apoplast Pathway - goes through non-living parts of root (cell walls). Walls are very absorbent and water can diffuse through them, as well as passing through spaces between them.

When water in apoplast reaches endodermis, its path is blocked by waxy ***** in cell walls (Casparian *****). Water now has to take symplast pathway. This is useful because it means water has to go through a cell membrane. Cell membranes control whether or not substances in the water get through. Once past the barrier, water moves into xylem.

Apoplast provides least resistance

Arteries:

• Carry blood from heart to rest of body
• Walls are thick and muscular and have elastic tissue to cope with high pressure produced by heartbeat
• Endothelium is folded, allowing artery to expand - also helps cope with high pressure
• All arteries carry oxygenated blood except pulmonary - takes deoxygenated to lungs

Arterioles:

• Form network throughout body
• Blood's directed to different areas of demand in body by muscles inside arterioles, which contract, to restrict blood flow or relax to allow full blood flow

Veins:

• Take blood back to heart under low pressure
• Have wider lumen that arteries
• Contain valves to stop blood flowing backwards
• Blood flow through veins is helped by contraction of body muscles surrounding them
• Veins carry deoxygenated blood except pulmonary veins, which carry oxygenated blood to heart from lungs