Structure of root and stem (:

Plant adaptations for mass transport.

'Root Pressure'
'Cohesive Theory'

Needs water for photosynthesis in pallisade cells, and to keep it turgid. Also, evaporation from leaves has a cooling effect, stopping them from overheating, and enzymes denaturing.

Epidermis- one cell thick, single cell have out growths called root hairs.
Exodermis- protection against pathogens.
Cortex- nonspecializing cells that often store starch.
Endodermis- Surrounds Xylem/Pholem, waxxy layer called casparian strip. Impermeable to water and mineral ions, selective.
Xylem- transports water and mineral ions.
Phloem- Transports organic substances (e.g. sucrose) around the plant.

Big thick roots are used for anchoring, not taking up water.
New xylem doesn't have any lignin, lignin can take on different patterns. Thin areas in vessels called pits allows water to move laterally. When fully ligininfied, moving laterally is the only option.

Xylem Vessels:

• Responsible for the movement of water and ions in the plant.
  
• Long tubes linked end to end of dead cells containing NO cytoplasm
  
• Develop near tip of root as elongated cells and become thickened with lignin.
  
• Young cells have rings of lignin.
  
• Old cells are completely ligninfied, apart from small gaps called pits.
• Pits allow water to move sideways into tissues if vessels get blocked.
  

Uptake of water by root hair:

• Larger roots anchor plant into soil (waterproof)
  
• Branch to form finer roots, not waterproof.
  
• Epidermis have extensions called root hairs. Increase surface area.
  
• Root hairs are exchange surfaces for uptake of water and minerals.
  

Root hairs are efficient because they have a large surface area, and a thin surface layer, so there's a shorter diffusion distance.

The soil solution is mostly water and has a very high water potential. The root hairs have sugars and amino acids dissolved in them, and have a low water potential. So, water moves by osmosis down this water potenital gradient into the root hair cell. Ion can also go in by active transport, as this gradient is in reverse.

Water movement take two route across the cortex. Apoplastic and Symplastic.
Apoplastic: Has to go between fibres, and join the symplastic when it reaches the non permeable casparian strip.
Symplastic: Pushes through the membrane, and faces far more resistance.