B7: Transport in plants
Transport in plants
Xylem and phloem:
Xylem: transports water and minerals from roots → stems → leaves
Phloem: transport sucrose and amino acids made by the plant, leaves → roots & stem
*xylem is always on the inside and phloem on the outside*
Arranged in vascular bundles
Xylem function:
Transport tissue for water and dissolved mineral ions
Adaptations:
no cross walls → long continuous tube
cells are dead → allows free passage o f water
thick outerwalls (lignin) → supports plant
Root hair cells
epidermis cells in the root
grow between soil → absorbs water and minerals
water enters by osmosis → water has higher water potential than the cytoplasm
Root hair increases surface area of cells
Increases rate of absorption by osmosis and mineral ions by active transport
Pathway of water
root hair cell → root cortex → xylem → leaf mesophyll
Transpiration
the loss of water vapor from plant leaves by evaporation of water at the surfaces of mesophyll cells that diffuse through the stomata
Evaporation happens rapidly when stomata are open
Movement in xylem only takes place in one direction: roots → leaves
Function:
Transports mineral ions
provide water to keep cells turgid
provide water for photosynthesis
keeps leaves cool
Factors that affect transpiration rate:
Temperature: increase → rate of transpiration increases
wind speed: increases → rate of transpiration increases
Water molecules are attracted to each other by cohesion → moves through xylem in a continuous stream
Transpiration produces a tension on water → faster transpiration→ faster water intake
Effects of temperature, wind speed and humidity
Wilting: when cells are not full of water → cell walls cannot support the plant
Translocation
The transport of sucrose and amino acids in the phloems from source to sink
sources: parts that release sucrose/amino acids
sinks: parts that use or store sucrose/amino acids
Goes in many directions