[transport] in plants
learningobjectives Identify the main parts of the transport system in plants xylem and phloem. Explain the structural adaptation of the xylem (ie lumen, lignin and dead cells) Explain the function of the phloem and the structure. (not in detail) Identify the arrangement of vascular tissues in the leaf and stem.
learningobjectives Describe the process of absorption of water and mineral salts in the plant through the roots. Briefly explain transpiration in regards to movement of water up the plant.
transportinplants transport water manufactured food osmosis capillary action transpirational pull translocation root hair cells xylem xylem phloem
transportvessels In flowering plants, the transport tissue consists of the xylem and the phloem.
xylemvessels The xylem is a long hollow tube-like structure that conducts water and mineral salts up the stem. It is also able to provide mechanical support for the plant.
xylemformation Cells grow together end to end Cross-walls disintegrate Lignin deposits to strengthen the xylem vessel
xylemfunctions Function Adaptation Conducting water and dissolved mineral salts from the roots to the stems and leaves Providing mechanical support for the plant Continuous long, hollow tube Empty lumen without protoplasm or cross-walls Walls are thickened with lignin, which is a hard and rigid substance
phloemvessels Made up of sieve tubes and companion cells Transports food manufactured in the leaves to other parts of the plant by translocation.
vascularbundles The xylem and the phloem group together to form a vascular bundle (literally a bundle of vessels) The distribution of the vascular bundles differ in different parts of the plant
relativedistribution Leaf Stem Root
watertransport Root Sap in root hair cell (A) has lower water potential than soil solution Water molecules enters root hair cell from soil solution by osmosis
watertransport Root The water potential in the sap of the root hair cell is now higher than that in the adjacent cell (B) Water molecules thus move from root hair cell (A) to adjacent cell (B) by osmosis This process continues from cell B to cell E until water reaches the xylem
watertransport Root When the concentration of the ions in the root hair cell sap is lower than that in the soil solution, the ions move into the cell by diffusion.
watertransport
Root Hair Cell These are enlarged images of a root hair cell. Analyse and discuss why root hair cells absorb water efficiently.
Root Hair Cell Adaptations Structural Adaptation Root hair cell is long and narrow Cell membrane prevents leaking of cell sap Living cell Function Increases surface area to volume ratio for faster absorption Maintains low water potential in cell for osmosis Provides energy from respiration for active transport of ions
Only a small portion of water absorbed by plants is used Transpiration A large portion of water that is absorbed is lost by evaporation through the stomata of the leaves This process of water vapour being lost mainly through the stomata is called transpiration
Transpiration is important because it cools the leaf transports water from the roots to the leaves for photosynthesis transports mineral salts from the roots to the leaves Transpiration
In the stem, water moves up the xylem primarily via transpirational pull The evaporation of water from the leaves removes water from the xylem vessels This creates a suction force which pulls water up the xylem vessels This suction force due to transpiration is known as transpirational pull Transpiration
Leaf Xylem Stem Root The This Water column creates escapes is from pulled of the a water from suction xylem the in the leaf xylem force vessels by in vessel is evaporation the pulled in roots xylem into upwards is the vessel pulled to leaves replace out to replace the water the lost water column in the stem xylem vessels
The rate of transpiration is higher when the temperature is high the humidity (amount of water vapour in the air) is low there is wind to blow away the humidity shell Transpiration
In summary, Water enters a plant by osmosis in the roots Transpirational Pull Water moves up the stem by transpirational pull in the xylem Water vapour leaves a plant by transpiration (evaporation) in the leaves
Show the movement of water molecules in the figure below when transpiration occurs: