root pressure and translocation

how is root pressure generated?

Mineral ions are actively transported into root. This decreases water potential in root and water moves from high water potential in the soil to low water potential in the roots. The influx of water into the root causes root pressure and this positive pressure potential will push water upwards through xylem in roots and stems

when is root pressure tended to be generated?

It tends to be generated when transpiration is insufficient which is at night time (when there is lower temperatures and decreased light intensity), high humidity levels and spring season (before leaves have opened on deciduous plants)

what is the purpose of root hairs?

Root hairs are lateral extensions of the root epidermal cells to increase surface area for water and nutrient uptake.

Outline how root hairs help with water and nutrient uptake.

1) active transport of mineral ions into root hair

2) water enters the root hairs by osmosis

3) water passes across the root from cell to cell osmosis

4) water is drawn up the xylem vessels because transpiration is constantly removing water from the top.

Define translocation

The bidirectional transport of organic compounds from source to sink

Define source.

Plant organ where organic compounds are synthesized (leaves) or stored (as starch in roots or tubers)

Define sink

Plant organ that uses or stores organic compounds

Define phloem

Phloem is vascular tissue in plants that translocates phloem sap (fluid containing water, minerals and carbon compounds such as sucrose, amino acids, hormones)

What is living cells is the phloem structure composed of?

1) sieve tube elements

2) companion cells

what are some adaptations of phloem sieve tubes?

Phloem sieve tube cells are specialized cells connected end to end to form phloem sieve tubes. Cells have reduced cytoplasm, limited organelles and no nucleus to maximize space to transport fluid. Sieve plates are porous end walls, allowing flow of sap.

What are some adaptations of companion cells?

Companion cells provide metabolic support for sieve tube cells, synthesizing molecules such as enzymes and ATP needed to sustain sieve tube cells. They also contain many mitochondria, which produces ATP for active transport to loas materials at source and unload at sink. They also contain multiple plasmodesmata, which are connections/ channels between companion cells and sieve cells for transport of materials.

What is phloem loading?

Phloem loading is the active loading of solutes (carbon compounds) from source into companion cells

What is the process of phloem loading?

Solutes are transported through plasmodesmata into sieve tube, lowering water potential in the phloem. Water moves from xylem into phloem sieve tube through osmosis (high to low water potential), increasing the. hydrostatic pressure in phloem.

Outline phloem loading

Hydrostatic pressure is always higher at the source than sink. Water will flow down the hydrostatic pressure gradient (high to low). Thus, phloem sap will always move from the source towards the sink.