Cohesion-Adhesion-Tension theory (1 Viewer)

[BlueGas]

What sort of questions are asked on this? Is the explanation I included a good meaning for this theory?

The constant loss of water from the plant stomates by passive transport leads to a transpiration stream (which is the constant upward flow of water through a plant), this is because of waters 2 properties, which are adhesive forces (the ability of molecules to attach to walls), and cohesive forces (the attraction of molecules to each other), hence leading to the capillarity (water rising up through the tissue) and hence the stream.

 

[kelly29930684]

Basically the question can be just on explain the theory, and they could already be a band 4 or 5 question.

Your response would be better if you remove the brackets and write them as normal sentences??
The transpiration stream in xylem occurs due to the physical forces that result from water and ions being moved out by passive transport. Water has been absorbed into the roots of plants by osmosis. Adhesive forces attracts between the water molecules and the wall of the xylem vessels, lead to capillarity and cohesive forces which attracts water molecules to each other to form a continuous stream. The continuous stream draw up the water in xylem tube to replace water loss from leaves by transpiration

 

[Jimmy_Arsenal]

NSB notes states the following:

Water loss at the surface of the leaf results in the osmotic movement of water across from adjacent internal cells into those that have just lost some water. This osmotic flow continues across the leaf – until it reaches the xylem tissue. When water molecules leave the xylem and move along the concentration gradient, this creates a tension in the column of water rising up the xylem. Due to the properties of adhesion and cohesion the water column does not break and so the entire water column is not pulled upwards. The combination of adhesive and cohesive forces, together with the suction pull of the transpiration – creates the transpiration stream. Mineral ions dissolved in the water are carried along by the transpiration stream and can move out by active transport – to reach the tissues where they are needed.

The sort of questions asked are either multiple choice or low mark short answer questions. There may be a question this year asking for comparisons between transport systems in plants and animals....who knows....


- Jimmy