biology

hi, can someone pls answer these questions for me I am on the verge of tears looking at them:

Use cohesion-tension theory to explain why water can't travel from roots to leaves
Use the mass flow hypothesis to explain why sucrose can't travel from the roots

pls help pls pls pls

Reply 1

kaorimiyazono

Do you mean can? I'm gonna explain this from 0 because I don't know how much you understand- I'm really sorry if this is too long or if you already knew some of the information I'm saying. I'm not being condescending I just wanna help you understand :smile:

Ok, so first you have to understand a key property about water: it has a dipole.
The oxygen atom is more electronegative than the hydrogens. This means that it pulls the negative electrons towards itself. Because of this, the O has a partially negative charge while the Hs have a partially positive charge. Since H2O is not symmetrical in its shape, this means that one side of it (the O side) is partially negative, and the other side (the Hs side) is partially positive. This is referred to as a dipole.

This dipole allows water to have cohesion and adhesion.
Cohesion = the ability of water to form hydrogen bonds with other water molecules. Cohesion is what allows there to be streams of water and drops of water to be held together. The water molecules form hydrogen bonds with each other and therefore hold each other together in drops and pull each other like a congo line in streams of water (like in roots).
Adhesion = the ability of a water molecule to form hydrogen bonds with other polar molecules or ions. This allows water to "hold onto" surfaces e.g. windows, leaves, roots.

Mass flow is simply the bulk movement of a fluid from an area of high fluid concentration to an area of low fluid concentration facilitated by cohesion/adhesion or by differences in pressure (going from high to low pressure). For example, water moves through roots via mass flow (facilitated by cohesion-adhesion) and blood moves around our blood vessels via mass flow (facilitated by cohesion-adhesion, but also by the pressure differences generated by the heart).

I hope this helped you answer those Qs :smile:

If something doesn't make sense I'm more than happy to answer any further Qs. If you wanna type up answers to the Qs in the OP I can also read them and give you feedback on them if that would be helpful.