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    Hi,

    On my syllabus it says the following points but I do not know how to explain them.

    Explain the importance of water potential and osmosis in the uptake of water by plants
    Explain the importance of water potential and osmosis on animal cells and tissues

    I would really appreciate any help!
    Thanks you
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    Nice question!

    Wow, GCSE and using the term 'water potential'. Ok I'll try my best to answer your questions (I'm just an average A level student so please take what I write with a pinch of salt!)

    Just before I tackle the questions I should probably make sure you understand what water potential and osmosis mean.
    The formal definition of osmosis isL 'The net movement of water molecules from a region of higher water potential to a region of lower water potential down a water potential gradient through a partially permeable membrane until dynamic equilibrium is reached'.
    This essentially means that the net effect of osmosis is water will move in down a concentration gradient (of water) until theres no longer a concentration gradient there (since more water has moved into the lower concentration than has left the lower concentration of water solution)
    Water potential is just a fancy word for 'concentration of water'

    Explain the importance of water potential and osmosis in the uptake of water by plants
    Where do plants get water from?
    1. The soil (root hair cells actively transport salts out into the soil, lowering water potential, so water moves in by osmosis into the root hair cells).
    2. Respiration (Aerobic respiration will produce water as a by-product. Btw I've got no idea how significant the volume of water produced is through respiration, but it produces it anyway).

    Why do plants specifically need water?
    1. Number one answer is photosynthesis - its very very important (i.e. 100% necessary) for photosynthesis to take place. Also, this is specific to plants only (plus some bacteria but that's besides the point).
    2. Turgidity: Plants have a cell wall which means that the 'best' state for their cells to be in is when they're loaded with water. This keeps the cell nice and big (whereas animal cells will lyse if too much water enters). The reason the plant need 'turgor' in its cells is so that it can stay nice and straight, so that the leaves are in the correct position and height to maximise the rate of photosynthesis.

    Explain the importance of water potential and osmosis on animal cells and tissues
    Why do animal cells specifically need water?
    1. To sweat (also known as 'evaporative cooling' ), does what it says on the tin, cools us down by evaporation (takes heat away). As a side point, this is really, really useful when the temperature outside is higher than our internal temperature, since every other method (conduction, convection and radiation) will result in us taking in heat from the environment. Only evaporative cooling can we lose heat.

    Not specific reasons to plants and animals (i.e. for both)
    1. Chemical/Metabolic reactions: Chemicals can dissolve in water and so water is a nice solvent.
    2. Transport: Its a good transport medium for water soluble substances (if you want to be fancy you can call them 'hydrophilic'.)
    3. Homeostasis: This is a bit of a weird point, but water is very good at maintaining a constant temperature, since it has a very high specific heat capacity (meaning you need a lot of energy to change its temperature).

    Hope I've helped at least a tiny bit! If you have any other questions feel free to ask.
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    (Original post by Spectral)
    Nice question!

    Wow, GCSE and using the term 'water potential'. Ok I'll try my best to answer your questions (I'm just an average A level student so please take what I write with a pinch of salt!)

    Just before I tackle the questions I should probably make sure you understand what water potential and osmosis mean.
    The formal definition of osmosis isL 'The net movement of water molecules from a region of higher water potential to a region of lower water potential down a water potential gradient through a partially permeable membrane until dynamic equilibrium is reached'.
    This essentially means that the net effect of osmosis is water will move in down a concentration gradient (of water) until theres no longer a concentration gradient there (since more water has moved into the lower concentration than has left the lower concentration of water solution)
    Water potential is just a fancy word for 'concentration of water'

    Explain the importance of water potential and osmosis in the uptake of water by plants
    Where do plants get water from?
    1. The soil (root hair cells actively transport salts out into the soil, lowering water potential, so water moves in by osmosis into the root hair cells).
    2. Respiration (Aerobic respiration will produce water as a by-product. Btw I've got no idea how significant the volume of water produced is through respiration, but it produces it anyway).

    Why do plants specifically need water?
    1. Number one answer is photosynthesis - its very very important (i.e. 100% necessary) for photosynthesis to take place. Also, this is specific to plants only (plus some bacteria but that's besides the point).
    2. Turgidity: Plants have a cell wall which means that the 'best' state for their cells to be in is when they're loaded with water. This keeps the cell nice and big (whereas animal cells will lyse if too much water enters). The reason the plant need 'turgor' in its cells is so that it can stay nice and straight, so that the leaves are in the correct position and height to maximise the rate of photosynthesis.

    Explain the importance of water potential and osmosis on animal cells and tissues
    Why do animal cells specifically need water?
    1. To sweat (also known as 'evaporative cooling' ), does what it says on the tin, cools us down by evaporation (takes heat away). As a side point, this is really, really useful when the temperature outside is higher than our internal temperature, since every other method (conduction, convection and radiation) will result in us taking in heat from the environment. Only evaporative cooling can we lose heat.

    Not specific reasons to plants and animals (i.e. for both)
    1. Chemical/Metabolic reactions: Chemicals can dissolve in water and so water is a nice solvent.
    2. Transport: Its a good transport medium for water soluble substances (if you want to be fancy you can call them 'hydrophilic'.)
    3. Homeostasis: This is a bit of a weird point, but water is very good at maintaining a constant temperature, since it has a very high specific heat capacity (meaning you need a lot of energy to change its temperature).

    Hope I've helped at least a tiny bit! If you have any other questions feel free to ask.

    Thank you so much for your help! I really appreciate it!

    So if water potential is to do with the concentration of water, does that mean that it is not specifically to do with the actual movement of water but it about the speed of rhe novement or how much water moves accross? Would a high water potential mean that less water would move to that location?

    Thank you!
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    Interesting question!

    Honestly for GCSE (or indeed A level even), understanding what water potential really is isn't required. (To be honest, I doubt I know much about it anyway).

    It was a bit 'oversimplified' to call water potential synonymous to concentration of water, since it isn't technically the same thing (although for our purposes its a good enough fit).

    Water potential is a measure of the potential energy of water (per unit volume) in the system (system refers to the solution we're talking about, be it carrot or salt water or pure water etc) relative to the pure (meaning no ions/impurities) water.
    Pure water is defined as having a water potential of 0kPa (yes it does have some potential energy, but we ignore it and set pure water's potential energy as = 0).
    Everything that is not pure water will have a negative water potential.

    Water potential essentially describes the 'tendency' of water to move from one area to another. This isn't just because of osmosis however, gravity and pressure also affects the water potential of a substance.

    Sorry, I'll start actually answering your question now.

    'So if water potential is to do with the concentration of water, does that mean that it is not specifically to do with the actual movement of water but it about the speed of rhe novement or how much water moves accross?'

    Answer: Sort of. Absolutely correct about its not really to do with the actual movement of water (since water is moving both ways). I'm not sure if its to do with the speed of movement though. It's very complicated to explain, but essentially if the two solutions are at the same temperature, the average 'speed' of the water molecules is the same in both, its not like water molecules move faster, it is just because more are moving one way than the other.
    Have you studied Le Chatalier's principle in chemistry? About equilibria and the like? If you have, this is the perfect way to think of water potential conceptually. The equilibrium position of this is where the difference in water potential between the solutions is zero - they are isotonic/have the same water potential. Like equilibrium reactions where both the forward and backward reaction are occurring (dynamic equilibrium), water is moving both ways. It eventually will reach a state where both solutions have the same water potential, which, looking at it from a macro perspective, there's no longer any change in number of water molecules moving in and out - the same number of water molecules are entering one solution as they are leaving it.

    So yes long story short, its number, not speed, of water molecules that is to do with the water potential.

    'Would a high water potential mean that less water would move to that location?'

    It's a bit of a trick question you put there! I don't know if i said this, but water potential is a relative thing (just like isotonic and hypo/hypertonic are). A high water potential (btw note a high water potential is a less negative one, since water potentials are 0 or less). If we put this 'high water potential' solution next to a solution of pure water (separated by a partially permeable membrane), more water will move into the high water potential solution (until equilibrium is reached). Sorry that was just me being picky.

    I know what you meant was 'if we have a solution with a higher water potential and a solution with a lower water potential, will less water move to that location?'
    The answer is yes, although water will be moving in, there will be more water moving out. Eventually though, the rate of water moving in and out will be equal, since equilibrium (i.e. no more differences in water potential) will be eventually reached, in which case the same number of water molecules will be moving in and out (no net movement).

    Sorry, this turned out to be longer than I expected. I hope I've clarified a bit more!
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    (Original post by musicangel)
    Hi,

    On my syllabus it says the following points but I do not know how to explain them.

    Explain the importance of water potential and osmosis in the uptake of water by plants
    Explain the importance of water potential and osmosis on animal cells and tissues

    I would really appreciate any help!
    Thanks you
    I'm going to explain in my own little way!!

    Basically in the root hair cells there are a high concentration of mineral ions, amino acids, nitrates etc... this has a low water potential

    These cause a lower water potential in the root hair cell, as the external environment around root hair cell (the soil) is mainly made up of water and few things dissolved within it. it therefore has a high water potential...

    Now, as the external environment (the soil) around the root hair cell has a high water potential this causes water to move through the root hair cell from an area of high water potential to an area of low water potential (inside the root hair cell) down the water potential gradient, therefore water moves into the root hair cell for that all important transpiration pull!.

    Water is only needed to be taken up via the root hair cell as its a carrier medium, osmotic process could supply the plant with water in the leaves..

    For animal cells and tissue

    Say you were a diabetic and couldn't metabolise your glucose properly, it then will stay in the blood causing all sorts of osmotic problems with your cells.

    As glucose is highly concentrated and insoluble being next to a cell will lower the water potential of the external environment of the cell causing water to move out of the cell down the water potential gradient and causing it to shrivel and die.


    Hope this helps! I'm studying a level biology (i'm at a2 level now)!!

    Goodluck!
 
 
 
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