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To answer this question, we will first note the definitions of and differences between osmosis and diffusion. The difficulty exists because the processes are considered similar and osmosis is considered a special type of diffusion with its own differences. In osmosis:
- water that is concentrated in one area is absorbed by the lower concentration elsewhere in an effort to balance the two.
- there is a transfer of molecules which can only take place in solutions.
- a semi-permeable membrane means that only some solvents (e.g. the water) that are contained in a solution can pass through.
- the process can be stopped or partially reversed.( As an example, imagine squeezing the water back out of the bread after it has soaked overnight).
- there is the potential for the transfer of molecules or particles from solutions, liquids and gases. Consider the process of making tea. The tea from the teabag transfers from the bag into the water.
- there is no membrane which means that solvent (e.g. water) and solute (most common examples are salt and sugar) molecules can transfer across.
- there can be no reversing of the process.
Therefore, the process of osmosis takes place when bread is dipped in water and left overnight because the water transfers from the dish into the bread to balance the contents of the bowl.
First, let's break down what we should already be confident in explaining.
Diffusion is the movement of particles from a high concentration down the concentration gradient towards a low concentration.
Think of a crowded, noisy playground filled with a lot of screaming, pushing, and shoving four year old kids (particles) waiting in a confined area (high concentration) to use a really tall slide (concentration gradient) where they will finish at the bottom of a open sandbox area (low concentration). Several kids excitedly slide down the slide landing in the sandbox.
in other words: crowd of kids at top -- slide-- bottom of slide in sandbox landing at the bottom (high concentration-- concentration gradient-- low concentration)``
Osmosis is a form of diffusion with two facts of note-- 1) the particles involved are WATER ONLY, and 2) THE WATER GOES THROUGH A SEMIPERMEABLE MEMBRANE.
With the bread example you gave, it can safely be said that there is little water in those cells.
The bowl of water on the other hand has plenty of water.
Once you dip the bread into the water the water will flow through the cell membranes within the bread 'soaking' the bread until it can no longer absorb any more, having reached equilibrium.
Hope the visuals described will aid your understanding.
First, let's look at some definitions of osmosis and diffusion. The definition of diffusion is the movement of particles from an area of high concentration to an area of low concentration. For example, if you spray Lysol in a small room the area of high concentration is in the aerosol can to the atmosphere (low area of concentration).
Osmosis is a similar process. It is the movement of water specifically from an area of high concentration to an area of low concentration. Essentially, the bread would absorb the water filtering through the bread (membrane) and spread throughout the bread.
When water moves from an area of high concentration to an area of low concentration it is osmosis. Any other substance would be diffusion.
Diffusion refers to movement of any particle down its concentration gradient; movement of particles from its higher concentration to its lower concentration.
Osmosis is same as diffusion however, the term is used only in the context of the movement of water molecules. Thereby, osmosis refers exclusively to the movement of water molecules down its concentration gradient i.e from its higher concentration to its lower concentration. In simple words, water would move from an area where water concentration is higher to an area where water concentration is lower.
(Students often get confused between concentration and amount. Please do not confuse concentration with amount.)
Now, in case of bread dipped in water- water will move into the bread as by virtue of osmosis, water will move from an area of its higher concentration to an area of its lower concentration.
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