Solutions, Solutes and Solvents

In order to understand exchange and transport, we need to have a good understanding of the concepts of solutions, solutes, solvents and concentration. We will start by looking at solutions, solutes and solvents, and then we will go on to look at concentration.

Many substances can dissolve in other substances. For example, glucose can dissolve in water. When a substance dissolves, its particles become spread out within the substance that it is dissolving in.

Diagram illustrating what happens when glucose dissolves in water. The diagram consists of two drawings of the same beaker, one of the left showing a beaker of water before glucose is dissolved in it, and one on the right showing the same beaker after glucose is dissolved in it. The beaker on the left is labelled "Water" and the beaker on the right is labelled "Water with glucose dissolved in it". There is an arrow labelled "Dissolving" pointing from the left beaker to the right beaker. Above the left beaker is a sugar cube, labelled "Cube of solid glucose". A zoomed in section on the sugar cube shows that it is made up of many glucose molecules packed together. A zoomed in section of the water in the left beaker shows that it is made up of water molecules (H2O). A zoomed in section of the solution in the right beaker shows that it is made up of water molecules with individual glucose molecules in between them.

When glucose dissolved in water, the glucose molecules become spread out amongst the water molecules.

The substance that dissolves is called the solute. The substance that the solute dissolves in is called the solvent. The mixture of solvent and solute that is formed is called a solution.

For example, when glucose dissolves in water, the glucose is the solute, the water is the solvent, and the mixture of glucose and water is the solution.

Diagram showing the relationship between a solution, a solute and a solvent. The diagram shows a beaker containing liquid. The liquid is labelled "Solution. A mixture made up of one substance dissolved in another substance.". A zoomed in section shows that the substance is made up of small hexagonal shaped molecules spread apart from each other and each surrounded by many water molecules (H20). One of the hexagonal molecules is labelled, "Solute. The substance that is dissolved.". One of the water molecules is labelled, "Solvent. The substance that solute is dissolved in.".

A solution is a mixture made up of one substance (the solute) dissolved in another substance (the solvent).

Water is a very important solvent in living things

Most of the liquids in living things are solutions in which water is the solvent. These include:

  • The cytoplasm of cells
  • Blood and other bodily fluids in animals
  • The liquids that are transported in xylem and phloem vessels in plants
Photograph of the leaves of a strawberry plant with droplets of clear liquid coming out at regular intervals around the outer edges of the leaves. (Note: this is called guttation).

In some plants, such as this strawberry plant, fluid from the xylem comes out in droplets at the edges of the leaves overnight. Like most liquids in living things, this xylem fluid is a solution in which water is the solvent.

Many of the liquids that living things interact with are also solutions in which water is the solvent. For example:

  • The bodies of water that aquatic organisms live in (such as rivers, lakes and oceans)
  • The liquid in soil
Photograph of a group of sea otters in water. Most of them are lying on their backs with their heads and feet sticking out of the water.

A group of sea otters in the ocean. The liquid in the ocean is a solution in which water is the solvent.

There can be multiple solutes dissolved in a solvent

It is possible for many different solutes to all be dissolved in the same solvent at the same time. In fact, this is the case for all of the solutions mentioned above. For example, the cytoplasm of a cell is made up of water with many different biological molecules dissolved in it.

Animated gif of pondweed cells, created from footage captured through a light microscope. One cell is fully visible, and seven others are partially visible but cut off at the edges of the image. Inside each cell there are many chloroplasts - which appear as small round green structures - flowing clockwise around the outer edge of the cell.

Footage of pondweed cells. The cells are very large and carry out a process called cytoplasmic streaming which causes the cytoplasm (and its contents, such as the chloroplasts seen here) to flow around the cell. The cytoplasm is a solution made up of water with many different solutes dissolved in it. Image: MarceloTeles via Wikimedia Commons (CC BY-SA 4.0 -


Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.


What is a solution?


What is a solute?


What is a solvent?


What is the most common solvent in biology?


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