In the figure below, we can see that in the sea there are several animals and various types of plants. And there are also very small beings - so small that they can only be seen with special devices like microscopes, which have special lenses that enlarge the image of the observed beings.
If we put a drop of seawater under the microscope, we will see a huge number of these little living things.
Think how many different organisms can be found in a garden: grass, rose bushes, worms, butterflies, beetles, ants, snails, thrush, lizards…
All living beings in a certain place and who maintain relations with one another form a community. The community of the sea below is composed of fish, algae, plants, microscopic beings, in short all the populations there.