A world beyond the naked eye
An alga with dozens of branches is a single cell. A tiny rotifer has organs. Look closer: pond water can hold them both.
Look through the microscope
Five life forms, up close
Change the slide, enlarge the photograph and find the suggested detail. Start with the green alga’s branching edge.
One cell
Every branch belongs to the same alga. Its two halves meet at a narrow waist. The green comes from chloroplasts, the parts of the cell that capture light for photosynthesis.
Follow the edge out to its smallest branches. Then compare the top half with the bottom: they are very similar, without being perfectly identical.
A colony
The green dots on the surface are cells. Together, they form a Volvox colony. The larger spheres inside are daughter colonies, developing before they are released.
Distinguish the tiny surface dots from the green spheres inside. The outer cells have fine filaments called flagella, whose beating propels the colony.
An animal
It has a mouth, a digestive tract and muscles. A rotifer is made of many cells, although it fits in the same microscopic field as single-celled organisms. In many rotifers, cilia around the mouth move water and draw in food particles.
At the broad end on the right, look for very fine filaments. Beating one after another, they can look like turning wheels. Further down, you can explore how this illusion works.
One cell
Each of the two shapes in the photograph is one cell. In the species Stentor coeruleus, researchers have observed something remarkable: after a cell is cut in two, each half can regenerate its missing parts if it retains part of the large nucleus.
Find the broad end, fringed with cilia. Their beating produces a current that brings in food. The shape can change as the cell contracts.
One cell
Diatoms build their cell walls from silica, a material also used to make glass. The transparent shell reveals the golden-brown interior of this living cell.
Follow the long outline, curved into a gentle S. Inside are the chloroplasts that help the alga use light. The full photograph retains the author’s scale bar.
Tiny does not mean simple
Micrasterias uses light. Stentor feeds and can rebuild parts of its body. Through a microscope, an organism’s outline cannot tell you how many cells it contains.
In Micrasterias, the whole branching shape belongs to one cell.
In Volvox, many cells form a sphere together.
In a rotifer, cells form tissues and organs.
The rotifer and its apparent wheels
Cilia are fine filaments that bend one after another. Together, their movements look like rotation. The name “rotifer” comes from this impression of a turning wheel.
Follow the marked, thicker filament. Its base stays in the same place while the movement travels around the circle.
Now try without the labels
Five photographs. Look at the shape, choose an answer and see what you recognised.
You took a closer look.
The same water can hold individual cells, colonies and animals. Now you know what differences to look for.
In Micrasterias, the whole branching shape belongs to one cell. In Volvox, many cells form a sphere together. In a rotifer, cells form tissues and organs.
Next time you pass a pond
Films on plants, clumps of algae and sediments can hold very different organisms. They do not all appear in the same sample. What you find depends on where you collect the water and when you look at it.
The Quekett Microscopical Club’s illustrated guide will help you recognise more of the life in a pond.
The photographs show real specimens. The explanations draw on the sources below; general descriptions do not replace species identification.
These photographs come from separate observations. Illumination and microscopy techniques affect how colours and outlines appear. Enlargement here brings the photograph closer; it does not represent a microscope’s optical magnification.
Images have been resized for the page and framed in circles in the explorer. The full photograph retains the author’s composition and scale bars. Photo credits and licences are listed with each specimen.
