These tiny choanoflagellates, found in every aquatic environment, sift out and eat bacteria, thereby providing an important link in the base of the food web that sustains all aquatic life. Recent research has, surprisingly, shown that they branched off the line of evolution leading to all animals very early in the evolution of complex life forms and they are therefore our - very distant - relatives.

From: The Kingdom Protista: The Dazzling World of Living Cells, 2006.

The planet abounds in cellulose but almost nothing can digest it. Termites have created a cooperative way to do so. They chew up wood and then ferment the chips in their stomach where an extraordinary gathering of unique bacteria and protists, found nowhere else on the planet, produce the cocktail of enzymes needed to access this vast food source. These microorganisms digest the cellulose and share the glucose and other sugars released with the host termite.

From: The Kingdom Protista: The Dazzling World of Living Cells, 2006.

Many plant tissues are made up of cells organised into precise arrangements. This video shows one way these patterns are created. Precisely controlled cell divisions lay down a new wall between the new cells. While the walls can grow and are somewhat flexible, they cannot move around and so these cell divisions set up a predetermined pattern that has a major effect on tissue geometry.

From: Living Cells Structure, Function, Diversity, 2007.

Oceans and lakes have enormous populations of tiny photosynthetic plants that are critically important to the survival of all marine organisms, even the largest whale. This is just one of the hundreds of thousands of species. It is a green alga, very distantly related to land plants.

From: The Kingdom Protista: The Dazzling World of Living Cells, 2006.

This large unicell feeds voraciously on tiny animals and planktonic cells. It is a dinoflagellate called Noctiluca. Sometimes it blooms in huge numbers and then, as its name indicates, it creates the beautiful phenomenon called phosphorescence.

From: The Kingdom Protista: The Dazzling World of Living Cells, 2006.

These dense sausage-shaped organelles called mitochondria undergo much of the oxidative chemistry that generates the cell's supply of ATP, used up in most energy-requiring reactions. Recent work has shown that these tiny bodies originally arose from bacteria that were eaten by primitive cells and, instead of being digested, became adapted to live inside the host cell.

From: Living Cells Structure, Function, Diversity, 2007.

Ciliates like these Paramecium are extraordinarily complex single-celled organisms. These cells are actively looking for food. The last sequence in the clip suggests that one cell is smart enough to remember how to back out of the maze of microscopic filaments and other objects it burrowed into.

From: The Kingdom Protista: The Dazzling World of Living Cells, 2006.

The cell has an elaborate cytoskeleton that contains two main constituents: microtubules (stiff rods that can be broken down and reassembled); and long flexible actin filaments, responsible for much of the fine movement and ruffling of the cell membrane seen in these shots.

From:Living Cells Structure, Function, Diversity, 2007.

Many fish can slowly or rapidly change their colour. The changes are brought about by special pigmented cells called chromatophores located in the scales. These cells are flattened or sometimes display numerous long fine extensions and they contain a mass of brightly coloured pigment granules. Under nervous stimulation, chromatophores can disperse the granules over their cytoskeleton of microtubules and then aggregate them. With thousands of granules working together in thousands of scales, the fish changes colour.

From: Living Cells Structure, Function, Diversity, 2007.

When food is plentiful, individual cells of slime molds are amoeboid and independent. When hard times come, they aggregate to form a slug-like stage called a pseudoplasmodium which moves about and then transforms into a fruiting body that releases resistant spores.

From: The Kingdom Protista: The Dazzling World of Living Cells, 2006.

The very common pond alga Spirogyra undergoes sex by the characteristic process known as conjugation.

From: The Kingdom Protista: The Dazzling World of Living Cells, 2006.

Before every cell division, chromosomes are carefully arranged inside the cell in such a way that each of the two new cells get one - and only one - copy of every chromosome. This precision ensures that each cell has a complete copy of its genetic heritage.

From Living Cells Structure, Function, Diversity, 2007.