PROTISTS

This group is made up of

Protozoa and Filamentous algae.

The simplest protist is

the amoeba.

WHAT IS AN AMOEBA?

The amoeba is a simple animal made up of just one cell.

It normally lives in ponds, ditches or slowly moving streams.

The amoeba is just visible to the naked eye.

It eats, respires, digests food and excretes waste.

It moves about, responds to stimuli, grows, is able to repair and reproduces.

HOW DOES AN AMOEBA FEED?

The habitat of the amoeba is the mud and water of ponds and ditches. In the mud, there are many microscopic plants known as desmids.

When the protoplasm of the amoeba comes into contact with one of these plants, it flows round the plant, forming a cup shaped projection. This is literally a food cup, which completely encloses and ingests the food. In this way a food-vacuole is formed in the endoplasm. An amoeba, however, does not feed entirely on plants it is also carnivorous feeding on tiny ciliates.

In the food vacuole, digestion commences and affected by similar processes to higher animals. Enzymes are secreted into the food vacuoles along with other digestive juices. The digested material is now in a solution that can be absorbed into the surrounding cytoplasm. Once all the digestible material has been absorbed the remainder is excreted by the animal.

HOW DOES AN AMOEBA RESPIRE?

Amoeba are simple animals and their whole surface is in contact with the water that surrounds them and which contains oxygen.

All the oxygen the amoeba needs passes through the outer surface inwards and carbon-dioxide which is a waste product, seeps outwards.

This takes place by simple diffusion. As the amoeba uses up oxygen on the inside, the concentrate of oxygen lowers, so there is less on the inside than in the water outside.

The oxygen then passes from the outer to the deeper parts of the protoplasm.

All living things need nutrition to provide energy and the protist kingdom is no exception.

If we look at the amoeba, it gives us an example of a simple free living protist.