Blood cell infected with malaria parasite

Malaria is caused by the single-celled parasite Plasmodium. It is transmitted from one person to another by certain species of blood sucking mosquito. The parasite spends part of its complex life cycle inside red blood cells.

More about microbes


Protozoa are single celled organisms. They come in many different shapes and sizes ranging from an Amoeba which can change its shape to Paramecium with its fixed shape and complex structure. They live in a wide variety of moist habitats including fresh water, marine environments and the soil.

  1. Amoeba proteus protozoa

    These are freshwater single-celled microbes that feed on bacteria and smaller protozoa. They use pseudopodia (cytoplasmic extensions) to engulf their food and for locomotion.

  2. The test (shell) of the British formaminiferan, Elphidium crispum.

    Foraminifera are single-celled protozoa which construct and inhabit shells. The shells are usually divided into chambers which are added during growth. These shells are made of calcium carbonate but some are made from sand and even silica.

  3. An illustration of the protozoan Trypanosoma brucei.

    This illustration depicts Trypanosoma brucei moving past human red blood cells in the blood. It is motile and has a single flagellum for locomotion.

    © John Bavosi / Science Photo Library

  4. Vorticella ciliate in compost heap.

    Vorticella is bell- shaped with a contractile stalk (bottom) to anchor itself to the surface. It has a flattened top with a mouth surrounded by a wreath of cilia (tiny hair-like projections). By beating these cilia the organism causes the water to swirl like water down a plug hole which draws bacteria into its mouth.

  5. Paramecium – a protozoan

    This single-celled organism lives in freshwater habitats. It is covered in cilia, short hair-like structures used for swimming and for wafting food into its groove-like mouth (centre).

Some are parasitic, which means they live in other plants and animals including humans, where they cause disease. Plasmodium, for example, causes malaria. They are motile and can move by:

  • Cilia - tiny hair like structures that cover the outside of the microbe. They beat in a regular continuous pattern like flexible oars.
  • Flagella - long thread-like structures that extend from the cell surface. The flagella move in a whip-like motion that produces waves that propel the microbe around.
  • Amoeboid movement - the organism moves by sending out pseudopodia, temporary protrusions that fill with cytoplasm that flows from the body of the cell.
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