The diversity of protoctist cell shape, arrangement and size

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                Claire Eke   U8750402   S204 TMA01

The diversity of protoctist cell shape, arrangement and size.

Protoctista are broadly defined as all the unicellular eukaryotes and any multicellular descendants that are neither plants, animals nor fungi (Ridge 2001). The kingdom includes nearly 30 Phyla with thousands of species living in different environments, and adapting in different ways to survive.

The most commonly known and simple protoctist is the Amoeba genus. Amoeba proteus (fig 1) is a single celled amoeba that lacks flagella. It has no cytoskeleton or external test and feeds by phagocytosis. Several pseudopods are formed enabling the organism to move. It has a single nucleus and may be up to 450 μm in size.

A much smaller group of organisms are the phylum Cryptophyta (fig 2). These unicellular, flat organisms are only 3-5μm in size and are discussed again later.

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Protoctista may have no flagella (like Amoeba proteus), one flagella, or be multiflagellates. The Cryptophyta (fig 2) have two flagella with stiff hairs, whilst Giardia lamblia (fig 3), has 8 flagella.

Flagella may be used for movement or feeding. In organisms that use flagella for feeding, the flagella are positioned around specialised areas of the cell (a gullet) and push food towards or into this gullet (fig 2.7, Ridge 2001)

Although most cells have one nucleus (fig 1), many have more. This can range from two, as in ...

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