Chapter 22: Protista

Protista Characteristics

• Contains single celled and simple multicellular organisms.

• Eukaryotic

• Some feed by taking in organic substances, others can photosynthesise.

Examples:

Amoeba: moves by means of pseudopods and is well known as a representative unicellular organism.

Algae: A large and diverse group of plant like organisms ranging from unicellular to multicellular forms.

Paramecium: Consist of a single cell yet are visible to the naked eye.

Amoeba

• Single cellular organism.

• It is a heterotroph and omnivorous.

• It lives in freshwater ponds (most likely to be found on the mud at the bottom).

Structure of Amoeba

• Protoplasm is the living part of the cell (nucleus and cytoplasm).

• The cytoplasm consists of the outer firm ectoplasm and the inner fluid endoplasm. The endoplasm contains food vacuoles, fat droplets and waste.

• The endoplasm is fluid-like. It has a grainy appearance due to the presence of food vacuoles and waste materials.

• Ectoplasm can become soft in places to allow the development of pseudopodia.

• The cell membran retains the cell contents and allows for gas exchange and osmosis.

• The nucleus controls the cell.

• The pseudopodia are used for movement and to engulf prey.

• Amoeba feeds by surrounding its prey with pseudopodia and secreting digestive enzymes into the vacuole created.

• Food can then be stored within the vacuole.

Contractile Vacuole

• Amoeba’s cytoplasm is more concentrated than the surrounding fresh water.

• As a result water constantly rushes in by osmosis.

• In order to deal with this uptake of water amoeba forms a contractile vacuole.

• Excess water enters the contractile vacuole.

• The contractile vacuole swells with water and moves to the edge of the cell where it bursts and expels the water.

• Then the cycle repeats.