Chapter 22: Kingdom Protista Leaving Certificate Biology Higher Level
Amoeba • Amoeba is a unicellular organism that lives in freshwater – For this reason, osmosis poses a problem for Amoeba • Amoeba feeds heterotrophically meaning it takes in food from other animals and plants – it is also an omnivore
Structure of Amoeba • Single cell with nucleus, granular protoplasm (due to many food vacuoles) and characteristic pseudopods for movement and feeding • The protoplasm is made up of an outer cytoplasm (ectoplasm) and inner cytoplasm (endoplasm) – Ectoplasm is more viscous (harder) than the endoplasm – Endoplasm is clearer in nature and more granular then the ectoplasm
Structure of Amoeba
Structure of Amoeba
Feeding in Amoeba • Amoeba feeds by extending its pseudopods around target and engulfing it much the same way in which macrophage/phagocytes belonging to the immune system engulf pathogens • Once engulfed, the area in which the food is held is called the food vacuole – digestive enzymes are released and the food is broken down and used by the Amoeba
Osmoregulation in Amoeba • Amoeba lives in freshwater and so its cytoplasm has more dissolved solutes than the surrounding environment meaning that the water concentration is lower inside Amoeba than outside • Water moves by osmosis down its concentration gradient so water will move into Amoeba continuously • This poses a problem – Amoeba would burst if it was not able to regulate water content • Amoeba regulates water content by having a large central ‘contractile vacuole’ in which excess cytoplasmic water is pumped out • Once the contractile vacuole is full it moves to the surface of the cell and fuses with the membrane spilling its contents back out to the environment
Osmoregulation in Amoeba H 2 O H 2 O H 2 O H 2 O H 2 O
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