AMOEBA.docx

Protista (Amoeba) Amoeba is a free-living eukaryotic organism that feeds on bacteria and other similar organisms in water. Some amoeba species live in fresh-water and some live in the sea. Structure (10) The cell is filled with two different types of cytoplasm: 1. Ectoplasm – A thick jelly-like mate...

Protista (Amoeba) Amoeba is a free-living eukaryotic organism that feeds on bacteria and other similar organisms in water. Some amoeba species live in fresh-water and some live in the sea. Structure (10) The cell is filled with two different types of cytoplasm: 1. Ectoplasm – A thick jelly-like material that forms a thin layer just inside the cell membrane 2. Endoplasm – A more fluid, jelly-like material that fills the rest of the cell. The cell organelles are suspended in the Endoplasm. The endoplasm is also involved in movement. Osmoregulation Osmoregulation is the process by which cells regulate the concentration of water within the cell. It is carried out as follows: 1. The contractile vacuole eliminates excess water which comes as a by-product of respiration, or which enters the cell by osmosis. 2. Water is actively transported into the contractile vacuole. Many mitochondria surround the contractile vacuole producing the necessary Energy. 3. The vacuole gradually increases in size and when full, moves through the cytoplasm to the surface of the cell where it bursts and expels the water. (11) Movement Movement is achieved by structures called pseudopodia which develop on Amoeba. Environmental conditions determine the direction of Amoeba’s movement. Chemicals released by their prey attract Amoeba, while other conditions repel it. This is known as chemotaxis. Once the pseudopodia appear, the endoplasm flows into them, causing Amoeba to move in that direction. This type of motion is described as amoeboid motion. Feeding Amoeba feed by a process known as phagocytosis. A layer of cell membrane surrounds the food particle, and it is taken into the endoplasm, forming a structure called a food vacuole. One or more lysosomes from the cytoplasm fuse with the food vacuole and supply the digestive enzymes to break down the food. The products are then adsorbed through the membrane into the cytoplasm. Undigested food is left behind as the food vacuole moves to the edge of the cell in a process called egestion. (12) Reproduction in Amoeba Reproduction is by a process called binary fission. - When Amoeba reaches a certain size, it withdraws its pseudopodia and becomes rounder in shape - The nucleus divides in two and the two nuclei move apart - The cytoplasm between the two nuclei divides in two in such a way that a nucleus is enclosed in each half - This results in two identical daughter cells and takes approximately 30 minutes