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WEEK 8
SUBJECT: BIOLOGY
TOPIC: EXCRETORY SYSTEM I
CONTENT:
(a) Excretory systems
EXCRETORY SYSTEMS
Definition: Excretory systems refer to all the cells and organs of any living organism which enables it to eliminate harmful substances away from the body.
Excretion is therefore the removal of toxic wastes of metabolism from the body of living organisms.
NEEDS FOR EXCRETION
Waste products produced in the body by excretion must not be allowed to remain in the because of the following reasons:
CONTRACTILE VACUOLES
Contractile vacuole is an organelle or a device found in Amoeba and other unicellular organisms or protozoans. It is a simple device, a small sac lined with a membrane lying freely in the cytoplasm. The cell membrane surrounding the amoeba is a semi permeable to water and because the osmotic pressure inside the animal is greater than outside the animal, water enters the cell by osmosis. To counter this, water is secreted into the contractile vacuole as fast as it enters the body. As this happens, the contractile vacuole expands and bursts, thus discharging its contents to the exterior through a small pore in the cell membrane after which the whole process is repeated. The energy required by the contractile vacuole is produced by the mitochondria found near the vacuole. The contents of the contractile vacuole are; water, carbon (iv) oxide and nitrogenous wastes.
Paramecium
The paramecium is a single-celled organism that propels itself by minute, hairlike projections called cilia. Cilia also create currents that sweep food particles toward the paramecium’s gullet for ingestion. The paramecium gets rid of excess water with the help of a contractile vacuole, which pumps water out of the cell.
FLAME CELLS IN FLATWORM
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