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Sub – Topic 6: LEVELS OF ORGANIZATION OF LIFE
The bodies of living things are highly organized. This organization occurs in levels, with the simplest structure occurring at the lowest levels (single cells) which interact to build up more complex structures (multicellular organisms).
The basic levels of organization of life in organisms are; cells, tissues, organs and systems.
Cell: This is the smallest unit of living organism. It is the first and simplest level of organization of life. Plants and animals are made up of cells. One-celled organisms are called unicellular organisms. They include Amoeba, Plasmodium, Euglena, Paramecium, etc. Organisms made up of many cells are called multicellular organisms e.g man, mango, trees etc. The single celled organism can carry out all life processes on its own.
Tissues: This is a group of similar cells which come together to perform a particular function. A tissue consists of two or more different types of cells aggregating together to perform a specific function e.g. the mesophyl layer in leaves, xylem tissue in stems, muscles, blood (a liquid tissue) etc. Organisms which exist at the tissue level include the hydra, jelly fish, sponge etc.
Organ: Is a group of similar tissues which come together to perform a specific function. Examples in plants are flowers, roots, leaves, seeds, a rhizome, a corm, an onion bulb, a tuber, etc. Examples in animals are the skin, stomach, heart, brain, liver, eyes, ears, kidney, etc.
System: This is a group of functionally related organs which work together to perform specific functions. Examples in plants include the shoot system and root system. Examples in animals include the digestive, nervous, excretory and circulatory systems. Examples in plants are the transport system, shoot and root system.
Sub – Topic 7: Complex multicellular organisms:
The climax of organization in higher living things is the aggregation of systems to form an organism. Complex multicellular organisms are composed of several organ systems which work harmoniously for the benefit of the organism. All animals from Platyhelminthes to Mammals, and all vascular plants are organized on this level.
Complexity of Organization In Higher Animals
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