Tissues, Organs and Systems
In organisms which are note complex than the Hydra, there are more types of specialized tissues. Each type usually carries out only one particular function. This is referred to ad 'division of labour' within the organism.
The main types of tissues in higher organisms are as follows:
• Surface tissues: These are known ad epithelial tissues in animals and dermal tissues in plants. They form a protective covering over the outer and inner body surfaces.
• Connective, supportive and packaging tissues: These bind other tissues together, fill up spaces in the body and provide support.
• Vascular tissues: These are the xylem and phloem tissues in plants and the blood in higher animals. They are concerned with the transportation of materials in the body.
• Muscular tissues: These are present in animals. they receive stimuli, transmit impulses to various parts of the body, and bring about responses to transmitted stimuli.
In higher plants and animals, different tissues are grouped together to form a structure of an organ with a special function. The heart is an organ made up of muscle tissue, connective tissue, nervous tissue and vascular tissue. These tissues work in a coordinated manner and enable the heart to carry out the broader function of pumping blood continuously. Each tissue by itself can only do part of the job or function.
Different functionally related organs form an organ system. Thus, the heart , blood and blood vessels form the circulatory system. Several organ systems carry out all the functions of a highly complex organism.
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