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What is Tissue? Why is it Important? Explain the difference between Plant and animal tissues
All living organisms are made of cells. A unicellular organism (e.g., Amoeba, Paramecium, etc.) has a single cell in its body, i.e., a single cell performs all basic life activities. For example, in Amoeba, movement of a cell, intake of food and respiratory gases (O2), intracellular digestion, metabolism, respiration, osmoregulation, and excretion are all done by the same cell. However, in multicellular organisms (e.g., human beings) there are millions of cells. Most of these cells are specialized to carry out only a few functions efficiently. These functions are taken up by different groups of cells: Thus, we can say that there is a division of labour in the multicellular organisms.
For example, in human beings, muscle cells contract and relax to cause movement of a body part, nerve cells or neurons carry messages, blood flows to transport oxygen, food, hormones, and waste materials (CO2, urea), and so on. Likewise, in plants, cells of phloem conduct food from leaves to other parts of the plant. Thus, we see that cells, which specialize in a function, are grouped together and form a tissue (Fr. tissue-woven). Blood, phloem, and muscle are all examples of tissues.
The term tissue was coined by Bichat in 1792. Study of tissues is called histology (Gk. histos = tissue; logos = study). Marie Francois Xavier Bichat (1771-1802) was a French anatomist and pathologist, the father of histology. Although working without the microscope, Bichat distinguished 21 types of elementary tissues from which the organs of the human body are composed. Marcello Malpighi (1628-1694) is considered the founder of histology. The term histology was coined by Mayer in 1819.
A group of cells similar in structure that work together to perform a particular function forms a tissue. All cells of a tissue have a common origin. For example, human nervous tissue (present in the brain, spinal cord, and nerves) has nerve cells or neurons which are basically the same structurally and functionally. All nerve cells basically have a cell body or soma (the nucleus-containing central part of a neuron) which has two types of branches, namely dendrites (to receive messages) and an axon (to convey messages away from the soma). All neurons of nervous tissue originated from the same germinal layer called ectoderm (more aptly the neural ectoderm).
Importance of Tissues
- The formation of tissues has brought about a division of labour in multicellular organisms.
- Tissues become organized to form organs and organs into organ systems.
- The workload of individual cells has decreased due to the origin of tissues.
- As a result of improved organization and higher efficiency, multicellular organisms have higher survival.
Why Plants and Animals are made of different types of Tissues?
Plants and animals are two different types of organisms. Plants are autotrophic organisms, so prepare their own food by photosynthesis. Moreover, plants are stationary or fixed organisms; they do not have to move from place to place in search of their food. Since they do not consume or need much energy, so most of the plant tissues are supportive, which provides them with structural strength. Most of these tissues such as the xylem, phloem, sclerenchyma, and cork are dead tissues; they do not contain living protoplasm. Animals, on the other hand, are heterotrophic organisms. They have to move in search of food, mate, and find shelter, so they need more energy compared to plants. Most of the tissues they contain are living (i.e., they have living protoplasm).
Differences between Plant and Animal Tissues
|1. In plants, dead supportive tissues are more abundant as compared to living tissues.
|1. In multicellular animals living tissues are more common as compared to dead tissues.
|2. They require less maintenance energy.
|2. They require more maintenance energy.
|3. There is a differentiation of meristematic and permanent tissues.
|3. Such differentiation is absent in them.
|4. Due to the activity of meristematic tissues plants continue to grow throughout life.
|4. Animals do not show growth after reaching maturity. Reparative growth is, however, present.
|5. Organisation of plant tissues is simple.
|5. Organisation of animal tissues is complex with the development of more specialized and localized organs and organ systems.
|6. Tissue organization is meant for the stationary habit of plants.
|6. Tissues organization is targeted towards the high mobility of animals.
Further, there are some tissues in plants that divide throughout life. They divide for the growth and reproduction of the plants. Such ever-dividing tissues are localized in certain regions of the plant body. Thus, based on the dividing capacity of the tissues, various plant tissues can be classified as meristematic and permanent tissues. In contrast to plants, growth in animals is uniform. So there is no such demarcation of dividing and non-dividing regions in animals.