Chapter 1: TISSUES
1. DIVISION OF LABOUR
An unicellular organisms has a single cell in its body that is a single cell performs all basic life activities.
For example in a moment of cell intake of food and respiratory gases intracellular digestion, metabolism,respiration and excretion are all done by the same cell. However,in multicellular organism there are millions of cell. most of the cells are specialised to carry out of you functions efficiently. these functions are taken by different groups of cell. Thus we can say that there is a division of labour in the multicellular organism. For example in human beings, muscles contract and relax to cause movement of the body part , nerve cells or neurons carry messages. Blood flows to transport oxygen, food,hormone and waste material and so on. Likewise in plant cells of pholem conducts food from leaves to other part of the plant.Thus,we see that cells which are specialised in functions are grouped together and form a tissue.Blood, pholem, muscle are all example of tissues.
The term tissue was coined by Bichat in 1792. Study of tissue is called histology.
A group of cells similar in structure that work together to perform a particular function forms a tissue.All cells of tissue have common origin. For example human nervous tissue has nerve cells or neurons which basically has a cell body or soma which has two types of branches,namely dendrites and an axon.All neurons of nervous tissue are originated from the same germinal layer called ectoderm.
Importance of tissues.
1.Formation of tissues has brought about division of labour in multicellular organisms.
2.Tissues become organised to from organs and organs into organ systems.
3.Workload of individual cell has decreased due to origin of tissues.
4.As a result of improved organisation 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 have not move from place to place in search of their food.Since they don't consume or need much energy so most of the tissues of plants are supportive, which provide them with structural strength.
Animals on the other hand,are heterotrophic organisms.They have to move in search of food,mate and shelter,so they need more energy as compared to plants.Most of the tissues they contain are living .
Further,there are some tissues in plants which divide throughout life.They divide for the growth and reproduction of the plants. Such ever-dividing tissues are localised in certain regions of the plant body.Thus,based on the dividing capacity of the tissues the various plant tissues can be classified as meristematic and permanent tissues.
1.Meristematic Tissues (Meristems)
Nature.Cells of Meristems divide continuously and help in increasing the length and girth of the plant.These cells show the following characteristic:
1.The cells of meristematic tissue are similar in structure and have thin cellulose cell walls.
2.The meristematic cells may be sperical,oval, polygonal or rectangular in shape.
3.The meristematic cells are completely arranged and do not contain any intercellular space between them.
4.Each meristematic cell contains dense or abundant cytoplasm and a single large nucleus.
Occurrence.Meristematic tissues are growth tissues and are found in those regions of the plant that grow.According to their position in the plant,meristems are apical, lateral and intercalary.
1.Apical meristems.These are situated at the growing tip of stems and roots,i.e.,at shoot apex and root apex.Apical meristems are also found at apices of the leaves.
2.Lateral meristems.These are found beneath the bark and in vascular bundles of dicot roots and stems.They occur in thin layers. Cambium is the region which is responsible for growth in thickness.
3.Intercalary meristems.They are located at the base of leaves or internode,e.g.,stems of grasses and other monocots.
2.Permanent Tissues
Different types of permanent tissues are formed due to difference in their specialization.Permanent tissues may be simple or complex.
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