Introduction to Tissue Level of Organisation
Tissues: An Overview
All living organisms are made up of millions of cells. These cells perform all the functions of the body—whether it is the beating of the heart or the movement of the hands. Let us find out how these cells perform so many different functions.
What can you conclude from the figures given above?
The given figures show that: cells having similar structures combine to perform the same function. This combination or cluster of cells is known as a tissue. For example, nerve cells combine to form the nervous tissue.
There are n number of cells in multicellular organisms. These cells make up the tissues, which in turn combine to make up the different organs. The different organs form the different organ systems and these organ systems unite to form the organism.
Cells → Tissues → Organs → Organ systems → Organism/Individual
On the other hand, unicellular organisms have only a single cell. This sole cell performs all cellular functions. For example, Amoeba. So, division of labour is a feature of multicellular organisms rather than of unicellular organisms. The tissues present in one organism are different from the tissues present in another. For example, the tissues present in animals are broadly classified as epithelial, connective, muscular and nervous tissues. In contrast, the tissues present in plants are broadly classified as meristematic and permanent.
Meristematic tissue, also known as meristem, is composed of immature and continuously dividing cells. In plants, the shoot and root tips are made up of meristematic tissues.
Let us observe meristematic tissues.
Characteristics of meristematic tissues:
- Meristems are made up of immature or [[mn:glossary]]undifferentiated[[/mn:glossary]] cells.
- Their cells are small in size.
- Their cells are highly active metabolically and contain a dense cytoplasm.
- Intercellular space is negligible and is often absent in case of meristematic tissues.
- The cell wall is thinner and has a prominent nucleus.
Types of Meristematic Tissues
Apical meristems: They are present at the tips of stems, roots and branches. They are responsible for the axial growth in a plant.
Types of Meristematic Tissues
Intercalary meristems: They are present at the base of the [[mn:glossary]]internodes[[/mn:glossary]]. They are responsible for the growth of the internodal region.
Lateral meristems: They are present on the lateral side of stems and roots. They are responsible for the radial growth of plants.[[mn:glossary]]Vascular cambium[[/mn:glossary]] and [[mn:glossary]]cork cambium[[/mn:glossary]] are examples of lateral meristem.
Example 1: Why do meristematic cells have small vacuoles or no vacuoles?
Solution: The function of meristematic cells is to divide rapidly and produce new mass of cells. Vacuole is a cell organelle used for storing waste substances, water, etc. Since meristematic cells are actively dividing and young cells, they do not have any waste material to store. So, vacuoles are usually small or not present at all in meristematic cells.
Example 2: Why are meristematic cells referred to as undifferentiated cells?
Solution: Meristematic cells are undifferentiated cells becaus...
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