What are Tissues?
When similar cells get aggregated to form an organized structure to carry out a specific function is tissue. Likewise, animal tissues and plant tissues also consist of numerous multicellular cells. A tissue is the collection of functionally and morphologically similar cells and their core materials.
Table of Contents
- Plant Tissues
- Types of Plant Tissues
- Meristematic Tissue
- Simple Permanent Tissues
- Complex Permanent Tissues
Plant tissue provides mechanical strength to the plant and has many dead cells also. It also gives flexibility and elasticity to plants and their organs. The plant tissues function in bending and stretching the plants; it regulates the transportation of water, nutrients and other materials.
With the continuous division of cells, new cells are produced, which results in the growth of plants. Importantly, tissues also function in photosynthesis. respiration, metabolism, regeneration, etc.
Types of Plant Tissues
On the basis of the capability of the plant cell to divide, there are two categories under which plant tissue falls: meristematic tissue and permanent (non-meristematic) tissue.
These are small, cuboidal and tightly packed cells that keep on growing and thus forming new cells. Such cells have the potential to divide and redivide. Such cells are present in the growing part of the plant, which helps in differentiating, enlarging and expanding the different types of tissues and thus benefits the plant in growth. The cells of the meristematic tissues lack vacuoles as vacuoles prevent quick cell division and give rigidity to the cell.
On the basis of regions of growth of the plants, meristematic tissues are of three types: Apical meristems, lateral meristems, and intercalary meristems.
- Apical Meristems are present on the tips of growing roots and stems. Thus, increasing their length and ultimately upsurging the growth of the plant.
- Lateral Meristems are present on the sides of the roots and stem. Thus, increasing their width or thickness, thus supporting the growth of the plant.
- Intercalary or Axillary Meristems are present at the base or internodes of the leaves. It helps in the development of the leaves, nodes and other organs of the plants.
Must Read: Plant Hormones
Simple Permanent Tissues
Permanent tissues originate from the old meristematic cells. When these (old meristematic cells) lose the potential to divide and expand, they turn into a permanent one.
An alternative term for permanent tissues is – matured meristematic tissue. So, such cells have a defined size and shape and perform specific functions. Such cells can be dead or living. These cells undergo the process of cellular differentiation, where they (cells) form a permanent size and shape and are ready to perform a specific function.
Such tissues differentiate into two different types of tissues, which are simple permanent tissues and complex permanent tissues.
Simple Permanent Tissues are of four types on the basis of their functions:
The cells have thick walls and provide mechanical support to the plants. These tissues are usually present in young plants, and thickened part of the cell wall of such cells is always there in newly growing parts of the plants.
The cells are living, irregularly thick, and elongated, comprised of pectin or cellulose with no or less intercellular spaces. These cells play the main role in providing mechanical strength as well as elasticity to the aerial and new growing parts of the plant.
These cells have a thick and longwall due to the presence of lignin. Sclerenchyma cells are dead and do not have a nucleus, cytoplasm as well as intercellular spaces.
These cells are present in the veins of the leaves, stems and near vascular bundles. Such cells provide strength and rigidity and also make the plant hard to bear external shock and stress.
These cells are abundantly present in plants, with an ample amount of intercellular spaces, where cells are loosely packed. These cells consist of cellulose and have large central vacuoles and nuclei.
These tissues play a significant role in the process of photosynthesis; it also stores water and nutrients. These tissues are present in stems, roots and leaves. The speciality of parenchymatous cells is that when they get wounded, they again get converted into meristematic plant tissue to get recovered. Parenchymatous tissues are generally present in the soft or non-woody parts of plants.
Must Read: Parts of Plant
Complex Permanent Tissues
As the name suggests, complex plant tissues play an important role in complex functions performed in plants, like in the transportation of water, minerals and nutrients to the leaves and other parts.
Unlike simple tissues, complex tissues comprise of more than cells, though they have the same origin. Also, they are targeted to perform the same function. These tissues are present in two forms which are Xylem and Phloem.
These cells are helpful in transporting nutrients and water to various parts of the plants. There are many elements in these cells like xylem fibres, xylem parenchyma, vessels and tracheids, out of which vessels play a significant role. These vessels are the small tubes that provide the supply of water and minerals in plants. This work is supported by the tracheids.
The only living cells in the xylem are the xylem parenchyma which plays the role of storing the food and transporting the water. The xylem fibres function in supporting plants and trees. The point to note is that the xylem is responsible for only vertical conduction (one direction).
Phloem parenchyma, phloem fibres, companion cells, and sieve tubes are the four elements of the phloem. It plays a role in transporting food and nutrients from leaves to various parts of the plants. The important point to note is that the conduction is bidirectional in the phloem; that is phloem transport the nutrients and minerals in both directions of the plants.
The sieve tubes consist of various sieve-tube cells or elements. They are responsible for providing organic substances like amino acids and sugars. Companion cells give metabolic support to the cells and consist of a sufficient amount of ribosomes and mitochondria than the sieve tube cells. The only dead tissues in the phloem are the phloem fibres.