Tissues

Introduction

· A group of cells that are similar in structure and work together to accomplish a particular function is known as tissue.

· Tissues are categorized as −

o Plant Tissue &

o Animal Tissue

· Let’s discuss them in brief −

Plant Tissue

· Following are the major types of plant tissue −

o Meristematic Tissues

o Permanent Tissues

§ Simple Permanent Tissues

§ Parenchyma

§ Collenchyma

§ Sclerenchyma

§ Epidermis

§ Complex Permanent Tissue

§ Xylem

§ Phloem

Meristematic Tissue

· Meristematic tissue mainly consists of actively dividing cells, and helps in increasing the length and thickening the stems of the plant.

· Meristematic tissue, commonly, present in the primary growth regions of a plant, for example, in the tips of stems or roots.

· Depending on the region (where the meristematic tissues are found); meristematic tissues are classified as apical, lateral, and intercalary (see the image given below).

· Apical meristem (as shown in the above image) is present at the growing tips of stems and roots and helps in their growth.

· Lateral Meristem is found in stem or root region and helps in their growth.

· Intercalary meristem is found at the base of the leaves or internodes (on twigs) and helps in growth.

Permanent Tissue

· Cells of meristematic tissue later differentiate to form different types of permanent tissue.

· Permanent Tissue is further categorized as −

o Simple Permanent Tissue and

o Complex Permanent Tissue

Simple Permanent Tissue

· Simple Permanent Tissue further categorized as −

o Parenchyma

o Collenchyma

o Sclerenchyma

o Epidermis

· Parenchyma tissue provides support to plants and also stores food.

· Sometimes, parenchyma tissue contains chlorophyll and performs photosynthesis, in such a condition, it is known as collenchyma.

· The collenchyma tissue provides flexibility to plant and also provides mechanical support (to plant).

· The large air cavities, which are present in parenchyma of aquatic plants, give buoyancy to the plants and also help them float, are known as aerenchyma.

· The Sclerenchyma tissue makes the plant hard and stiff. For example, the husk of a coconut is made up of sclerenchymatous tissue.

· The cells of Sclerenchyma tissue normally are dead.

· The outermost layer of cells is known as epidermis.

· The epidermis is usually made up of a single layer of cells.

· The entire surface of a plant has the outer covering of epidermis, which protects all the parts of the plant.

Complex Permanent Tissue

· The complex tissue, normally, consists of more than one type of cells which work together as a unit.

· Complex tissues help in the transportation by carrying organic material, water, and minerals up and down in the plants.

· Complex Permanent Tissue is categorized as;

o Xylem and

o Phloem

· Xylem, normally, consists of tracheid, vessels, xylem parenchyma, and xylem fibers.

· Xylem is accountable for the conduction of water and mineral ions/salt.

· Phloem, normally, is made up of four types of elements namely −

o Sieve tubes

o Companion cells

o Phloem fibers and

o Phloem parenchyma

· Phloem tissue transports food from leaves to other parts of the plant.