Biology - 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 −

  • Plant Tissue &

  • Animal Tissue

• Let’s discuss them in brief −

Plant Tissue

• Following are the major types of plant tissue −

  • Meristematic Tissues

  • 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 −

  • Simple Permanent Tissue and

  • Complex Permanent Tissue

Simple Permanent Tissue

• Simple Permanent Tissue further categorized as −

  • Parenchyma

  • Collenchyma

  • Sclerenchyma

  • 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;

  • Xylem and

  • 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 −

  • Sieve tubes

  • Companion cells

  • Phloem fibers and

  • Phloem parenchyma

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