TISSUES, ORGANS, ORGAN SYSTEMS, ORGANISM Part-1

 

Tissues-A group of cells that have a common origin and work together to achieve a particular function forms a tissue.

Types of tissue

  • Plant Tissues
  • Animal Tissues

Plant tissues

On the basis of their dividing capacity plant tissue are of two types:

  • Meristemtic tissues
  • Permanent tissues

Meristematic Tissues-

  • These are simple living tissues in which the cells are always young and actively divide throughout the duration of the plant's life.
  • Presence of thin primary cellulosic cell wall
  • Intercellular spaces are not present, i.e. compact tissue.
  • Actively dividing cells are present in growing region of plants e.g., root and shoot tips.

Classification of Meristematic tissues-

Apical meristem

  • Found on the growing tips of stems and roots
  • Its cell division in this tissue results in the elongation of stem and root, therefore involved in primary growth of plant.

Intercalary meristem

  • Present behind the apex and help in longitudinal growth.
  • It is a part of apical meristem that is left behind during growth period.
  • These are located at the base of leaf and internode region.
  • These are function to increase in the length of leaf (Primary), e.g., in bamboo stem, grass stem, mint stem etc.

Lateral meristem-

  • It is also known as secondary meristem.
  • It is present along sides of longitudinal axis of the plant.
  • These are function to give rise to the vascular tissues and cause growth in girth of stem and root.
  • They are responsible for secondary growth.

Permanent Tissue

  • These tissues are composed of those cells which have lost their capacity to divide.
  • The cells of this tissue have definite shape, size and thickness.
  • These tissues may be dead or living and loose the capacity to divide.
  • The division and differentiation of the cells of meristematic tissue give rise to permanent tissues.
  • On the basis of structure and composition permanent tissue are classified into two types-Simple and Complex permanent tissues.

Simple permanent tissue –

  • These tissues contain only one kind of cell type. Typically, they play a structural role.
  • These are supportive in function and are of three types:-Parenchyma, Collenchyma and Sclerenchyma.

Parenchyma:

  • These are fundamental tissue and first time evolved in bryophyte.
  • Cells of these tissues are thin walled, oval or spherical in structure.
  • Cell walls are mainly made up of cellulose and pectin.
  • They contain living cells with large intercellular space.
  • Their main function is support and storage.
  • They are of two types generally Chlorenchyma and Aerenchyma.

Collenchyma

  • It is living mechanical tissue which contains elongated cells with thick corners.
  • They contain living cells with no intercellular space.
  • It provides mechanical support and elasticity to plant.
  • It helps in bending of leaves and stems.

Sclerenchyma

  • Cells of this tissue are dead and possess very thick lignified walls.
  • Composed of long, narrow, and thick-walled cells.
  • Intercellular spaces are not found.
  • Cells are dead, present in seeds, nuts, the husk of a coconut, fibres of jute etc.

                            

Complex permanent tissues

  • Composed of more than one type of cells.
  • It is also known as conducting or vascular tissue.
  • Both xylem and phloem are the type of complex permanent tissue.

Xylem

  • It is also known as wood, vascular and mechanical tissue.
  • It helps in transportation of water and minerals from soil to plant.
  • It consists of four types of cells- Tracheids, vessels, xylem parenchyma and xylem fibres.
  • Tracheids and vessels have thick walls, and most of them are dead cells when mature.
  • Tracheids and vessels are tube like in structure which allows them to transport water and minerals
  • Food is stored by the xylem parenchyma.
  • The function of xylem fibers is mostly supporting.

               

Phloem

  • They transport food material from the leaves to the different parts of the plant.
  • Phloem is made up of the following components – sieve tubes, companion cells, and phloem parenchyma and phloem fibres.
  • Sieve tubes are tubular cells with perforated walls
  • Phloem conducts food in both directions.
  • Among all the components, phloem fibres are the only dead cells.

Animal tissues

  • These tissues are classified into four types Based on the function they perform: epithelial tissue, connective tissue, muscular tissue and nervous tissue.

Epithelial Tissues

  • Cells of epithelium are single layer and set very close to each other.
  • Tissue rests on a non-cellular basement membrane.
  • Their primary function is protection.
  • Epithelial tissues are classified as Simple squamous epithelium, Cuboidal epithelium and Columnar epithelium

Simple Squamous epithelium

  • The squamous epithelium is a tissue layer that is extremely thin and flat.
  • They are semi-permeable and, thus, perfect for gaseous exchange. 
  • They are present in the lining of the oesophagus and the mouth.

Cuboidal epithelium

  • They are cube-shaped cells and form the lining of salivary glands and kidney tubules.
  • They give mechanical support also form glandular epithelium when they form glands.

Columnar epithelium

  • Consists of elongated or column-like cells.
  • These tissues are found in lining the organs which help in absorption and secretion, such as the lining of the intestines.
  • These cells form into ciliated columnar epithelium, similar to that found in the respiratory system, when cilia are present.


Stratified Squamous Epithelium

  • When squamous epithelium is organized in numerous layers in a certain pattern, stratified squamous epithelium is formed.
  • This type of tissue is found in our skin.