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Tissues-theory Biology-day-10 Target-ssc-cgl-2018

Tissues-theory Biology-day-10 Target-ssc-cgl-2018

TISSUES

  • The term tissue was coined by Bichat (Father of Histology) in 1792.
  • A Group of cells that perform a specific function are called tissues. All cells of a tissue have common origin.
  • Study of tissues is called HISTOLOGY.

Importance of tissues

  • It brings division of labour in multicellular organisms.
  • They become organised to form organs and organs into organ systems.9
  • Workload of individual cell is decreased.
  • As a result of improved organisation and higher efficiency they survive longer.

Meristematic tissues

  • They divide continuously and help in increasing the length and girth of the tree.
  • The cells of meristematic tissue are similar in structure and have thin cellulose cell walls. They contain few vacuoles or no vacuoles at all.
  • Its cells are always alive.
  • They grow on the tip of roots and are found in the growing regions of the plant. They are apical, lateral and intercalary.
  1. Apical Meristem… These are situated at the root and shoot apex. Responsible for the growth of the length of the tree.
  2. Lateral Meristem… These are found beneath the bark. Responsible for the girth or thickness of the tree.
  3. Intercalary Meristem… These are present at the internode. Responsible for the growth of the organs (leaves, internodes etc.) of tree.

Tissues-theory
Permanent tissues

  • The cells which are made by the division of meristematic tissues and take up a permanent shape, size and function are called permanent tissues. This process is called differentiation.
  • The cells of the permanent tissue do not divide further.
  • Its cells may be dead or alive.

PARENCHYMA TISSUES

  • The cells of the parenchyma tissues are living and also have the tendancy to divide.
  • The cells are round or isodiametric.
  • Parenchyma cells are found in leaves, stems, roots and flowers of the plants. It is also present in xylem and phloem.

Functions :

  • Serves as packing tissues. Fills the space between other tissues and maintains the shape of the cell.
  • In herbaceous plants, they acts as primary support due to their turgid or osmotic nature.
  • It serves as food storage tissue.
  • There is an intercellular air space which allows the exchange of gases.
  • It also stores waste products of plants.
  • The parenchyma tissues in which chloroplast is present are called chlorenchyma.
  • The parenchyma tissues which have large air cavities to give buoyancy to the plant are called aerenchyma.

COLLENCYMA TISSUES

  • It is a living cell. It has many features of parenchyma, but it is different from it because collenchyma contains some extra starch deposited on their corners.
  • It is present below the epidermis of dicotyledon.
  • It is not present in monocots leaves, roots and stems.

Functions :

  • It is the chief mechanical tissue in young dicotyledonous stems.
  • It gives tensile strength and flexibility to the organs in which it is present.

SCLERENCHYMA TISSUES

  • These are dead cells. Its cell walls is thickened by lignin and thus its cell walls are called lignified.
  • Cells of sclerenchyma are of two types…
  • Fibres… consists of very long, narrow, thick and lignified cells.
  • Sclereids called grit or stone cells are irregular shaped, are dead and are found in various parts of the plants.

Functions:

  • It gives strength, elasticity and flexibility to the plant body.
  • It Is mainly mechanical and protective in function.

PROTECTIVE TISSUE

It includes epidermis and cork

Epidermis:

  • It is present in the outermost layer of the plant body such.
  • It is one cell thick and is covered with cuticle. It is a waterproof layer of a waxy substance called cutin secreted by epidermial cells.
  • The cells of epidermis are elongated and do not contain any intercellular space between them.
  • It protects the plants from desiccation and infections. It also helps to reduce water loss and prevents the entry of pathogens.
  • The aerial surfaces of many plants bear cutinised hair. They are called trichomes. They reduce the rate of transpiration.
  • In roots, the younger parts are covered with uncutinised layer of epidermis called epiblema. Some of them give rise to tubular outgrowths called root hair which increase the absorptive surface area of the root.

Cork:

  • A the plant grows older a strip of secondary meristem called phellogens or cork cambium replaces epidermis of stem.
  • Cork cambiums are types of tissue which have only one type of cell. They are rectangular and their protoplasts are vacuolated and contains tannins and chloroplasts.
  • They give off new cells on its both sides forming the secondary cortex or phellodrem on inner sides.
  • The layer of cells which is cut by cork cambium on the outer side ultimately becomes several layers thick cork.
  • They are thickened with suberin deposits. This makes the cells impermeable to water and gases.

Function:

It is protective in function. Prevents desiccation, infection and mechanical injury.

STOMATA

  • The small pores present in epidermis of leaves is called stomata.
  • It is bounded by a pair of specialised two kidney shaped cells called guard cells.
  • Guard cells are the only epidermal cells which contains chloroplast. Rest are colourless.
  • It allows gaseous change to occur. It allows water vapour to escape too.

COMPLEX PERMANENT TISSUES

  • They consist of cells of more than one type having a single origin.
  • They transport water, mineral salts and food material to various parts.

They are of two types:

  1. Xylem
  • This is usually called wood and is a conducting tissue.
  • The determination of the age of a plant is done by counting annual rings of the xylem tissue. This method is called dendrochronology.

Function:

Conduction of water and minerals. It provides mechanical consistency.

  1. Phloem
  • It is a conducting tissue and its main function is to conduct food prepared by plants.
  • The companion cells of phloem are found in angiosperm.
  • Subsidiary cells are closely associated with guard cells.

ANIMAL TISSUE

They can be divided into epithelial tissues, connective tissues, muscular tissues and nervous tissues.

Epithelial tissue

  • It covers the external surface of the body an internal surface of many organs.
  • They are arranged close to each other.
  • There are no blood vessels providing nourishment to it. The receive nourishment from connective tissues. They mainly covers and lines the free surface.

Connective tissue

  • They connect and bind different types of organs or tissues.
  • It provides structural framework and mechanical support to the body.
  • It plays role as defense tissues and repair fat storage.
  • Blood is the only tissue found in the form of a fluid.

Tissues-theory
Muscular tissue

  • Also known as contractile tissue.
  • All muscles are made up of this tissue.
  • There are 693 muscles in human body.
  • The largest muscle is Gluteus Maximus (muscle of hip) and the smallest muscle is Stapedius.
  • These are of three types:-
  1. Unstriped – These are found on the walls of those parts which do not controlled by will and called involuntary muscle. It controls the motions of those organs that move on their own.
  2. Striped – These are found in the parts of the body that moves voluntary.
  3. Cardiac – These are found on the walls of the heart. The contraction and expansion of the heart is takes place due to these muscles.

Nervous Tissue

  • It is also known as sensitive tissue.
  • These tissues made up the nervous system of human body.

It is made up of two specific cells:-

  1. Nerve cell or Neurons
  2. Neuroglia

 

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