Tissues

Group of cells that are similar in structure and perform that same function is called a tissue. E.g., phloem, xylem, blood are examples of tissue.

In multicellular organisms, cells become specialised to perform different functions. Similar cells group together to form tissue for eg. muscular tissue. These tissues perform specific functions, for example, nerve cells carry messages, muscular tissues cause movement, blood flows to transport oxygen etc. Thus, tissues in multicellular organisms show division of labour.

A simple tissue is made up of only one type of cells. There are three types of simple tissues in plants are:

1) Parenchyma

2) Collenchymas

3) Sclerenchyma.

The apical meristem occurs at the growing tips of roots and shoots and increases the length of the stem and root.

Husk of a coconut is made up of sclerenchymatous fibres.

Phloem is a conducting or vascular tissue of the plants. Phloem is made up of four types of elements: sieve tubes, companion cells, phloem fibres and phloem parenchyma.

Muscular tissue is a contractile tissue made up of muscles. This tissue is responsible for movement in our body.

The cells of the nervous tissue are called nerve cells or neurons. A neuron or nerve cell is structural and functional unit of the nervous tissue (brian, spinal cord and nervous). It consists of cell body which has cytoplasm and a nucleus. Cell organelles such as golgi apparatus, mitochondrial, etc are also present in the cyton. Each neuron has a single long part, called the axon and many short, branched parts called dendrites which help transfer signal from one nerve cell to another.

The features of cardiac muscle are:

(i) These muscles are involuntary.

(ii) Cardiac muscle cells are cylindrical, branched and uninucleate.

(iii) These show rhythmic contraction and relaxation throughout the life.

Areolar tissue is a connective tissue which fills the space inside the organs, supports internal organs and helps in repair of tissues.

Group of cells that are similar in structure and perform same function is called a tissue. E.g., phloem, xylem, blood are examples of tissue.

Xylem is a conducting or vascular tissue of the plants. It consists of four types of elements: (i) Tracheids (ii) Vessels; (iii) Xylem parenchyma; (iv) Xylem fibres.

The differences between cell walls of parenchyma, collenchymas and sclerenchyma are:

Stomata perform following functions:

(i) They allow exchange of gases (CO₂ and O₂) with atmosphere.

(ii) They help in the process of transpiration.

The three types of muscle fibres are:

(i) Striated muscle

(b) Unstriated muscle

(c) Cardiac muscle:

It is cardiac muscles which are exclusively present in the wall of heart. It contracts and relaxes continousely with a rhythm, but it never gets fatigued.

Differences between striated, unstriated and cardiac muscles are as follows:

(a) Squamous epithelium forms inner of our mouth.

(b) Tendon connects muscle to bone in humans.

(c) Phloem is a conducting tissue that transports food in plants.

(d) Adipose tissue stores fat in out body.

(e) Vascular tissue (Blood and lymph)

(f) Nervous tissue present in the brain.

Skin - Epithelial tissue (squamous epithelium);

Bark of tree - Cork (protective tissue);

Bone – Skeletal connective tissue;

Lining of kidney tubules - Cuboidal epithelial tissue;

Vascular bundle - Complex permanent tissue_xylem and phloem.

Parenchyma is a simple permanent tissue which is present in the soft parts of plants such as: cortex, pericycle, pith, and medullary rays in primary stem and root.

Epidermis forms the entire outermost layer of the plant. It acts as a protective tissue and protects the plant from excessive heat or cold and attack of parasitic bacteria and fungi. Stomata present on epidermis help in gaseous exchange and transpiration.

The cork cells are dead and compactly packed without intercellular spaces. Their cell walls are coated with suberin (a waxy substance) which makes these impermeable to water and gases. Thus, the cork proctects underlying tissue from loss of water, infection and mechanical injury.