Tissues

The group of cells similar in structure that work together to achieve a particular function forms a tissue. This group of cells has a common origin

Xylem is a complex tissue. It is made up of following four kinds of cells or elements:

1. Tracheids
2. Vessels
3. Xylem parenchyma
4. Xylem fibres

Simple tissues are made up of one type of cells which coordinateto perform a common function. Complex tissues are made up of more than one type of cells. all these coordinate to perform a common function.

The differences between cell walls of parenchyma, collenchymas and sclerenchyma are given in the following table:

The small pores present in the epidermis of the leaf are stomata. Stomata are enclosed by two kidney shaped cells called guard cells.
Functions of Stomata:

1. Exchange of gases, particularly CO¬2 and O2, with atmosphere.
2. Loss of water in the form of vapour during transpiration.

Cardiac muscles are involuntary muscles which show characteristics of both smooth and striated muscles. These muscles occur in the walls of the heart.
Functions of Cardiac Muscles

1. Cardiac muscles contract and relax rapidly, rhythmically and tirelessly throughout life. They contract endlessly from early embryonic stage until death.
2. The contraction and relaxation of heart muscles help to pump and distribute blood to various parts of body.

Striated, Unstriated and Cardiac muscles are three types of muscle tissues. Their different characteristics are as follows:

1. Squamous epithelium
2. Tendon
3. Phloem
4. Adipose tissue
5. Blood
6. Nervous tissue

1. Skin - Stratified Squamous epithelium
2. Bark of tree - Cork protective tissue
3. Bone - Connective tissue
4. Lining of kidney tubule - Cuboidal epithelium (Cuboidal epithelial tissue)
5. Vascular bundle - Complex permanent tissue (Xylem and Phloem)

Parenchyma is a simple permanent tissue of angiospermic plants. It is present in cortex and pith of stem and roots. It is also present in mesophyll of leaves. When it contains chlorophyll, it is called Chlorenchyma, found in green leaves.

Epidermis is a protective tissue of angiospermic plants. It provides protections to underlying tissues. Epidermis forms outer covering of various plant organs such as roots, stem, leaves, and flowers and remains in direct contact with the environment. Any substance whether solid, liquid or gas can enter into the plant or move outside only after passing through this layer. Epidermis helps in absorption, secretion, gaseous exchange and transpiration. It helps in preventing the entry of pathogens.

The cork cells are dead cells and do not have any intercellular spaces. The cell wall of the cork cells are coated with suberin (a waxy substance). Suberin makes these cells impermeable to water and gases. Cork is protective in function; it protects underlying tissues from desiccation, infection and mechanical injury.