Organisation in the Living World

Meristematic tissues are small thin walled cells, which have unique capicity to divide continuosly. Thus, these are responsible for the growth of a plant.

The cell wall of sclerenchyma is thick due to the presence of a chemically complete substance called lignin.

Sclerenchyma is made of dead cells that are packed together closely. They are elongated with pointed ends.

Collenchyma is found in the stem and petioles of the leaves. Its function is to provide support and flexibility.

Sclerenchyma is made of dead cells that are packed together closely. However, parenchyma cells may be oval, spherical or polygonal. The cell wall is thin and there are spaces between the cells. It stores food and water in the roots and stems of the plants.

Sclerenchyma is found in the stem and the veins of leaves. It provides strength to the plant body.

There are two types of plant tissues:

1. Meristematic tissues: Apical and lateral
2. Permanent tissues: Simple and complex

Phloem is responsible for the transport of food from the leaves to different parts of the plant. It is a living tissue made mostly of sieve cells and companion cells.

Tracheids are the components of xylem that conduct water from the roots to the leaves. These are elongated cells with thick, and lignified walls.

Epithelial tissue covers the outer surface of the whole body. It also lines the internal organs, cavities and other parts of the body.

Xylem is mostly made of dead cells.

Squamous epithelium forms the outermost layer of skin, and lines the body's cavities and other parts. These include the heart, alveoli, the blood and lymph vessels and the oesophagus.

Squamous epithelium comprises cells which are thin, flat and irregular in shape. The tissue provides protection against injury and facilitates diffusion.

Microvilli help to increase the surface area so as to facilitate absorption and secretion.

Cuboidal epithelium is present in glands such as thyroid, salivary and sweat glands. It also lines the inner wall of ducts and tubes like bronchioles.

Columar epithelium lines the inner walls of the stomach, intestine, pharynx and larynx. It is made of elongated, and column-like cells.

Elastic tissue is made of yellow fibres. Therefore, it is also called yellow fibrous tissue.

Cardiac muscles are specialised involuntary muscles present in the heart. They help the heart to pump blood day and night.

Areolar tissue forms a continuous layer under the skin. Further, it packs the spaces between the various organs so that they remain in place.

The cytoplasm of a nerve cell is called neuroplasm.

Muscular tissues facilitate the process of digestion.

Adipose tissue provides insulation to the body against cold. It also protects various parts of the body from injury.

Bone is the hardest connective tissue. Its cells called osteoblasts lie within a matrix containing inorganic substances like calcium, phosphates and magnesium.

RBCs or erythrocytes help to transport oxygen to various body parts.

White blood cells are present in the blood, and they help to protect the body against infections.

Nervous tissue is composed of specialized cells called neurons, which transmit message from all parts of the body to brain and spine and vice - versa.

A neuron comprises the cyton or cell body, a tail-like structure called the axon and dendrites that are short fibre-like structures arising from the cyton.

Spirogyra cells join each other at the ends to form a filament. Thus, it is a multicellular organism.

Meristematic tissue, which helps the stem and root grow in thickness is called cambium. It forms a sort of ring under the bark or is present in strips inside the stem and root.

Atomic level -> Molecular level -> Cellular level -> Tissue level -> Organ level -> Organ system level.