Support And Movements in plants

Support And Movements in plants.

Support in plants

The parts of plants are stem, root and leaves. The most important function of the stem is to give support to plant. It also acts as supply line between root and aerial parts of the plants. Different types of cells are involved for support in the stems. These organs provide support to the parts by following ways:

1. Turgor pressure:

The internal hydrostatic pressure in plant cell is called turgor pressure. Water enters into the living cells of epidermis. cortex and pith by osmosis. This water produce turgor pressure in the cells. This pressure keeps the plant rigid. It prevents the plant from bending. If these cells lose turgidity, the herbaceous stem wilts. The turgor pressure is very important for the turgidity of the plants.

Sometimes, plants loss water due to ex-osmosis. Such plants loses turgor. Thus some part of the pant wilt. Therefore, maintenance of turgor pressure is an important phenomenon in plants. High osmotic pressure of vacuoles generate the turgor pressure. The vacuole is bounded by a membrane called tonoplast. The tonoplast contains a number of active transport systems. Despite the high concentration of the extracellular fluid, these systems pump ions into the vacuole or compartments.

Thus the vacuole has higher ionic concentration. So water enters into the vacuole and provides turgidity. This. turgidity provides mechanical support to the soft tissues of plants.

2. Vascular bundle:

The xylems in vascular bundle are tough and inextensible structure. They

function like steel rod in concrete. They are arranged in rings. Wind imposes major stress in terrestrial ecosystems. They xylem provides very effective resistance against the wind stress. They increase the weight bearing ability of the plant. The vascular bundles of some plants are strengthened by additional sclerenchyma fibers. They form bundle сар.

Chollenchyma and sclerenchyma:

These are heavily lignified cells. They give support to the plants. 

Sclerenchyma cells:

They have thick secondary cells wall. This wall is impregnated with lignin. Lignin is an organic substance. It makes the cell wall tough and hard. Most of the sclerenchyma cells are non-living. Sclerenchyma are present in xylem tissues Their primary function is to provide support to the plant. There are three types of Sclerencyma cells:

(i). Fibers (Tracheids):

These are long and cylindrical cells. They present in the form of solid bundle in xylem or bundle caps.

(ii). Sclerides:

These are shorter than fibers. These are found in seed coats and nut shells. They provide protection.

(iii). Vessels (Trachea):

These are long tubular structures. They join end to end to form long water conducting pipe in xylem.

Movements in plants

Organisms show response to the internal and external stimuli. Animals show response to external stimuli in the form of motion. Similarly, plants also show movement. Animals change their location in response to stimuli. Plants are fixed. So they change their growth pattern.

There are two types of movements: autonomic movements and paratonic

movements.

1. Autonomic movement:

The spontaneous movement due to internal causes is called autonomic movement. There are. three types of autonomic movement. These are: Tactic movements, Turgor movement and Growth movement.

(i). Tactic Movement:

These are movement of the entire cell or organism due to external stimuli. The tactic movements may be positive if these are toward the stimuli or these may be negative, if these are away from the stimulus. The tactic movements are further classified on the basis of nature of stimulus:

(ii). Turgor Movements:

The movements due to differential changes in turgor and size of cells by gaining and losing water are called turgor movement. For example, rapid movement of leaflets in Touch Me Not and sleep movement of plants.

(iii). Growth movement:

The movement due to unequal growth on the two sides of plant organs like stem, root, tendrils are called growth movement. 

2. Paratonic Movements:

The movements due to external causes are called paratonic movement. There are following types of paratonic movements:

(i). Tropic Movements:

The movements in curvature of whole organ towards or away form the stimuli such as light, gravity and touch are called tropic movement.

(ii). Nastic Movement:

The non-directional movement of the plant in response to external stimuli are called nastic movement.