Life Processes in Living Organisms
Transportation of Water and Minerals in Plants (Group B)
In animals, control and coordination is governed by the nervous system. However, plants do not have a nervous system.
Then, how do plants respond to stimuli?
Plants respond to stimuli by showing movement.
Have you ever seen any movement in plants?
- When you touch a sensitive plant such as touch- me- not (Mimosa pudica), the plant folds its leaves and droops.
- When a seed germinates, the root grows down in the soil and the stem grows up in the air.
In the first example, touch is the stimulus and the plant responds by folding its leaves. Therefore, the plant shows movement by folding its leaves.
In the second example, the seed germinates and shows directional movement.
In the first example, movement is independent of growth i.e. there is no growth involved. However, in the second example, the movement of the seedling is caused by growth. If the seedling is prevented from growing, then it will not show any movement.
Thus, plants exhibit both growth-dependent and growth-independent movements.
In plants (like animals), the information is carried from cells by electro-chemical means. However, there is no specialized tissue for the conduction of information. In fact, plants change their shape by changing the amount of water in them. This results in swelling and shrinking. This change of shape results in movement.
You must have seen plants such as peas and grapes with tendrils. Movement in these plants occurs in the growing stem of the tendrils. When the tendrils come in contact with a supporting object, they coil and cling around it. Plants respond to stimuli slowly by growing in a particular direction. This type of growth is directional.
Nastic movements in plants
Nastic movements are the movements in plants that take place in response to the environment stimulus. One of the main feature of the nastic movement is that the direction of the movement is independent of the direction of stimulus.
For example, the movement of organs like leaves and petals that are directed by the touch as in the leaflets of touch me not plant, wherein the plant droops when touched from any side.
The various kinds of nastic movements shown by plants are:
It is the movement of a plant in reponse to an external stimuli like touch, vibration etc. For example, Mimosa plant responds by "folding up of leaves" when touched. The sensitive part of the plant involved in this type of movement is called pulvinus which is a soft, swollen structure present at the base of the leaf.
Some plants show movement in plant part in response to the light. For example, flowers of sunflower and lotus open in morning.
It is the movement of plant parts in response to the rise and fall in temperature. For example, flower of crocus and tulip open with a rise in temperature and close with a drop in temperature.
Do You Know?
Do you know which organs make up the nervous system?
The nervous system is made up of the brain, spinal chord, and nerve cells or neurons.
Let us first study about the structure of the functional units of the nervous system i.e., the neurons.
Structure of a neuron
The three main parts of a neuron are the axon, dendrite, and cell body. The axon conducts messages away from the cell body. The dendrite receives information from the next cell and conducts it towards the cell body. The cell body contains the nucleus, mitochondria, and other organelles. It is mainly concerned with maintenance and growth of the cell.
Arrangement of neurons
Neurons are arranged end to end, forming a chain. This helps in the continuous transmission of impulses. Each neuron receives an impulse through its dendrite and transmits it to the next neuron in a sequence through its axon.
Neurons are not connected. Synapse or a small gap occurs between the axon of one neuron and dendron of the next neuron.
A synapse in the muscle fibre is also known as neuromuscular junction. Let us discuss the working of a synapse in detail.
A nerve is a collection of nerve fibres (or axons) enclosed in a tubular medullary sheath. This sheath acts as an insulation and prevents mixing of impulses in the adjacent fibres.
Types of neurons
Neurons are of three types.
How does a nerve impulse travel?
The dendrite end of the neuron collects information and triggers a chemical re…
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