The ability of living organisms to respond to external influences is one of its most important properties with which it is born. What significance does this ability have for all living things? Let's find out more.
The concept of "irritability"
From the point of view of physiology, any reaction of the body to environmental influences is considered irritability. Since the conditions of existence are constantly changing, its inhabitants must have time to adapt to them in order to survive. This is an innate property of the nervous system. Although representatives of wildlife, who do not have it, are also very active in responding to external influences.
Plant Taxis
The ability of living organisms to respond to external influences is also characteristic of plants. And this despite the fact that they do not have a nervous system. Try to touch the leaves of the mimosa shrub - literally before your eyes they will begin to take shape in response to mechanical irritation. This is a manifestation of irritability in the form of motor reactions - taxis. Naturally, plants do not cover significant distances. Their movements are growth and arise in response to a number of factors. They can be lighting, gravity, pressure or chemical compounds. Checking for taxis is easy. To do this, simply turn the houseplant away from the light, and after a while its leaf blades will again settle in its direction.
Animal instincts and reflexes
But the ability of living organisms to respond to external influences in multicellular animals is due to the presence of the nervous system. It consists of specialized cells called neurons. In them, as a result of external influence, electrical impulses arise. According to the processes, they are transmitted to the centers of the brain, where they are analyzed. After that, the signals are transmitted back to the working bodies. This process happens almost instantly. Such responses of animal organisms to irritation are called reflexes. They can be of two types.
Congenital ensure the vital activity of an organism from the moment it is born. These are respiratory, sucking, grasping, blinking, protective reflexes. Some reactions form in animals only throughout life. These are acquired reflexes. For example, a dog can be trained to perform an action after a specific command. In many animals, a system of complex behavioral reactions is formed from birth - instinct. This is mating behavior, care for offspring, bird flights, migration, construction of honeycombs by insects, etc.
Unicellular animals are also able to respond to changing environmental conditions. This happens in the form of taxis, as in plants. If a drop of salt and fresh water is applied to a glass slide on which the ciliates are located, then the simplest will begin to move towards the second. The movement can be carried out both from the source of irritation, and to it. For example, the unicellular alga chlamydomonas moves toward a source of sunlight. This provides the best conditions for the implementation of the photosynthesis process.
External Response: Importance for Living Organisms
First of all, the ability of all living organisms to respond in a certain way to environmental influences is protective. In animals, nervous regulation is very fast. Due to this, they immediately respond to various stimuli. Along with nervous, humoral regulation of functions is also characteristic of animals. It is carried out using endocrine glands. Its effect is much slower. For example, the pituitary gland secretes growth hormone for many years, during which quantitative changes in the body gradually occur. In their entirety, nervous and humoral regulation are a harmonious and perfect system of work and irritability of organisms.
So, the response of all living things to stimuli provides the conditions for their existence, protection and the basis of adaptation. The ability of living organisms to respond to external influences manifests itself in the form of taxis and reflexes.