The study of cellular Biology Topics is essential to understanding the workings of all living organisms.
Characteristics of Living Organism – Growths, Reproduction, and Metabolism
Life is a unique, complex organization of molecules that expresses itself through chemical reactions that lead to growth, development, responsiveness, adaptation, and reproduction.
Life is easier to recognize than to define. Life appears to be an extremely complex organization of non-living materials, operating in accordance with some physio-chemical principles. This complexity is reflected in the organisation of living systems greater than that of non-living ones. We know that all materials-living or non-living are formed of certain basic units called atoms. Atoms are combined in specific ways to form various kinds of molecules. Living systems are mixtures of very large and complex molecules functioning together in a coordinated manner. The chemistry of the principal constituents of protoplasm is in large part responsible for the attributes of life. Living organisms have the capacity to extract and transform energy from their component materials. Self-replication is a property that can be regarded as unique of the living state.
Characteristics of Life
1. Definite Shape and Size:
Every kind of living organism has its own peculiar shape and limited size. One organism can not attain the size or shape of another organism. Non-living things are often shapeless or amorphous as to compared the amorphous (with shape) nature of living beings.
Living organisms have the ability to change in both internal and external environments and thus ensure that they maximize their chances of survival for example on touching the pinnules of Mimosa pudica close up in pairs and droop down and succession from the tip backward.
Living organisms recognize internal and external stimuli and respond to the change in the environment. Any change in light intensity, touch, contact with chemical substances, internal enzymes, hormones, etc., may act as a stimulus. A plant placed in a dark chamber always moves towards the source of light. The body of a snail is withdrawn, when touched, within the shell. The delicate leaves of sensitive plants droop down to the touch. These are all examples of various types of responsiveness.
Young individuals grow in size. During growth, anabolism exceeds catabolism, and new protoplasmic substances are formed and added to the existing protoplasmic materials, as a result, the living cell increases in bulk. The method of growth in which new substances are added between already existing matters is known as intussusception. In a non-living body growth in bulk may take place by simple deposition of identical matters on its outer surface, this is called accretion. The living organism, on the other hand, grows by transforming simple materials into more complex forms.
All organisms operate a network of thousands of chemical reactions. The sum total of all chemical reactions occurring in an organism due to specific interactions amongst different types of molecules within the interior of cells is called metabolism. It involves the transformation of matter and energy within an organism and their exchange with the environment. All activities of an organism including growth, movements, development, responsiveness, respiration, circulation, reproduction, etc., are due to metabolism.
The metabolic activities are of two kinds. The constructive metabolism is called anabolism. It is also called constructive metabolism since it involves the synthesis of complex substances from simpler ones. Photosynthesis is an anabolic process. Catabolism includes breakdown reactions. It is also known as destructive metabolism because it involves breaking of complex substances into simpler ones. The potential energy present in the complex substances is converted into kinetic energy. Respiration is an example of catabolism. It releases energy for performing different body activities.
All living organisms’ body is made up of cells and each cell is composed of protoplasm (Gk. protos = first, plasma = form). Protoplasm is a colloidal mixture of different kinds of carbohydrates, lipids, proteins, nucleic acids, enzymes, and small amounts of many inorganic materials, in the water. The physical arrangement of protoplasm facilitates complex chemical activity by increasing the number of interactions between the many kinds of molecules. Protoplasm is essentially the same in all living organisms. An organism is alive till its protoplasm remains alive. Thus, the physiochemical properties of protoplasm in a regulated and organized fashion is expressed as life in all living organism. Protoplasm and cellular structure are absent in viruses.
All living organisms require energy for different metabolic activities that occur in the body. The energy is released during the breakdown of certain energy-rich compounds by the process of respiration. The energy released is stored in the molecules of ATP.
Organisation is the basic character of all living organisms. A living being has multiple levels of organisation The cell is regarded as a structural and functional unit of an organism. In multicellular organisms, the organizational pattern is of higher grades. These groups of cells performing a particular type of function form a tissue. Similarly, collections of tissues having common functions constitute an organ. The organs may differ in their form and function within an organism but there exists an inter-relationship and cooperation amongst the organs. At the time of functioning all the organs act in harmony for the benefit of the entire organism. The co-related and harmonious activities of all the organs of higher organisms in their respective natural conditions exhibit an excellent organisation of a living body.
All plants, except some heterotrophic forms (fungi), in general, are autotrophs, i.e., they can synthesize their food out of inorganic materials. All animals, in general, are heterotrophs i.e., dependent on other plants or animals for food. The nutritional process in animals includes absorption of soluble food and assimilation of it into protoplasmic materials. Assimilation is the ultimate goal or final stage of nutrition. By way of nutrition, the energy stored within food material is incorporated in protoplasm.
10. Energy Utilization:
Living beings constantly require energy to perform various activities of the body. Energy is obtained from food which is either manufactured by the cells or acquired from outside.
Hereditary characteristics determined by the genes in all living organisms are liable to sudden and permanent change, and thereby new combination of characters appears in the offspring. Generally, all living organisms produce offspring, which are exact copies of the organism. But occasionally new combinations of traits are suddenly produced within the offspring caused by mutation.
12. Adaptation and Evolution:
All organisms adapt to environmental changes and gradually evolve into new types of organisms. Living beings possess variations and have the ability to evolve with time. Useful inheritable variations in form, function, and behavior which help an organism to adjust well and successfully in its environment are called adaptations. Due to adaptation various morphological and physiological modifications of living beings take place. An organism is considered best adapted to an environment when it possesses inherited traits that enhance its survival and ability to reproduce in that environment. Adaptations allow the organisms to overcome seasonal and other changes in the environment.
Reproduction is one of the most important characteristics of living beings. The continuity of race is maintained through reproduction. Adult individuals possess the power of reproduction. Some organisms reproduce asexually through fission, buds, and spores. Others produce garnets that fuse to form the young ones. Asexual reproduction is uniparental while sexual reproduction is generally biparental. Some organisms do not reproduce, e.g., mules, sterile worker bees, and infertile human couples.
14. Movement and Locomotion:
Living beings show movements of their parts. Some are able to move from one place to another place. This phenomenon is called locomotion. The spontaneous movements of protoplasm is the inherent property of all plant and animal cells. In unicellular animals pseudopodia, cilia, flagella, etc. are the organs for locomotion. In higher animals definite organs for locomotion are present. In plants, locomotion is restricted to lower types only. In unicellular alga Chlamydomonas, the zoospores and antherozoids move with the help of flagella. The higher plants move only their organs in response to external stimuli. Such movements are called induced movements.
15. Life Cycle:
All organisms possess a definite life cycle of birth, growth, maturation, reproduction, ageing, and death. It is completed in a definite life span ranging from a few hours to several years.
They have the ability to maintain a constant internal environment in a self-regulated manner. Changes in the external environment do not have much impact on the internal environment as living beings have a self-regulated system to adjust and maintain the internal environment.
17. Secretion and Excretion:
In these catabolic processes, during metabolic activities, the protoplasm of the cell produces some new useful chemical substances. These useful substances are called secretory products and the process is called secretion. For example, enzymes and hormones are the secretory products. A number of metabolic by-products are formed which on accumulation in the body cause harmful effects. These byproducts are either expelled out of the body (animals) or stored inside aging tissues (in plants). The process of elimination of harmful metabolic products from the body is called excretion.
18. Rhythmicity or Periodicity:
All physiological activities of living beings take place in a definite rhythm. The metabolic activities like respiration, nutrition, secretion, etc., go on actively for a definite period and then become comparatively passive. After a requisite interval, it again becomes active. Our heartbeat, breathing movements, etc., are carried on in a definite rhythm. Growth and reproduction are also periodic in nature.
It is the ability to form lost parts. A small fragment can regenerate the whole organism in plants and some lower groups of animals (Planaria, Hydra). In higher animals, it is limited to certain organs.
20. Senescence and Death:
The living organism after birth grows gradually upto a certain stage and then becomes adult. The adults reproduce and give rise to offspring. This active phase of life continues for a certain period of time, and then gradually decreases. This phase of life is called senescence. Finally, all symptoms of life disappear and this is known as death. Living organisms can not avoid senescence and death.