Biology examines the structure, function, growth, origin, evolution, and distribution of living things. It classifies and describes organisms, their functions, how species come into existence, and the interactions they have with each other and with the natural environment.
Four principles form the foundation of modern biology: cell theory, evolution, genetics, and homeostasis.
Growth and Change:
All living organisms have the ability to grow and change. Increase in mass and increase in the number of individuals are two characteristics of the growth. Multicellular organisms grow by cell division. A seed under the right conditions will sprout and form a seedling that will grow into a larger plant. Even the smallest bacteria grow by binary fission. The growth is also required for the persistence of the species.
The growth of plant takes place throughout the life and at a specific portion of the body but the growth in the animal is time-bound and overall. After some period, the growth in animal occurs by cell division of certain tissues to replace the lost cells. In unicellular organisms, the growth is by the increase in the mass.
Nonliving objects like mountains, boulders and sand dunes also grow but this growth is due to accumulation of substance on their surface.
Thus both the living and non-living grow. Hence growth cannot be considered as characteristic of the living system.
Growth of Sunflower from Seed to Flower
All living organisms (multicellular and unicellular) have the ability to reproduce. Living things make more organisms like themselves. If a species does not reproduce the next generation, the species will go extinct. Reproduction is the process of producing the next generation.
Reproduction may be a sexual or an asexual process.
Sexual reproduction involves two parents and the fusion of gametes, haploid sex cells from each parent. Sexual reproduction produces offspring that are genetically unique and increases genetic variation within a species.
Asexual reproduction involves only one parent. It occurs without a fusion of gametes and produces offspring that are all genetically identical to the parent. Genetic variation is not possible in asexual reproduction.
Many organisms like mules, sterile worker bee, warblers, infertile human couples, etc. do not reproduce. Thus reproduction cannot be considered as characteristic feature of living organisms.
Every living organism is made of structures called cells. Organisms that are very different such as ferns, fish, and elephants all look similar at the cellular level. A cell is the basic unit of structure.
Organisms are organized at the microscopic level from atoms up to cells. Atoms are arranged into molecules, then into macromolecules, which make up organelles, which work together to form cells.
Beyond cellular level, cells are organized in higher levels to form multicellular organisms. Cells together form tissues, which make up organs, which are part of organ systems, which work together to form an entire organism.
Beyond organism level, organisms form populations which make up parts of an ecosystem. Different ecosystems collectively form biosphere.
In unicellular organisms, all the functions are performed by one and the same cell. Thus cellular organization is a defining feature of living organisms.
Metabolism is essentially a collection of chemical reactions occurring within the body (or cell). In body two activities are continuously taking place anabolic activities (making up) and catabolic activities (breaking up).
All living organisms are made up of chemical substances. These chemical substances belong to different classes like carbohydrates, lipids, proteins, etc. Collectively they are called biomolecules. During anabolic activities, food material is digested, absorbed and assimilated in the body. In catabolic activities, the stored substances are broken down by hydrolysis or oxidation to produce energy in the form of ATP which is required for doing regular activities by the body.
Metabolism includes processes such as protein synthesis, chemical digestion, cell division, or energy transformation.
Metabolism is observed in all living organisms. Hence metabolism is a defining feature of all living beings.
Living organisms keep their internal environments within a certain range (they maintain a stable internal condition), despite changes in their external environment. This process is called homeostasis and is an important characteristic of all living organisms.
By this process, the body temperature, sugar level in the body is maintained at constant level.
It is vital characteristics of life. If it is disturbed, it will result in diseases and if not controlled can threaten the life of the organism.
Responding to the Environment:
All living organisms respond to their environment. Living things know what is going on around them (consciousness) and respond to the changes in the environment. The response may be physical, chemical or biological. Human beings are only animals with self-consciousness. When touch me not plant is touched its leaves close. The Venus flytrap traps insects.
The stem of plant moves in the direction of light and above the ground. (positively phototropic and negatively geotropic. The Root grows towards the soil and away from light (positively geotropic and negatively phototropic).
Behaviour of Touch Me Not Plant (Mimosa Pudica)
Behaviour of Venus Fly Trap
Heredity means that our genetic information can be passed from one generation to another. This way characteristics are transferred from one generation to the other.
An adaptation refers to the process of becoming adjusted to an en ronment. Adaptations may include structural, physiological, or behavioral traits that improve an organism’s likelihood of survival.
What are Living Organisms?
Living organisms are self-replicating, evolving and self-regulating interactive system that can respond to external stimuli.