- The term living is derived from the word “lifende” meaning living or having life.
- A living thing relates to any organism that exhibits the characteristic of life or being alive.
- Thus we can define living Things as the organisms which comprise of life and have the ability to eat, grow, respire, reproduce, procure and use energy for the metabolic process.
CHARACTERISTICS OF LIVING THINGS
There are certain characteristics, on the basis of which an organism can be classified as living or nonliving.
These characteristics include the following;
- Living things have different levels of complexity and organization which is not found in non-living objects.
- At its most basic level, a living thing is composed of one or more cells. Cells are the basic structural and functional unit of a living organism.
- Cells of the same kind are further organized together into clusters known as tissues.
- A tissue is a group of cells that bring about a shared function. Each tissue has a specific function, depending on its constituent cells.
- Tissues then join together to form organs, such as the stomach and kidney.
- A number of organs working together give rise to an organ system i.e. digestive system, circulatory system etc.
- The complex organization of various organ systems constitutes an organism. Organism is an individual entity that encompasses all properties of life.
- Living organisms are sensitive in nature. They can detect and respond to various internal and external stimuli.
- For example;
- Plants can bend toward a source of light, climb on fences and walls, or respond to touch.
- Tiny micro-organisms can also move in response to chemicals (a process known as chemotaxis)
- An organism responds to the stimulus by number of effectors such as muscles and glands
- Movement of living organisms towards a specific stimulus is termed as positive response
- Movement of living organisms away from a stimulus is known as negative response
- For generating an appropriate response to a stimulus, the organism must coordinate and integrate its responses. For this purpose, the living organisms possess a complex system of nerves and chemical regulators, which enable the organism to coordinate its actions.
- All living things have the ability to divide and produce offspring by the process of reproduction. Reproduction in living organisms is of two types;
- Asexual reproduction
- sexual reproduction
- Among plants and simple animals, reproduction is frequently an extension of the growth process. Such reproduction is known as asexual reproduction.
- Asexual reproduction involves only one parent, and the offspring are generally identical to the parent cell.
- bacteria grow and quickly reach maturity, after which they split into two organisms by a process called binary fission.
- More complex organisms involve a sophisticated type of reproduction known as sexual reproduction
- In sexual reproduction, two parents contribute to the formation of a new individual.
- During this process, a new variety of traits can be produced.
- In flowering plants, the pollen (male gamete) fuses with the ovum (female gamete) forming an offspring having traits of both parents.
- One of the most noticeable and prominent features of living organisms is their ability to grow.
- Growth is the process which involves organisms to take in material from the environment and organize them into its own structures.
- Organisms grow by following specific instructions coded for by their genes.
- These genes provide instructions that regulate cellular growth and development.
- To attain growth, an organism consumes some of the energy it acquires during metabolism.
- A non living organism does not exhibit this characteristic.
- All living organisms involve chemical processes that take place within their cells.
- The chemical processes that occur within a living organism with the purpose of maintaining life are collectively known as metabolism. Nonliving things do not exhibit metabolism.
- Metabolism can be appropriately divided into two types;
- Catabolism is a destructive process.
- it involves the breakdown of molecules in order to attain energy
- energy is released during catabolism.
- Anabolism is a constructive process.
- It involves the synthesis of all biological compounds needed by the cells
- Energy is consumed during this process.
- Living organisms have the ability to adapt to their environment by the process of evolution.
- During evolution the organisms in the population become more suitable to metabolize, respond, and reproduce in a specific environment.
- They attain abilities to cope with their environment, which their ancestors did not have.
- This variation in characteristics of organisms due to evolution is unique to living things and cannot be found in nonliving matter.
- Homeostasis is a self-regulatory process through which living organisms maintain their internal environment from the harms and fluctuations of the external environment.
- Organisms need certain optimum conditions of pH, temperature and light to function properly.
- Organisms living in cold areas, such as the polar bear, have body structures that help them tolerate low temperatures and conserve body heat.
- Structures that help in this type of insulation include fur, feathers, blubber, and fat.
- In hot climates, organisms undergo processes like perspiration in order to get rid of body heat.
CLASSIFICATION OF LIVING ORGANISMS
The basic classification of living organisms commences by dividing them into two major groups:
- Plants are autotrophic, multicellular organisms that are capable of producing their own food by photosynthesis
- Plants play an important role in the production of oxygen.
- They have unlimited growth at localized regions
- Plants are non-motile due to absence of locomotive organs
- They do not possess a nervous system however hormones regulate many metabolic processes within plants.
CLASSIFICATION OF PLANTS
Plants are categorized into two basic types
- Vascular plants
- Non-Vascular Plants
Vascular plants are the plants that consist of specialized water conducting xylem and food translocation phloem tissues
The major types of vascular plants are
- Non-vascular plants are the type of plants that lack specialized vascular tissues (xylem and phloem) for water conduction and support.
- They also lack true stem, leaves and roots.
- Non-vascular plants usually have three types
- Animals are heterotrophic organisms that cannot generate their own food and depend on external sources for nutrition.
- These are multicellular eukaryotic organisms that have evolved from unicellular prokaryotes
CLASSIFICATION OF ANIMALS
The animal kingdom has been divided into two major types:
Vertebrates are the animals that consist of backbone in their body. They are also known as chordates.
These animals include:
Invertebrates are animals that lack a backbone in their body and instead have soft bodies or a hard covering. They are also known as non-chordates
- Arihant’s handbook of biology. The living world. Page no: 1-6.
- NCERT biology; textbook for class 11. The living world. Page no: 1-62.