We can see a variety of things in our surroundings. These things can be broadly categorised into living and non-living things. But how to distinguish between these living and non-living things? The living things exhibit several characteristics that are essential for life. These characteristics of living organisms make them different from non-living things. Biology is the science of living things that majorly includes the study of animals, plants and different microorganisms.  These living beings are classified into five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia.

Levels of Organisation of Living Organisms

All Living beings are highly organised and structured, following a hierarchy from the simplest to the complex. There are the following levels of body organization:

1. Cellular Level: The cell is considered the basic unit of life and constitutes the smallest level of organization of living beings. Bacteria and protozoans are unicellular organisms and exhibit a cellular level of body organization. All life processes are being performed by a single cell.

2. Tissue Level: In multicellular organisms, similar or dissimilar cells having a common origin and a common function combine to form a tissue. Hydra exhibits tissue level body organization.

3. Organ Level: Different tissues are organized to form distinct organs. Helminths have organ level body organization.

4. Organ System Level: A group of organs that coordinates to perform a significant function forms the organ system.

5. Individual-level: A multicellular organism consisting of many organs and organ systems forms an individual. Plants and animals are complex organisms that exhibit the individual level of organisation.

Life Processes – Characteristics of Living Organisms

The basic functions performed by living organisms to keep themselves alive are called life processes. All living organisms exhibit the following life processes in common:

1. Nutrition
2. Respiration
3. Growth
4. Movement and Locomotion
5. Excretion
6. Sensitivity
7. Reproduction

Nutrition in Living Organisms

Nutrition is the biological process of obtaining food to get the energy to perform several physical and physiological activities. A nutrient-rich diet is required for living beings to keep themselves healthy. These nutrients include carbohydrates, fats, proteins, enzymes, vitamins, and minerals.

1. Nutrition in green plants involves photosynthesis, in which the water and carbon dioxide are utilized to synthesize simple sugars (glucose) in the presence of sunlight.

2. Animals cannot prepare their food, so they are called heterotrophs. The food is ingested, digested, absorbed, and then assimilated by body cells and further utilized to grow, repair, and obtain energy.

3. Complex organisms like humans intake food through the mouth and have a well-defined digestive system for food processing.

4. Simple organisms like Amoeba do not have any specific organ, hence engulf food by using pseudopodia. Likewise, Bacteria feed by absorbing food molecules from their surroundings.

Respiration in Living Organisms

Respiration is one of the essential life processes. The oxygen inhaled during breathing is utilized for the oxidative breakdown of food to release energy. Respiration is a biochemical process that occurs in body cells to break down nutrients to release energy. Oxygen is usually needed for respiration. The word equation for respiration involving oxygen is as follows:

Glucose + Oxygen \( \to \) Carbon dioxide + Water + Energy

1. Plants get oxygen by diffusion. Diffusion occurs individually in roots, stem, and leaves.

2. Complex organisms like mammals, birds, reptiles, etc., have a well-developed respiratory system and perform cellular respiration to produce energy.

3. Simple organisms most often depend on the simple diffusion of respiratory gases. Some bacteria, yeast, respire anaerobically (in the absence of oxygen) to produce energy.

Growth in Living Beings

Growth is a permanent increase in the overall size and the dry mass of an organism. Body cells of organisms have the ability to divide and hence increase their numbers which in turn leads to the overall growth of an organism.
Cells are always involved in making more complex biomolecules such as proteins that cause an increase in the dry mass of an organism.

1. Plants continue to grow throughout life.
2. Growth stops in animals when they reach a certain age.
3. In unicellular organisms like Amoeba, bacteria, algae, yeast, etc., growth refers to reproduction (cell division).

Movement & Locomotion in Living Organisms

Movement and locomotion are remarkable characteristics of all living beings. All living organisms can move without applying any external force to them. Animals can move from one place to another using their appendages. It is called locomotion.

1. Advanced invertebrates, fishes, amphibians, reptiles (except snakes), birds, and mammals have locomotory organs for locomotion. Animals exhibit locomotion in search of food, to escape from predators and unfavourable surrounding conditions.

2. Animals can also move their body parts with the help of joints and muscular contractions.

3. Some animals remain fixed at a place but can move their parts, such as tentacles of the sea anemone.

4. Plants are anchored in the soil with the help of roots. Therefore, they do not show locomotion. However, the movement of roots, stem, and leaves can be observed when subjected to some external stimuli such as light, water, gravity, etc. These are called tropic movements in plants. The opening and closing of stomata is an example of movement in plants.

5. Movement in creepers and climbers can be distinctly observed. Unicellular organisms have pseudopodia (in Amoeba), flagella and cilia (Paramecium, bacteria, etc.) for locomotion.

Excretion in Living Organisms

All living beings produce toxic substances during several metabolic reactions. Excretion is the removal of these wastes from the body. The primary wastes produced in animals are carbon dioxide and nitrogenous wastes (ammonia, urea, uric acid).
1. Vertebrates have specific organs for the removal of these wastes.
2. Simple organisms like Amoeba, Hydra, etc., do not have any specific organ for excretion. They remove the wastes through the body surface, contractile vacuole, specific body pores.
3. Plants lack specific organs for excretion. They remove gaseous wastes through stomata in leaves and lenticels in the stem. Other solid wastes are removed by the shedding of leaves, peeling of bark, and falling of fruits.

Sensitivity in Living Organisms

Sensitivity is defined as the ability of living beings to detect the changes in the surrounding environment and react against them. Different animals have different types of sense organs.
1. In human beings, the response and reaction to specific stimuli are carried by specific sense organs, including eyes, ears, nose, tongue, and skin.
2. Advanced animals have a nervous system and endocrine system to control and coordinate.

3. Plants do not have a nervous system and sense organs, but they can sense things and react to the surrounding atmospheric changes. Mimosa pudica (four O’clock) plant has sensitive pads called pulvini at the base of the leaf. The folding up of leaves on touch is due to the loss of water from pulvini.

4. Plants coordinate their behaviour under the regulation of different phytohormones.

Reproduction in Living Organisms

Living beings produce their own kind. This process is called reproduction. Asexual reproduction involves a single parent giving rise to identical offspring. Most of the lower animals show asexual reproduction. Sexual reproduction involves two parent organisms producing male and female gametes that fuse to give rise to the offspring that are not identical to their parents and instead show variations. Plants reproduce vegetatively (asexual reproduction) through roots, stem, and leaves and sexually through flowers.

Importance of Life Processes

1. Life processes play an essential role in maintaining vital functions and hence sustaining life.
2. All life processes play a crucial role to maintain good health.
3. The sum total of life processes is the overall growth and development of organisms.
4. Reproduction is the key characteristic of every living being that ensures the survival of species and continuity of life.

Inter-relationship Between Life Processes in Higher Animals

1. All life processes are directly or indirectly related to each other. The food we intake gets digested in the digestive system.
2. The food is absorbed in the blood and mixed with the oxygen inhaled during breathing to obtain energy through respiration in the cells. The energy is utilized in physical activities, reproduction, etc. As a whole, the respiratory and circulatory systems work together to circulate required nutrients throughout the body.
3. The blood further collects the metabolic wastes and transports them to the excretory organs and gaseous wastes to respiratory organs for removal.

Difference Between Living and Non-living Things

Living Things	Non-living Things
Living things are organisms that are made up of cells and exhibit signs of life.	Non-living things are objects that do not exhibit any sign of life.
Living things require food, water, and air for their survival.	Non-living things have no basic requirements for their existence.
Movement and growth are remarkable features of living things.	Non-living things neither grow nor move without applying external force.
Living things respond to internal and external stimuli.	Non-Living things do not react to any stimulus or environmental change.
Living things can produce their own kinds for the continuity of life on the earth.	Non-living things cannot produce replicas.

Summary

The things that have a specific lifespan are called living organisms. During their lifespan, all living organisms share several key characteristics in common. These characteristics include intake of food to obtain energy. The energy is utilized for the purpose of growth, reproduction, etc. Besides this, self-regulating movement and change in body posture are remarkable and observable features of living beings.

Cessation of all vital activities leads to the death of an organism. In this article, we get to know about specific characteristics to determine whether the things are living or non-living. Also, we learnt about the interdependence of living characteristics on each other.

FAQs

Q.1. What are the examples of living organisms?
Ans: Humans, insects, birds, bacteria, plants, etc., are examples of living organisms.

Q.2. Is a human an example of an organism?
Ans: A human is a multicellular complex organism that consists of several organs and organ systems to perform different living activities.

Q.3. Is death a characteristic of living things?
Ans: Death cannot be considered as one of the living characteristics because it is the state when all the living activities of an organism cease.

Q.4. How do living things grow?
Ans: All living beings are made up of cells. These cells divide rapidly and lead an organism to grow in size.

Q.5. What are the six characteristics of a living organism?
Ans: The six main characteristics of a living organism include nutrition, respiration, growth, movement and locomotion, excretion, and reproduction.