What is Living? Difference Between Living and Non-Living

 

What is Living?

Difference Between Living and Non-Living

NEET (UG) Biology – Detailed Exam-Oriented Notes

Introduction

One of the most fundamental questions in biology is:

“What is living?”

At first glance, it may appear simple to distinguish living organisms from non-living things. Humans, plants, animals, and microorganisms are clearly living, whereas rocks, water, tables, and air are non-living. However, scientifically defining life is more difficult than it seems.

Biologists identify living organisms based on certain characteristic features such as growth, reproduction, metabolism, cellular organization, responsiveness, and consciousness.

This topic forms the foundation of biology and is extremely important for NEET (UG) because many conceptual and NCERT-based questions are directly asked from it.

Definition of Life

There is no single universally accepted definition of life, but living organisms generally possess the following characteristics:

1. Cellular organization
2. Metabolism
3. Growth
4. Reproduction
5. Response to stimuli (consciousness)
6. Adaptation and evolution

Among these, metabolism and consciousness are considered the most defining properties of living organisms.

Characteristics of Living Organisms

1. Growth

Definition

Growth is an irreversible increase in mass and number of cells.

In Living Organisms

• Growth occurs internally due to cell division.
• It is controlled genetically and metabolically.

Examples

• A seed grows into a tree.
• A child grows into an adult.

Growth in Plants

Plants show growth throughout life because of meristematic tissues.

Types of Plant Growth

1. Primary growth → increase in length
2. Secondary growth → increase in girth

Growth in Animals

Animals usually show growth only up to a certain age.

Example:

• Humans stop growing after maturity.

Why Growth Alone Cannot Define Life

Some non-living things also increase in size externally.

Examples:

• Mountains increase due to deposition.
• Crystals enlarge by accumulation of material.

Thus:

Growth by itself is not an absolute characteristic of living organisms.

2. Reproduction

Definition

Reproduction is the process by which organisms produce offspring similar to themselves.

Importance

• Ensures continuity of species
• Transfers genetic information
• Maintains population

Types of Reproduction

A. Asexual Reproduction

Only one parent is involved.

Examples

Organism	Method
Amoeba	Binary fission
Hydra	Budding
Yeast	Budding
Planaria	Regeneration

B. Sexual Reproduction

Two parents are involved.

Features

• Formation of gametes
• Fusion of gametes
• Genetic variation

Examples

Humans, flowering plants, frogs, birds.

Why Reproduction Alone Cannot Define Life

Some living organisms do not reproduce.

Examples

• Mule
• Sterile worker bees
• Infertile humans

Hence:

Reproduction is important but not an absolute defining feature of life.

3. Metabolism- The Defining Feature of Life

Definition

Metabolism is the sum total of all chemical reactions occurring inside living cells.

It includes:

1. Anabolism
2. Catabolism

A. Anabolism

Constructive metabolic reactions.

Examples

• Photosynthesis
• Protein synthesis
• Formation of glycogen

These reactions require energy.

B. Catabolism

Breaking down complex substances into simpler ones.

Examples

• Respiration
• Digestion

These reactions release energy.

Importance of Metabolism

• Produces energy
• Maintains body functions
• Repairs tissues
• Supports growth and reproduction

Why Metabolism is the Hallmark of Life

All living organisms possess metabolism.

Non-living objects do not perform metabolic reactions independently.

Even isolated cellular reactions outside the body indicate life-derived activity.

Therefore:

Metabolism is considered the most important defining property of living organisms.

4. Cellular Organization

Cell — Structural and Functional Unit of Life

All living organisms are made up of cells.

Cell Theory

Proposed by:

• Matthias Schleiden
• Theodor Schwann

Modified by:

• Rudolf Virchow

Types of Organisms Based on Cell Number

Type	Example
Unicellular	Amoeba, Bacteria
Multicellular	Humans, Mango tree

Levels of Organization in Multicellular Organisms

Cells → Tissues → Organs → Organ Systems → Organism

Importance of Cellular Organization

• Division of labour
• Efficient functioning
• Coordination among body parts

Non-living things lack cellular organization.

5. Consciousness and Response to Stimuli

Definition

Living organisms can sense and respond to changes in the environment.

This ability is called:

• Irritability
• Consciousness
• Responsiveness

Examples

Stimulus	Response
Light	Plants bend toward light
Heat	Sweating in humans
Pain	Withdrawal reflex
Touch	Mimosa leaves fold

Importance

This property helps organisms:

• Survive
• Adapt
• Avoid danger
• Obtain food

Consciousness as a Defining Feature

According to NCERT:

The most obvious and technically complicated feature of all living organisms is the ability to sense surroundings and respond to environmental stimuli.

6. Adaptation

Definition

Adaptation is the ability of organisms to adjust to environmental conditions for survival.

Examples

Organism	Adaptation
Camel	Hump stores fat
Cactus	Spines reduce water loss
Polar bear	Thick fur

7. Evolution

Living organisms evolve over time.

Evolution produces:

• Diversity
• New species
• Better adaptation

Non-living things do not evolve biologically.

Diversity in the Living World

Living organisms show enormous diversity.

They differ in:

• Shape
• Size
• Habitat
• Nutrition
• Reproduction

Viruses — Living or Non-Living?

Viruses occupy a borderline position.

Living Characteristics of Viruses

• Possess genetic material (DNA or RNA)
• Reproduce inside host cells
• Mutate and evolve

Non-Living Characteristics

• No cellular organization
• No metabolism outside host
• Can be crystallized

Thus:

Viruses are considered connecting links between living and non-living.

Examples:

• HIV
• Influenza virus
• Bacteriophage

Difference Between Living and Non-Living Things

Feature	Living Things	Non-Living Things
Cellular organization	Present	Absent
Metabolism	Present	Absent
Growth	Internal	External if present
Reproduction	Usually present	Absent
Response to stimuli	Present	Absent
Consciousness	Present	Absent
Adaptation	Present	Absent
Evolution	Occurs	Does not occur
Life span	Definite	No life span
Movement	May occur	Usually absent

Exceptions in Living Organisms

Biology contains exceptions, which are important for NEET.

Characteristic	Exception
Reproduction	Mule, sterile bees
Growth	Adult animals stop growing
Cellular organization	Viruses acellular
Metabolism	Dormant seeds show very low metabolism

Important NCERT Statements for NEET

1. Growth is not a defining property of living organisms.

2. Reproduction cannot be an all-inclusive defining characteristic of living organisms.

3. Metabolism is a defining feature of all living organisms.

4. Consciousness is the defining property of living organisms.

These statements are frequently asked in NEET.

NCERT-Based Conceptual Points

Dead Organisms

A dead organism:

• No longer performs metabolism
• Cannot reproduce
• Cannot respond to stimuli

Thus, life processes cease after death.

Dormancy

Some organisms show inactive phases.

Examples:

• Seeds
• Hibernating animals
• Bacterial spores

Despite inactivity, they are living because metabolic processes can resume.

Flowchart: Characteristics of Living Organisms

Living Organisms

       ↓

--------------------------------

| Growth                     |

| Reproduction               |

| Metabolism                 |

| Cellular organization      |

| Consciousness              |

| Adaptation                 |

| Evolution                  |

--------------------------------

NEET Important One-Liners

• Cell is the structural and functional unit of life.
• Metabolism is the hallmark of life.
• Consciousness is the defining feature of life.
• Viruses are borderline between living and non-living.
• Growth in living organisms is internal.
• Reproduction is not universal in living organisms.

Frequently Asked NEET Questions

1. Which is the defining feature of living organisms?

Answer:

Metabolism and consciousness.

2. Why is growth not considered a defining property?

Because non-living things like crystals also grow externally.

3. Why are viruses called connecting links?

Because they show both living and non-living characteristics.

4. What is metabolism?

The sum total of all biochemical reactions occurring in a living organism.

5. Who proposed cell theory?

Matthias Schleiden and Theodor Schwann.

Mnemonics for NEET

Characteristics of Life

“MR G CCE”

• M → Metabolism
• R → Reproduction
• G → Growth
• C → Cellular organization
• C → Consciousness
• E → Evolution

Previous NEET-Type MCQs

MCQ 1

Which of the following is the hallmark of life?

A. Growth
B. Reproduction
C. Metabolism
D. Movement

Answer:

C. Metabolism

MCQ 2

Which of the following can be crystallized?

A. Bacteria
B. Virus
C. Fungi
D. Protozoa

Answer:

B. Virus

MCQ 3

Growth in non-living objects occurs by:

A. Cell division
B. Internal synthesis
C. Accumulation of material on surface
D. Metabolism

Answer:

C. Accumulation of material on surface

MCQ 4

Which statement is correct?

A. All living organisms reproduce
B. All reproducing things are living
C. Metabolism occurs only in living organisms
D. Growth is unique to living organisms

Answer:

C. Metabolism occurs only in living organisms

Summary

Living organisms are distinguished from non-living things by several unique characteristics such as metabolism, cellular organization, growth, reproduction, responsiveness, adaptation, and evolution.

Among all these:

• Metabolism is the hallmark of life.
• Consciousness and response to stimuli are considered defining features.

No single property alone can completely define life because exceptions exist. Therefore, life is understood as the combined manifestation of all living processes.

Quick Revision Table

Property	Living	Non-Living
Metabolism	Yes	No
Consciousness	Yes	No
Growth	Internal	External
Reproduction	Usually	No
Cellular organization	Present	Absent
Evolution	Yes	No

Recommended NCERT Chapter

Biology Class 11

Chapter 1:

The Living World

This chapter is extremely important for NEET and should be studied line-by-line from NCERT.