1.1.4 Characteristics of Living Organisms

Characteristics of Living Organisms

Introduction

All living things, from the smallest bacteria to the largest elephant or tree, share certain basic characteristics that distinguish them from non-living things such as stones, water, or air. These features are known as the characteristics of living organisms or life processes.

Understanding these characteristics is essential in Biology because they help us to identify, classify, and study living organisms scientifically.

Every living organism, regardless of size or complexity, must perform certain functions to stay alive — such as feeding, movement, respiration, growth, excretion, and reproduction. The study of these life processes helps biologists understand how living systems work and how they interact with the environment.

In this section, we will discuss each of the major characteristics of living organisms in detail, with clear examples and explanations relevant to human life, animals, and plants.

1. Nutrition

Definition

Nutrition is the process by which living organisms obtain and use food or nutrients for energy, growth, and repair of body tissues.

Food provides the raw materials needed to build new cells and the energy required to perform life processes.

Importance of Nutrition

Provides energy for movement, growth, and reproduction.

Supplies materials for repair of worn-out tissues.

Helps in regulation of body processes (through vitamins and minerals).

Enables organisms to build resistance against diseases.

Types of Nutrition

There are two main types of nutrition:

a. Autotrophic Nutrition

Organisms that make their own food from simple substances are called autotrophs.

Example: Green plants and some bacteria.

They use sunlight, water, and carbon dioxide to make glucose through photosynthesis.

Equation of Photosynthesis:

6CO2 + 6H2O ➡️{light, chlorophyll} C6H12O6 + 6O2

b. Heterotrophic Nutrition

Organisms that cannot make their own food and must obtain it by feeding on other organisms are called heterotrophs.

Examples: Humans, animals, fungi.

Types of heterotrophic nutrition include:

Herbivores – feed on plants (e.g., cow, goat).

Carnivores – feed on other animals (e.g., lion, eagle).

Omnivores – feed on both plants and animals (e.g., humans).

Saprophytes – feed on dead matter (e.g., fungi).

Parasites – feed on living hosts (e.g., tapeworms).

Without nutrition, living organisms would not be able to grow, move, or survive.

2. Respiration

Definition

Respiration is the process by which living organisms break down food (usually glucose) to release energy.

This energy is used for all life activities such as movement, growth, and repair.

Equation for Respiration

Glucose + Oxygen \rightarrow Carbon\ Dioxide + Water + Energy

Or in symbols:

C_6H_{12}O_6 + 6O_2 → 6CO_2 + 6H_2O + Energy

Types of Respiration

1. Aerobic Respiration: Takes place in the presence of oxygen. It produces large amounts of energy.

Example: Humans, animals, and most plants.

2. Anaerobic Respiration: Takes place in the absence of oxygen and produces less energy.

Example: Yeast (used in brewing and baking).

Importance of Respiration

Provides energy for all body activities.

Enables growth and repair of tissues.

Helps in temperature regulation.

Provides energy for muscle contraction during movement.

Without respiration, life cannot continue because no energy would be available for vital processes.

3. Movement

Definition

Movement is the ability of an organism or part of it to change its position or place.

It allows organisms to find food, escape danger, and interact with their environment.

Types of Movement

Locomotion: Movement of the whole body from one place to another (e.g., walking, swimming, flying).

Movement of parts: Movement of specific parts such as plant leaves turning toward sunlight or human eyes blinking.

Examples

Animals: Walk, swim, crawl, or fly to search for food or mates.

Plants: Do not move from place to place but show movement in parts (e.g., sunflower turns toward sunlight; roots grow downward).

Importance of Movement

Helps organisms find food and shelter.

Enables escape from predators.

Aids in reproduction (e.g., movement of sperm towards egg).

Allows adaptation to environmental changes.

Movement is powered by energy from respiration and is one of the most visible signs of life.

4. Growth

Definition

Growth is the permanent increase in size, mass, and number of cells in an organism.

It occurs as a result of cell division and the addition of new materials to the body.

Characteristics of Growth

Irreversible: Once an organism grows, it cannot return to its previous smaller size.

Gradual: It happens over time.

Requires nutrients and energy.

Examples

A baby growing into an adult.

A seed germinating and developing into a mature plant.

Regrowth of tissue after injury.

Importance of Growth

Indicates that life processes are active.

Enables organisms to reach maturity and reproduce.

Allows repair and replacement of damaged tissues.

Growth continues throughout life in some organisms (e.g., trees) but stops at maturity in others (e.g., humans).

5. Excretion

Definition

Excretion is the process by which living organisms remove metabolic waste products from their bodies.

Metabolic wastes include substances produced during chemical reactions inside cells, such as carbon dioxide, urea, and water.

Importance of Excretion

Prevents the accumulation of toxic substances.

Helps maintain internal balance (homeostasis).

Keeps cells and tissues healthy.

Regulates water and salt balance in the body.

Excretory Organs

Humans/Animals: Kidneys (remove urea), lungs (remove carbon dioxide), skin (removes sweat).

Plants: Use stomata and lenticels to remove gases like oxygen and carbon dioxide; some wastes are stored in leaves or bark and later removed when the plant sheds them.

Difference Between Excretion and Egestion

Process Definition Example

Excretion Removal of metabolic waste Sweat, urine

Egestion Removal of undigested food Faeces

6. Sensitivity (Irritability)

Definition

Sensitivity or irritability is the ability of an organism to detect and respond to changes (stimuli) in its environment.

A stimulus is anything that causes a reaction — for example, light, temperature, sound, or touch.

Examples

Humans react to heat by sweating.

Plants grow towards light (phototropism).

Animals run from danger.

Snails withdraw into their shells when touched.

Importance of Sensitivity

Helps organisms avoid danger.

Enables search for food or mates.

Allows adaptation to environmental changes.

Maintains internal stability (homeostasis).

Without sensitivity, living organisms would not survive in changing environments.

7. Reproduction

Definition

Reproduction is the process by which living organisms produce new individuals of their own kind.

It ensures the continuity of life and prevents species from becoming extinct.

Types of Reproduction

1. Asexual Reproduction:

Involves only one parent.

Offspring are identical to the parent.

Common in simple organisms (e.g., bacteria, yeast, amoeba, some plants).

Examples:

Binary fission in amoeba.

Budding in yeast and hydra.

Vegetative propagation in plants (e.g., potato tubers, runners in strawberry).

2. Sexual Reproduction:

Involves two parents (male and female).

Offspring are genetically different from parents.

Found in animals, humans, and flowering plants.

Requires fusion of male gamete (sperm) and female gamete (egg/ovum) to form a zygote.

Importance of Reproduction

Maintains species population.

Introduces variation for adaptation and evolution.

Allows inheritance of traits from parents to offspring.

8. Respiration vs. Photosynthesis

It’s important to distinguish between respiration (which releases energy) and photosynthesis (which stores energy).

Process Photosynthesis Respiration

Takes place in Green plants (chloroplasts) All living cells (mitochondria)

Requires Light, CO₂, water Glucose, O₂

Produces Glucose, O₂ CO₂, water, energy

Type of process Energy-storing Energy-releasing

Both are essential and interdependent processes that sustain life on Earth.

9. Excretion vs. Secretion vs. Egestion

Term Definition Example

Excretion Removal of metabolic wastes Urine, sweat

Secretion Release of useful substances Saliva, enzymes

Egestion Removal of undigested food Faeces

These distinctions are key to understanding body function and homeostasis.

10. Death

While not a “characteristic of life,” death marks the end of all life processes.

After death:

Respiration stops.

Movement ceases.

Cells break down (decomposition).

Death allows recycling of nutrients back into ecosystems — an essential part of nature’s balance.

11. Summary Table: Characteristics of Living Organisms

Characteristic Description Example

Nutrition Taking in and using food Humans eating; plants photosynthesizing

Respiration Releasing energy from food Breathing, cellular respiration

Movement Changing position Animals walking, plants bending

Growth Permanent increase in size Seed germination, child development

Excretion Removal of metabolic wastes Urine, sweat, oxygen from plants

Sensitivity Responding to stimuli Eyes reacting to light

Reproduction Producing new organisms Birth, seed formation

12. Importance of Studying Life Processes

Studying these characteristics allows scientists and students to:

Distinguish living things from non-living things.

Understand how organisms survive and adapt.

Apply knowledge in health, agriculture, and environmental management.

Appreciate the unity and diversity of life on Earth.

13. Key Differences Between Living and Non-Living Things

Living Things Non-Living Things

Show all seven life processes Do not perform life processes

Made of cells Not made of cells

Grow and reproduce Do not grow or reproduce

Respond to stimuli Do not respond

Die and decompose Do not die