What is Living? Characteristics of Living Organisms
What is Living?
Living organisms are entities that exhibit life processes such as growth, reproduction, metabolism, and response to environmental stimuli.
Biologists identify living organisms based on a combination of characteristics rather than a single defining feature.
Characteristics of Living Organisms
The major characteristics of living organisms include:
- Growth
- Reproduction
- Response to stimuli
- Metabolism
- Self-organization
- Adaptation
- Consciousness
Growth as a Characteristic of Living Organisms
Growth refers to an increase in size, mass or number of cells.
In Unicellular Organisms
Growth occurs through cell division, where one cell divides to form two new cells.
In Multicellular Organisms
Growth occurs by increasing the number and size of cells.
Important Note
Non-living objects may increase in size by external accumulation of material, whereas living organisms grow internally through cellular activities.
Reproduction as a Characteristic of Living Organisms
Reproduction is the process by which living organisms produce offspring of their own kind.
Unicellular Organisms
Cell division serves both growth and reproduction.
Multicellular Organisms
Reproduction involves specialized reproductive organs and processes.
Limitation
Some living organisms such as sterile worker bees, mules and infertile humans cannot reproduce, so reproduction alone cannot define life.
Consciousness and Response to Stimuli
Living organisms can sense environmental changes and respond appropriately.
Examples
- Plants bend toward light.
- Humans respond to temperature changes.
- Animals react to danger.
This ability to perceive and respond to stimuli is a key feature of life.
Metabolism: The Defining Characteristic of Life
Metabolism refers to all chemical reactions occurring inside living cells.
Types of Metabolism
- Anabolism – Building complex molecules.
- Catabolism – Breaking down molecules to release energy.
All living organisms perform metabolic reactions, while non-living things do not.
Therefore, metabolism is considered one of the most important defining characteristics of life.
Difference Between Living and Non-Living Things
| Feature | Living Things | Non-Living Things |
|---|---|---|
| Growth | Internal growth | External accumulation |
| Reproduction | Usually present | Absent |
| Metabolism | Present | Absent |
| Response to Stimuli | Present | Absent |
| Cellular Organization | Present | Absent |
Summary
- Living organisms exhibit growth, metabolism and responsiveness.
- Growth alone cannot define life.
- Reproduction is common but not universal.
- Response to stimuli is a major characteristic.
- Metabolism is considered the defining feature of life.
Frequently Asked Questions
What is living?
An organism capable of performing life processes such as growth, metabolism and response to stimuli.
What are the main characteristics of living organisms?
Growth, reproduction, metabolism and responsiveness.
Why is metabolism considered the defining feature of life?
Because all living organisms perform metabolic reactions while non-living things do not.
Can growth alone define life?
No. Non-living things can also increase in size through external accumulation.
Can all living organisms reproduce?
No. Some living organisms are sterile or infertile.