Lesson 2: Characteristics of Living Things
What if you discovered a creature that can survive the vacuum of space — without oxygen, food, or even water? Sounds impossible, yet it exists. To truly understand how such organisms survive, we must first uncover the fundamental characteristics that define life itself. In this lesson, you will explore the seven characteristics of living things — the biological rules that separate living organisms from non-living matter.
Video Explainer: The Science of Life
The Seven Characteristics That Define Life
Living organisms are not defined by appearance, size, or habitat. Instead, they are identified by specific biological processes that occur continuously throughout their existence. These processes allow organisms to obtain energy, maintain internal balance, respond to their environment, and ensure survival of their species.
Biologists recognize seven universal characteristics shared by all living things — from microscopic bacteria to complex multicellular organisms.
1. Nutrition: Fuel for Life
Nutrition is the process by which organisms obtain and utilize nutrients from their environment. These nutrients — including carbohydrates, proteins, lipids, vitamins, minerals, and water — are essential for energy production, growth, repair, and regulation of body processes.
- Carbohydrates provide immediate energy
- Lipids store long-term energy
- Proteins support growth and tissue repair
- Vitamins and minerals regulate metabolic processes
- Water maintains temperature and chemical balance
I am a carbohydrate, I am sweet, and I fuel your body with energy. Who am I?
Answer: Glucose — the primary energy source used in cellular respiration.
2. Respiration: Releasing Energy
Respiration is the chemical process that breaks down nutrients to release energy required for life activities such as movement, growth, and repair.
Most organisms use oxygen during respiration to efficiently release energy from carbohydrates. Without respiration, cells would be unable to function.
If an astronaut ran out of oxygen in space, which characteristic of life would fail first?
3. Excretion: Removing Waste
Excretion is the removal of metabolic waste products produced during life processes. These wastes can be toxic if allowed to accumulate.
Examples include:
- Carbon dioxide removed through breathing
- Urea removed through urine
- Salts and water removed through sweat
Which is a form of excretion — breathing, sleeping, or growing?
4. Sensitivity: Responding to the Environment
Sensitivity is the ability of organisms to detect changes in their environment and respond appropriately. These changes are known as stimuli.
Responses help organisms survive threats and maintain balance — such as shivering in cold conditions or blinking in bright light.
What stimulus do you react to instantly — loud sounds, bright light, or bad smells?
5. Movement: Internal and External Motion
Movement refers to the change in position of an organism or its parts.
- Animals move through locomotion
- Plants show movement in shoots and roots
- Internal movement transports substances
Water transport through xylem is a form of movement — even though it’s invisible.
6. Growth: Permanent Increase in Size
Growth is the permanent increase in size and mass of an organism due to cell division and enlargement.
What grows faster — hair or nails?
7. Reproduction: Continuity of Life
Reproduction is the process by which organisms produce offspring. It ensures the survival and continuity of a species.
Reproduction prevents extinction — without it, life would end.
Key Concepts
- Living things share seven defining characteristics
- Energy is essential for all life processes
- Waste removal maintains internal balance
- Reproduction ensures species survival
Reflection Questions
Quick Poll
Audio Recap
Flashcards
Discussion
- Which characteristic best distinguishes living from non-living things?
- Can an organism be alive if one characteristic is missing?
- Which characteristic do viruses lack?