Chapter 5 · Question 5
What criteria do we use to decide whether something is alive?
Q5
What criteria do we use to decide whether something is alive?
Answer Revealed
Direct Answer:
Visible movement such as walking, breathing, or growth is the most common criterion, but molecular movements like metabolic reactions inside cells are the defining feature of life.
Simple Explanation
We usually look for movement to tell if something is alive — like a dog moving or a plant growing. But even when an organism appears still, life is actually about the invisible chemical reactions happening inside its cells.
Exam-Ready Structure
The most visible criterion for life is movement — either locomotion, breathing, or growth. However, movement alone is not sufficient because non-living things can also show movement (e.g., a car moves, a cloud grows). The fundamental criterion for life is molecular movement — the continuous chemical reactions (metabolism) occurring inside every living cell. If these metabolic reactions stop, the organism is no longer alive. Therefore, visible movement is a useful indicator, but molecular movement inside cells is the definitive test of whether something is living.
Key Points
- Visible movement is the common criterion
- Growth and locomotion are outward signs of life
- Molecular movement inside cells is the fundamental criterion
- Metabolic reactions define whether an organism is alive
Common Mistakes
- Equating any movement with life without considering metabolic activity
- Not distinguishing between visible movement and molecular movement
Answer Sources
- Visible and molecular movementtextbook section | Science | Life Processes | What are life processes? | Pages 1