Characteristics of Life

Living things are made of cells and share metabolism, response to stimuli, homeostasis, reproduction and heredity, and adaptation and evolution. Metabolism balances anabolism, building large molecules, with catabolism, breaking them down for energy. Cells stay alive by keeping that balance, while viruses sit on the edge of life without a cell structure or independent metabolism. Slide the energy input and watch anabolism and catabolism change.

What is a Living Organism?

🌱 What Does it Mean to Be Alive?

①What is the difference between a stone and a tree? — A tree grows, responds, and uses energy

②Living organisms share common properties

③Understanding these reveals "what life is"

Visualizing Cells and Metabolism

Energy input5

🔬 Key Observations

①Higher energy → anabolism (synthesis) becomes more active

②Catabolism (breakdown) stays at a baseline — survival energy

③Cells maintain homeostasis through balance of anabolism and catabolism

Six Characteristics of Life

Characteristics of Life

Common Properties of Living Things

Anabolism vs Catabolism

Metabolism Comparison

ChartAnabolism vs Catabolism

Item	Anabolism	Catabolism
Direction	small → large molecules	large → small molecules
Energy	absorbed (endothermic)	released (exothermic)
Examples	photosynthesis, protein synthesis	cellular respiration, digestion
ATP	ATP consumed	ATP produced

Key of Metabolism

metabolism = anabolism + catabolism

Foundation of life — balance of synthesis and breakdown

Worked Examples

Example 1

Which of the following are anabolic processes? (a) photosynthesis (b) cellular respiration (c) protein synthesis (d) digestion

Anabolism builds large molecules from small ones and absorbs energy.

Photosynthesis (CO₂+H₂O→glucose) and protein synthesis (amino acids→protein) are anabolic. Respiration and digestion are breakdown (catabolic).

▸ (a), (c)

Anabolism = building / absorbs energy; catabolism = breaking down / releases energy.

Example 2

Explain why a virus shows both living and non-living characteristics, in terms of cells and metabolism.

Living traits: it carries genetic material (DNA/RNA) and reproduces inside a host cell, where heredity and mutation occur.

Non-living traits: it has no cell structure of its own and cannot perform independent metabolism, existing as a protein crystal outside a host.

▸ Genetic material/reproduction (living) vs no cell structure/no independent metabolism (non-living)

It fails the "cell" and "independent metabolism" criteria of life, so it sits at the living/non-living boundary.

Summary

Six Characteristics of Life

Cell · Metabolism · Stimulus·Response · Homeostasis · Reproduction·Heredity · Adaptation·Evolution

Properties shared by all living things

CSAT-style

Which pairing of a characteristic of life with its example is INCORRECT?

①Metabolism — ATP produced by cellular respiration

②Stimulus and response — a plant bending toward light

③Homeostasis — keeping body temperature constant

④Reproduction and heredity — parental traits passed to offspring

⑤Metabolism — a rock worn down by wind and rain

▸ ⑤ Metabolism — a rock worn down by wind and rain

Metabolism is a living organism synthesizing and breaking down matter using energy inside cells.

Weathering of a rock is only a physical/chemical change, not a life process, so the pairing is incorrect.

🎯 Exam Points

①Cell: structural/functional basic unit of life

②Metabolism = anabolism (synthesis, absorbs energy) + catabolism (breakdown, releases energy)

③Homeostasis: keeps internal environment stable (negative feedback)

④Viruses: no cell structure, no independent metabolism → biology/non-biology debate

⑤Adaptation/evolution occur at population level, not individual

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Chemistry II · Electrochemistry

Cells and Cell Division

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