Characteristics of Life

Cells

Cells are the basic structural and functional units of all living organisms. Understanding cells is fundamental to biology.

• Louis Pasteur's Contributions: Louis Pasteur was a pioneering scientist who disproved the Theory of Spontaneous Generation, which posited that life could arise from non-living matter. Pasteur's experiments supported the Cell Theory, which states that all living things are composed of cells and that all cells arise from pre-existing cells.

• Cell Theory vs. Spontaneous Generation: Cell Theory is a foundational concept in biology, while Spontaneous Generation is a disproven hypothesis.

Replication via Cell Division

Replication is the process by which cells make copies of themselves, ensuring the continuity of life.

• Cell Division: The process by which a parent cell divides to form two or more daughter cells. This is essential for growth, development, and reproduction in living organisms.

Processing Information

Living organisms process information to maintain internal stability and respond to their environment.

• Homeostasis: The ability of an organism to maintain a stable internal environment despite changes in external conditions.

• Biotic Relationships: Biotic factors are living components of an ecosystem. Relationships among biotic factors include predation, competition, and symbiosis.

Requiring and Acquiring Energy

All living organisms require energy to carry out life processes. Energy is acquired through various means such as photosynthesis or consumption of other organisms.

Evolution

Evolution is the process by which populations of organisms change over generations through variations in their genetic material.

• Meaning of 'Life Evolves': Life evolves through genetic changes that are passed on to offspring, leading to adaptation and diversity.

• Branches of the Tree of Life: The tree of life represents the evolutionary relationships among all living organisms. The three main domains are Archaea, Bacteria, and Eukarya.

• Taxonomic Classification System: Organisms are classified into hierarchical categories: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species.

• Binomial Nomenclature: A system for naming species using two names: the genus and the species (e.g., Homo sapiens). The genus name is capitalized, the species name is lowercase, and both are italicized.

• Viruses: Viruses are often confused with living organisms because they can reproduce and evolve, but they lack cellular structure and independent metabolism, so they are not considered truly alive.

What is Science?

Nature of Science

Science is a systematic approach to understanding the natural world through observation and experimentation.

• Science vs. Pseudoscience: Science relies on empirical evidence and testable hypotheses, while pseudoscience lacks rigorous testing and evidence.

• Observational vs. Experimental Studies: Observational studies involve watching and recording natural phenomena without intervention, while experimental studies involve manipulating variables to test hypotheses.

• Theory in Science: In science, a theory is a well-substantiated explanation of some aspect of the natural world, based on a body of evidence. In everyday language, 'theory' may refer to a guess or speculation.

• Examples of Scientific Theories: Examples include the Theory of Evolution, Cell Theory, and Germ Theory of Disease.

Key Terms and Definitions

The following table lists important biological terms and their meanings. Understanding these terms is essential for success in biology.

Additional info: Some definitions and explanations have been expanded for clarity and completeness.