Introduction to Biology

Key Terms and Definitions

This section introduces foundational vocabulary essential for understanding biology. Each term is defined to provide clarity and context for further study.

• Biology: The scientific study of life and living organisms.

• Life: The condition that distinguishes living organisms from nonliving matter, characterized by growth, reproduction, response to stimuli, and metabolism.

• Emergent Property: A characteristic of a system that arises from the interaction of its parts, not present in individual components.

• Biosphere: The global sum of all ecosystems; the zone of life on Earth.

• Ecosystem: A community of living organisms interacting with their physical environment.

• Cell: The basic structural and functional unit of all living organisms.

• Prokaryotic: Cells lacking a nucleus and membrane-bound organelles (e.g., bacteria).

• Eukaryotic: Cells containing a nucleus and membrane-bound organelles (e.g., plants, animals).

• DNA (Deoxyribonucleic Acid): The molecule that carries genetic information in living organisms.

• Gene: A segment of DNA that codes for a specific protein or function.

• Genome: The complete set of genetic material in an organism.

• Taxonomy: The science of classifying organisms.

• Domain: The highest taxonomic rank, grouping organisms based on fundamental differences (e.g., Bacteria, Archaea, Eukarya).

• Kingdom: A major taxonomic category below domain (e.g., Animalia, Plantae).

• Protist: A diverse group of mostly unicellular eukaryotic organisms.

• Evolution: The process by which populations of organisms change over generations.

• Natural Selection: The process by which organisms better adapted to their environment tend to survive and reproduce.

• Artificial Selection: The intentional breeding of organisms by humans for desired traits.

• Science: The systematic study of the natural world through observation and experimentation.

• Discovery Science: Science based on observation and analysis of data.

• Hypothesis-Driven Science: Science that begins with a hypothesis and tests it through experiments.

• Scientific Method: A systematic approach to inquiry involving observation, hypothesis formation, experimentation, and analysis.

• Hypothesis: A testable explanation for an observation or phenomenon.

• Controlled Experiment: An experiment in which only one variable is changed at a time.

• Theory: A well-substantiated explanation of some aspect of the natural world, based on a body of evidence.

• Technology: The application of scientific knowledge for practical purposes.

Properties and Processes Associated with Life

Seven Characteristics of Living Organisms

All living things share a set of fundamental properties and processes that distinguish them from nonliving matter.

1. Order: Living things exhibit complex organization, from molecules to cells to tissues.

2. Regulation: Organisms maintain stable internal conditions (homeostasis).

3. Growth and Development: Organisms increase in size and change over their life cycle, guided by genetic instructions.

4. Energy Processing: Living things acquire and use energy to power activities and chemical reactions.

5. Response to Environment: Organisms detect and react to stimuli in their surroundings.

6. Reproduction: Living things produce offspring, passing on genetic material.

7. Evolutionary Adaptation: Populations change over time as individuals with advantageous traits survive and reproduce.

Hierarchy of Life

Ten Levels of Biological Organization

Biological systems are organized into a hierarchy, each level building on the previous one. This structure helps scientists study life from molecules to the biosphere.

1. Biosphere: All environments on Earth that support life.

2. Ecosystem: All living organisms and nonliving components in a particular area.

3. Community: All populations of different species living in an ecosystem.

4. Population: Individuals of the same species living in a specific area.

5. Organism: An individual living thing.

6. Organ System: Groups of organs working together to perform specific functions.

7. Organ: A structure composed of tissues that performs a specific function.

8. Tissue: A group of similar cells performing a common function.

9. Cell: The smallest unit of life.

10. Molecule: A group of atoms bonded together, forming the chemical basis of life.

Additional info: The hierarchy may be visualized as a pyramid, with molecules at the base and the biosphere at the top.

Roles in Ecosystems

Producers, Consumers, and Decomposers

Within ecosystems, organisms play specific roles in the flow of energy and cycling of nutrients.

• Producers: Organisms (usually plants and algae) that convert solar energy into chemical energy via photosynthesis.

• Consumers: Organisms that obtain energy by eating other organisms (e.g., animals, some protists).

• Decomposers: Organisms (such as bacteria and fungi) that break down dead organic matter, recycling nutrients back into the ecosystem.

Example: In a forest ecosystem, trees are producers, deer are consumers, and fungi are decomposers.