Biology: The Scientific Study of Life

What is Life?

Biology is the scientific discipline concerned with the study of life and living organisms. To define life, biologists identify a set of properties that are common to all living things.

• Order: Living things exhibit complex but ordered organization, from molecules to entire organisms.

• Reproduction: Organisms reproduce their own kind, ensuring the continuation of their species.

• Growth and Development: Information carried by genes controls the pattern of growth and development in all organisms.

• Energy Processing: Organisms take in energy and use it to power all their activities.

• Regulation: Organisms have regulatory mechanisms that maintain a beneficial internal environment (homeostasis).

• Response to the Environment: All organisms respond to environmental stimuli.

• Evolutionary Adaptation: Over generations, populations evolve adaptations that make them better suited to their environments.

The cell is the structural and functional unit of life. All living things are composed of one or more cells.

The Hierarchy of Biological Organization

Levels of Organization

Biologists study life across a broad range of scales, from molecules to the entire planet. This organization is hierarchical, with each level building on the one below it and exhibiting new emergent properties.

• Biosphere: All life on Earth and all the places where life exists.

• Ecosystem: All living things in a particular area, along with all the nonliving components of the environment.

• Community: The entire array of organisms inhabiting a particular ecosystem.

• Population: All the individuals of a species living within the bounds of a specified area.

• Organism: An individual living thing.

• Organ System: A group of organs that work together to perform a specific function.

• Organ: A body part that carries out a particular function in the body.

• Tissue: A group of cells that work together to perform a specialized function.

• Cell: The fundamental unit of life.

• Organelle: A membrane-enclosed functional structure within a cell.

• Molecule: A chemical structure consisting of two or more units called atoms.

Emergent properties arise at each new level of organization, resulting from the specific arrangement and interactions of component parts.

Domains of Life

Classification of Life

Taxonomists classify the diversity of life into three domains based on cell structure and genetics:

• Domain Bacteria: Consists of prokaryotic organisms with simple cells.

• Domain Archaea: Also prokaryotic, but genetically distinct from bacteria; often found in extreme environments.

• Domain Eukarya: Includes all eukaryotic organisms, such as protists, fungi, plants, and animals.

Each domain is further divided into kingdoms and other taxonomic groups.

The Process of Science

Scientific Inquiry

Science is a systematic way of understanding the natural world through observation and experimentation. The scientific method is an evidence-based process that includes:

• Observation: Gathering data about phenomena.

• Hypothesis: A tentative explanation that can be tested.

• Prediction: A logical statement about what will happen if the hypothesis is correct.

• Experimentation: Testing the hypothesis through controlled experiments or further observations.

• Data Analysis: Interpreting results to support or refute the hypothesis.

A scientific theory is a broad explanation supported by a large body of evidence.

Controlled Experiments

In a controlled experiment, researchers manipulate one variable (the independent variable) and observe the effect on another variable (the dependent variable). A control group is used for comparison to the experimental group.

• Example: Testing camouflage in mice by comparing predation rates on camouflaged versus non-camouflaged models.

Clinical trials and observational studies are used to test hypotheses in humans.

The Nature of Scientific Process

The process of science is repetitive, nonlinear, and collaborative. It involves:

• Exploration and discovery

• Analysis and feedback from the scientific community

• Societal benefits and outcomes

Five Unifying Themes in Biology

1. Evolution: The Core Theme of Biology

Evolution explains both the unity and diversity of life. Charles Darwin's theory of evolution by natural selection describes how populations change over time as individuals with advantageous traits survive and reproduce.

• Natural Selection: The process by which individuals with certain inherited traits are more likely to survive and reproduce.

• Artificial Selection: Humans selectively breed plants and animals for desired traits.

All species share a common ancestry, represented as branches on the tree of life.

2. Life Depends on the Flow of Information

Genetic information, primarily in the form of DNA, is responsible for heredity and for programming cellular activities. Information from the environment also regulates gene expression and body processes.

• DNA: The molecule that stores genetic information.

• Gene Expression: The process by which information from a gene is used to synthesize proteins.

3. Structure and Function are Correlated

At every level of biological organization, structure and function are closely related. For example, the shape of a protein determines its function, and the structure of nerve cells enables them to transmit signals.

4. Life Depends on the Transfer and Transformation of Energy and Matter

Energy flows through ecosystems, entering as sunlight, converted to chemical energy by producers, passed to consumers, and lost as heat. Matter cycles between the environment and living organisms.

• Producers: Organisms (like plants) that convert solar energy to chemical energy.

• Consumers: Organisms that obtain energy by eating other organisms.

• Decomposers: Organisms that break down dead matter, returning nutrients to the environment.

5. Life Depends on Interactions Within and Between Systems

Biological systems are composed of many interacting parts. Emergent properties arise from these interactions. Systems biology is an approach that models the complex interactions within biological systems.

Summary Table: Properties of Life

Key Equations and Concepts

• Photosynthesis (energy transformation):

• Central Dogma of Molecular Biology (information flow):

Review Questions

• Describe seven properties common to all life.

• Compare the three domains of life.

• Describe the levels of biological organization from molecules to the biosphere.

• Define science and distinguish between a hypothesis and a scientific theory.

• Describe the structure of a controlled experiment.

• Explain how DNA determines an organism's structures and functions.

• Compare the dynamics of nutrients and energy in an ecosystem.

• Explain how systems biology is used to understand biological systems.