Investigating Life

Scientific Investigation

Scientific investigation is the process by which scientists explore natural phenomena, gather data, and develop explanations based on evidence. It relies on systematic observation and experimentation.

• Observation: The act of noticing and describing events or processes in a careful, orderly way. Observations may include new technological improvements.

• Data: Quantified information collected during observations or experiments.

Main Types of Scientific Approaches

• Descriptive Science (Discovery Science): Focuses on observation-based discovery, describing aspects of the natural world.

• The Scientific Method: Involves proposing and testing hypotheses through experimentation and prediction.

  • Experimental/Hypothesis-Driven Science: Uses predictions to test hypotheses.

  • Observing: Involves proposing and testing hypotheses.

  • Experiment Types:

    • Controlled Experiments: Manipulate one variable while keeping others constant to determine its effect.

    • Comparative Experiments: Predict that groups will be different and compare data from different sample groups.

Hypotheses and Null Hypotheses

A hypothesis is a tentative answer to a scientific question that can be tested and must be falsifiable. The null hypothesis states that there is no effect or difference; it is what researchers try to disprove, reject, or nullify.

• Null Hypothesis: No statistical significance exists in a set of given observations; no effect.

• Statistical Significance: Indicates whether observed differences are likely due to chance. Commonly accepted standard is a p-value of 0.05 or lower.

Theories, Laws, and Principles

Scientific knowledge is organized into hypotheses, theories, and laws/principles, each with distinct roles in explaining natural phenomena.

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

• Law/Principle: A statement that describes or predicts a range of natural phenomena based on repeated experiments or observations.

  • Examples: Laws of Thermodynamics, Bernoulli's Principle

Logic in Scientific Investigation

Scientists use both inductive and deductive logic to develop and test hypotheses.

• Inductive Logic: Uses observations or facts to develop a tentative answer or hypothesis.

• Deductive Logic: Uses general principles to predict specific facts that must be true if the hypothesis is correct.

• Experiments are designed to test these predictions.

Model Systems

Model systems are organisms used to understand biological processes that are common to many forms of life. This is possible because all life shares a common ancestor, genetic code, and similar building blocks.

• Examples: Escherichia coli (bacteria), Mus musculus (mouse), Arabidopsis thaliana (plant)

Experiment Types

Controlled Experiments

Controlled experiments are designed to test the effect of a single variable by keeping all other variables constant.

• Use samples and groups that are as similar as possible.

• Manipulate one or more factors being tested (independent variable).

• Compare experimental groups with data from an unmanipulated control group.

• Independent (predictor) variable: The variable being manipulated ("x axis").

• Dependent (response) variable: The response that is measured ("y axis").

Comparative Experiments

Comparative experiments predict that groups will be different and gather data from different sample groups for comparison.

Statistical Tests

Statistical tests are used to objectively decide if a measured difference is meaningful.

• Calculate probabilities in observed vs. experimental variation.

• Commonly accepted standard: p-value of 0.05 or lower.

• Important considerations:

  • Null hypothesis: no difference exists

  • Data collection and sample size

  • Quantification

  • Reproducibility

  • Power

Life and Its Properties

Origin and Diversity of Life

Earth formed approximately 4.6 to 4.5 billion years ago, but life did not evolve until about 600 million years later. All living organisms today originated from one life form.

• If life had multiple origins, we would not expect to see such striking similarities in gene sequences, genetic code, and amino acids.

Properties of Life

Life exhibits several key properties:

• It is organized

• It is diverse

• It changes

• There are interactions among life

• It is complex

Levels of Organization of Organisms

Biological classification organizes living things into hierarchical categories based on shared characteristics.

• Domain (3): Archaea (Prokaryotic), Bacteria (Prokaryotic), and Eukarya (Eukaryotic: Protists, Fungi, Plants, Animals)

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

Binomial Nomenclature

Binomial Nomenclature is the naming system in which two terms are used to denote a living species or organism. The first term indicates the genus, and the second indicates the species.

• Example: Homo sapiens (Homo = genus, sapiens = species)

Members of the same species will only mate, reproduce, and produce viable offspring with members of their own species.

Summary Table: Comparison of Scientific Terms

Summary Table: Levels of Biological Organization

Key Equations and Concepts

• Statistical Significance: p-value calculation

• Hypothesis Format:

  • "If" (hypothesis), "Then" (prediction)

Additional info: Some definitions and examples have been expanded for clarity and completeness. Tables have been recreated to summarize comparisons and classifications.