Biology: The Study of Life

What is Biology?

Biology is the scientific study of living organisms and their interactions with the environment. The term "biology" comes from the Greek words bios (life) and logos (study).

• Biology = the study of living organisms.

• "-ology" = the study of.

• Subfields include: microbiology, genetics, physiology, ornithology (birds), herpetology (reptiles/amphibians), botany (plants), ecology.

Five Fundamental Characteristics of Life

Defining Features of Living Things

All living organisms share five key characteristics that distinguish them from non-living matter.

1. Energy – Organisms acquire and use energy (e.g., eating, photosynthesis).

2. Cells – All living things are made of membrane-bound cells.

3. Information – Hereditary information (DNA/genes) and the ability to respond to the environment.

4. Replication – All organisms can reproduce.

5. Evolution – Populations evolve over time.

A "living entity" is defined as one or more cells.

Domains of Life & Biological Classification

Major Domains

Life is classified into three major domains based on cellular structure and genetics.

• Prokaryotes

  • Domain Bacteria

  • Domain Archaea

• Eukaryotes

  • Domain Eukarya

Classification Hierarchy

Organisms are classified using a hierarchical system:

• Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

• Example: Humans = Homo sapiens

  • Homo = genus

  • sapiens = species

Scientific Theory

Definition and Structure

A scientific theory is an explanation for a general phenomenon, supported by strong evidence. Theories have two components:

• Pattern – What occurs in the natural world.

• Process – What explains the pattern.

Key Biological Theories

• Cell Theory

  • All organisms are made of cells.

  • All cells come from preexisting cells.

• Theory of Evolution by Natural Selection

  • Organisms share common ancestry.

  • Evolution explains structure and diversity.

The Scientific Method

Steps in Scientific Investigation

The scientific method is a systematic approach to answering questions and testing hypotheses.

1. Make observations → ask questions.

2. Form a hypothesis (testable explanation).

3. Make a prediction (what should happen if hypothesis is correct).

4. Design & run an experiment.

5. Analyze results.

6. Accept, reject, or modify the hypothesis.

• Control groups must be included.

• Experiments must be repeatable.

• Supernatural explanations cannot be tested by science.

Variables in Experiments

Types of Variables

Experiments involve manipulating and measuring variables:

• Independent variable – what the scientist changes.

• Dependent variable – what is measured.

Control group – baseline group with no experimental treatment.

Good experiments are repeatable and consistent.

Famous Experiments

Pasteur’s Experiment (Cell Theory)

• Hypothesis: Cells come from other cells, not spontaneous generation.

• Results: Supported; no spontaneous generation observed.

Other Examples

• Giraffe Necks

  • Hypothesis 1: Long necks help giraffes reach higher food.

  • Hypothesis 2: Long necks help males fight better and win mates.

  • Evidence supports sexual competition.

• Desert Ant Navigation

  • Hypothesis: Ants use a "pedometer" (count steps and stride length).

  • Experiment: Ants given stilts or stumps.

  • Stumps stopped short, stilts overshot, normal ants reached nest.

  • Conclusion: Ants calculate distance with stride length and number.

Evaluating Scientific Information

Reliable vs. Unreliable Sources

• Reliable sources: Peer-reviewed journals.

• Less reliable sources: Books, news, internet, ads.

Statistics in Biology

Role of Statistics

Statistics are used to extend small sample results to populations and test significance.

Key Takeaways

• Science is evidence-based, testable, and repeatable.

• Biology explains life’s diversity through cells, evolution, and the scientific method.

• Always identify variables, controls, and hypotheses in experiments.

Classification Hierarchy Table

The following table summarizes the main levels of biological classification:

Key Terms & Definitions

• Hypothesis: A testable statement that explains an observation.

• Experiment: A procedure to test a hypothesis under controlled conditions.

• Control Group: The group in an experiment that does not receive the experimental treatment.

• Variable: Any factor, trait, or condition that can exist in differing amounts or types.

• Scientific Theory: A well-substantiated explanation of some aspect of the natural world.