Human Biology, Science, and Society

Introduction to Biology

Biology is the scientific study of life, encompassing the diversity of living organisms and their processes. The term "biology" is derived from the Greek prefix "bio-" meaning "life" and the suffix "-ology" meaning "the study of." Most life forms on Earth are microscopic and require specialized tools to observe.

• Biology: The science that investigates living organisms and life processes.

• Cell: The smallest, most basic unit of life.

• Organism: Any individual form of life, from bacteria to plants and animals.

Unicellular vs. Multicellular Organisms

Living organisms can be classified based on the number of cells they possess:

• Unicellular organisms: Consist of a single cell (e.g., bacteria, some protists).

• Multicellular organisms: Composed of many cells that may be specialized for different functions (e.g., animals, plants, fungi).

Characteristics of Life

Defining Features of Living Organisms

All living organisms share a set of characteristics that distinguish them from nonliving things:

• Composed of cells, the smallest unit of life

• Use smaller structures to build larger ones (organization)

• Respond to environmental stimuli

• Maintain homeostasis (stable internal conditions)

• Capacity to reproduce (asexually or sexually)

• Acquire and utilize energy from surroundings

• Genetic information (DNA) functions as the hereditary material

• Undergo changes over time for adaptation and improved survival (evolution)

Note: Viruses are not considered alive because they do not meet all these criteria independently.

Life’s Organizational Hierarchy

Levels of Biological Organization

Life is organized into a hierarchy, from the smallest chemical building blocks to the entire biosphere:

Emergent Properties

Emergent properties are new characteristics that arise at each level of organization, which are not present in the individual components alone. For example, life emerges at the cellular level, even though molecules themselves are not alive.

• "The whole is greater than the sum of its parts."

Introduction to Taxonomy

Classification of Life

Taxonomy is the branch of science that classifies, identifies, and names organisms. Organisms are grouped into hierarchical categories, from the broadest (domain) to the most specific (species):

The Three Domains of Life

All life is classified into three domains:

• Bacteria: Prokaryotic, unicellular organisms without a nucleus

• Archaea: Prokaryotic, unicellular organisms, often found in extreme environments

• Eukarya: Eukaryotic organisms, can be unicellular or multicellular, with a nucleus

Kingdoms of the Eukarya Domain

The domain Eukarya is further divided into four kingdoms:

• Animalia: Multicellular, heterotrophic organisms

• Plantae: Multicellular, autotrophic organisms

• Fungi: Mostly multicellular, decomposers

• Protista: Mostly unicellular, some multicellular

Categorizing Life Based on Energy Acquisition

Organisms are also classified by how they obtain energy:

• Autotrophs (Producers): Make their own food, usually via photosynthesis

• Heterotrophs (Consumers): Obtain energy by eating other organisms

• Decomposers: Obtain energy from wastes and dead organisms

Most energy utilized by life originates from the sun, and with every transfer of energy, some is lost as heat.

The Scientific Method

Steps of the Scientific Method

The scientific method is a systematic procedure used to answer questions, test ideas, and build scientific knowledge. The main steps include:

1. Make an observation

2. Ask a question

3. Formulate a hypothesis and make a prediction

4. Design and conduct an experiment

5. Collect and interpret data

6. Draw conclusions

7. Peer review and publish

Predictions, Hypotheses, and Theories

• Prediction: An expected outcome of an event (answers "what will happen?").

• Hypothesis: A proposed, testable explanation for an observation (answers "what will happen and why?").

• Theory: A testable and broad hypothesis supported by a large body of evidence.

Basic Theories of Biology

Experimental Design

Variables in Experiments

Experiments are designed to test hypotheses by manipulating variables:

Controls in Experiments

Control groups are essential for preventing false positives and negatives:

Additional info: Well-designed experiments include both negative and positive controls to ensure the reliability of results and to distinguish true effects from experimental error.