Nature of Science: Characteristics of Life (Unit 1 - Lesson 3)

Nature of Science

Introduction

The nature of science involves understanding how scientific knowledge is developed, tested, and applied. In biology, this includes investigating the characteristics that define living organisms and the processes that sustain life.

Scientific Inquiry and Investigation

Scientific Questions and Hypotheses

• Scientific Questions: Questions that can be tested through observation and experimentation.

• Hypothesis: A testable explanation for an observation or scientific problem.

Scientific Evidence and Measurement

• Evidence in science is gathered through careful observation, experimentation, and measurement.

• Measurements must be accurate and repeatable to ensure reliable results.

Ethical Investigations

• Ethical considerations are essential in planning and conducting scientific investigations, ensuring the welfare of living organisms and the integrity of data.

Analyzing Relationships and Constructing Explanations

• Scientists analyze data to identify patterns and relationships.

• Scientific explanations are constructed based on evidence and logical reasoning.

Characteristics of Life

Introduction

Living organisms share a set of characteristics that distinguish them from non-living things. To be considered alive, an entity must exhibit all of these characteristics.

The Eight Characteristics of Life

• Cellular Organization: All living things are composed of one or more cells, which are the basic units of life. Organisms can be unicellular (single-celled) or multicellular (many-celled).

• Reproduction: Living things can reproduce, creating new organisms. Reproduction can be asexual (one parent, identical offspring) or sexual (two parents, genetically diverse offspring).

• Metabolism (Obtaining and Using Energy): All living things obtain and use energy to power the chemical reactions necessary for life. This includes processes like photosynthesis and cellular respiration.

• Homeostasis: The ability to maintain a stable internal environment despite changes in external conditions. For example, humans sweat to cool down when overheated.

• Heredity (Universal Genetic Code): Living things have DNA, which carries genetic information passed from parents to offspring.

• Responsiveness: Organisms respond to stimuli in their environment, such as light, temperature, sound, and gravity.

• Growth and Development: Living things grow (increase in size) and develop (change in form or function) over time.

• Adaptation Through Evolution: Populations of organisms change over generations through the process of evolution, allowing them to better survive in their environments.

Summary Table: Characteristics of Life

Characteristic	Description	Example
Cellular Organization	Composed of one or more cells	Bacteria (unicellular), Humans (multicellular)
Reproduction	Ability to produce offspring	Binary fission in bacteria, sexual reproduction in animals
Metabolism	Obtain and use energy	Photosynthesis in plants, eating food in animals
Homeostasis	Maintain stable internal conditions	Regulating body temperature
Heredity	Pass genetic information to offspring	DNA inheritance
Responsiveness	Respond to environmental stimuli	Plants growing toward light
Growth and Development	Increase in size and complexity	Caterpillar becoming a butterfly
Adaptation Through Evolution	Change over generations	Development of antibiotic resistance in bacteria

Cellular Organization and Homeostasis

Unicellular vs. Multicellular Organisms

• Unicellular organisms consist of a single cell that performs all life functions.

• Multicellular organisms have specialized cells organized into tissues, organs, and organ systems.

• Both types must maintain homeostasis to survive.

Specialization in Multicellular Organisms

• Cells in multicellular organisms become specialized for specific tasks (e.g., muscle cells, nerve cells).

• Specialized cells communicate and work together to maintain homeostasis.

Classification of Life

Domains and Kingdoms

• Organisms are classified into three domains: Archaea, Bacteria, and Eukarya.

• Within these domains, organisms are further classified into six kingdoms: Archaebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia.

Comparison Table: Domains and Kingdoms

Domain	Kingdom(s)	Key Features
Archaea	Archaebacteria	Prokaryotic, often live in extreme environments
Bacteria	Eubacteria	Prokaryotic, found in many environments
Eukarya	Protista, Fungi, Plantae, Animalia	Eukaryotic, cells with nuclei

Viruses vs. Living Organisms

Comparison

• Viruses share some characteristics with living things (e.g., genetic material) but lack others (e.g., cellular structure, metabolism).

• Viruses cannot reproduce or carry out metabolism independently; they require a host cell.

Cell Theory

Key Points

• All living things are composed of cells.

• Cells are the basic units of structure and function in living things.

• All cells arise from pre-existing cells.

Additional info: Cell theory and specialization will be covered in more detail in Unit 3, but foundational concepts are introduced here.