Common Properties and Processes of Life

Defining Life: Key Characteristics

Biology is the study of living organisms, all of which share several fundamental properties that distinguish them from non-living matter.

• Order: Living things are highly organized, with cells as the basic structural and functional units.

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

• Growth and Development: Organisms grow and develop according to specific instructions coded in their DNA.

• Energy Processing: Living things obtain and use energy to power their activities, often through chemical reactions such as cellular respiration or photosynthesis.

• Response to Environment: Organisms respond to environmental stimuli, allowing adaptation and survival.

• Regulation: Homeostasis maintains stable internal conditions despite external changes.

• Evolutionary Adaptation: Populations evolve over generations, with traits best suited to the environment becoming more common.

Example: Plants grow toward light (response to environment), use sunlight for photosynthesis (energy processing), and reproduce via seeds (reproduction).

Biological Organization and Emergent Properties

Hierarchy of Biological Organization

Life is organized into a hierarchy, from the smallest chemical units to the entire biosphere. Each level exhibits emergent properties not present at lower levels.

• Biosphere: All environments on Earth that support life.

• Ecosystem: All organisms living in a particular area, plus the nonliving components they interact with.

• Community: All populations of different species living in an area.

• Population: Individuals of the same species living in an area.

• Organism: An individual living thing.

• Organ System: Group of organs working together (e.g., respiratory system).

• Organ: Structure composed of tissues performing a specific function.

• Tissue: Group of similar cells performing a function.

• Cell: Fundamental unit of life.

• Organelle: Specialized structure within a cell.

• Molecule: Chemical structure consisting of two or more atoms.

Emergent Properties: New properties arise at each level due to the arrangement and interactions of parts. For example, a functioning organ system emerges from the coordinated activity of organs.

Cell Theory

Fundamental Principles of Cells

The cell theory is a cornerstone of biology, stating:

• All living things are composed of cells.

• Cells arise from pre-existing cells.

• Cells are the basic unit of structure and function in living organisms.

Shared Characteristics of Cells:

• Enclosed by a membrane that regulates passage of materials.

• Contain DNA as genetic material.

• Obtain and use energy for cellular functions.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles; generally smaller and simpler (e.g., bacteria, archaea).

• Eukaryotic Cells: Have a nucleus and complex organelles; found in plants, animals, fungi, and protists.

Example: Human nerve cells are eukaryotic, while Escherichia coli is a prokaryote.

Central Dogma of Molecular Biology

Flow of Genetic Information

The central dogma describes how genetic information is transferred within biological systems:

• DNA stores genetic information.

• Information is transcribed from DNA to RNA.

• RNA is translated to synthesize proteins.

Equation:

Proteins carry out most cellular functions, and the sequence of DNA determines the structure and function of these proteins.

Unity and Diversity of Life

Genetic Basis and Evolution

All life shares a common genetic code (DNA), which is responsible for heritable traits. Despite this unity, diversity arises from evolutionary changes and adaptations.

• Unity: All organisms descended from a common ancestor and share fundamental molecular mechanisms.

• Diversity: Differences in DNA sequences and adaptations to various environments result in the vast variety of life forms.

Taxonomy and Phylogenetic Trees

Classifying Life

Taxonomy is the science of naming, describing, and classifying organisms into a hierarchy based on similarities and evolutionary relationships.

• Species: Basic unit of classification; millions identified, many more undiscovered.

• Phylogenetic Tree: Diagram showing evolutionary relationships; branch points indicate common ancestors.

Example: Red pandas and giant pandas share a more recent common ancestor with each other than with other bears.

Three Domains of Life

Highest Level of Classification

All life is classified into three domains based on cellular structure and genetics:

Example: Humans belong to the domain Eukarya.

Evolution and Natural Selection

Mechanisms of Evolution

Evolution is the process by which species change over time, primarily through natural selection.

• Descent with Modification: Species inherit traits from ancestors, but modifications accumulate over generations.

• Natural Selection: Individuals with advantageous traits are more likely to survive and reproduce, passing those traits to offspring.

Key Points of Natural Selection:

• Variation exists within populations.

• Traits must be heritable.

• More offspring are produced than can survive.

• Selective pressures favor certain traits, leading to adaptation.

Example: Peppered moths in polluted environments evolved darker coloration due to selective predation.

The Scientific Method

Process of Scientific Inquiry

The scientific method is a systematic approach to investigating natural phenomena and acquiring knowledge.

• Observation: Gathering information using the senses.

• Question: Formulating a question based on observations.

• Hypothesis: Proposing a testable and falsifiable explanation.

• Prediction: Making logical, testable statements ("if...then...").

• Experiment: Testing predictions through controlled experiments or observational studies.

• Analysis: Interpreting data to support or refute the hypothesis.

• Conclusion: Drawing conclusions and sharing results.

Controlled Experiment: Manipulates one independent variable while keeping others constant; includes control and experimental groups.

Observational Study: Collects data without manipulation, often used when experiments are not feasible.

Types of Reasoning:

• Deductive Reasoning: Uses general premises to make specific predictions.

• Inductive Reasoning: Uses specific observations to develop general conclusions.

Example: "All spiders have eight legs. A tarantula is a spider. Therefore, a tarantula has eight legs." (Deductive reasoning)

Why Study Biology?

Societal and Personal Relevance

Understanding biology is essential for making informed decisions about health, environment, and technology. It enables individuals to critically evaluate issues such as vaccinations, gene editing, and GMOs.

• Biology provides a deeper understanding of ourselves and the planet.

• Scientific knowledge is collaborative and self-correcting, adapting as new evidence emerges.

Additional info: The notes are based on introductory lecture slides for a General Biology course, covering foundational concepts and processes relevant for college-level students.