Chapter 1: The Character of Living Organisms – Key Concepts in General Biology

Characteristics of Living Organisms

Overview of Life's Defining Features

Biologists identify several fundamental characteristics that distinguish living organisms from nonliving matter. These features are essential for understanding what constitutes life and how living things function.

• Molecular Composition: Living organisms possess unique molecular compositions, including specific biomolecules not found in nonliving things.

• Energy and Raw Materials: All living things require energy and raw materials to sustain life processes.

• Cellular Organization: Living things are composed of cells, which may be unicellular or multicellular.

• Homeostasis: The ability to maintain a stable internal environment is crucial for life.

• Response to Environment: Organisms can sense and respond to changes in their external environment.

• Growth and Reproduction: Living things grow and reproduce, creating new individuals.

• Evolution: Populations of living organisms evolve over time through inheritable changes.

Key Chemicals of Life

Biomolecules in Living Organisms

Living organisms are composed of specific types of molecules that are essential for structure and function.

• Proteins: Serve as enzymes, structural components, and signaling molecules.

• Carbohydrates: Provide energy and structural support.

• Lipids: Form cell membranes and store energy.

• Nucleic Acids: Store and transmit genetic information (e.g., DNA and RNA).

Energy, Raw Materials, and Metabolism

Requirements for Life Processes

To sustain life, organisms must acquire energy and raw materials from their environment and use them in metabolic processes.

• Energy: Defined as the capacity to do work. Organisms obtain energy from food, sunlight, or chemical sources.

• Raw Materials: Include essential chemicals such as oxygen, water, carbon dioxide, amino acids, and sugars.

• Metabolism: The sum of all chemical reactions occurring within cells. These reactions enable growth, repair, and maintenance.

Equation:

$\text{Metabolism} = \text{Catabolism} + \text{Anabolism}$

Catabolism breaks down molecules to release energy, while Anabolism builds complex molecules from simpler ones.

Cellular Organization

Cells as the Fundamental Units of Life

All living things are composed of cells, which are the smallest units capable of performing all life functions.

• Cells: Basic structural and functional units of life.

• Cell Theory: All cells arise from pre-existing cells through division.

• Unicellular vs. Multicellular: Some organisms consist of a single cell, while others are made of many specialized cells.

Homeostasis

Maintaining Internal Stability

Homeostasis refers to the maintenance of a stable internal environment despite external changes. This is vital for proper cellular function.

• Definition: A dynamic state of equilibrium in the body.

• Examples:

  • Regulating body temperature (e.g., sweating, shivering)

  • Water reabsorption in kidneys

Response to External Environment

Adaptation and Sensitivity

Living organisms can detect and respond to stimuli in their environment, which is essential for survival.

• Examples in Animals: Shielding eyes from bright sunlight.

• Examples in Plants: Leaves turning toward sunlight; roots growing toward water sources.

Growth and Reproduction

Increase in Size and Creation of New Individuals

Growth and reproduction are fundamental processes that distinguish living things from nonliving matter.

• Growth: Increase in size and number of cells.

• Reproduction: Production of new individuals, either sexually or asexually.

• Contrast with Nonliving Things: Nonliving objects may increase in size (e.g., crystals) but do not reproduce.

Evolution of Populations

Genetic Change Over Time

Populations of living organisms undergo evolution, which is the process of inheritable change across generations.

• Population: A group of individuals of the same species living in a specific area.

• Evolution: Change in genetic traits within a population over time, often driven by natural selection.

• Example: Development of antibiotic-resistant bacteria.

Case Study: Bacterial Evolution and Antibiotic Resistance

Mechanism of Resistance to β-Lactam Antibiotics

Some bacteria evolve resistance to antibiotics, such as β-lactam drugs, through genetic changes that alter their molecular targets.

• β-Lactam Antibiotics: Include penicillins and cephalosporins; contain a β-lactam ring essential for their function.

• Resistance Mechanism: Bacteria produce enzymes (β-lactamases) that break the β-lactam ring, rendering the antibiotic ineffective.

• Example: Resistant bacteria survive and proliferate in the presence of antibiotics, illustrating evolution in action.

Equation (β-lactam ring hydrolysis):

$\text{β-lactam antibiotic} + \text{β-lactamase} \rightarrow \text{inactive product}$

Classification of Living Things

Major Domains and Kingdoms

Living organisms are classified into three domains and several kingdoms based on cellular structure and genetic relationships.

Domain	Kingdoms	Characteristics
Bacteria	—	Prokaryotic, unicellular
Archaea	—	Prokaryotic, unicellular, often extremophiles
Eukarya	Protista, Animalia, Fungi, Plantae	Eukaryotic; unicellular or multicellular

• Protista: Mostly unicellular or simple multicellular; eukaryotic.

• Animalia: Multicellular; eukaryotic; heterotrophic.

• Fungi: Multicellular (except yeasts); eukaryotic; decomposers.

• Plantae: Multicellular; eukaryotic; photosynthetic.

Biological Organization and Human Classification

Levels of Organization and Taxonomy

Biology studies life at multiple levels, from molecules to ecosystems. Humans are classified within the domain Eukarya and have unique features.

Taxonomic Rank	Human Classification
Domain	Eukarya
Kingdom	Animalia
Phylum	Chordata
Class	Mammalia
Order	Primates
Family	Hominidae
Genus	Homo
Species	Homo sapiens

• Defining Features of Humans:

  • Upright posture and bipedal locomotion

  • Opposable thumbs for grasping

  • Large brain relative to body size

  • Complex language (spoken and written)

Example: Fossil analysis of skeletal features (e.g., pelvis, skull, hand bones) helps determine evolutionary relationships to humans.