Ch_1_Life_Organization-module 1 
Chapter 1: Characteristics of Living Things and the Organization of the Living World
Characteristics of Life
Despite the staggering variety of life, biologists have largely agreed on a set of characteristics that define living things.
Some entities, like viruses, exhibit certain characteristics of life but not all.
Understanding these characteristics may aid in the search for extraterrestrial life.
The 6 Characteristics of Life
Organization
Acquisition of materials and energy
Reproduction and Development
Response to stimuli
Homeostasis
Adaptation
1. Organization
Life is organized in a nested hierarchy, allowing complexity to build upon simpler structures.
Cells are considered the smallest unit of life.
Hierarchical Levels: Cells → Tissues → Organs → Organ Systems.
Continuation of Organization
Beyond individual organisms, organization continues:
Populations: Groups of a single species in a specific location.
Communities: Different species interacting in an area.
Ecosystems: Communities plus abiotic components (e.g., geological features, weather).
Biosphere: All ecosystems combined.
2. Acquisition of Materials and Energy
Energy: Required for work, obtained through different means:
Animals: Must consume food for energy.
Plants: Convert sunlight into food through photosynthesis.
Both groups must acquire materials to sustain cellular functions.
3. Reproduction and Development
Life originates from pre-existing life.
DNA: Contains genetic information (genes) that is passed to offspring.
Reproduction can occur in two ways:
Sexual Reproduction: Involves combining genetic material from two parents.
Asexual Reproduction: Involves a single individual.
Organisms undergo growth (increase in size) and development (changes from birth to death).
4. Response to Stimuli
Stimulus: An external cue prompting a reaction from an organism.
Responses can vary widely and do not always involve movement; they can occur at cellular or biochemical levels.
5. Homeostasis
Organisms strive to maintain a relatively constant internal environment (homeostasis).
Significant deviations from homeostasis can lead to difficulties or death.
6. Capacity for Adaptation
Environmental factors are constantly changing (both long-term, like land mass shifts, and short-term, like seasonal weather).
Adaptations: Traits developed that enhance survival within environments.
Natural Selection: Individuals better suited for their environments are more likely to reproduce, leading to population adaptations over generations.
Evolution: The process whereby species change to adapt to their environments, explaining both unity and diversity of life.
The Classification of Living Things: Introduction
Around 2 million species known, with estimates suggesting as many as 1 trillion.
Taxonomy: The science of naming and sorting organisms into groups (taxa).
Linnaeus's classification system from the 1700s laid the groundwork for traditional taxonomy; it also follows a hierarchical structure.
Classification of Living Things Continued
Systematics: A modern approach categorizing organisms based on evolutionary relationships.
Classifying a species in a taxon is often a hypothesis that may be revised with new data (e.g., DNA analysis).
Challenges in Classification
Ongoing debates exist over changing long-established naming conventions and whether species fit neatly into the hierarchical models.
Groups (Taxons) of Traditional Taxonomy
Domain (Most Inclusive)
Kingdom
Phylum
Class
Order
Family
Genus
Species (Least Inclusive)
1. The Three Domains
Life is categorized into three domains:
Prokaryotes: Simple, single-celled organisms without a nucleus.
Archaea: Ancient organisms found in extreme environments.
Bacteria: Ubiquitous and mostly harmless, with a few pathogenic species.
Eukarya: More complex cells with a membrane-bound nucleus, including most familiar organisms.
2. Kingdoms
The next most inclusive group are the kingdoms:
Eukaryotic Kingdoms:
Protista: Diverse and often classified as a catch-all group.
Fungi: Multicellular decomposers (e.g., mushrooms, molds).
Animalia: Multicellular organisms that ingest food (includes vertebrates and invertebrates).
Plantae: Multicellular producers that photosynthesize.
New classification systems are being proposed to reflect modern data, such as the concept of 'supergroups.'
Kingdom Protista
Often described as a "grab-bag" containing both unicellular and multicellular organisms; they gain nutrition via absorption, photosynthesis, or ingestion, found primarily in aquatic environments.
Kingdom Fungi
Comprises organisms including mushrooms, mold, yeast, and rusts; mainly multicellular and absorbs nutrients to play critical roles as decomposers.
Kingdom Animalia
Includes the most recognizable organisms, with invertebrates being the most diverse; vertebrates include fish, amphibians, reptiles, birds, and mammals; all are multicellular and reliant on ingested food.
Kingdom Plantae
Comprises various organisms like mosses, ferns, and trees; primarily multicellular and produce food through photosynthesis, serving as key land-based producers.
Middle Classifications
Understanding the order of classifications from Phylum through Species is important; use mnemonics for ease of recall (e.g., "Dominating Kings Play Cards On Fat Green Stools").
The hierarchy signifies relatedness; as organisms become categorized into smaller groups, they become more closely related with more shared traits.
Scientific Names
Naming species involves two parts: genus name (capitalized) and species name (not capitalized).
Names are italicized in typed format or underlined when handwritten. For example:
Homo sapiens (humans)
Quercus alba (white oak)
Panthera tigris (tigers).
The full name must be used initially, and thereafter the genus name can be abbreviated (e.g., H. sapiens).
This unique naming system mitigates confusion that arises from common names.