Living Organisms
Learning Objectives
Summarize the characteristics of living organisms.
Understand how living things are organized.
Learn how to use scientific names and taxonomic levels.
Analyze the meaning of evolution and adaptation.
Defining Biology: What Does It Mean to Be Living?
Definition: Biology is the study of living organisms and how they have evolved.
Evolution's Role: While not a central theme in Biology I, evolution is a foundational concept: "Nothing makes sense in biology unless we look at it through the lens of evolution."
The Question of Life: The concept of "living" was explored using examples:
Milo (The instructor's deceased dog): Was alive.
A Rock: Not alive.
A Virus: The subject of debate; initial thoughts often question its living status.
Underlying Similarities: Milo, the rock, and a virus all share:
Same Particles: Protons, neutrons, electrons.
Same Chemical Elements.
Obey Same Physical and Chemical Laws.
Group Activity: Students discussed whether the three examples were alive and why, submitting a brief group consensus on Canvas.
Characteristics of Living Organisms
To be considered alive, an organism generally exhibits several key characteristics. (Note: different lists may exist, but this list aims to be simple and comprehensive).
Cells & Organization:
All living organisms are composed of cells. Some are unicellular (one cell), others are multicellular (multiple cells).
Cells are organized in a specific way; in multicellular organisms, cells often organize into tissues.
Use Energy & Metabolism:
Living organisms require energy to maintain their order and structure.
Metabolism: Refers to all the chemical reactions within cells that require energy and sustain life. (Examples: Plants perform photosynthesis; humans have different metabolic processes).
Respond to the Environment:
Living things react to stimuli from their surroundings.
Example: Plants lean towards light (phototropism); humans withdraw a foot if stepped on.
Regulate (Homeostasis):
Homeostasis: The ability to maintain stable internal conditions regardless of external changes.
Examples: Regulating body temperature, pH levels. There are limits to regulation (e.g., extreme cold without protection).
Grow, Develop, Reproduce (Genetics):
Living organisms grow (increase in size/complexity) and develop (mature).
They reproduce, passing genetic material (DNA) to offspring. This involves genetics, which will be covered later in the semester.
Discussion Point (Mules): Animals that are sterile (e.g., mules) are still considered alive because they exhibit other characteristics like growth and development, even if they cannot reproduce.
Evolve (Populations):
Living things (populations, not individuals) change over time.
Purpose: Evolution promotes reproductive success and survival.
Relevance: Evolution is not just a historical concept (Darwin); it is an active area of research, particularly in the context of climate change and species adaptation.
Viruses: Are They Alive?
Conclusion: Viruses are not considered alive.
Reasoning: They are acellular (meaning "without cells").
While they may appear to use energy or have metabolism, they are parasitic and rely entirely on the host cell's metabolism, response, and regulation.
Viruses do not grow, develop, or reproduce independently; they hijack host cells for these processes.
By definition, a virus must use another cell, and all viruses cause disease in some organism (plants, bacteria, humans, etc.).
Organization of Living Things
Living things are organized in a complex hierarchy, from the smallest fundamental units to the largest ecological systems.
Levels of Organization:
Atoms: Basic building blocks of matter.
Molecules: Atoms chemically bonded together (e.g., molecules of life).
Cells: The basic unit of life, separated from the environment by a membrane, capable of transport.
Tissues: Groups of similar cells working together (e.g., skin tissue, blood tissue).
Organs: Different tissues organized to perform specific functions (e.g., heart, brain, eye).
Organ Systems: Groups of organs working together (e.g., circulatory system, nervous system).
Organism: A complete living individual (e.g., a human).
Population: Organisms of the same species living together (e.g., Northeastern students).
Community: Different populations interacting within an area.
Ecosystem: A community together with its non-living environment.
Biosphere: The entire portion of Earth inhabited by life.
Biology I Focus: This class will focus primarily on the atomic, molecular, and cellular levels.
Interconnectedness: All living things, including humans, plants, animals, bacteria, fungi, and viruses, are interconnected within the biosphere.
Scientific Names & Taxonomic Levels
This section covers the classification of organisms.
Early Classification (Aristotle - Before CE):
Considered the "Father of Taxonomy" (classification).
Proposed a classification system from simple, inanimate things (air, water, earth) to intermediate (plants, worms) and up to humans at the "top of the chain."
Shortcomings: Reflected the belief that humans were the most perfect/complex, and that species did not change (no understanding of evolution).
Contribution: Established the fundamental idea of classifying organisms.
Modern Classification (Linnaeus - th Century): (1701–1778) – Systema Naturae
Classified organisms based on similarities, though this was primarily based on physical appearance, not DNA (as we do now).
Binomial System (Two Names):
Every organism receives two names, using Latin terms (e.g., Homo sapiens).
Universality: Latin is used to ensure universal understanding among scientists globally.
Formatting: Scientific names are either italicized (when typed) or underlined (when handwritten).
Components: The first name is the genus, and the second is the species.
Taxonomic Hierarchy (Classification Pyramid): Linnaeus developed a system of ranked categories.
Higher levels contain a broader range of organisms, while lower levels contain increasingly specific groups.
Order (Broadest to Most Specific):
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Mnemonic: "Dumb Kids Prefer Candy Over Fresh Green Spinach" (or similar)
Biology I Focus: This class will discuss domains and use examples of genus and species.
Biology II Relevance: More detailed classification of different organisms is covered in Biology II.
Evolution & Adaptation
Evolutionary Theory (Darwin): "It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change."
Application: This concept extends beyond biology to personal success: adapting to new situations and making the best of circumstances leads to better outcomes and happiness.
Historical Context: Acknowledgement of the historical predominance of white men in early scientific discoveries, with anticipation of future diversity.
Adaptation: Any modification that makes an organism better suited to its environment.
Key Distinction: Evolution and adaption occur at the population level over time, not within individual organisms.
Process: Evolution (descent with modification) results in promoting traits that increase chances of survival and reproductive success.
Example: Polar Bear (Ursus maritimus) Adaptations:
Camouflage: White fur blends with snow and ice.
Insulation: Thick layer of fat and dense fur for cold environments.
Heat Conservation: Small, round ears and a large, stocky body shape reduce heat loss.
Movement on Ice: Sharp claws and specific foot structures for traction on ice.
Vision: Adaptations for reduced glare in snow and improved underwater vision.
Swimming: Excellent swimming abilities for hunting in water (important for hunting and navigating melting ice due to climate change).
Significance: This example underscores the importance of adaptation and evolution, particularly in the face of current challenges like climate change. These concepts are extensively covered in Biology II.
Conclusion
The class concluded early, with a reminder for students to ensure their group formation and Poll Everywhere participation were correctly registered.