Biology notes: Levels of organization, cells, taxonomy, and ecosystems

Living vs Nonliving: organizing principles

Even small organisms like a water flea have organized sensory, hormonal, reproductive systems and well-organized structure, similar to humans
Table salt is well organized but not a linear organism; it is not complex in the biological sense
Ocean waves are not living despite having movement; they are complex in some ways but lack the organized structure of living organisms
Key distinction: living organisms are both complex and organized
Nonliving entities can be organized, but lack the combination of complexity and organization that defines life

Seven hallmarks of living organisms (energy, nutrients, growth, response, reproduction, regulation, adaptation)

1) Organization and complexity

Living things are ordered, complex, and organized; this contrasts with simple nonliving items
2) Energy and nutrients required
All living things require energy to survive; without energy, you die
Essential nutrients are required; deficiency symptoms lead to death
“Nutrition” is essential; some nonliving or nonmetabolic systems do not require them
3) Growth and development
Living organisms grow and develop; humans reach a certain height but show growth in other tissues (e.g., hair, nails)
Evidence of growth and development includes hair growth and nail growth
4) Respond to environmental stimuli
External forces act as stimuli; organisms respond (e.g., pinching triggers a reaction like flinching or crying out)
Response is an organism’s capability to sense and react to external forces
5) Reproduction
Living organisms reproduce to give rise to new individuals; example: humans having children
6) Regulation (homeostasis)
Regulation maintains internal conditions within a narrow range (homeostasis)
Example: body temperature ~ T o 37^ ext{o} ext{C} (equivalently 98.6^ ext{o} ext{F}))
Homeostasis involves keeping things like sugar concentration in blood within healthy limits
7) Adaptation and evolution
Organisms adapt to changing environments (adaptation)
Evolution is described as a longer-term process that shapes populations over generations
Adaptation enables survival in changing environments; evolution describes inherited changes over time

Hierarchy of life: from atoms to the biosphere

Atoms form molecules; example: water molecule
- Water is formed from two hydrogen atoms and one oxygen atom, yielding the molecule ext{H}_2 ext{O}
Macromolecules build larger structures
Organelles are subcellular components with specialized functions (e.g., mitochondria)
- Structurally: double membrane bounding and unique functions
Cells: the smallest unit of life; all cells are bounded by a plasma membrane
Tissues: groups of similar cells performing a common function
Organs: tissues combine to form organs (e.g., breast)
Organ systems: organs work together to form organ systems on multicellular organisms
Organism: a complete individual organism (e.g., cow)
Population: individuals of the same species living in the same area at the same time
Community: all living organisms in a habitat interacting with each other
Ecosystem: community plus abiotic (nonliving) components such as climate, soil, water, and energy flow
Biosphere: all ecosystems on Earth, including the atmosphere, hydrosphere, lithosphere, and all living beings
Note on single-celled organisms vs multicellular organisms: basic building blocks exist at the cellular level, which collectively build up to higher levels of organization

Organizational flow in an example (breast) and related questions

The level six in the hierarchy is an organ
Tissues combine to form an organ; what tissue makes the breast? Possible answer: glandular tissue
Adipose tissue is fatty tissue
Cells form tissues; tissues form organs; organs form organ systems in a multicellular organism
Exam-style prompts may ask to order levels of organization using the breast as an example

Key components of the cellular and genetic foundation

The smallest unit of life is the cell; all cells are enclosed by a membrane (plasma membrane)
Plasma membrane is the scientific name for the cell membrane; it acts as a boundary
All living organisms use a genetic code as the universal language of heredity
Eukaryotic cells contain a nucleus and organelles; generally larger and more complex than prokaryotic cells
Prokaryotic cells lack a defined nucleus and have simpler structure
DNA in the nucleus can form chromatin; a single DNA molecule in a eukaryotic nucleus has a double-helix structure composed of nucleotides
- Nucleotides: A, T, G, C
Approximate number of cells in the human body: 3.7 imes 10^{13} (i.e., ~37 trillion) cells
DNA structure: double helix; order of nucleotides encodes genetic information
Comparative genomics: despite high similarity (e.g., 99% similarity between humans and other humans), small differences (~1–2%) correspond to large functional and phenotypic differences
Modern medical record-keeping has shifted from paper to digital systems; this enables large-scale data storage but also raises concerns about system reliability and data security

Taxonomy, diversity, and classification

Taxonomists study naming and classification of living things: two primary goals are naming and classifying species
Three domains and six kingdoms framework discussed:
- Domains: ext{Bacteria}, ext{Archaea}, ext{Eukarya}
- Kingdoms (within domains): typically listed as six kingdoms: ext{Eubacteria}, ext{Archaebacteria}, ext{Protista}, ext{Fungi}, ext{Plantae}, ext{Animalia}
In class discussions, there is a note that “Prokarya” is not one of the domains; it is a term sometimes used for prokaryotes historically, but not a domain in the current three-domain model
Darwin’s theory and the Origin of Species: referenced as a foundational work in evolutionary biology

Ecosystems: energy flow and nutrient cycling

Ecosystems are governed by energy flow and nutrient exchange between living and nonliving components
Energy pathway: sunlight is the primary energy source for most ecosystems
- Energy enters as solar radiation; autotrophs (producers) convert it into chemical energy
- Heterotrophs (consumers) obtain energy by eating producers or other consumers
- Energy exit: most energy leaves as heat to the environment, making energy flow effectively one-way (one-directional)
- Represented conceptually as: E{ ext{sun}} ightarrow E{ ext{producers}}
  ightarrow E{ ext{consumers}} ightarrow E{ ext{heat}}
Nutrients and elements cycle: elements taken up by organisms are returned to soil, water, or air after organisms die and decompose
- Example phrasing from lecture: “from the dust to the dust” and nutrients returning to soil, water, or air
Abiota vs biota
- Abiota refers to nonliving components of the environment (abiotic factors and physical environment)
- Ecosystems include both living organisms and abiotic components
Global prevalence: there are numerous distinct ecosystems across the world (roughly twelve to thirteen mentioned in class)

Population, community, ecosystem, biosphere: definitions and relationships

Population: individuals of the same species inhabiting the same area at the same time
- Example: You and your cousin are both humans in the same area, thus part of the same population; your uncle in Korea belongs to a different population due to geographic separation
Community: all living organisms in a particular habitat, interacting with each other
Ecosystem: community plus abiotic environment; includes energy flow and nutrient cycles
Biosphere: all ecosystems together, including the atmosphere and all living and nonliving components of Earth

Real-world connections and implications

Data management in health care as a real-world example
- Transition from paper charts to digital records increases data storage and accessibility but creates risks if computer systems fail or are insecure
- Emphasizes importance of data reliability, privacy, and redundancy in clinical settings

Quick practice prompts discussed in class

Question: What is the correct order of levels of organization when using the breast as an example?
- Answer guide: Tissue -> Organ -> Organ system (breast as an organ); tissue examples include glandular tissue; adipose (fat) tissue is also present but not glandular tissue; tissues combine to form an organ; multiple organs form organ systems
Question: How do we define a population?
- Answer: Individuals of the same species inhabiting the same area at the same time, capable of interaction
Question: What is the difference between a community and an ecosystem?
- Answer: Community = all living organisms in a habitat; Ecosystem = community plus abiotic environment

Governing principles and overarching ideas

The sun is the primary energy source for most ecosystems
Energy flow is one-way, with heat released to the environment
Nutrients cycle through the environment; elements return to soil, water, or air after organisms die
The biosphere comprises all ecosystems and their interactions with the atmosphere
Levels of organization build on simpler units to form more complex structures, from atoms to the biosphere

Evolution and adaptation: philosophical and practical implications

Adaptation enables organisms to cope with changing environments; evolution describes how populations change over generations
Ethical and practical implications arise when studying diversity, taxonomy, and conservation in the real world

Quick reference notes and constants

Normal body temperature: T ext{ (body)} o 37^ ext{o} ext{C} ext{ (approximately } 98.6^ ext{o} ext{F)}
Nucleotides in DNA: A, T, G, C
DNA: double helix; DNA in eukaryotes is organized with chromatin in the nucleus
Major command terms: abiota = nonliving parts of the environment; biota = living organisms
Approximately 3.7 imes 10^{13} cells in the human body (≈ 37 trillion)
Key structural progression: Atom → Molecule → Macromolecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere