Foundations of Biology: Properties of Life and Hierarchy

Properties of Life

• Life is defined by a set of properties, not just by any single trait. Key idea: order alone does not define life (microscope, desk, rocks have order too), but life is a highly organized system that is made up of one or more cells.
• Order: life is a highly organized structure; even single-celled organisms have order and function through their internal organization.
• Sensitivity to stimuli (response to environment): living things respond to their surroundings. Examples:
  • Humans respond to a poke or bright light by moving or shielding themselves.
  • Protists respond to light sources or chemical gradients to find food.
• Reproduction: for something to be alive, it must be able to produce new individuals. Reproduction can be diverse:
  • Single-celled organisms often reproduce clonally by copying DNA and dividing to form new individuals.
  • In all organisms, there must be a means of inheritance to pass on genetic information.
• Inheritance: DNA is the genetic material that carries instructions for making more of the organism.
  • In simplest terms: heredity is transmitted via DNA carried in individual cells.
• Growth and development: organisms grow and change over their lifetimes according to genetic instructions.
  • Examples include humans: growth from babies to adults and developmental changes (puberty).
  • Even single-celled organisms undergo growth or shape changes during their life cycle to reproduce.
• Regulation (homeostasis): living things regulate their internal environments to maintain stable conditions.
  • Humans are endotherms: generate heat internally; regulate body temperature via sweating (cooling) or shivering (warming).
  • Blood chemistry (pH, ion concentration) is regulated; kidneys filter ions and manage waste.
  • Even single-celled organisms regulate internal/external ion concentrations; extreme changes can be lethal (e.g., distilled water can cause protists to burst due to excessive water intake).
  • Not all regulation is internal in cold-blooded organisms (ectotherms) like lizards: they regulate temperature by moving in the environment; some species maintain a narrow temperature range by behavior.
• Energy processing: living things process energy to function and grow.
  • Heterotrophs: obtain energy by consuming other organisms.
  • Autotrophs: plants convert sunlight into chemical energy via photosynthesis; this chemical energy powers the organism and supports other life via the food chain.
  • Energy use is affected by factors like body size and activity; e.g., birds show disproportionate energy needs as size changes, affecting wing design and flight energetics.
• Adaptation to the environment: organisms are typically adapted to their ecosystems.
  • Desert vs rainforest vs temperate forests illustrate different environmental pressures.
  • Arctic polar bears: double-layer fur, small ears, and other insulation adaptations to cold; prevents energy loss and supports survival in extreme cold.
  • Bird wing morphologies reflect habitat use: broader wings in complex habitats for maneuverability; long, narrow wings for sustained soaring.
  • Hummingbirds' shoulder mobility allows wing rotation for hovering.
• Growth and development reiterates the role of genetic instructions in maturation and reproductive readiness.
• Viruses: a note on whether viruses are alive by these seven criteria:
  • They possess order and structure and can respond to stimuli in limited ways, but reproduction requires a host cell; they do not independently regulate their internal environment or carry out metabolic energy processing in the way cellular life does.
  • This illustrates why the boundary between life and non-life is fuzzy and why viruses are often discussed as a gray area in biology.
• Energy and practical implications discussed:
  • The discussion of lab-grown meat as an example of applying biology to real-world issues, illustrating how life science concepts are used in technology and ethics.
• Summary: All seven properties must be present for something to be considered alive; absence of any one property challenges the classification as living.

Hierarchy of Organization and Levels

• Life is organized in a nested hierarchy from the very small to the very large.
• Atom: the smallest unit of an element; examples include a single atom of hydrogen or lead. An atom has a nucleus with protons and neutrons and electrons circling, mostly empty space.
• Molecule: two or more atoms bound by chemical bonds (often through sharing electrons). Example given: ethanol (two carbons and hydroxyl group).
• Organelle: specialized structures within cells, bound by membranes, performing defined functions (e.g., mitochondria, chloroplasts).
  • Mitochondria: powerhouse of the cell; organelles composed largely of proteins bound in a membrane, responsible for energy transformations within the cell; they have a distinct origin story (endosymbiotic theory) acknowledged but not discussed in depth here.
  • Chloroplasts: plant organelles responsible for photosynthesis; contain pigments (chlorophyll) and enable light-driven energy capture; chloroplasts give plants their green color.
• Cell: the smallest unit that can be considered a living unit; organisms below this level (e.g., simple molecules or organelles alone) are not regarded as living.
  • A single bacteria or a single protist is considered an organism (a living thing) when it is a cell.
• Tissues: groups of similar cells carrying out a common function; multiple tissues come together to form organs.
• Organ: a structure composed of multiple tissues performing a specific set of functions (e.g., skin as an organ composed of multiple tissue layers).
• Organism: an individual living thing composed of organs and organ systems working together.
• Population: a group of organisms of the same species in a given area or context.
• Community: a group of populations of different species living together in an area; multiple species interacting.
• Ecosystem: the community plus abiotic (non-living) components such as nutrients, energy flow, and physical environment; includes both living and non-living elements in a defined area.
• Biosphere: the global sum of all ecosystems; the entire planet where all life interacts with the physical environment.
• Taxonomy (how we categorize life within this hierarchy):
  • Species: the most specific unit; can interbreed under natural conditions (biological species concept).
  • Genus: a group of related species (e.g., Canis includes wolves, dogs, coyotes).
  • Family: a broader grouping (e.g., Canidae includes dogs, wolves, foxes, and related animals).
  • Order: a wider grouping (e.g., Carnivora includes many meat-eating mammals).
  • Class: broader category (e.g., Mammalia includes all mammals).
  • Phylum: broader still (e.g., Chordata includes animals with a nerve cord and notochord, such as vertebrates and some invertebrates).
  • Kingdom: a large grouping (e.g., Animalia: multicellular, heterotrophic animals).
  • Domain: the widest category shown here; for eukaryotes, includes organisms with a nucleus that contains DNA; protists and animals fall under Eukaryota, distinguishing them from bacteria and archaea.
• Example taxonomy path using Canidae and Canis lupus:
  • Species: Canis lupus
  • Genus: Canis
  • Family: Canidae
  • Order: Carnivora
  • Class: Mammalia
  • Phylum: Chordata
  • Kingdom: Animalia
  • Domain: Eukaryota
• Further notes on classification:
  • Within Kingdom Animalia, most members are multicellular and heterotrophic.
  • The Domain Eukaryota includes organisms with a nucleus-containing cell and encompasses protists as well as fungi, plants, and animals.
• Relationship to human examples:
  • Humans fit within the same hierarchical framework: Canis is just used as a contrasting example to illustrate hierarchical levels, not as a direct human classification.
• Key takeaways about taxonomy:
  • The levels of organization become increasingly inclusive as you move up the hierarchy.
  • The domain level is the broadest grouping discussed here; all life forms with a nucleus (eukaryotes) are placed in Eukaryota, distinguishing them from bacteria and archaea.

Organelles, Cells, and Basic Cell Biology Notes

• Organelles are intracellular structures that carry out specific functions within the cell, bounded by membranes.
• Mitochondria: provide cellular energy through metabolic processes; often described as the powerhouse of the cell.
• Chloroplasts: sites of photosynthesis in plants; enable conversion of light energy into chemical energy; contain chlorophyll that gives plants their green color.
• Cells: the smallest unit that can be considered alive; organisms below this level are not recognized as living in this hierarchy.
• Tissues and organs: tissues are collections of similar cells; organs are composed of multiple tissues working together to perform a function.
• The organization inside organisms underpins all physiological processes, from metabolism to homeostasis and response to the environment.

Energy, Metabolism, and Environmental Interactions

• Heterotrophs vs Autotrophs:
  • Heterotrophs must obtain energy by consuming other organisms.
  • Autotrophs (e.g., plants) perform photosynthesis to convert sunlight into chemical energy stored as chemical energy.
• Energy processing and usage:
  • The amount of energy used depends on factors such as body size and activity (e.g., flight in birds requires substantial energy investment).
  • A smaller bird and a larger bird will have different energy requirements for flight; a 5 lb bird will have different energy needs than a 10 lb bird, etc., illustrating how size influences energy budgets.
• Examples of energy-related adaptations:
  • Polar bears rely on insulation (double-layer fur, reduced ear size) to minimize energy loss in extreme cold.
  • Bird wing morphology reflects ecological needs: broader wings for maneuverability in complex habitats; long, narrow wings for sustained soaring.
  • Hummingbirds can rotate their shoulders to hover, enabling a unique flight style that affects energy expenditure and ecological niche.
• Energy balance and life processes show how metabolism, growth, reproduction, and adaptation are interlinked through energy budgets.

Life vs. Viruses: A Discussion of Boundaries

• Viruses illustrate the gray area in defining life by the seven properties:
  • They have order and structure and can respond to stimuli in limited ways.
  • Reproduction is not autonomous; viruses require a host cell to replicate, contrasting with cellular life that can reproduce independently.
  • They do regulate some internal processes only in the context of hijacking a host; their metabolism and homeostasis do not operate independently.
• This highlights that life is a spectrum, and benchmarks like the seven properties are used as a framework rather than absolute boundaries.

Nature of Science, Hypotheses, and Peer Review

• Core aim of science in biology includes understanding life through a framework built on chemistry and physics and observable evidence.
• Scientific inquiry often starts with a hypothesis and proceeds through testing, observation, and evidence collection.
• Peer review: researchers submit work to other scientists to validate methods, data, and conclusions before broad dissemination.
• The lecture notes that some topics (like the nature of science and peer review) may be introduced later in the course and revisited as students gain more experience with the process.

Recap and Key Takeaways

• Seven core properties define life: order, sensitivity to stimuli, reproduction/inheritance, growth/development, regulation (homeostasis), energy processing, and adaptation to the environment.
• Life is organized hierarchically from atoms to the biosphere, with increasing levels of complexity and inclusivity at each step.
• DNA is the genetic material that carries instructions for reproduction and inheritance; cells contain organelles (mitochondria, chloroplasts) that perform essential functions.
• Taxonomy organizes life into nested categories (domain, kingdom, phylum, class, order, family, genus, species) with real-world examples like Canis lupus to illustrate hierarchy.
• Viruses challenge rigid definitions of life, illustrating the boundaries of the life/non-life distinction.
• The study of biology is grounded in scientific inquiry and peer review, with an emphasis on using chemistry and physics to explain biological processes and phenomena.
• Real-world examples discussed (polar bears, bird wing morphologies, hummingbird flight, distilled water affecting protists) connect theoretical concepts to observable natural phenomena.

Quick Reference: Notable Examples and Concepts

• Polar bear adaptations to Arctic environments: double-layer fur, small ears, insulation strategies.
• Bird wing morphology as habitat indicators: broad wings for complex habitats; long, narrow wings for soaring; hummingbird shoulder rotation enables hovering.
• Proximal regulation: endothermy (human metabolism and temperature regulation via sweating and shivering) and osmoregulation (kidneys maintaining ion balance).
• Distilled water protist example: demonstrates why single-celled organisms must regulate internal ion concentrations to avoid osmotic imbalance.
• Lab-grown meat: mentioned as a contemporary application of biology to industry and ethics, demonstrating real-world relevance of life science.
• Taxonomic path example for Canis lupus: Canidae → Carnivora → Mammalia → Chordata → Animalia → Eukaryota, with Genus Canis and Species lupus illustrating nested classification.
• Domain concept: Eukaryota includes organisms with nuclei containing DNA, including protists and animals, distinguishing them from prokaryotes.
• Species concept: biological species concept highlights that members within a species can interbreed, illustrating reproductive isolation and genetic continuity within taxa.