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Properties of Life and Biological Organization

Properties of Life

  • By the end of the section, you should be able to:
    • Identify and describe the properties of life and determine if something is ‘alive’
    • Describe the levels of biological organization
    • Understand how living organisms are classified based on shared characteristics
  • Key idea: Biology includes the smallest molecules and entire ecosystems; life exists across a vast scale (scale of nature) from subcellular to global to cosmic levels.

The Three Central Questions in Biology

  • From its earliest beginnings, biology has wrestled with three questions:
    • What are the shared properties that make something ‘alive’?
    • How do we find meaningful levels of organization in living structures?
    • How do we classify the diversity of life so we can better understand it?
  • These questions frame all subsequent study in biology and guide how we think about life, its organization, and its diversity.

What is Biology?

  • Biology is the scientific study of living organisms and their interactions with each other and their environment.
  • It encompasses a wide range of topics, including:
    • Genetics, evolution, ecology, physiology, and more
  • Purpose: to understand the complexity of life on Earth by exploring how organisms live, interact, and adapt.

What Is Life? A Defining View

  • Quote: “The phenomenon we call life defies a simple, one-sentence definition. We recognize life by what living things do.”
    • Campbell and Reece (2008). Biology 8th Ed. Pearson.
  • Implication: Life is best understood through patterns of behavior and capabilities rather than a single strict definition.

The Scale of Nature (Size and Organization Across Life)

  • Biology includes the smallest molecules and entire ecosystems; life spans a broad scale:
    • Subatomic/atomic to macroscopic levels (examples include atoms, DNA, hair, viruses, bacteria, cells, organs, organisms, populations, communities, ecosystems, biosphere)
    • Examples and anchors on the scale include:
    • DNA, Hair, Virus, Bacteria, Fruit fly, Paramecium, Protein, Mitochondrion, Chicken egg, Heart, Cell, Frog egg, Human, Whale
    • Typical size progression (order-of-magnitude examples):
    • 1~ ext{nm} \,( ext{approx. }10^{-9} ext{ m})
    • 10~ ext{nm} \,( ext{approx. }10^{-8} ext{ m})
    • 100~ ext{nm} \,( ext{approx. }10^{-7} ext{ m})
    • 1~ ext{μm} \,( ext{approx. }10^{-6} ext{ m})
    • 10~ ext{μm} \,( ext{approx. }10^{-5} ext{ m})
    • 100~ ext{μm} \,( ext{approx. }10^{-4} ext{ m})
    • 1~ ext{mm} \,( ext{approx. }10^{-3} ext{ m})
    • 1~ ext{cm}, 10~ ext{cm}, 1~ ext{m}, up to larger scales like ecosystems and the biosphere
  • The scale is often depicted as a progression from subcellular to organismal to ecological contexts, illustrating how structure spans many orders of magnitude.

Nested Hierarchy of Life

  • Living things are organized into a nested hierarchy:
    • Organelles: e.g., nucleus (an organelle within a cell)
    • Cells: e.g., human blood cells
    • Tissues: e.g., human skin tissue
    • Organs and Organ Systems: e.g., stomach and intestine; digestive system
    • Organisms, Populations, and Communities: e.g., a forest with many pine trees; a population of pines; the forest's plant and animal species form a community
    • Ecosystems: a coastal ecosystem includes living organisms and their environment
    • The Biosphere: all ecosystems on Earth
  • This nesting shows that higher levels emerge from the organization of lower levels and that properties can change across scales while remaining connected to lower-level processes.

Structure and Function

  • Structure refers to:
    • 1) size and shape
    • 2) organization (arrangement of parts)
    • 3) composition (what it’s made of)
  • Function refers to the role or job performed by the component.
  • Central idea: An object’s structure causes it to function in a particular way in a living organism.
  • Key biology principle: Structure determines function.

Structure-Function Relationships Across Scales

  • Structure-function relationships can be observed at all levels of life:
    • Organelles
    • Molecules
    • Cells
    • Organs
    • Organisms
    • Ecosystems
  • Across these scales, changes in structure are tied to changes in function, illustrating how organization enables biological activity.

Three Core Questions Revisited

  • From its earliest beginnings, biology has wrestled with three questions:
    • What are the shared properties that make something ‘alive’?
    • How do we find meaningful levels of organization in living structures?
    • How do we classify the diversity of life so we can better understand it?
  • These questions frame how we study life at all scales, from molecular to ecological.

The Diversity of Life

  • The diversity of life is vast, reflecting a wide array of forms, processes, and interactions across scales.
  • This diversity invites classification, comparison, and explanation through shared properties and evolutionary history.

Evolution: The Unifying Principle in Biology

  • Quotation: “Nothing in biology makes sense except in the light of evolution.” — Theodosius Dobzhansky
  • Evolution is the primary source of biological diversity.
  • It provides the explanatory framework for understanding similarities and differences among organisms, their relatedness, and their adaptations.
  • The diversity of life arises through processes of variation, heredity, and differential survival and reproduction over time.

Morphology vs Molecules in Determining Relatedness

  • Relatedness among organisms can be inferred using:
    • Morphological traits (anatomical features, structure)
    • Molecular features (DNA, proteins, other biomolecules)
  • Both data types contribute to constructing relationships and classifications among taxa.
  • Example approach (modified from Spaulding et al. 2009):
    • Phylogenetic analyses can combine Morphology and Molecules to resolve evolutionary relationships.
  • This dual approach helps reconcile traditional classifications with modern molecular data.

Groupings by Morphology vs Molecules

  • A representative example shows how different data streams (structure vs molecular data) can support or revise groupings such as orders, families, and higher taxa.
  • The integration of morphology and molecular data is a common strategy in systematics for determining relatedness.

Summary: Core Takeaways

  • We define life based on a unique and combined set of properties:
    • order, responsiveness to environments, reproduction, evolutionary adaptation, growth & development, regulation/homeostasis, and energy processing
  • Living organisms display a nested hierarchy of organization, from molecules to entire ecosystems
  • All levels of organization demonstrate the principle: “structure determines function.”
  • Evolution is the source of biological diversity and provides the framework to understand relatedness among organisms
  • Next time: Scientific Process - B2e Ch 1.1 and The Story of Life Ch 1