Chapter 1.1 notes

Criteria for defining living things

  • Living things vs non-living things

    • Intuition example: a tiger is living; Howard’s rock at the stadium is not living

    • The line between living and non-living is drawn by what living things can do compared to non-living things

  • Core capabilities often used to define life (as outlined in the transcript)

    • Respirate: living things can take in matter and convert it to a different form and acquire energy from it

    • Reproduce: living things can reproduce

    • Regulation: living things can regulate their internal environment despite external changes

    • Origin of life hypothesis: scientific evidence strongly suggests all life originated from non-living ancestors of the first living thing; i.e., a single origin or common ancestor

    • The evidence for a single origin is that living things share certain capabilities and characteristics

  • Important caveat on teaching points

    • Some bullets may not make immediate sense; they represent a semi-comprehensive list of properties that distinguish living from non-living things

Common origin and shared features

  • If all living things share a set of common features, it strengthens the argument for a single common ancestor

  • Concept of a “common ancestor” (K): one initial organism from which all current life descended

Macromolecules and cellular composition

  • Living things are composed of a common set of macromolecules

    • Macromolecules: large, complex molecules essential for life (to be discussed in a dedicated lecture later)

    • Despite vast differences in appearance, life relies on many of the same building blocks

  • Cells as a fundamental unit of life

    • All living things are or can be composed of cells

    • Variation in cell number: can be single-celled (e.g., bacteria) or multicellular (
      ^{13}$$

  • Controversy: not all scientists agree that all living things must be composed of cells

Interdependence, structure, and energy use

  • Living things depend on intricate interactions among structurally complex parts to maintain the living state

    • This complexity is tied to maintaining function and homeostasis

  • Energy input is needed to maintain complex structure

    • Living systems harness energy from the environment and use it to carry out their functions

Genetic information and heredity

  • All living things contain genetic information

    • This is widely accepted and will be explored in depth (genes and DNA) later in the course

  • DNA as a blueprint

    • DNA holding the blueprint contains instructions for building an organism

    • We will learn about genes, DNA, and related concepts more extensively later

  • Energy and matter processing related to genetics

    • Living things convert molecules and matter from the environment into new biological molecules

    • They can take in atoms and molecules of one type and push out molecules of another type

  • Reproduction and genetic continuity

    • Living things have a fundamental set of genes

    • The genetic blueprint among diverse life (bacteria, humans, elephants, plants) is not entirely different at the core when examined at a deeper level

    • Genetic information can be copied and passed on to reproduce

    • Evolution occurs through gradual changes in genetic information

    • The concept that changing the genetic blueprint can alter an organism’s properties will be covered in-depth later

Viruses: the edge of life

  • Viruses are on the edge of life with respect to the criteria for life

    • They meet some criteria but not all

  • Virus structure and diversity

    • Two broad shapes discussed: round (spherical) viruses and funky-shaped viruses

    • Round viruses typically infect humans/animals; funky-shaped viruses infect bacteria (bacteriophages)

    • Despite shapes, viruses are built from macromolecules similar to those in cells

  • Genetic material and evolution

    • Viruses contain genetic information (DNA or RNA)

    • They can evolve by changing their genetic information, leading to new properties

    • COVID-19 and its variants are used as an example of viral evolution

  • Replication and cellular dependence

    • Viruses cannot replicate on their own; they must infect a host cell and use the host’s cellular machinery to reproduce

    • Because they are not cells, and cannot self-replicate independently, many scientists classify them as not living or on the border of life

  • Philosophical and practical implications

    • The classification of viruses as living or non-living is nuanced and debated

    • This gray area highlights that life is a spectrum rather than a strict binary in some definitions

Real-world example: COVID-19 and viral evolution

  • COVID-19 epidemic demonstrated how a virus can evolve over time

    • Variants emerged with different properties (e.g., level of infectiousness, severity)

    • Some variants were more infectious, others more deadly; shifts occurred in response to immune pressure and vaccines

    • Viruses adapt to evade immune systems and vaccines, illustrating ongoing evolutionary dynamics

  • Practical implications

    • Understanding viral evolution helps in vaccine design and public health responses

    • The example emphasizes why viruses are studied as part of the discussion of life and biology

Connections to broader biology and course themes

  • Foundational principles

    • Life is characterized by energy harvesting, growth, reproduction, regulation, and genetic information processing

  • Energetics and metabolism

    • A recurring theme in later chapters: organisms harness energy to maintain structure and function

  • Genetics and heredity

    • The central role of DNA (and variation through mutation) in evolution and organismal traits

  • Cellular biology and macromolecules

    • Emphasis on the commonality of building blocks across life and the complexity of cellular organization

  • Ethics, philosophy, and practical implications

    • The edge-of-life status of viruses invites ongoing discussion about what constitutes life and how we classify living systems

  • Preparatory note for future topics

    • Anticipation of deeper dives into macromolecules, genetics, and cellular biology in later lectures

Summary takeaways

  • Living things can be distinguished by their abilities: energy acquisition, metabolism, growth, reproduction, and homeostatic regulation

  • Life is likely rooted in a single common ancestor, given the shared features across diverse organisms

  • Life is built from common macromolecules and organized into cells (though there is debate about whether all life must be cellular)

  • Energy flow and genetic information are central to living processes

  • Viruses challenge the boundaries of life by possessing genetic material and evolutionary capacity but lacking independent replication and cellular structure

  • Real-world examples like COVID-19 illustrate how life-like entities can evolve rapidly in response to environmental pressures

  • The material lays the groundwork for later, deeper exploration into macromolecules, genetics, and cellular biology