Difficulty: Introductory | Prerequisites: None
This chapter lays the groundwork for everything else in BIO 311C. It defines what makes something "alive," introduces the model organisms you will see referenced throughout the course, and establishes how scientists design experiments. If you are behind, start here: the vocabulary and frameworks from Chapter 1 appear in nearly every later unit. Understanding biological hierarchy, domains, and the scientific method is assumed knowledge for Chapters 2 and 3.
All living things share eight properties (reproduction, growth, order, metabolism, respiration, response to stimuli, adaptation, and movement). Biologists study life using model organisms, holistic or reductionist approaches, and controlled experiments. Life is organised in a hierarchy from atoms up to the biosphere, and all organisms fall into three domains: Bacteria, Archaea, and Eukarya.
Emergent properties of life
The characteristics shared by all living organisms: reproduction, growth and development, order and structure, metabolism, respiration, response to environmental stimuli, adaptation and evolution, and autonomous movement. Think of these as the checklist for deciding whether something counts as "alive."
Model system (model organism)
A species chosen for laboratory study because it is practical to work with and its biology teaches us principles that apply broadly. In simple terms, scientists pick a handful of organisms (like E. coli or fruit flies) and study them deeply, rather than trying to examine every species.
Holism (holistic approach)
Studying a whole, intact organism to understand behaviour, nutrition, or physiology. Think of it as zooming out to see the full picture, e.g. testing a drug on a living rat.
Reductionism (reductionist approach)
Studying life at the level of cells, tissues, or molecules rather than the whole organism. In simple terms, you break the system down into smaller parts to understand the pieces.
In vivo
Experiments conducted in or on a living organism under natural or near-natural conditions. Can be holistic or reductionist. Think "in life" (vivo = living).
In vitro
Experiments performed outside a living organism, in artificial conditions such as a test tube or petri dish. Always reductionist. Think "in glass" (vitro = glass).
Biological hierarchy
The levels of organisation in living systems, from smallest to largest: atoms, molecules, macromolecules, organelles, cells, tissues, organs, organ systems, organisms, populations, communities, ecosystems, biomes, biosphere.
Domain
The highest taxonomic rank. The three domains are Bacteria, Archaea, and Eukarya.
Kingdom
The taxonomic rank below domain. Eukarya contains four kingdoms: Protista, Fungi, Plantae, and Animalia.
Hypothesis
A testable prediction or explanation formed from observations. In simple terms, it is an educated guess that an experiment can support or reject.
Theory
A well-supported explanation of natural phenomena, backed by repeated experimental evidence. This is stronger than a hypothesis.
Scientific law
A description of a natural phenomenon that holds true universally and without exception. Think of it as a pattern so consistent it is treated as a rule.
Positive control
A treatment in an experiment that is already known to produce a result. It confirms the experiment is working properly.
Negative control
A treatment expected to produce no effect, essentially a placebo. It provides a baseline for comparison.
All living organisms share eight properties. Each one is necessary, and no single property on its own is sufficient to define life.
Reproduction: genetic material (DNA) is copied and passed to offspring.
Growth and development: organisms progress through defined developmental stages.
Order and structure: cells and organisms have structures that correlate with their functions.
Metabolism: organisms take in nutrients and break down large molecules for energy and building materials.
Respiration: oxygen is consumed and CO2 is released during the breakdown of food to generate usable energy (ATP).
Response to environmental stimuli: organisms sense environmental cues, respond accordingly, and maintain homeostasis.
Adaptation and evolution: over generations, populations change in response to selective pressures, producing new forms.
Autonomous movement: living organisms can move on their own. Even plants and fungi exhibit movement toward light or nutrient sources.
Biologists use model organisms because it is impractical to study every species in depth. Findings from model organisms are generalised to understand broader biological principles.
Prokaryotic models (unicellular, no membrane-bound nucleus): E. coli, Salmonella
Eukaryotic models (membrane-bound nucleus and organelles):
Plants: Arabidopsis (a small flowering plant related to cabbage and mustard), corn, rice
Fungi: yeast (Saccharomyces cerevisiae)
Animals: fruit fly (Drosophila), nematode (C. elegans), mice, zebrafish, human cell lines
Holistic: study the whole organism. Used for behavioural, nutritional, and physiological research. Example: testing an anti-ageing drug on rats.
Reductionist: study at the cellular, molecular, or tissue level. The whole organism is not used. Example: culturing human cells in a dish to study gene expression.
Both approaches are valuable; they answer different kinds of questions.
In vivo ("in life"): experiments on living organisms under natural or controlled living conditions. Can be holistic or reductionist.
In vitro ("in glass"): experiments in artificial, non-living conditions such as test tubes or petri dishes. Strictly reductionist.
In situ (not tested on this exam, but useful to know): experiments conducted to determine where molecules like DNA and RNA are located within cells or tissues.
Life is organised in nested levels, each building on the one below:
Atoms (C, H, N, S, O, P and other elements)
Molecules (water, amino acids, sugars)
Macromolecules (proteins, carbohydrates, lipids, nucleic acids)
Organelles (membrane, nucleus, mitochondria)
Cells
Tissues
Organs (heart, lungs, brain)
Organ systems (digestive, circulatory, reproductive)
Organisms (plants, animals, fungi)
Populations (groups of the same species)
Communities (multiple populations in one area)
Ecosystems (communities plus their physical environment)
Biomes (desert, forest, tundra)
Biosphere (all living parts of Earth)
The taxonomic hierarchy runs: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
Bacteria: unicellular prokaryotes.
Archaea: prokaryotic, but adapted to extreme environments (high heat, salinity, acidity). Share some features with eukaryotes.
Eukarya: all organisms with membrane-bound nuclei. Contains four kingdoms:
Protista: mostly unicellular, heterotrophic
Fungi: multicellular (some unicellular), heterotrophic, absorb nutrients
Plantae: multicellular, photosynthetic (monocots and dicots)
Animalia: multicellular, heterotrophic
Inductive reasoning: moving from specific observations to a broad generalisation.
Deductive reasoning: moving from a broad principle to a specific prediction.
A hypothesis is formed from observations or predictions and must be testable.
Experiments use controlled environments with:
A positive control (known to produce a result, confirms the method works)
A negative control (expected to produce no result, serves as a baseline)
Supported hypotheses may become a theory (well-supported explanation). If results hold universally without exception, they may be described as a law.
Students often think "theory" means "guess." In science, a theory is a well-tested explanation supported by substantial evidence. A guess is closer to a hypothesis.
Students confuse Archaea with Bacteria because both are prokaryotic. Archaea are distinct: they thrive in extreme environments and share molecular features with eukaryotes.
Students sometimes list "cells" as a property of life. Cellular organisation is part of "order and structure," not a separate emergent property in this course's framework.
Students assume in vivo is always holistic. In vivo experiments can also be reductionist, for example studying a single organ within a living animal.
True or False: Archaea are eukaryotes that live in extreme environments.
False. Archaea are prokaryotic.
Fill in the blank: An experiment performed in a test tube under non-living conditions is called an _____ study.
In vitro.
True or False: A negative control is expected to produce a positive result.
False. A negative control should produce no effect.
Fill in the blank: The four kingdoms of Eukarya are Protista, Fungi, _____, and Animalia.
Plantae.
True or False: Inductive reasoning moves from broad generalisations to specific predictions.
False. Inductive reasoning moves from specific observations to broad generalisations. The reverse is deductive reasoning.
⚠️ Know all eight emergent properties of life and be able to give an example for each.
⚠️ Be able to match model organisms to their domain (prokaryote vs. eukaryote) and kingdom.
⚠️ Distinguish between in vivo and in vitro, and know which approaches (holistic, reductionist) apply to each.
⚠️ The biological hierarchy from atoms to biosphere is a classic exam question. Know the correct order and at least one example at each level.
⚠️ Understand the difference between positive and negative controls and be able to identify them in an experimental scenario.
Q: List three emergent properties of life and give one example of each.
A: Reproduction (DNA replication and cell division), metabolism (breaking down glucose for energy), response to environmental stimuli (a plant bending toward light).
Q: What is the difference between a positive control and a negative control?
A: A positive control is a treatment known to produce a result, used to verify the experiment is functioning correctly. A negative control is a treatment expected to produce no effect, used as a baseline for comparison.
Q: Name the three domains of life and state whether each is prokaryotic or eukaryotic.
A: Bacteria (prokaryotic), Archaea (prokaryotic), Eukarya (eukaryotic).
Q: A researcher cultures human liver cells in a petri dish to study how a toxin affects gene expression. Is this an in vivo or in vitro experiment? Is it holistic or reductionist?
A: In vitro (cells are outside the living organism, in artificial conditions). Reductionist (studying at the cellular level, not the whole organism).
Q: Place the following in order from smallest to largest: organ, cell, molecule, organism, tissue, atom.
A: Atom, molecule, cell, tissue, organ, organism.
The biological hierarchy introduced here reappears in Chapter 2, where you zoom in to atoms, molecules, and chemical bonds. The macromolecules at level 3 of the hierarchy (proteins, carbohydrates, lipids, nucleic acids) are the entire focus of Chapter 3. Understanding domains and kingdoms will matter when you reach genetics and evolution later in the course.
Emergent properties of life, model organisms, E. coli, Arabidopsis, Drosophila, yeast, holism vs reductionism, in vivo vs in vitro, biological hierarchy, levels of organisation, three domains of life, Bacteria, Archaea, Eukarya, four kingdoms, Protista, Fungi, Plantae, Animalia, scientific method, hypothesis, theory, law, positive control, negative control, inductive reasoning, deductive reasoning, BIO 311C, introductory biology, University of Texas