Biology 201: Week 2 Lecture Notes — SI, Study Guides, Life, Evolution, and Structure-Function

SI Resources, Schedules, and Study Approach

• SI = Supplemental Instruction: free, student-led study resource with organized sessions and planned activities.
• Drop-in hours: office hours with SIs in a less structured format (informal Q&A).
• Summer’s office hours change: previously one session on Thursday; now Friday from 2 to 3 PM.
• If Summer’s times don’t fit your schedule, you can find additional hours for BIO 200 SI sections on the Canvas page under Supplemental Instruction.
  • The page shows all SI sections and sessions; you can attend any available SI session if your own schedule conflicts.
  • For STEM labs, drop-in hours function similarly to office hours.
• All SI sessions are aligned with each other, so you can benefit from any session regardless of which SI leader you attend.
• Location: Supplemental Instruction schedule is accessible on the Canvas page.

Canvas, Study Guides, and Learning Objectives

• Week two announcements: Week 2 materials and lecture content are available on Canvas.
• Slides for today’s class are labeled as Lecture Two; assignments and study guides are listed there as well.
• Study guides contain:
  • Learning objectives for the unit (what you should be able to do by the end of the unit).
  • Page references linking to where information is found in the textbook.
  • Self-assessment questions to gauge mastery of the objectives.
• Example learning objective shown: distinguish hypotheses from theory (theory requires substantial evidence from many experiments and sources).
• Today’s biology objectives include:
  • List the characteristics common to all living things.
  • Organize life into broad categories (three domains).
  • Understand how evolution accounts for unity and diversity of life and the role of natural selection in that process.
• The study guides are suggested study materials because:
  • They point you to where in the text to find needed information.
  • They identify what information is essential for executing on the learning objectives.
• Exam alignment: Learning objectives on the study guides are intended to reflect the types of questions that will appear on the exam (e.g., distinguishing prokaryotes from eukaryotes).
• If you don’t like the study guide questions, you can generate practice questions using tools like ChatGPT to practice the learning objectives.
• Practical advice: Use the Pearson pre-reading assignments alongside the textbook readings to reinforce understanding via applied questions.
• The professor emphasizes that study guides help determine which parts of the chapter to focus on, especially when the text contains more information than needed for the exam.
• Q&A format: The instructor invites questions about where to find resources on campus, SI, study guides, Pearson, etc., and reserves time at the end for questions.

What Does It Mean to Be Alive? Core Features and Cellular Basis

• All living things share core properties, though organisms may express them differently:
  • Organized structure: life maintains an organized internal structure, requiring energy input to sustain organization.
  • Homeostasis: organisms regulate their internal environment relative to the outside (viruses lack robust homeostasis due to lacking cellular membranes and controls).
  • Metabolism: organisms metabolize to harvest/use energy (fermentation, cellular respiration; photosynthesis in plants/algae).
  • Growth and reproduction: life grows and reproduces; viruses do not independently reproduce.
  • Response to the environment: organisms sense and respond to external cues (varies by organism).
  • Evolution: life evolves over time.
• The fundamental unit of life is the cell; cells come in two broad categories:
  • Prokaryotic cells (no nucleus): Bacteria, Archaea.
  • Eukaryotic cells (nucleus): Eukarya (includes animals, plants, fungi, some single-celled organisms).
• Viruses: debated whether alive. They have an organized structure and can evolve rapidly but typically cannot maintain homeostasis, cannot metabolize on their own, cannot reproduce independently, and do not grow by themselves.
  • They rely on host cellular machinery for energy and replication.
  • Debate about whether they respond to the environment (some evidence suggests interactions with host cells trigger changes) but hard to classify as alive by standard criteria.
• Energy harvesting pathways in cells:
  • Fermentation and cellular respiration (energy from nutrients).
  • Photosynthesis (energy from light, in plants/algae) to store energy chemically for later use.
• Cellular communication and signaling:
  • Receptors (e.g., dopamine, glucose regulation) mediate uptake/release of molecules and trigger cellular processes such as division or differentiation.
• Cells can regulate their internal environment, including water balance and pH, via proteins and channels.
• Growth and development can involve cell division and replication of genetic material (DNA) so that daughter cells inherit the genome.

Domains of Life and Cellular Classification

• Three domains of life (evolutionary categories):
  • Bacteria (prokaryotes, typically single-celled; no nucleus; diverse habitats).
  • Archaea (prokaryotes, often single-celled; many extremophiles; also present on human skin).
  • Eukarya (eukaryotes; includes animals, plants, fungi, and some single-celled organisms like certain algae).
• Functional division based on nucleus:
  • Prokaryotes (Bacteria + Archaea): lack a membrane-bound nucleus; DNA resides in a region of the cell rather than inside a membrane-bound nucleus.
  • Eukaryotes (Eukarya): have a nucleus that stores DNA in a membrane-bound compartment.
• Visual takeaway: Amoeba example used to illustrate a eukaryotic cell with a nucleus; bacteria and archaea lack a defined nucleus.
• Evolutionary relationships:
  • Humans and other mammals share a close evolutionary relationship with other eukaryotes via common descent.
  • Despite superficial differences (e.g., bones in limbs), many organisms share fundamental cellular features and a universal genetic code.
• Unity and diversity in life arise from common descent and subsequent diversification through natural selection (discussed next).

Evolution: Unity, Diversity, and the Role of Natural Selection

• Unity across life arises from:
  • Universal genetic code: all life uses DNA/RNA and shares a common code for translating genetic information into proteins. This universal code enables cross-species genetic engineering (e.g., antifreeze gene from fish used in yeast or crops) because the same genetic code is read by cellular machinery.
  • Shared cellular structures and metabolic pathways at the cellular level.
• Diversity arises from natural selection acting on variation over time:
  • Variation: populations harbor genetic and phenotypic variation due to mutations and recombination.
  • Heritability: traits that vary are encoded in DNA and can be passed to offspring.
  • Differential survival and reproduction: individuals with advantageous traits leave more offspring, changing trait frequencies over generations.
• History and people:
  • Charles Darwin and Alfred Russel Wallace independently conceived natural selection as the mechanism driving evolution; Darwin is more prominently credited.
• Mechanism of natural selection:
  • There is overproduction of offspring; more individuals are born than survive to reproduce.
  • Variation in traits exists in a population.
  • Traits that increase survival or reproductive success become more common over generations; traits that are disadvantageous may be lost.
• Classic example: beetle coloration (brown vs green) and predator pressure leading to shifts in trait frequencies over generations.
• Fitness in an evolutionary sense:
  • Fitness corresponds to an organism's ability to survive and reproduce long enough to pass on its genes.
  • Not merely surviving, but reproducing and contributing to the gene pool matters for evolution.
• Speed of evolution is influenced by factors such as:
  • Population size, lifespan (rate of reproduction), and environmental pressures (predation, resources).
  • Microbes (e.g., bacteria) evolve quickly due to rapid reproduction and strong selective pressures (e.g., antibiotic resistance).
• Speciation through natural selection:
  • Continued environmental pressures and geographic isolation can lead to divergence and the emergence of new species (speciation).
  • Galápagos finches are a classic example: island isolation and differing food resources select for different beak shapes/sizes.
• Structure determines function:
  • The relationship between anatomy and function explains how changes in structure (e.g., bones, wings, beaks) relate to ecological roles and abilities.
• Common descent and unity in diverse life:
  • Similarities across life (e.g., bone structure in mammals) reflect a shared ancestry and the retention/modification of ancestral features.

Speciation, Adaptation, and the Beak Debate

• Speciation occurs gradually over many generations through accumulation of changes and reproductive isolation.
• It can be difficult to identify exact species boundaries, but populations can diverge enough to be considered separate species when they no longer interbreed effectively.
• Example of beak evolution in Galápagos finches illustrates how resource availability drives morphological changes (e.g., beak size and shape) that increase feeding efficiency and survival.
• Structure-function relationship:
  • Different structures enable different functions (e.g., flight adaptations, aquatic swimming adaptations).
  • This concept is revisited as a foundational idea for understanding how chemistry builds life in the next unit.
• The lecture ends with a transition toward the chemistry of life and how molecular components underpin biological structure and function.

Preview: Chemistry of Life and Structure–Function Link

• Before diving into cells and organisms, we examine the chemical components that build life on Earth.
• Central idea: structure determines function; the chemical makeup of biomolecules (proteins, lipids, nucleic acids) underpins how they perform roles in cells.
• The upcoming topic will connect molecular composition to cellular processes, enabling understanding of why certain molecules are suited to specific tasks in biology.
• Final thought exercise for next class:
  • Imagine you are an astrobiologist exploring life on a distant planet. What elements would you look for to assess the potential for life?

Practical Notes: Exam Preparation and Study Strategies

• Focus on the study guide learning objectives; exam questions will be designed around these objectives (e.g., distinguishing prokaryotes vs. eukaryotes).
• Use the dynamic study modules in Pearson to practice with adaptive questions; you can review or improve scores and retake assignments for credit (depending on how the platform is configured for your course).
• Dynamic study modules adapt to incorrect responses by repeating content to reinforce understanding.
• Pearson tools offer additional practice tests and end-of-chapter quizzes, but be mindful: some questions may cover material outside the current learning objectives.
• Open eTextbook and integrated study tools (including AI-assisted study features) are available for additional review; combine these with study guides for best results.
• For the upcoming exam, you should be able to:
  • Explain how evolution accounts for both unity and diversity of life.
  • Describe the three domains of life and contrast prokaryotic and eukaryotic cells.
  • Explain the universal genetic code and its implications for biotechnology.
  • Outline the three criteria of natural selection and illustrate with a practical example.
  • Discuss the concept that structure determines function and how this drives evolutionary changes (e.g., beak shape, limb structure).