Exam Prep, Lab Reports, Ocean Acidification, and Cell Size – Comprehensive Study Notes

Exam logistics and quiz expectations

• Exam scheduled during the lecture next Thursday.
• You’ll need a Scantron; format will be mostly multiple choice.
• If there are short answer questions, they will be pulled directly from the study guides and material covered in class.
• If you encounter confusion about quiz answers, contact the instructor to prevent studying the wrong material (clicking errors on the answer button can happen).
• The instructor wants students to study the right material and asked to report any issues early.

Welcome introductions and class insights

• The instructor reviewed all welcome introductions and enjoyed the activity.
• A fun discussion prompt: What's the least interesting thing about you? Responses often reveal unexpected or interesting aspects; e.g.,
  • Some students said their Filipino heritage is the least interesting thing, which the instructor argues is actually interesting and worthy of discussion.
  • A common theme: many students have jobs while also going to school.
• Animal-themed prompts: most common animals named included dogs, turtles, owls, bunnies, sloths, wolves, cats, pandas, hawks, and various birds; some students expressed interest in being birds or specific species.
• This discussion revealed a mix of personal interests and everyday life experiences among the class.

Lab 1 feedback and tips for improvement

• The instructor has begun providing comments on Lab 1 reports (progress noted after reviewing about 15 submissions so far).
• Key reminders:
  • Submit the entire lab report; partial submissions are not ideal and may not receive full credit.
  • Review the definitions of theory, hypothesis, and conclusion; many students confused these terms.
  • Distinctions emphasized:
  • A hypothesis is a testable statement; you cannot prove a hypothesis true—support it with evidence from an experiment.
  • A conclusion is derived from a single experiment and should summarize what happened, the results, and your interpretation.
  • A theory is built from thousands of conclusions across many studies and represents the closest thing to truth/fact we have in science.
  • The most common issue was weak conclusions in Lab 1 (one sentence, e.g., describing indifference or attraction without listing substances tested).
  • The conclusion should convey what happened in the experiment, the results, and what you understand from the results; include the substances tested and the observed effects.
• Feedback on Lab 2:
  • If the conclusion is still weak, you can resubmit (the system will mark the first submission as on-time and the resubmission as late, but the instructor will review the improved version).
  • The instructor will be stricter grading Lab 2, so use this opportunity to improve and learn.

Lab activities this week and upcoming labs

• This week: first half of microscope skills, focusing on practical microscopy with living specimens; minimal discussion of organisms, emphasis on skills and confidence.
• This lab is foundational; the next lab will build on it (cytology).
  • Microscope lab this week and cytology lab next week; cytology focuses on organelles, labeling, and cell sizing.
• Post-lab assignment due later this week: review all microscope parts.
  • Tip: completing the post-lab prelab (before lab) is advantageous.
• Prelab for next week: page 40 of the lab manual (organelles table: nucleus, bacteria, plant/animal cells).
  • Task: identify which cell types have specific organelles, describe appearance, and state function.
  • Example: nucleus present in animal and plant cells; bacteria lack a nucleus; function is to store and protect DNA.
• Chapter transition: next week begins Chapter 3 on cell size, followed by Chapter 4 covering energy and enzymes (bridging chemistry and physics concepts in metabolism).

Worksheet and in-class activity logistics

• The in-class worksheet (assigned in the assignments) covers questions 1–13:
  • Mix of fill-in-the-blank and short-answer responses.
  • Content follows the 15-minute video (roughly one question per minute).
• Submission options before leaving class:
  • Submit online via the platform, or
  • Write on paper, take a photo, and submit, or
  • Type your responses.
• Deadline: due today before you leave class.

Ocean acidification video: overview and significance

• Vanessa O’Brien’s expedition to Challenger Deep (nearly 11,000 meters below) motivated by ocean acidification concerns and to collect samples for further research.
• The 2020 London Natural History Museum paper compared shells from 1875 (HMS Challenger) with modern samples, finding shell thickness reductions up to 76% in some species.
• Ocean acidification context:
  • Described as a ground-zero phenomenon for ocean chemistry changes driven by atmospheric CO₂ increases.
  • Projected to make oceans ~150% more acidic by the end of the century, a rate of change not previously observed.
  • The phenomenon has wide ecological and economic implications, including impacts on biodiversity and local economies dependent on marine resources.
• Real-world implications and communities affected:
  • Washington State example: ocean acidification linked to high mortality of some marine organisms and threats to local economies.
  • Deep-sea reefs and coral ecosystems as habitats that support vast biodiversity; dissolution or weakening of calcium carbonate skeletons threatens these ecosystems.
• Human communities and economics:
  • Alaska example: commercial fisheries (e.g., salmon) are a major economic activity; ocean acidification adds to the challenges of managing fisheries alongside other climate impacts.
  • Exxon Valdez oil spill (1989) cited as a major environmental disaster, illustrating how one event can have long-lasting ecological and economic consequences; ocean acidification adds a persistent, cumulative threat alongside such events.
• Technological and policy responses discussed:
  • Ocean-based carbon capture solutions (e.g., ocean-assisted direct air capture) are being explored; a sample technology mentioned captures about 37 tons of CO₂ per year per unit and is containerized for scalability.
  • A hypothetical global scale requirement was discussed: to capture current global CO₂ emissions at existing rates would require a very large number of containers (stated as about 36,000,000 containers, highlighting the scale of the challenge).
  • There is ongoing debate about feasibility, cost, and scalability of such interventions.

Ocean chemistry and the mechanism of acidification (chemistry deep-dive)

• Central premise: increased atmospheric CO₂ dissolves in seawater and alters carbonate chemistry, impacting calcifying organisms.
• Key species and reactions:
  • Calcium carbonate builders are primarily CaCO₃, formed from Ca²⁺ and CO₃²⁻ in seawater.
  • Carbonate availability is reduced when carbonate ions (CO₃^{2-}) combine with hydrogen ions (H⁺) to form bicarbonate (HCO₃⁻):
    ext{CO}3^{2-} + ext{H}^+ ightleftharpoons ext{HCO}3^-
  • Dissolved CO₂ reacts with water to form carbonic acid (H₂CO₃), which dissociates to yield more H⁺ and HCO₃⁻, increasing acidity:
    ext{CO}2( ext{aq}) + ext{H}2 ext{O}
    ightleftharpoons ext{H}2 ext{CO}3
    ightleftharpoons ext{H}^+ + ext{HCO}_3^-
  • The bicarbonate (HCO₃⁻) itself can further dissociate to produce additional H⁺ and CO₃^{2-} (less common as a dominant path in seawater under acidification, but part of the system’s equilibria):
    ext{HCO}3^- ightleftharpoons ext{H}^+ + ext{CO}3^{2-}
• Net chemical consequence:
  • As CO₂ dissolves and carbonic acid forms, more H⁺ is produced, lowering pH (increasing acidity) and shifting carbonate equilibria away from CO₃^{2-} toward HCO₃⁻, reducing the availability of carbonate ions needed for CaCO₃ formation.
  • Reduced CO₃^{2-} availability leads to thinner shells and slower growth in calcifying organisms such as mollusks and corals.
• Practical analogy to help intuition:
  • Carbonate is like a resource for building shells; hydrogen ions act like a sink that binds carbonate to form bicarbonate, making carbonate less available for shell-building.
• Le Chatelier’s principle application:
  • If you increase a reactant, the system shifts to produce more products; if you increase a product, the system shifts to consume products.
  • In this context, increasing H⁺ (due to CO₂ dissolution) pushes equilibrium away from carbonate (CO₃^{2-}) toward bicarbonate (HCO₃⁻), reducing CaCO₃ formation.
• Important definitions and relations:
  • Calcium carbonate (CaCO₃) formation requires Ca²⁺ and CO₃^{2-}.
  • Dissolution of CaCO₃ or failure to form CaCO₃ occurs when CO₃^{2-} is depleted by reaction with H⁺.
  • Acidic conditions (lower pH) lead to more dissolution of calcium carbonate structures and hinder calcification.
• Conceptual takeaway: biology-chemistry-physics nexus
  • Biology: calcifying organisms rely on calcium carbonate structures.
  • Chemistry: carbonate speciation and acid-base equilibria govern ion availability.
  • Physics: diffusion and fluid dynamics influence nutrient/waste exchange in marine systems; temperature and oxygen levels interact with CO₂ effects.
• Related resources and study aids:
  • Labexchange.org offers interactive animations on ocean acidification, diffusion, enzymes, and related topics; recommended as a supplementary learning tool.

Cell size: lower and upper limits, and cellular organization (Chapter 3)

• Core question: Are cells big or small? Answer: generally small.
  • Why small? Smaller size supports more efficient exchange of materials (nutrients in, waste out) across the cell membrane.
  • Why not infinitely small? Cells must be large enough to house essential machinery (DNA, ribosomes, etc.).
• Definitions:
  • Prokaryotic cells: smaller, simpler cells lacking a nucleus; examples include bacteria; internal DNA is not enclosed by a membrane-bound nucleus.
  • Eukaryotic cells: larger, more complex cells with nucleus and membrane-bound organelles; includes cells in plants, animals, fungi, and single-celled eukaryotes.
• Core components present in both cell types (basic schematic):
  • DNA, ribosomes, plasma membrane (cell membrane), cytoplasm (cytosol).
  • Prokaryotes: DNA in the nucleoid region (not membrane-bound), ribosomes, cell membrane, cytoplasm; no nucleus or membranous organelles.
  • Eukaryotes: nucleus with DNA, multiple membrane-bound organelles (mitochondria, chloroplasts in photosynthetic cells, etc.), ribosomes, cytoplasm, cell membrane.
• Size and complexity differences:
  • Prokaryotic cells are the smallest and oldest form of life; minimal cellular machinery.
  • Eukaryotic cells are larger and more complex, capable of more functions, and contain specialized organelles.
  • Some eukaryotes are microscopic; some are single-celled, while others are multicellular (e.g., plants, animals, fungi).
• Multicellularity and specialization:
  • In multicellular organisms, cells differentiate into specialized types (e.g., skin cells vs. muscle cells) with distinct structures and functions.
• Upper and lower size limits: why not too small or too large?
  • Lower limit: cells must be large enough to accommodate essential machinery (DNA, ribosomes, etc.).
  • Upper limit: cell must maintain efficient exchange with the environment; otherwise the surface area to volume ratio (SA:V) becomes insufficient to meet metabolic demands.
• Surface area–to–volume ratio (SA:V) concept and intuition:
  • The surface area of a cell is the membrane that governs material exchange; the volume reflects internal demands for nutrients, space, and waste accumulation.
  • As a cell grows, its volume increases faster than its surface area, reducing SA:V and limiting exchange efficiency.
• Analogies used to illustrate SA:V limits:
  • One-door room analogy: a single gateway limits nutrient inflow and waste outflow; doubling the internal volume without increasing gateway count reduces functional efficiency.
  • Wrapping paper analogy: surface area is like the amount of wrapping paper; volume is the number of chocolates packaged; when you double the chocolates but don’t proportionally increase wrapping paper, you can't optimally wrap or access all items.
• Implications for cell function:
  • Cells must maintain an optimal SA:V to support metabolism, growth, and homeostasis.
  • When size increases excessively, the cell may become inefficient or fail to sustain life processes.
• Practical takeaway for exams and understanding:
  • Remember the definitions and contrasts between prokaryotic and eukaryotic cells.
  • Understand why SA:V imposes size constraints and how this ties to cellular efficiency and specialization.

Chapter previews and next steps

• Next week: introduction to Chapter 4, focusing on energy and enzymes (bridging biology with physics concepts).
• The following week: Chapter 4 in full, emphasizing metabolism and the interplay of chemistry and physics in biological systems.
• Reminders: keep up with prelab and postlab assignments; use resources like LabExchange for visual and interactive understanding.

Key terms and concepts to review (summary)

• Theory vs. Hypothesis vs. Conclusion:
  • Hypothesis: a testable statement; cannot be proven true, only supported by evidence.
  • Conclusion: interpretation of data from a single experiment; should summarize what happened and what was learned.
  • Theory: well-supported by thousands of conclusions and experiments; closest to the notion of truth in science.
• Ocean acidification chemistry (recap):
  • CO₂ dissolution → carbonic acid → increased H⁺ → lower pH; decreased CO₃²⁻ availability for CaCO₃ formation.
  • Key equilibria: ext{CO}2( ext{aq}) + ext{H}2 ext{O}
    ightleftharpoons ext{H}2 ext{CO}3
    ightleftharpoons ext{H}^+ + ext{HCO}_3^-
  • Further dissociation: ext{HCO}3^- ightleftharpoons ext{H}^+ + ext{CO}3^{2-}
  • Carbonate binding with hydrogen: ext{CO}3^{2-} + ext{H}^+ ightleftharpoons ext{HCO}3^-
  • Calcium carbonate formation: ext{Ca}^{2+} + ext{CO}3^{2-} ightarrow ext{CaCO}3(s)
• Important numbers mentioned:
  • Challenger Deep depth: nearly 11{,}000 ext{ meters} below the surface.
  • Shell thickness reduction observed: up to 76 ext{%} thinner in modern samples vs. 1875 samples.
  • Projected ocean acidity by end of century: about 150 ext{%} more acidic.
  • CO₂ capture claim: 37 ext{ tons of CO}_2/ ext{year} per container in ocean-assisted direct air capture; scale-up discussion suggested that ~36{,}000{,}000 containers would be needed to capture current global CO₂ emissions.
• Prelab expectations (lab manual): page 40 table covering organelles across bacteria, plants, and animals; identify presence/absence, appearance, and function of nucleus and other organelles.
• Illustrative examples for cell size: small bacterial cells; larger eukaryotic cells with membranous organelles; examples of specialization in multicellular organisms.