BIOL 1406 Comprehensive Lab Exam Study Guide

Lab Exam 1: Scientific Foundations, Chemistry, and the Cell

The Scientific Method and Experimental Design

• The Scientific Method Steps:

  • Observation: Noticing a phenomenon or identifying a problem using senses or data.
  • Question: Formulating a specific, answerable question based on the observation.
  • Hypothesis: Proposing a tentative, testable, and falsifiable explanation for the observed phenomenon.
  • Prediction: Creating an "If… then…" statement that describes the expected outcome of an experiment if the hypothesis is correct.
  • Experimentation: Designing and conducting a procedure to test the hypothesis.
  • Data Collection and Analysis: Gathering measurements (quantitative) or observations (qualitative) and interpreting results (often using statistics).
  • Conclusion: Determining whether the data supports or refutes the hypothesis. It is never "proven," only supported.

• Applying the Scientific Method to Observations:

  • Scenario: A student notices plants on a windowsill grow taller than plants in a dark corner.
  • Observation: Light intensity varies between the two locations.
  • Hypothesis: Increased light exposure increases the growth rate of the plants.
  • Prediction: If plants are given 12 hours of light, they will grow taller than those given 4 hours of light.

• Controlled Experiments:

  • Independent Variable: The factor specifically manipulated by the researcher (e.g., amount of light).
  • Dependent Variable: The factor being measured or observed in response to the independent variable (e.g., plant height in $\text{cm}$).
  • Control Group: The group kept under standard conditions; it does not receive the experimental treatment and serves as a baseline for comparison.
  • Experimental Group: The group that receives the manipulation of the independent variable.
  • Constants (Controlled Variables): All other factors kept identical between groups to ensure results are due to the independent variable only (e.g., same soil, same pot size, same water volume).

Mathematical Conversions in Biology

• Metric System Units:

  • Length: Meter ($\text{m}$).
  • Mass: Gram ($\text{g}$).
  • Volume: Liter ($\text{L}$) or cubic decimeters ($dm^3$).
  • Temperature: Celsius ($^{\circ}\text{C}$).

• Conversion Scale Factors:

  • Kilo ($k$): $10^3$ ($1,000$ units).
  • Centi ($c$): $10^{-2}$ ($0.01$ units).
  • Milli ($m$): $10^{-3}$ ($0.001$ units).
  • Micro ($\mu$): $10^{-6}$ ($0.000001$ units).
  • Nano ($n$): $10^{-9}$ ($0.000000001$ units).

pH Scale and Buffers

• The pH Scale:

  • A logarithmic scale measuring hydrogen ion concentration: $\text{pH} = -\log[H^+]$.
  • Acidic: $\text{pH} < 7$ (High $[H^+]$, low $[OH^-]$).
  • Neutral: $\text{pH} = 7$ (Equal $[H^+]$ and $[OH^-]$; e.g., pure water).
  • Basic (Alkaline): $\text{pH} > 7$ (Low $[H^+]$, high $[OH^-]$).
  • Each unit change on the scale represents a $10\times$ difference in acidity.

• Buffers:

  • Substances that resist changes in pH by accepting hydrogen ions when they are in excess and donating them when they are depleted.
  • Essential for maintain homeostasis in biological systems (e.g., the bicarbonate buffer system in human blood).

Macromolecules and Biochemical Testing

• Types of Macromolecules:

  • Carbohydrates: Source of energy and structural support (e.g., glucose, starch, cellulose).
  • Proteins: Composed of amino acids; perform catalysis, transport, and structural roles.
  • Lipids: Hydrophobic molecules for energy storage and membranes (e.g., fats, phospholipids).
  • Nucleic Acids: Genetic information storage (DNA and RNA).

• Biochemical Tests:

  • Test for Starch: Use Iodine (Lugol's solution). A positive result turns from yellow-brown to blue-black.
  • Test for Reducing Sugars: Use Benedict's Reagent. Requires heating. A positive result changes from blue to green, yellow, orange, or brick-red depending on concentration.
  • Test for Protein: Use Biuret Reagent. A positive result changes from light blue to violet or purple (indicates presence of peptide bonds).

Osmosis and Tonicity

• Osmosis: The passive diffusion of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration.

• Solution Types (Tonicity):

  • Isotonic: Equal solute concentration inside and outside the cell. No net water movement.
  • Hypertonic: Higher solute concentration outside the cell. Water leaves the cell, causing it to shrink (crenation in animal cells, plasmolysis in plant cells).
  • Hypotonic: Lower solute concentration outside the cell. Water enters the cell, causing it to swell and potentially burst (lysis in animal cells; plant cells become turgid due to the cell wall).

Lab Exam 2: Microscopy and Enzyme Kinetics

Microscopy

• Parts of the Microscope and Functions:

  • Ocular Lens (Eyepiece): The lens you look through, usually $10\times$ magnification.
  • Objective Lenses: Mounted on the revolving nosepiece (e.g., $4\times$, $10\times$, $40\times$, $100\times$).
  • Stage: The flat platform where the slide is placed.
  • Condenser: Focuses light onto the specimen.
  • Iris Diaphragm: Controls the amount of light reaching the specimen.
  • Coarse Adjustment Knob: Large knob used for initial focusing (only on low power).
  • Fine Adjustment Knob: Small knob used for precise, high-power focusing.

• Magnification Calculations:

  • $\text{Total Magnification} = \text{Ocular Magnification} \times \text{Objective Magnification}$.
  • Example: $10\times \text{ (ocular)} \times 40\times \text{ (high dry)} = 400\times \text{ total magnification}$.

• Microscopy Concepts:

  • Resolution: The ability to distinguish two close points as separate entities.
  • Parfocal: The ability of a microscope to remain in focus when switching between objectives.
  • Field of View: The visible area seen through the ocular; it decreases as magnification increases.

• Viewing a Specimen:

  1. Start with the lowest power objective (scanning lens) and the stage at its highest position.
  2. Use the coarse adjustment knob to lower the stage until the specimen is in view.
  3. Center the specimen in the field of view.
  4. Switch to a higher power objective and use ONLY the fine adjustment knob.

• Wet Mount Slide Preparation:

  1. Place a drop of water or stain on a clean slide.
  2. Place the specimen in the drop.
  3. Lower a coverslip at a $45^{\circ}$ angle to minimize air bubbles.

Diffusion and Transport

• Diffusion Terminologies:

  • Solute: The substance being dissolved.
  • Solvent: The dissolving medium (usually water).
  • Concentration Gradient: The difference in concentration between two areas.

• Rate of Diffusion Factors:

  • Temperature: Higher temperature increases kinetic energy, increasing diffusion rate.
  • Molecular Size: Smaller molecules diffuse faster than larger ones.
  • Concentration Gradient: A steeper gradient (greater difference) increases diffusion rate.

Enzyme Activity

• Enzyme Fundamentals:

  • Enzymes are biological catalysts that lower the activation energy of a reaction.
  • Catalase: An enzyme found in many living cells that breaks down hydrogen peroxide ($H_2O_2$), a toxic byproduct of metabolism.
  • Reaction: $2H_2O_2 \rightarrow 2H_2O + O_2(g)$.

• Measuring Enzyme Activity:

  • Activity is measured by the rate of product formation (e.g., volume of oxygen gas bubbles produced) or the rate of substrate disappearance.

• Factors Affecting Activity:

  • Optimal Temperature: The temperature at which enzyme activity is highest. Deviation (especially high heat) leads to denaturation (loss of 3D shape and function).
  • Optimal pH: The pH level where the enzyme is most active.
  • Concentration: Increasing enzyme or substrate concentration generally increases the rate until a saturation point is reached.

Lab Exam 3: Bioenergetics, Cell Division, and Genetics

Cellular Respiration and Fermentation

• Cellular Respiration: An aerobic process (requires oxygen) used to convert glucose into ATP.
  • Equation: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$.
• Fermentation: An anaerobic process (occurs without oxygen).
  • Alcoholic Fermentation: Glucose is converted to Ethanol and $CO_2$ (common in yeast).
  • Lactic Acid Fermentation: Glucose is converted to Lactic Acid (common in muscle cells).

Photosynthesis

• Process: Converting light energy, $CO_2$, and water into chemical energy (glucose) and oxygen.
  • Equation: $6CO_2 + 6H_2O + \text{Light} \rightarrow C_6H_{12}O_6 + 6O_2$.
• Photosynthetic Pigments:
  • Chlorophyll a: Main pigment; reflects green.
  • Chlorophyll b and Carotenoids: Accessory pigments that broaden the spectrum of light absorbed.

The Cell Cycle and Division

• Interphase: The majority of the cell cycle.

  • G1 Phase: Cell growth.
  • S Phase: DNA Replication (Synthesis).
  • G2 Phase: Preparation for mitosis.

• Mitosis (Nuclear Division):

  1. Prophase: Chromosomes condense, spindle forms, nuclear envelope breaks down.
  2. Metaphase: Chromosomes line up at the metaphase plate (center).
  3. Anaphase: Sister chromatids are pulled apart to opposite poles.
  4. Telophase: Nuclear envelopes reform; chromosomes de-condense.

• Cytokinesis: Division of the cytoplasm. In animal cells, a cleavage furrow forms. In plant cells, a cell plate forms.

• Meiosis: Process consisting of Meiosis I and Meiosis II that produces four non-identical haploid gametes.

  • Prophase I: Homologous chromosomes pair up and crossing over occurs (genetic exchange).

Genetic Inheritance

• Terminologies:

  • Gene: A segment of DNA coding for a protein.
  • Allele: Alternative forms of a gene.
  • Genotype: The genetic makeup (e.g., $\text{AA, Aa, aa}$).
  • Phenotype: The physical expression of a trait (e.g., purple flowers).
  • Homozygous: Having two identical alleles ($\text{AA}$ or $\text{aa}$).
  • Heterozygous: Having two different alleles ($\text{Aa}$).

• Genetic Crosses:

  • Monohybrid Cross: Tracking one trait. A cross between two heterozygotes ($\text{Aa} \times \text{Aa}$) yields a $3:1$ phenotype ratio.
  • Dihybrid Cross: Tracking two traits. A cross between individuals heterozygous for both traits yields a $9:3:3:1$ phenotype ratio.

• Blood Typing:

  • Type A: Has A antigens and anti-B antibodies.
  • Type B: Has B antigens and anti-A antibodies.
  • Type AB: Has A and B antigens; no antibodies (Universal recipient).
  • Type O: No antigens; anti-A and anti-B antibodies (Universal donor).
  • Rh Factor: Indicates the presence ($Rh^+$) or absence ($Rh^-$) of the D-antigen.

Lab Exam 4: Molecular Biology and Evolution

DNA Technology: PCR and Gel Electrophoresis

• Polymerase Chain Reaction (PCR):

  • Purpose: To amplify (make millions of copies of) a specific DNA segment.
  • Steps:
    1. Denaturation ($\approx 95^{\circ}\text{C}$): Heat separates the double-stranded DNA.
    2. Annealing ($\approx 55^{\circ}\text{C}$): Primers bind to target sequences.
    3. Extension ($\approx 72^{\circ}\text{C}$): Taq Polymerase adds nucleotides to the primers.
  • Equipment: Thermal cycler, micropipettes, PCR tubes.

• Gel Electrophoresis:

  • Purpose: To separate DNA fragments by size.
  • Components: Agarose gel, buffer solution, power supply, loading dye, ethidium bromide or SYBR Safe (to visualize DNA).
  • Process: DNA is negatively charged and migrates toward the positive electrode (anode). Smaller fragments move through the gel pores faster and further than larger fragments.

Molecular Genetics (Central Dogma)

• DNA Replication: Semi-conservative process where DNA copies itself during the S phase.
• Transcription: The process of copying a gene's DNA sequence into a messenger RNA (mRNA) sequence inside the nucleus.
• Translation: The process where mRNA is read by ribosomes to assemble amino acids into a polypeptide chain (protein) in the cytoplasm.

Evolution and Natural Selection

• Natural Selection: The process whereby organisms better adapted to their environment tend to survive and produce more offspring.
  • Requires variation, heritability, and differential reproductive success.
• Evolution: A change in the frequency of alleles in a population over generations.
• Mutations: Changes in the DNA sequence; the ultimate source of genetic variation.
  • Point Mutation: A change in a single nucleotide.
  • Silent Mutation: No change in amino acid sequence.
  • Missense Mutation: Changes one amino acid.
  • Nonsense Mutation: Creates a premature stop codon.
  • Frameshift Mutation: Insertion or deletion that shifts the reading frame, altering all subsequent amino acids in the protein chain.