bio lab exam review

  1. Measurement & Standard Curve

    KEY FORMULAS

    • C1V1 = C2V2 (Dilution formula for making solutions)

      • C1 = initial concentration, V1 = initial volume

      • C2 = final concentration, V2 = final volume

      • Units for concentration must be consistent (e.g., M, \text{mg/mL} ) and units for volume must be consistent (e.g., L, mL).

    • Percent Error:
      \text{Percent Error} = \frac{|\text{Observed} - \text{Expected}|}{\text{Expected}} \times 100

      • Used to measure the accuracy of an experimental value compared to a known or theoretical value.

    STANDARD CURVE BASICS

    • Used to determine unknown concentrations from absorbance values. Based on the Beer-Lambert Law.

    HOW TO READ THE GRAPH

    • X-axis = Concentration (e.g., \text{mg/mL}, \mu M )

    • Y-axis = Absorbance (unitless)

    • Should be a straight line (Beer-Lambert Law applies to dilute solutions). Deviations indicate the law is no longer applicable (e.g., concentrated solutions).

    • Equation format:
      y = mx + b

      • y represents absorbance, x represents concentration.

      • m is the slope (extinction coefficient related), b is the y-intercept (ideally zero, but can represent background absorbance).

      • Plug your absorbance into y

      • Solve for x (your unknown concentration)

    • Example:
      If your absorbance is 0.45 and the standard curve is
      y = 0.8x + 0.1
      Set 0.45 = 0.8x + 0.1 \rightarrow \text{solve for x} . ( x = \frac{0.45 - 0.1}{0.8} = \frac{0.35}{0.8} = 0.4375 \text{ units} )

  2. Enzymes

    KEY CONCEPTS

    • Enzymes are biological catalysts that lower activation energy of reactions, speeding them up without being consumed.

    • Affected by temperature, pH, and substrate concentration.

      • Temperature: Each enzyme has an optimal temperature. Too high causes denaturation (loss of 3D structure and function). Too low slows reaction rate but doesn't usually denature.

      • pH: Each enzyme has an optimal pH. Deviations from optimal pH can alter enzyme shape and charge, leading to denaturation or reduced activity.

      • Substrate concentration: As substrate concentration increases, reaction rate increases until all enzyme active sites are saturated.

    Graphs You Must Know

    1. Rate vs. Substrate Concentration

      • Increases then plateaus (saturation).

      • The plateau represents the V_{max} (maximum reaction rate) when all enzyme active sites are occupied.

    2. Rate vs. Temperature

      • Bell curve \rightarrow too hot = denaturation.

      • Shows an optimal temperature where enzyme activity is highest.

    3. Rate vs. pH

      • Bell curve \rightarrow optimal pH peak.

      • Shows an optimal pH where enzyme activity is highest.

    4. Michaelis-Menten (if covered)
      V = \frac{V{\text{max}} [S]}{Km + [S]}

      • V is the reaction velocity, V_{max} is the maximum reaction velocity.

      • [S] is the substrate concentration.

      • Km (Michaelis constant) is the substrate concentration at which the reaction velocity is half of V{max}. A low K_m indicates high enzyme affinity for the substrate.

  3. Forensic Biology + Bioinformatics (1 & 2)

    Electrophoresis

    • DNA flows negative \rightarrow positive (DNA is acidic due to negatively charged phosphate groups).

    • Shorter fragments move farther down the gel (e.g., agarose or polyacrylamide gel matrix) because they encounter less resistance.

    Reading a Gel

    • Lanes = individuals/samples.

    • Compare band patterns to a DNA ladder/marker (fragments of known size).

    • Match band patterns to determine:

      • identity

      • paternity

      • crime scene match

    • Restriction Enzymes

      • Cut DNA at specific sequences (recognition sites).

      • More cuts \rightarrow more/smaller fragments on gel. Often used to create DNA fingerprints (RFLPs).

    BLAST basics

    • Used to identify unknown DNA sequences by comparing them to known sequences in a database (Basic Local Alignment Search Tool).

    • Know:

      • Query sequence: The unknown sequence you are searching with.

      • E-value (Expectation Value): Represents the number of hits you would expect to see by chance when searching a database of this size. Small = good (low probability that the match is random).

      • Percent identity: The extent to which two sequences are the same.

      • Coverage: How much of the query sequence aligns with the database sequence.

  4. Cell Division (Mitosis & Meiosis)

    Graph You MUST Recognize

    • Time spent in each phase graph:

      • Usually a pie chart or bar graph.

      • Interphase = longest, most cells will be there.

      • Details: Interphase consists of G1 (cell growth), S (DNA synthesis/replication), and G2 (further growth, preparation for mitosis). Mitosis (M phase) is typically much shorter.

    Chromosome Count

    • Mitosis: 2 identical diploid cells

      • Details: Somatic cells divide to produce two daughter cells genetically identical to the parent cell. Chromosome number remains the same (2n).

    • Meiosis: 4 genetically unique haploid gametes

      • Details: Occurs in germline cells to produce gametes (sperm/egg) with half the number of chromosomes (n). Involves two rounds of division (Meiosis I and Meiosis II) and introduces genetic variation through crossing over and independent assortment.

  5. Cellular Respiration

    FORMULAS

    • Overall:
      \text{C6H12O6} + 6O2 \rightarrow 6CO2 + 6H_2O + \text{ATP}

      • Details: This is the aerobic respiration equation, summarizing the breakdown of glucose in the presence of oxygen to produce ATP, carbon dioxide, and water.

    • ATP yields:

      • Glycolysis: 2 ATP (net) - occurs in cytoplasm, produces pyruvate.

      • Krebs (Citric Acid Cycle): 2 ATP (from 1 glucose) - occurs in mitochondrial matrix.

      • ETC (Electron Transport Chain) and Oxidative Phosphorylation: \sim 28 \text{ ATP} - occurs on inner mitochondrial membrane, uses oxygen as final electron acceptor.

      • \sim 32 \text{ ATP} total (can vary based on shuttle systems for NADH).

    Graphs You’ll See

    • Oxygen consumption vs. time

      • Higher slope = higher metabolic rate.

      • Details: Increased oxygen consumption directly correlates with increased aerobic respiration rates. Often observed in respirometers.

    • CO_2 production vs. time

      • Steeper line = more respiration.

      • Details: CO_2 is a byproduct of cellular respiration (e.g., in pyruvate oxidation and Krebs cycle), so its production rate indicates respiration activity.

    • How to interpret:

      • More oxygen consumed = higher cellular respiration.

  6. Photosynthesis

    FORMULA

    6CO2 + 6H2O \rightarrow \text{C6H12O6} + 6O_2

    • Details: This summarizes the process where plants convert light energy into chemical energy (glucose) using carbon dioxide and water, releasing oxygen as a byproduct. Occurs in chloroplasts.

    Key Graphs

    1. Rate vs Light Intensity

      • Increases then plateaus.

      • Details: Up to a certain point, more light means a faster rate of photosynthesis. The plateau occurs when another factor (like CO_2 concentration or enzyme availability) becomes limiting.

    2. Rate vs CO_2 Concentration

      • Increases then plateaus.

      • Details: Similar to light intensity, increasing CO_2 concentration boosts photosynthetic rate until another factor becomes limiting.

    3. Rate vs Wavelength (Action Spectrum)

      • Peaks at blue and red wavelengths.

      • Lowest at green wavelengths.

      • Details: This graph shows the effectiveness of different light wavelengths in driving photosynthesis. Chlorophylls primarily absorb blue and red light, reflecting green light, which is why plants appear green.

  7. Gene Expression & Regulation

    Lac Operon (Common test question)

    • ON when lactose present AND glucose low.

      • Details: Lactose acts as an inducer, binding to the repressor and removing it from the operator. Low glucose levels lead to high cAMP, which binds to CAP, activating transcription. This ensures the cell only produces enzymes for lactose metabolism when lactose is available and a more preferred energy source (glucose) is scarce.

    • OFF when glucose present (even if lactose is present).

      • Details: Glucose is the preferred energy source. High glucose levels lead to low cAMP, so CAP does not activate transcription efficiently, even if lactose is present.

    Graphs

    • \beta-galactosidase activity vs. lactose concentration (or time after addition).

    • Expression is highest when lactose is added (and glucose is absent/low).

      • Details: Graph will show low or no activity without lactose, and then a significant increase in activity after lactose induction, especially if glucose is not available.

    DNA \rightarrow RNA \rightarrow Protein (Central Dogma of Molecular Biology)

    • Transcription \rightarrow Translation

      • Transcription: DNA sequence is copied into an mRNA molecule by RNA polymerase in the nucleus (eukaryotes) or cytoplasm (prokaryotes).

      • Translation: mRNA sequence is used as a template to synthesize a protein by ribosomes in the cytoplasm. Involves tRNAs carrying specific amino acids.

  8. Heredity (Punnett Squares, Probability)

    Formulas

    • Probability: multiply independent events.

      • Example: Aa \times Aa \rightarrow chance of aa is \frac{1}{4} (from (1/2 A, 1/2 a) for each parent, so (1/2 a) * (1/2 a) = 1/4).

      • Details: When calculating the probability of two or more independent events occurring together, multiply their individual probabilities.

    • Chi-square formula: \chi^2 = \sum \frac{(O - E)^2}{E}

      • Used to test if data fits Mendelian ratios.

      • Details: O = observed value, E = expected value. A low \chi^2 value suggests that the observed results are close to the expected results, indicating the null hypothesis (e.g., data fits Mendelian ratios) should not be rejected. Requires calculating degrees of freedom and comparing to a critical value from a chi-square table.

    Ratios to Recognize

    • Monohybrid: 3:1 (phenotypic ratio for a cross between two heterozygotes, e.g., Tt x Tt).

    • Dihybrid: 9:3:3:1 (phenotypic ratio for a cross between two double heterozygotes for two unlinked genes, e.g., TtRr x TtRr).

      • Details: These ratios are fundamental to Mendelian genetics and indicate complete dominance for the genes involved.

  9. Microscopy

    Key Concepts

    • Magnification: The ability to enlarge an image. Total magnification = (objective lens magnification) \times (ocular lens magnification).

    • Resolution: The ability to distinguish between two separate points. Higher resolution means clearer detail.

    • Field of View: The bright circular area seen through the eyepiece. As magnification increases, field of view decreases.

    • Depth of Field: The vertical distance that remains in focus at one time. As magnification increases, depth of field decreases.

    Types of Microscopes (briefly)

    • Compound Light Microscope: Uses light and multiple lenses to magnify samples. Good for live samples, relatively inexpensive.

    • Electron Microscope (TEM/SEM): Uses electrons instead of light, providing much higher magnification and resolution. Samples must be dead, dehydrated, and often coated.

    How to Use/Read

    • Always start with the lowest power objective lens.

    • Adjust light (diaphragm, illuminator) for optimal contrast.

    • For higher magnification, use fine adjustment knob only.

  10. Scientific Method & Experimental Design

    Steps of Scientific Method

    1. Observation: Noticing phenomena.

    2. Question: Asking why or how.

    3. Hypothesis: A testable explanation (If…then…). They are usually framed to be falsifiable.

      • Null hypothesis (H_0): States no significant difference or effect.

      • Alternative hypothesis (H_1): States there is a significant difference or effect.

    4. Experimentation: Designing and conducting tests to prove or disprove the hypothesis.

    5. Data Analysis: Interpreting results, often involving statistical tests.

    6. Conclusion: Accepting or rejecting the hypothesis based on data. Conclusions should be supported by evidence.

    Experimental Design

    • Independent Variable (IV): The factor that is manipulated or changed by the experimenter (cause). Plotted on the X-axis.

    • Dependent Variable (DV): The factor that is measured or observed; it responds to changes in the independent variable (effect). Plotted on the Y-axis.

    • Control Group: A group in an experiment or study that does not receive treatment by the researchers and is then used as a benchmark to measure how the other tested subjects do. Essential for comparison.

    • Constants: Factors that are kept the same in all groups to ensure only the independent variable is affecting the dependent variable.

    • Repeated Trials/Replicates: Multiple measurements or experiments to ensure reliability and reduce the impact of random errors.

    • Sampling Size: Larger sample sizes generally lead to more statistically significant and reliable results.

    Data Interpretation

    • Identify trends, relationships, and anomalies in data.

    • Understand the meaning of measures of central tendency (mean, median, mode) and variability (standard deviation, range).

    • Be able to interpret simple statistical tests (e.g., p-values related to the chi-square test; a p-value < 0.05 often indicates a statistically significant difference).