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General Biology Lab Exam Key Concepts

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  • Accuracy vs. Precision

    Accuracy means close to the correct value.
    Precision means results are close/repeatable.
    Ideal results are both accurate and precise.

  • Graduated Cylinder

    Used to measure liquid volume.

  • Micropipette Usage

    Use the smallest appropriate micropipette for better precision.
    P-10: 1–10 µL, P-100: 10–100 µL, P-1000: 100–1000 µL.

  • Unit Conversion: mL to µL

    1 mL = 1000 µL

  • Water Density

    Water density is approximately 1 g/mL, so 5 mL water weighs 5 g.

  • Meniscus Reading

    Read the bottom of the meniscus at eye level for accurate volume measurement.

  • Percent Error Formula

    \(\%Error=\frac{|Experimental-Accepted|}{Accepted}\times100\)

  • Total Magnification of Compound Microscope

    \(Total\ Magnification=Ocular\times Objective\)
    Ocular lens is 10×; multiply by objective lens.

  • Difference between Compound and Dissecting Microscope

    Compound: light from below, thin specimens, 2D image.
    Dissecting: light reflects off, thick specimens, 3D image.

  • Spectrophotometer Measures

    Measures absorbance or transmittance of light by a sample.

  • λmax in Spectrophotometry

    Wavelength where absorbance is highest.

  • Color Absorption and Transmission

    The color you see is the color transmitted, not absorbed.
    Example: Purple solution absorbs green light (~490–570 nm).

  • Four Major Biological Macromolecules

    Carbohydrates, Lipids, Proteins, Nucleic acids.

  • Qualitative vs Quantitative Tests

    Qualitative: Is it there? (color change)
    Quantitative: How much is there? (numerical value)

  • Sudan IV Test

    Detects lipids; positive result is red-orange or greasy translucent spot.

  • I2KI Test

    Detects starch; positive result is blue-black or dark purple color.

  • Biuret Test

    Detects proteins by peptide bonds; positive result is purple color.

  • Diffusion

    Movement of solute from high to low concentration.

  • Osmosis

    Movement of water across a selectively permeable membrane toward higher solute concentration.

  • Tonicity: Hypotonic Solution

    Less solute outside; water enters cell.
    Animal cells may lyse; plant cells become turgid.

  • Tonicity: Hypertonic Solution

    More solute outside; water leaves cell.
    Animal cells crenate; plant cells plasmolyze.

  • Dialysis Tubing Cutoff

    Substances smaller than 13,000 Da can cross; glucose and iodine cross, starch and albumin do not.

  • Sodium-Potassium Pump

    Moves Na⁺ out and K⁺ in; requires ATP to maintain ion gradients.

  • Dilution Formula

    \(C_1V_1=C_2V_2\)
    Used to calculate concentrations after dilution.

  • BSA Standard Curve Equation

    \(y=mx+b\)
    y = absorbance, x = concentration.

  • Calculate Unknown Concentration from Standard Curve

    \(x=\frac{y-b}{m}\)
    Plug in absorbance (y) to find concentration (x).

  • % Solution (w/v) Formula

    \(\%=\frac{grams}{mL}\times100\)
    Grams of solute per 100 mL solution.

  • Water Quality: TDS and Hardness

    TDS = total dissolved solids; Hardness mainly from calcium and magnesium ions.