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BIO 121 Lab Midterm Review: Key Concepts and Applications

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Scientific Method

Understanding and Applying the Scientific Method

The scientific method is a systematic approach used in biology to investigate observations, solve problems, and test hypotheses. Mastery of this process is essential for designing experiments and interpreting results.

  • Steps of the Scientific Method:

    1. Observation: Noticing and describing phenomena in a detailed manner.

    2. Question: Formulating a question based on observations.

    3. Hypothesis: Proposing a testable explanation or prediction.

    4. Experiment: Designing and conducting controlled tests to evaluate the hypothesis.

    5. Data Collection: Gathering and recording results from the experiment.

    6. Analysis: Interpreting data to determine if it supports or refutes the hypothesis.

    7. Conclusion: Drawing conclusions and communicating findings.

  • Application: Each step should be logically connected, and experiments must include controls and replicates for reliability.

  • Example: Testing the effect of light on plant growth by comparing plants grown in light versus darkness.

Metric System

Using and Converting Metric Units

The metric system is the standard system of measurement in science, based on units of ten. Understanding conversions is crucial for accurate data collection and analysis.

  • Common Units: meter (m), liter (L), gram (g)

  • Prefixes: kilo- (103), centi- (10-2), milli- (10-3)

  • Conversion Example: To convert millimeters (mm) to centimeters (cm):

    • 1 cm = 10 mm

    • Thus, 25 mm = 2.5 cm

  • Formula:

pH and Buffers

Understanding pH, Standard Curves, and Buffer Function

pH measures the hydrogen ion concentration in a solution, indicating its acidity or alkalinity. Buffers are substances that minimize changes in pH when acids or bases are added.

  • Standard Curve: A graph plotting known pH values against a measurable property (e.g., color intensity). Used to determine the pH of unknown solutions by comparison.

  • How Buffers Work: Buffers absorb excess H+ or OH- ions, maintaining a stable pH.

  • Importance: Buffers are essential in biological systems to maintain optimal conditions for enzyme activity and cellular processes.

  • Example: The bicarbonate buffer system in blood helps maintain pH around 7.4.

  • Equation:

Biological Molecules

Organic vs. Inorganic Molecules and Biochemical Assays

Biological systems contain both organic (carbon-based) and inorganic molecules. Identifying and understanding these molecules is fundamental in biology.

  • Organic Molecules: Contain carbon and hydrogen; examples include carbohydrates, proteins, lipids, and nucleic acids.

  • Inorganic Molecules: Do not contain both carbon and hydrogen; examples include water (H2O), salts, and minerals.

  • Biochemical Assays:

    • Reducing Sugars: Benedict's test (positive result: color change from blue to orange/red).

    • Starch: Iodine test (positive result: blue-black color).

    • Proteins: Biuret test (positive result: violet color).

    • Lipids: Sudan III or brown paper test (positive result: red-stained oil droplets or translucent spot).

  • Basic Structure of an Amino Acid:

    • Central carbon (α-carbon)

    • Amino group (–NH2)

    • Carboxyl group (–COOH)

    • Hydrogen atom

    • R group (side chain, varies among amino acids)

  • Functions of Proteins:

    • Enzymatic catalysis (e.g., amylase)

    • Structural support (e.g., collagen)

    • Transport (e.g., hemoglobin)

    • Defense (e.g., antibodies)

    • Signaling (e.g., hormones)

Microscopy

Parts and Functions of the Compound Light Microscope

The compound light microscope is a key tool for observing cells and tissues. Understanding its parts and their functions is essential for proper use.

  • Major Parts:

    • Ocular lens (eyepiece): Magnifies the image, usually 10x.

    • Objective lenses: Provide additional magnification (e.g., 4x, 10x, 40x, 100x).

    • Stage: Holds the slide in place.

    • Coarse and fine focus knobs: Adjust the focus of the image.

    • Light source: Illuminates the specimen.

    • Condenser: Focuses light onto the specimen.

    • Diaphragm: Controls the amount of light passing through the specimen.

    • Arm and base: Provide support and stability.

  • Proper Use: Always start with the lowest power objective and use coarse focus first, then fine focus.

Cell Structure

Comparing Plant and Animal Cells

Plant and animal cells share many features but also have distinct differences. Recognizing these is important for cell identification and understanding function.

  • Similarities:

    • Both are eukaryotic (have a nucleus and membrane-bound organelles).

    • Contain mitochondria, endoplasmic reticulum, Golgi apparatus, and cytoplasm.

  • Differences:

    Feature

    Plant Cell

    Animal Cell

    Cell Wall

    Present (cellulose)

    Absent

    Chloroplasts

    Present (photosynthesis)

    Absent

    Central Vacuole

    Large, central

    Small or absent

    Shape

    Usually rectangular

    Usually round or irregular

    Lysosomes

    Rare

    Common

  • Identification: Plant cells can be identified by the presence of a cell wall, chloroplasts, and a large central vacuole in images or drawings.

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