General Biology: Laboratory Tools, Scientific Method, Organic Molecules, Microscopy, and Cell Structure

Metric System and Unit Conversions

Metric Prefixes and Conversions

The metric system uses prefixes to indicate multiples or fractions of base units. Understanding these prefixes is essential for accurate measurement and conversion in biology.

• Kilo-: $10^3$

• Centi-: $10^{-2}$

• Milli-: $10^{-3}$

• Micro-: $10^{-6}$

• Nano-: $10^{-9}$

Example 1: Convert 1 kilometer (km) to millimeters (mm). $1\ \text{km} = 1,000,000\ \text{mm}$ This is a difference of $10^6$, so move the decimal point 6 places to the right.

Example 2: Convert 1 cm to meters. $1\ \text{cm} = 0.01\ \text{m}$ This is a difference of $10^{-2}$, so move the decimal point 2 places to the left.

Temperature Reference: 0°C is freezing, 100°C is boiling.

Laboratory Equipment for Measuring Volume

Common Laboratory Glassware

• Beakers: Used for rough measurements of volume. They are useful for holding and mixing liquids and come in different capacities. Not highly precise.

• Graduated Cylinders: Used for more precise liquid volume measurement. They come in different sizes and have graduation marks for accuracy.

• Dropper/Transfer Pipettes: Disposable pipettes used to transfer small amounts of liquid. They are not highly accurate but useful for moving drops between containers. Capacity usually ranges from 1 to 3 mL.

• Micropipettes: Used for very small volumes, typically in microliters (μL). They are used with microcentrifuge tubes and require proper technique to avoid contamination.

The Process of Science

Scientific Method and Variables

The scientific method is a systematic approach to answering questions about the natural world.

• Observation: Asking questions about phenomena (e.g., "What causes this? How does this work?").

• Hypothesis: An educated guess or proposed explanation for an observation.

• Scientific Theory: A hypothesis that has been repeatedly tested and supported by evidence. Theories are widely accepted but can be disproven with new evidence.

• Independent Variable: The variable that is manipulated to observe its effect.

• Dependent Variable: The variable that is measured; it is affected by the independent variable.

• Standardized (Constant) Variables: Variables that are kept the same across all experimental groups.

Atoms, Molecules, and Organic Compounds

Basic Chemical Concepts

• Atoms: The basic building blocks of matter.

• Protons: Determine the element; the atomic number is the number of protons.

• Molecule: Contains two or more atoms bonded together.

Organic Molecules and Functional Groups

• Organic Molecules: Contain a carbon backbone with hydrogen, oxygen, and other atoms. Examples include carbohydrates, lipids, proteins, and nucleic acids. These are also called biomolecules.

• Functional Groups: Specific groups of atoms within molecules that have characteristic properties. They are important in hydrolysis (breaking down) and synthesis (building up) of biomolecules.

Polarity and Solubility

• Polar/Ionic Molecules: Have positive and negative charges in certain areas and will easily dissolve in water.

• Nonpolar Molecules: Repelled by water and will not dissolve in it, but will dissolve in nonpolar liquids like oil.

Electrolytes, Acids, Bases, and pH

• Electrolytes: Substances that release ions in water and can conduct electricity.

• Acid: Releases hydrogen ions (H+) in water.

• Base: Releases hydroxide ions (OH-) in water.

• pH Scale: Measures hydrogen ion concentration; ranges from 0 (acidic) to 14 (basic). Each number represents a tenfold difference in H+ concentration.

Biological Tests for Organic Molecules

Common Reagents and Their Uses

Test	Purpose	Positive Result
Benedict's Solution	Tests for reducing sugars	Color change from clear blue to pale green to orange-brown (glucose turned orange, starch turned green)
Iodine Potassium Iodide (IKI)	Tests for polysaccharides (starch)	Color change from yellow-orange to deep blue-black (starch turned dark purple)
Biuret Reagent sodium hydroxide followed by copper sulfate	Tests for proteins	Color change from clear blue to violet (albumen changed)
Sudan IV	Tests for lipids	Lipid dissolves and stains deep red (corn oil changed)

• Electrolyte Test: Salt and baking soda produce bright light; lemon juice produces dim light.

• Solubility: Most substances tested were soluble except cornstarch.

• pH: Lemon juice was acidic; other substances were basic.

Microscopy

Types of Microscopes and Their Functions

• Microscope: An instrument used to view small objects not visible to the naked eye.

• Resolution: The ability to distinguish two points as separate; also called resolving power.

• Reflected Illumination: Light is reflected from above the object.

• Transmitted Illumination: Light passes through the object from below.

Types of Microscopes

• Stereomicroscope: Simple lens for low magnification (up to 50x).

• Compound (Light) Microscope: Uses multiple lenses and transmitted light. Magnification ranges from 40x to 1,500x. Objects must be very small or thin.

• Electron Microscope (EM): Uses a beam of electrons for very high magnification (hundreds of thousands to over 1,000,000x) and resolution (down to 2 nm). Used for detailed surface and internal structure studies.

Parts of the Microscope

• Condenser: Located on top of the iris diaphragm; focuses light onto the specimen.

Cell Structure and Types

Common Features of All Cells

• Cell (Plasma) Membrane: A lipid bilayer that encloses the cell, providing shape, support, and regulating the passage of substances.

• Ribosomes: Small structures that synthesize proteins.

• Cytoplasm: Semi-liquid substance containing water, dissolved molecules, gases, and organelles.

• DNA: The genetic material that holds the instructions for cell function and reproduction.

• Proteins: Essential molecules for structure, energy storage, and biochemical reactions.

Types of Cells

• Prokaryotic Cells:

  • Typically very small

  • Very little internal structure

  • Usually have a cell wall

  • No nucleus; DNA is not enclosed in a membrane

  • Almost all are unicellular

  • no membrane-bound organelles

  • tend to cluster

• Eukaryotic Cells:

  • Larger and more complex

  • Many membrane-bound organelles (e.g., mitochondria, Golgi apparatus)

  • All protists, plant and animal cells are eukaryotic

  • DNA is enclosed in a nuclear membrane

  • Can be unicellular or multicellular

Animal Cell Organelles (as shown in diagram)

• Cell membrane

• Nuclear membrane

• Nucleolus

• Nucleoplasm

• Chromatin

• Centrioles

• Cytosol

• Microvilli

• Cilia

• Ribosomes

• Rough endoplasmic reticulum

• Smooth endoplasmic reticulum

• Golgi apparatus

• Mitochondria

• Vesicle

• Lysosome (hydrolytic enzymes)

• Peroxisome (catalase or peroxidase enzyme)

Example: Mitochondria are the site of cellular respiration, converting glucose into ATP (energy).

Additional info: The notes and diagram focus on animal cell organelles, but plant cells share many of these structures and also contain chloroplasts, a large central vacuole, and a cell wall.