Scientific Method

Steps of the Scientific Method

The scientific method is a systematic approach used in scientific investigation to acquire new knowledge or correct and integrate previous knowledge.

• Hypothesis Formation: Developing a testable statement or prediction based on observations.

• Data Collection: Gathering information through observation or experimentation.

• Hypothesis Testing: Conducting experiments to determine if the hypothesis is supported.

• Reviewing Scientific Literature: Before starting an experiment, researchers should review existing scientific literature to ensure the experiment has not already been performed.

Key Terms:

• Independent Variable: The variable that is manipulated or changed in an experiment.

• Dependent Variable: The variable that is measured or observed in response to changes in the independent variable.

• Control Variable: The variable that is kept constant to serve as a baseline for comparison.

Example: In a plant growth experiment, the amount of sunlight (independent variable) is changed, plant height (dependent variable) is measured, and soil type (control variable) is kept the same.

Scientific Notation and Metric Conversions

Scientific Notation

Scientific notation is a way to express very large or very small numbers using powers of ten.

• Format: , where a is a number between 1 and 10, and n is an integer.

• Example: 1234.95 becomes .

Metric Conversions

The metric system is based on powers of ten and uses standard prefixes.

• Length: 1 meter (m) = 100 centimeters (cm) = 1000 millimeters (mm)

• Mass: 1 kilogram (kg) = 1000 grams (g) = 1,000,000 milligrams (mg)

• Volume: 1 liter (L) = 1000 milliliters (mL) = 1000 cubic centimeters (cm3)

Example Conversions:

• 3.9 meters = 390 centimeters

• 22.4 liters = 22,400 milliliters

• 85.08 grams = 0.08508 kilograms

Metric Measurements and Density

Metric Prefixes and Units

• Centi- (c): 0.01

• Milli- (m): 0.001

• Kilo- (k): 1000

Volume Measurement

• Water Displacement: Used to measure the volume of irregularly shaped objects by noting the change in water level.

• 1 mL = 1 cm3: This equivalence is important in laboratory measurements.

Density

• Definition: Density is mass per unit volume.

Formula:

• Objects with density less than water (1 g/mL) will float; those with greater density will sink.

Microscopy

Parts and Functions of the Microscope

• Objective Lens: The lens closest to the specimen; provides primary magnification.

• Ocular Lens: The eyepiece through which you view the specimen.

• Coarse Focus Knob: Used for large adjustments in focus; moves the stage up and down.

• Fine Focus Knob: Used for small, precise adjustments in focus.

• Condenser: Regulates the amount of light entering the microscope.

• Working Distance: The distance between the objective lens and the specimen when in focus.

Microscope Types and Magnification

• Compound Microscope: Used for viewing small, thin specimens at high magnification.

• Dissecting Microscope: Used for viewing larger, three-dimensional specimens at lower magnification.

• Transmission Electron Microscope (TEM): Provides the highest magnification (up to 1,000,000x) and is used to view internal structures of cells.

Microscope Usage

• The image seen through a microscope is inverted compared to the original orientation.

• The field of view decreases as magnification increases.

Cell Structure

Prokaryotic vs. Eukaryotic Cells

• Prokaryotes: Lack a nucleus; have a peptidoglycan cell wall (e.g., bacteria).

• Eukaryotes: Have a nucleus and membrane-bound organelles (e.g., plant and animal cells).

Cell Components

• Nucleus: Contains genetic material; found in eukaryotic cells.

• Cell Wall: Provides structure; present in plant cells and prokaryotes, but not in animal cells.

• Flagella: Long, whip-like structures for locomotion (e.g., sperm cells).

• Cytoplasm: Gel-like substance filling the cell interior.

• Rough Endoplasmic Reticulum (RER): Studded with ribosomes; site of protein synthesis.

• Peroxisomes: Organelles containing enzymes for breaking down fatty acids and detoxification.

Basic Chemistry for Biology

Atoms, Molecules, and Compounds

• Atom: The smallest unit of an element that retains its properties.

• Molecule: Two or more atoms bonded together.

• Compound: A molecule containing two or more different elements.

Atomic Structure

• Atomic Number: Number of protons in an atom.

• Atomic Mass Number: Total number of protons and neutrons.

Solutions and Solvents

• Solution: A uniform mixture of two or more substances.

• Solvent: The substance in which the solute dissolves; water is known as the universal solvent.

• Electrolyte: A substance that conducts electricity when dissolved in water.

Acids, Bases, and pH

pH Scale

• pH: A measure of hydrogen ion concentration; scale ranges from 0 (acidic) to 14 (basic).

• Acids: Substances that donate hydrogen ions (H+).

• Bases: Substances that accept hydrogen ions or release hydroxide ions (OH-).

• Buffers: Substances that minimize changes in pH.

Example: A substance with pH 5 is acidic; adding a buffer can increase its pH to 6, making it less acidic.

Organic Molecules and Biological Tests

Types of Organic Molecules

• Carbohydrates: Simple sugars and starches; tested with Benedict's test (positive result: color change).

• Proteins: Chains of amino acids joined by peptide bonds; tested with Biuret reagent (positive result: pink color).

• Lipids: Fats and oils; tested with water solubility or other reagents.

Testing for Organic Molecules

• Benedict's Test: Detects simple sugars; requires heating.

• Biuret Test: Detects proteins; positive result is a pink or purple color.

• Iodine Test: Detects starch; positive result is a blue-black color.

Summary Table: Key Laboratory Measurements and Conversions