General Biology Lab Study Guide: Scientific Process, Microscopy, pH, Cells, and Membranes

Lab 1: Scientific Process

Introduction to the Scientific Method

The scientific method is a systematic approach used by scientists to explore observations, answer questions, and test hypotheses. Understanding its steps and terminology is fundamental to biological research.

• Scientific Method Steps: Observation, question, hypothesis, prediction, experiment, data collection, analysis, and conclusion.

• Hypothesis: A testable statement that explains an observation or answers a scientific question.

• Null Hypothesis: A statement that there is no effect or no difference; used as a default position for statistical testing.

• Prediction: A logical statement about what will happen if the hypothesis is correct.

• Variable: Any factor, trait, or condition that can exist in differing amounts or types.

• Independent Variable: The variable that is changed or controlled in a scientific experiment.

• Dependent Variable: The variable being tested and measured in an experiment.

• Qualitative Data: Descriptive data (e.g., color, texture).

• Quantitative Data: Numerical data (e.g., length, mass, volume).

Example: Testing the effect of sunlight on plant growth. The amount of sunlight is the independent variable; plant height is the dependent variable.

Experimental Design

• Controlled Experiment: An experiment in which only one variable is changed at a time, while all others are kept constant.

• Control Group: The group in an experiment that does not receive the experimental treatment and is used as a benchmark.

• Positive Control: A group where a known response is expected.

• Negative Control: A group where no response is expected.

Example: In a drug efficacy test, the positive control receives a drug known to work, while the negative control receives a placebo.

Lab 2: The Microscope and pH

Microscope Use and Principles

Microscopes are essential tools in biology for observing small objects and organisms. Understanding their parts and functions is crucial for laboratory work.

• Resolving Power: The ability of a microscope to distinguish two close objects as separate.

• Magnification: The process of enlarging the appearance of an object.

• Total Magnification: Calculated as the product of the magnification of the ocular lens and the objective lens.

Formula:

$\text{Total Magnification} = \text{Ocular Lens Magnification} \times \text{Objective Lens Magnification}$

• Field of View: The visible area seen through the microscope.

• Proper Use: Always start with the lowest magnification and use coarse focus before fine focus.

pH and Solutions

pH is a measure of the hydrogen ion concentration in a solution, indicating its acidity or alkalinity.

• pH Scale: Ranges from 0 (most acidic) to 14 (most basic), with 7 being neutral.

• Acidic Solution: pH < 7

• Basic (Alkaline) Solution: pH > 7

• Neutral Solution: pH = 7

• Relationship: $\text{pH} = -\log_{10}[\text{H}^+]$

• Buffer: A solution that resists changes in pH when acids or bases are added.

Example: Blood is buffered to maintain a pH around 7.4.

Lab 3: The Cell

Prokaryotic and Eukaryotic Cells

Cells are the basic units of life. They can be classified as prokaryotic or eukaryotic based on their structure.

• Prokaryotes: Cells without a nucleus (e.g., bacteria, cyanobacteria).

• Eukaryotes: Cells with a nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).

• Similarities: Both have cell membranes, cytoplasm, ribosomes, and genetic material.

• Differences: Eukaryotes have a nucleus and organelles; prokaryotes do not.

Example: Escherichia coli is a prokaryote; Homo sapiens cells are eukaryotic.

Cell Organelles and Their Functions

• Chloroplasts: Site of photosynthesis in plant cells.

• Mitochondria: Powerhouse of the cell; site of cellular respiration.

• Ribosomes: Synthesize proteins.

• Endoplasmic Reticulum (ER): Synthesizes and transports proteins and lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Central Vacuole: Stores water and maintains turgor pressure in plant cells.

• Plasmid: Small, circular DNA in prokaryotes.

• Cell Wall: Provides structure and protection (in plants, fungi, and some prokaryotes).

• Plasma Membrane: Regulates entry and exit of substances.

• Cytoplasm: Gel-like substance where cellular processes occur.

• Cytosol: The fluid portion of the cytoplasm.

Comparison Table: Prokaryotic vs. Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No	Yes
Organelles	No (except ribosomes)	Yes
Cell Wall	Yes (most)	Some (plants, fungi)
Size	Small (1-10 μm)	Larger (10-100 μm)

Lab 4: The Cell Membrane

Membrane Structure and Transport

The cell membrane is a selectively permeable barrier that controls the movement of substances in and out of the cell.

• Osmosis: The diffusion of water across a semi-permeable membrane.

• Diffusion: The movement of molecules from an area of higher concentration to lower concentration.

• Isotonic Solution: Solute concentration is equal inside and outside the cell; no net water movement.

• Hypotonic Solution: Lower solute concentration outside the cell; water enters the cell.

• Hypertonic Solution: Higher solute concentration outside the cell; water leaves the cell.

• Aquaporins: Channel proteins that facilitate water movement across the membrane.

• Endocytosis: Process by which cells take in substances by engulfing them in a vesicle.

• Exocytosis: Process by which cells expel substances using vesicles.

Example: Red blood cells placed in a hypotonic solution will swell and may burst due to water influx.

Osmosis and Tonicity Table

Solution Type	Effect on Animal Cell	Effect on Plant Cell
Isotonic	No net change	No net change
Hypotonic	Cell swells, may burst	Turgid (normal)
Hypertonic	Cell shrinks (crenates)	Plasmolyzed

Formula for Osmosis:

$\Psi = \Psi_s + \Psi_p$

Where $\Psi$ is water potential, $\Psi_s$ is solute potential, and $\Psi_p$ is pressure potential.

Example: The contractile vacuole in Paramecium expels excess water to prevent the cell from bursting in hypotonic environments.

Additional info: These study notes are based on a list of lab review questions and learning objectives for a General Biology course, covering foundational topics in scientific inquiry, microscopy, cell structure, and membrane transport.