General Biology: Core Concepts, Scientific Method, and Basic Chemistry Study Guide

Week 1: Core Comprehension Worksheet and Practice Problems

Introduction

This study guide covers foundational topics in General Biology, including the characteristics of life, the scientific method, cell structure, and basic chemistry relevant to biological systems. The content is organized to help students understand, recall, and apply key biological concepts.

Characteristics of Life

What Does It Mean to Say That Something is Alive?

• Definition: Living organisms share several fundamental characteristics that distinguish them from non-living matter.

• Key Characteristics:

  • Made of one or more cells

  • Ability to replicate (reproduce)

  • Process hereditary information (in the form of DNA)

  • Acquire and use energy (metabolism)

  • Capable of evolving (as a byproduct of replication and the presence of genes)

• Example: A bacterium is alive because it is cellular, can reproduce, and uses energy, while a virus is not considered alive as it cannot replicate without a host cell.

The Scientific Method

Steps and Terminology

• Experiment: A study where researchers test the effect of a well-defined factor on a particular phenomenon.

• Hypothesis: A testable statement that explains a phenomenon or a set of observations.

• Null Hypothesis: A hypothesis that specifies what the results will be if the main hypothesis being tested is not correct.

• Prediction: A measurable or observable result that must be correct if a hypothesis is valid.

• Control: Factors held constant throughout the experiment to ensure that results are due to the hypothesis being tested.

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

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

• Example: In Pasteur’s experiment testing spontaneous generation, the independent variable was whether the flask was open to air or not, and the dependent variable was whether cells appeared in the broth.

Hypothesis vs. Prediction

• Hypothesis: A proposed explanation for an observation, which can be tested by experimentation.

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

• Example: Hypothesis: "Cells arise from pre-existing cells." Prediction: "If broth is boiled and sealed, no cells will appear."

Cell Theory

Louis Pasteur’s Experiment

• Purpose: To test whether cells arise spontaneously or from pre-existing cells.

• Method: Broth was boiled in two types of flasks: one open to air, one with a swan-neck that prevented dust from entering.

• Results: Cells only appeared in the open flask, supporting the hypothesis that cells come from pre-existing cells.

• Conclusion: Spontaneous generation was not supported; life does not arise from non-living matter under these conditions.

Cells: Types and Components

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: Lack a nucleus; include bacteria and archaea.

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles; include animal, plant, fungi, and protist cells.

• Key Differences:

  • Prokaryotes: No nucleus, generally smaller, single-celled.

  • Eukaryotes: Nucleus present, larger, can be multicellular.

• Example: Animal and plant cells are eukaryotic; bacteria are prokaryotic.

Cell Organelles and Functions

• Nucleus: Contains genetic material (DNA).

• Ribosomes: Site of protein synthesis.

• Chloroplasts: Site of photosynthesis in plant cells.

• Mitochondria: Site of cellular respiration and energy production.

Biological Molecules and Chemistry

Atoms, Elements, and Molecules

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

• Atomic Number: Number of protons in an atom’s nucleus; defines the element.

• Atomic Mass: Sum of protons and neutrons in the nucleus.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Example: Carbon-12 has 6 protons and 6 neutrons; Carbon-14 has 6 protons and 8 neutrons.

Subatomic Particles

• Proton: Positive charge, found in the nucleus.

• Neutron: No charge, found in the nucleus.

• Electron: Negative charge, found in electron shells around the nucleus.

Electron Shells and Valence

• Electron Shell: Energy levels where electrons are found around the nucleus.

• Valence Electrons: Electrons in the outermost shell; determine chemical reactivity.

• Valence Number: Number of unpaired electrons in the outer shell.

Chemical Bonds

• Covalent Bond: Atoms share electron pairs.

• Polar Covalent Bond: Electrons are shared unequally due to differences in electronegativity.

• Nonpolar Covalent Bond: Electrons are shared equally.

• Ionic Bond: Electrons are transferred from one atom to another, creating charged ions.

• Example: Water (H2O) has polar covalent bonds; sodium chloride (NaCl) has ionic bonds.

Electronegativity

• Definition: The tendency of an atom to attract electrons in a chemical bond.

• Order (from highest to lowest): O > N > C ≈ H

• Application: In CO2, oxygen atoms have a partial negative charge due to higher electronegativity.

Scientific Variables and Graphing

Independent and Dependent Variables

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

• Dependent Variable: The variable that is measured or observed.

• Example: In a drug trial, the independent variable is the drug dosage, and the dependent variable is the observed effect (e.g., cell viability).

Types of Graphs

• Bar Chart: Used for categorical (discrete) data.

• Histogram: Used for continuous data, showing frequency distribution.

• Box-and-Whisker Plot: Shows the spread and variability of data.

• Scatterplot: Used to show relationships between two continuous variables.

Example Table: Cell Viability Data

The following table compares cell viability under different treatments:

Cell Line	Viability (No treatment)	Viability (100 nM Drug X)
Hepatocytes (Liver cells)	100%	50%
Neurons (Brain cells)	100%	10%

Macromolecules: DNA, RNA, and Proteins

Genetic Information Flow

• Central Dogma: Information flows from DNA → RNA → Protein.

• Gene: A segment of DNA that encodes a functional product, usually a protein.

• ATP: Adenosine triphosphate, the primary energy currency of the cell.

Atomic Structure and Bonding

Atomic Number and Mass

• Atomic Number (Z): Number of protons in the nucleus.

• Atomic Mass (A): Number of protons plus neutrons.

• Formula:

  • $\text{Atomic mass} = \text{Number of protons} + \text{Number of neutrons}$

Lewis Structures and Molecular Geometry

• Lewis Structure: Diagram showing the bonding between atoms and the lone pairs of electrons in a molecule.

• Example: Methane (CH4) has a central carbon atom bonded to four hydrogen atoms in a tetrahedral geometry.

Bonding in Carbon Compounds

• Carbon: Can form four covalent bonds, allowing for complex organic molecules.

• Hydrocarbon Chains: Nonpolar, hydrophobic; found in lipids.

• Functional Groups: Specific groups of atoms within molecules that have characteristic properties (e.g., hydroxyl, carboxyl, amino).

Summary Table: Subatomic Particles

Particle	Charge	Location
Proton	+1	Nucleus
Neutron	0	Nucleus
Electron	-1	Electron shells

Scientific Method: Application and Analysis

• Designing Experiments: Identify variables, controls, and ensure repeatability.

• Data Interpretation: Use appropriate graphs and statistical analysis to interpret results.

• Drawing Conclusions: Compare results to predictions and hypotheses; consider alternative explanations.

Key Equations and Definitions

• Atomic Mass: $\text{Atomic mass} = \text{Number of protons} + \text{Number of neutrons}$

• Central Dogma: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

Additional info:

• Some context and definitions have been expanded for clarity and completeness.

• Tables and examples have been inferred and formatted for study purposes.