Chek Yo Delf Ultimate Study Guide

The Scientific Method and Experimental Design

• Sequential Process of the Scientific Method:

  • 1. Observe: Notice details and collect information about natural phenomena. Observations can be qualitative (describing qualities such as color, texture, or appearance) or quantitative (involving precise measurements or numerical counts).

  • 2. Ask a Question: Formulate a clear question directly based on the observation made.

  • 3. Form a Hypothesis: Propose a tentative explanation that can be tested through experimentation and possesses the potential to be proven false. Hypotheses must be specific and measurable. For example, "Fertilized plants will grow taller" is a valid hypothesis because height is measurable, whereas "Fertilized plants will grow better" is too vague unless "better" is explicitly defined.

  • 4. Predict: State what should specifically happen during testing if the hypothesis is correct.

  • 5. Design and Repeat an Experiment: Conduct rigorous testing to evaluate the hypothesis. Executing only a single trial is insufficient for producing reliable scientific results; experiments must be repeated.

  • 6. Collect and Analyze Data: Gather experimental measurements and display them systematically using tables (to organize raw values) and graphs (to reveal underlying patterns).

  • 7. Draw a Conclusion: Explicitly state whether the collected empirical data supports or refutes the hypothesis. Scientific conclusions are tentative and subject to revision when new evidence appears.

• Scientific Theory:

  • Definition: A comprehensive explanation supported by a broad body of repeated scientific evidence across multiple studies.

  • Nature: A scientific theory is not a simple everyday "guess"; it must remain open to continuous empirical testing and potential modification or revision.

• Experimental Design and Variables (Plant Growth Example):

  • Experimental Group: The subjects receiving the specific treatment being tested (e.g., Plant A, which receives fertilizer).

  • Control Group: The baseline subjects that do not receive the experimental treatment, providing a standard of comparison (e.g., Plant B, which receives no fertilizer).

  • Independent Variable: The single factor intentionally manipulated by the researcher (e.g., the presence or absence of fertilizer).

  • Dependent Variable: The outcome or variable being measured to determine the treatment's effect (e.g., plant height or total growth).

  • Controlled Variables: All environmental conditions kept strictly identical across both experimental and control groups so that fertilizer is the only variable tested (e.g., plant species, pot size, soil composition, water volume, light exposure, and ambient temperature).

• Reading Data and Formulating Inferences:

  • Quantitative Findings from Plant Experiment: Plant A (fertilizer treated) grew from $10\,\text{cm}$ to $68\,\text{cm}$. Plant B (control) grew from $7\,\text{cm}$ to $45\,\text{cm}$. The data directly supported the hypothesis that fertilizer causes plants to grow taller.

  • Stated Fact vs. Inference: A stated fact is a value or condition copied or counted directly from a data table (e.g., "Group 1 received $12\,\text{hours}$ of light per day"). An inference is an evidence-based logical deduction (e.g., "light exposure affects plant growth").

  • Light Duration Experiment Findings: Plants exposed to $12\,\text{hours}$ of light per day produced the greatest number of leaves, achieved the greatest overall height, and had the highest survival rate after $30\,\text{days}$ compared to groups receiving less light or no light.

Atomic Structure, Elements, and Energy Levels

• Elements, Atoms, and the Periodic Table:

  • Periodic Table: Lists pure chemical elements, not molecules. Originally created by Dmitry Mendeleev, it has been updated continuously as new elements and data are discovered.

  • Atom: The smallest basic unit of an element that retains the distinct chemical identity of that element.

  • Molecules: Chemical combinations of two or more bonded atoms. For example, carbon dioxide ($\text{CO}_2$) consists of $1$ carbon atom and $2$ oxygen atoms.

  • Central Role of Carbon: Carbon is the foundational element for living organisms. It occurs naturally in carbon dioxide ($\text{CO}_2$), graphite in pencils, diamonds, coal, and charcoal.

  • Abundant Cosmic Elements: Hydrogen and helium are the most common elements in the universe and serve as the primary components of stars.

• Subatomic Particles and Parameters:

  • Proton: Positively charged particle located inside the atomic nucleus. Significantly heavier than an electron.

  • Neutron: Neutral (uncharged) particle located inside the atomic nucleus. Significantly heavier than an electron.

  • Electron: Negatively charged particle orbiting outside the nucleus within defined energy levels/regions.

  • Atomic Number: The number of protons in an atom's nucleus. It uniquely identifies the element.

  • Mass Number: The combined total of protons and neutrons in an atom's nucleus ($\text{Mass Number} = \text{Protons} + \text{Neutrons}$).

  • Neutral Atoms: Contain equal numbers of protons and electrons ($\text{Protons} = \text{Electrons}$).

  • Calculating Neutrons: Calculated using the formula: $\text{Neutrons} = \text{Mass Number} - \text{Atomic Number}$.

• Key Element Symbols and Numbers:

  • Hydrogen ($\text{H}$): Atomic number $1$ ($1$ proton, $1$ electron in a neutral atom).

  • Helium ($\text{He}$): Atomic number $2$ ($2$ protons, $2$ electrons in a neutral atom).

  • Carbon ($\text{C}$): Atomic symbol $\text{C}$.

  • Sodium ($\text{Na}$): Atomic number $11$ ($11$ protons, $11$ electrons in a neutral atom).

  • Potassium ($\text{K}$): Atomic symbol $\text{K}$.

  • Iron ($\text{Fe}$): Atomic symbol $\text{Fe}$.

  • Copper ($\text{Cu}$): Atomic symbol $\text{Cu}$.

• Isotopes:

  • Definition: Atoms of the exact same element that have identical numbers of protons but different numbers of neutrons.

  • Hydrogen Isotopes (all possess $1$ proton):

  • Protium: Contains $0$ neutrons.

  • Deuterium: Contains $1$ neutron.

  • Tritium: Contains $2$ neutrons.

  • Average Atomic Mass vs. Mass Number: The average atomic mass printed on the periodic table is often a decimal because it reflects the weighted average of all naturally occurring isotopes of that element. It must not be confused with the mass number of a single atom, which is always a whole number.

• Electrons and Energy Level Calculations:

  • Valence Electrons: Electrons located in the outermost energy level of an atom; they are directly involved in forming chemical bonds.

  • Electron Shell Filling: Electrons fill lower, inner energy levels before filling outer levels.

  • Atomic Models: Simple Bohr diagrams are used to introduce atomic structure, although real atomic structures are more complex.

  • Maximum Electron Capacity Formula: Calculated using $2n^2$, where $n$ is the energy level number. Order of operations: square the level number ($n^2$) first, then multiply by $2$ ($2 \times n^2$).

  • Maximum Capacity Calculations per Energy Level:

  • Energy Level $n=1$: $2(1^2) = 2$ maximum electrons.

  • Energy Level $n=2$: $2(2^2) = 8$ maximum electrons.

  • Energy Level $n=3$: $2(3^2) = 18$ maximum electrons (Calculation: $3^2 = 9$, then $2 \times 9 = 18$).

  • Energy Level $n=4$: $2(4^2) = 32$ maximum electrons.

  • Formula Application Scope: The formula $2n^2$ determines the maximum capacity of an energy level, not necessarily the actual number of electrons a specific element possesses in that level.

• Element Types and Properties:

  • Metals: Physical properties include high luster/shininess, high electrical conductivity, ductility (can be drawn into thin wires), and malleability (can be hammered or reshaped).

  • Nonmetals: Poor conductors of electricity; many exist as gases at room temperature; solid forms are typically dull and brittle.

  • Metalloids / Semimetals: Possess intermediate properties of both metals and nonmetals (e.g., silicon and germanium).

Chemical Bonding, Compounds, and Molecular Interactions

• Ionic Bonds (Electron Transfer):

  • Formation Mechanism: Forms between a metal and a nonmetal through the complete transfer of one or more valence electrons.

  • Cation: A positively charged ion formed when an atom loses negative electrons.

  • Anion: A negatively charged ion formed when an atom gains negative electrons.

  • Memory Check: Losing a negative electron leaves an ion with a net positive charge.

  • Sodium Chloride Example: Sodium ($\text{Na}$) transfers its $1$ valence electron to chlorine ($\text{Cl}$). Sodium becomes a cation ($\text{Na}^+$) and chlorine becomes an anion ($\text{Cl}^-$). Their opposing full electrical charges attract and balance in table salt ($\text{NaCl}$).

  • Emergent Properties: Chemical and physical properties of the compound ($\text{NaCl}$) differ completely from those of reactive sodium metal and toxic chlorine gas.

  • Properties of Ionic Compounds: Hard, brittle solids with high melting and boiling points; they conduct electricity when dissolved in water.

• Covalent Bonds (Electron Sharing):

  • Formation Mechanism: Forms when nonmetal atoms share pairs of valence electrons to achieve chemical stability.

  • Shared Electron Pairs:

  • Single Covalent Bond: Shares $1$ pair of valence electrons.

  • Double Covalent Bond: Shares $2$ pairs of valence electrons.

  • Triple Covalent Bond: Shares $3$ pairs of valence electrons.

  • Nonpolar Covalent Bonds: Valence electrons are shared equally between atoms. Example: Molecular hydrogen ($\text{H}_2$), where two hydrogen atoms attract shared electrons with identical strength.

  • Polar Covalent Bonds: Valence electrons are shared unequally due to differences in electronegativity. Example: Water ($\text{H}_2\text{O}$), where the oxygen atom attracts shared electrons more strongly than the hydrogen atoms do, giving oxygen a slight negative charge and hydrogens a slight positive charge.

• Bonding Distinctions in Water:

  • Polar Covalent Bonds: Intramolecular bonds holding hydrogen and oxygen atoms together within a single water molecule.

  • Hydrogen Bonds: Intermolecular attractions occurring between separate, individual water molecules.

Cell Biology, Chromosomes, DNA, and RNA

• Organelles and Cellular Structures:

  • Nuclear Membrane: A double-layered structure surrounding the cell nucleus that features nuclear pores. DNA remains contained inside the nucleus, while messenger RNA ($\text{mRNA}$) passes through the pores into the cytoplasm.

  • Nucleolus: A dense structure inside the nucleus responsible for producing ribosomes.

  • Ribosomes: Cellular structures that synthesize proteins; they exist either freely floating in the cytoplasm or attached to intracellular membranes.

• Chromosomes and DNA Packaging:

  • Chromatin vs. Chromosomes: DNA is spread out/uncoiled when a cell is not actively dividing. Before division, DNA wraps tightly around specialized packing proteins to form condensed chromosomes.

  • Structural Packing: Proteins help pack roughly $1\,\text{meter}$ of linear DNA inside a single cell nucleus.

  • Chromosome Counts Across Species:

  • Humans: $46$ total chromosomes, organized into $23$ pairs ($23$ inherited from each parent).

  • Chimpanzees and Gorillas: $48$ total chromosomes.

  • Fruit Flies: $8$ total chromosomes.

  • Gene Definition: A specific segment of DNA that contains the genetic instructions for a functional trait or product.

• DNA Structure and Rules:

  • Double Helix: DNA is structured as a double-stranded helix held together by hydrogen bonds between nitrogenous base pairs. Bacterial DNA is circular.

  • Nucleotide Components: Each single nucleotide subunit contains a phosphate group, a five-carbon sugar (deoxyribose), and a nitrogenous base.

  • Structural Arrangement: The outer backbone sides consist of alternating deoxyribose sugar and phosphate groups; the nitrogenous bases form the inner rungs.

  • Base Pairing Rules and Hydrogen Bonds:

  • Adenine ($\text{A}$) pairs exclusively with Thymine ($\text{T}$) via $2$ hydrogen bonds.

  • Cytosine ($\text{C}$) pairs exclusively with Guanine ($\text{G}$) via $3$ hydrogen bonds.

  • Chargaff's Rule: In any double-stranded DNA sample, the amount of Adenine equals Thymine ($\text{A} = \text{T}$), and the amount of Cytosine equals Guanine ($\text{C} = \text{G}$).

• Structural Comparison of DNA and RNA:

  • Sugar: DNA contains Deoxyribose sugar; RNA contains Ribose sugar.

  • Base Composition: DNA contains Adenine, Thymine, Cytosine, Guanine ($\text{A, T, C, G}$); RNA contains Adenine, Uracil, Cytosine, Guanine ($\text{A, U, C, G}$). Uracil ($\text{U}$) replaces Thymine ($\text{T}$) in RNA.

  • Number of Strands: DNA is usually double-stranded ($2$ strands); RNA is usually single-stranded ($1$ strand).

  • RNA Functional Types:

  • Messenger RNA ($\text{mRNA}$): Transcribes genetic code from DNA and carries the copied message to the cytoplasm.

  • Transfer RNA ($\text{tRNA}$): Located in the cytoplasm, delivers amino acids during protein synthesis.

  • Ribosomal RNA ($\text{rRNA}$): Structural component that helps form functional ribosomes.

Organic Macromolecules: Chemical Reactions, Carbohydrates, and Lipids

• Macromolecules and Metabolic Reactions:

  • Macromolecules: Large organic molecules. Four major biological groups: Carbohydrates, Lipids, Proteins, and Nucleic Acids.

  • Monomer: A smaller building-block subunit.

  • Polymer: A large molecule constructed from many repeating joined monomer units.

  • Dehydration Synthesis (Condensation Reaction): Joins monomer units into polymers by removing/releasing a molecule of water ($\text{H}_2\text{O}$).

  • Hydrolysis Reaction: Breaks down polymers into individual monomer units by adding a molecule of water ($\text{H}_2\text{O}$). Essential for digesting food.

  • Direct Reaction Contrast: Remove water to join units; add water to separate units.

• Carbohydrates and Sugars:

  • Functional Roles: Serves as immediate energy sources, short-term energy storage, and structural components.

  • Atomic Ratio: Commonly taught Carbon:Hydrogen:Oxygen ratio is $1:2:1$.

  • Glucose Chemical Formula: $\text{C}_6\text{H}_{12}\text{O}_6$.

  • Monosaccharides (Single Sugar Units; names typically end in "-ose"):

  • Glucose: Critical cellular energy source and monomer for larger polysaccharides.

  • Fructose: Monosaccharide found in fruits.

  • Galactose: Monosaccharide component of milk sugar.

  • Ribose: Five-carbon sugar component of RNA.

  • Deoxyribose: Five-carbon sugar component of DNA.

  • Structural Isomers: Molecules that share identical molecular formulas (same numbers and types of atoms) but possess different structural arrangements. Glucose, fructose, and galactose are isomers with the identical formula $\text{C}_6\text{H}_{12}\text{O}_6$.

  • Disaccharides (Two Joined Sugar Units):

  • Maltose: Formed by joining $\text{Glucose} + \text{Glucose}$ (associated with malt).

  • Lactose: Formed by joining $\text{Glucose} + \text{Galactose}$ (milk sugar).

  • Sucrose: Formed by joining $\text{Glucose} + \text{Fructose}$ (table sugar).

  • Polysaccharides (Many Joined Sugar Units):

  • Starch: Energy storage polysaccharide in plants. Found in grains, bread, rice, potatoes, and pasta.

  • Glycogen: Energy storage polysaccharide in animals. Stored in liver and muscle tissue; supplies energy between meals or during fight-or-flight responses.

  • Cellulose: Structural polysaccharide in plant cell walls, wood, and cotton. Humans lack enzymes to digest cellulose, so it acts as insoluble dietary fiber. Cows digest cellulose using symbiotic gut bacteria.

  • Chitin: Structural polysaccharide found in insect exoskeletons and used in surgical sutures.

• Lipids:

  • General Characteristics: Diverse structural group unified by being nonpolar and hydrophobic (do not dissolve in water).

  • Lipid Categories and Primary Roles:

  • Fats (Triglycerides): Functions include long-term energy storage, thermal insulation against heat loss, and protective organ cushioning. Excess abdominal fat can harm health.

  • Waxes: Protective coatings that prevent water loss in plants.

  • Phospholipids and Cholesterol: Essential structural components of cell membranes. Excess cholesterol can narrow arteries, increasing risks of heart attack or stroke.

  • Steroid Hormones: Act as chemical signaling messengers; examples include estrogen and testosterone.

Self-Assessment, Conceptual Verification, and Practice Questions

• Energy Level Practice:

  • Question: Calculate the maximum number of electrons in energy level $n=4$ using $2n^2$.

  • Answer: Square the level number ($4^2 = 16$), then multiply by $2$ ($2 \times 16 = 32$ maximum electrons).

• Subatomic Particle Practice:

  • Question: How are proton and neutron counts determined from atomic number and mass number?

  • Answer: Protons equal the atomic number. Neutrons equal mass number minus atomic number ($\text{Neutrons} = \text{Mass Number} - \text{Atomic Number}$).

• Isotope Verification:

  • Question: Why are two isotopes classified as the same element despite different atomic masses?

  • Answer: They possess identical proton counts (atomic number), which defines the element, but differ in neutron counts.

• Ionic Identification Practice:

  • Question: Identify the cation and anion when sodium transfers an electron to chlorine.

  • Answer: Sodium loses an electron to become the positively charged cation ($\text{Na}^+$); chlorine gains an electron to become the negatively charged anion ($\text{Cl}^-$).

• Chemical Bond Contrast:

  • Question: What is the fundamental difference between ionic and covalent bonding?

  • Answer: Ionic bonding involves full electron transfer between atoms; covalent bonding involves sharing electron pairs.

• Water Bond Differentiation:

  • Question: How do polar covalent bonds in water differ from hydrogen bonds?

  • Answer: Polar covalent bonds hold hydrogen and oxygen together within one $\text{H}_2\text{O}$ molecule; hydrogen bonds are attractions between separate $\text{H}_2\text{O}$ molecules.

• Chemical Reaction Check:

  • Question: Which reaction joins units and what happens to water? Which reaction separates units and what happens to water?

  • Answer: Dehydration synthesis joins units by releasing water; hydrolysis separates units by adding water.

• Monomer vs. Polymer Distinction:

  • Question: What is the structural difference between a monomer and a polymer?

  • Answer: A monomer is a single repeating building block; a polymer is a large chain of joined monomers.

• Disaccharide Subunits Check:

  • Question: What are the component monosaccharides of maltose, lactose, and sucrose?

  • Answer: Maltose = glucose + glucose; Lactose = glucose + galactose; Sucrose = glucose + fructose.

• Polysaccharide Role and Location Comparison:

  • Question: How do starch, glycogen, cellulose, and chitin differ in function and location?

  • Answer: Starch stores energy in plants (potatoes, grains); Glycogen stores energy in animal liver/muscles; Cellulose provides structure in plant cell walls; Chitin provides structure in insect exoskeletons.

• Cellulose Digestion Verification:

  • Question: Why can cows digest cellulose while humans cannot?

  • Answer: Humans lack the digestive enzymes to break cellulose bonds; cows utilize symbiotic gut bacteria that produce cellulose-cleaving enzymes.

• Isomer Definition Check:

  • Question: What makes glucose, fructose, and galactose isomers?

  • Answer: They share the identical chemical formula ($\text{C}_6\text{H}_{12}\text{O}_6$) but have different atomic structural arrangements.

• Lipid Properties Check:

  • Question: What two physical properties do all lipids share, and what are their primary biological functions?

  • Answer: All lipids are nonpolar and hydrophobic. Primary functions include long-term energy storage, insulation, organ cushioning, cell membrane structure, protective coatings, and hormonal messaging.

Course Logistics, Exam Scope, and Test Administration

• Examination Date and Schedule:

  • Exam Date: Scheduled for October $6$.

  • Review Session: Attend the mandatory review on Tuesday.

• Curriculum Scope and Resources:

  • PowerPoint Coverage: Study the Organic Molecules presentation through slide $54$.

  • Video Assignment: Watch the Amoeba Sisters DNA video.

  • Exclusions: Transcription and translation are explicitly excluded from this exam scope.

• Technical and Testing Environment Requirements:

  • Browser Requirement: Install Respondus LockDown Browser prior to exam administration.

  • Hardware Requirements: Must have a fully functioning web camera.

  • Identity and Room Protocols: Student ID must be ready, face must remain clearly visible, and the test must be taken in a well-lit room.