Comprehensive Study Notes: Scientific Inquiry, Cell Biology, and General Chemistry

Fundamentals of Biology and Scientific Inquiry

• Definition of Biology: Biology is the scientific study of life.

• Key Characteristics and Functions of Life:

  • Order

  • Evolutionary adaptations

  • Regulation

  • Reproduction

  • Response to the environment

  • Growth and development

  • Energy processing

• Evolution:

  • Defined as the change in the inherited traits of a biological population over successive generations.

  • Involves changes in the characteristics of a species over time.

  • Species: Individuals that can reproduce naturally and produce fertile offspring.

• Five Unifying Themes of Life:

  1. Organization: Cells serve as the fundamental unit of structure and function.

  2. Information: Expression and transmission of hereditary (genetic) information via genes, response to environmental information, and maintenance of homeostasis.

  3. Energy and Matter: Processing of energy and cycling of matter through pathways such as photosynthesis and cellular respiration.

  4. Interactions:

  • Internal interactions between structural components within living organisms (organs, tissues, cells, and molecules).

  • External interactions between biological organisms and their physical environment.

  1. Evolution: The overarching framework explaining the diversity and unity of life over time.

  • Note: Reductionism is not a unifying theme of biology.

Experimental Design and Data Analysis

• Scientific Method Core Principles:

  • Scientists make observations and form testable hypotheses.

  • For each hypothesis, an experimental study is designed to evaluate its specific predictions.

• Experimental Groups and Variables:

  • Control Group: Provides a standard for baseline comparison against experimental conditions.

  • Variable: Any quantity or condition that can change within an experiment.

  • Independent Variable: The variable that is manipulated or controlled by the experimenter (plotted on the $x$-axis; analogized as "your parents").

  • Dependent Variable: The variable that is observed and measured for changes in response to the independent variable (plotted on the $y$-axis; analogized as "you").

  • Controlled Variable: A variable that is kept constant across all experimental conditions to ensure a fair test.

• Data Collection: Data consists of collected and recorded observations.

• Real-World Application Example: Testing COVID-19 vaccine effectiveness (e.g., BioNTech/Pfizer vaccine, Moderna) in healthy individuals.

• Graphing Framework (ALKS):

  • A: Axis

  • L: Labels

  • K: What you know

  • S: Synthesis

Methods of Scientific Reasoning and Logic

• Inductive Reasoning:

  • Logic based on specific observations or experimental results.

  • Primary mechanism by which hypotheses arise.

  • May lead to a general conclusion or scientific theory.

  • Progression: Observation $\rightarrow$ Pattern $\rightarrow$ Tentative Hypothesis $\rightarrow$ Theory.

  • Example: Observing apples falling from a tree leading to Newton's law of universal gravitation.

• Deductive Reasoning:

  • Logic used specifically for testing an existing hypothesis or established theory.

  • Utilizes standard "if/then" conditional statements.

  • May lead to scientific confirmation.

  • Requires a large volume of data to establish true causality rather than mere coincidence.

  • Progression: Theory $\rightarrow$ Hypothesis $\rightarrow$ Observation $\rightarrow$ Confirmation.

  • Example: Predicting and discovering the planet Neptune based on the mathematical orbits of known planets.

• Hypothesis Testing Example:

  • Observation: A desk lamp does not work.

  • Question: Why does the desk lamp not work?

  • Hypothesis 1: The light bulb is burnt out.

  • Hypothesis 2: The light bulb is not screwed in properly.

  • Outcome: Both hypotheses are testable and can be either accepted or rejected through experimental testing.

Hierarchy of Life and Cell Theory

• Levels of Biological Organization:

  • Life is studied across multiple scales, proceeding hierarchically:     $\text{Biosphere} \rightarrow \text{Biomes} \rightarrow \text{Ecosystems} \rightarrow \text{Community} \rightarrow \text{Population} \rightarrow \text{Organism} \rightarrow \text{Organ} \rightarrow \text{Tissue} \rightarrow \text{Cell} \rightarrow \text{Organelles} \rightarrow \text{Molecules} \rightarrow \text{Atoms}$

  • Biosphere: The global ecosystem; the sum of all ecosystems across the planet.

  • Ecosystem: The community of living organisms interacting with non-living elements in a given area.

  • Community: An aggregate group of populations of different species coexisting within a specified area.

  • Population: A group of individuals belonging to the exact same species residing in a defined area.

• Reductionism:

  • An analytical approach that reduces complex biological systems to simpler, more manageable components for study.

• Cell Structure and Classification:

  • The cell is the smallest unit of organization capable of performing all activities required for life.

  • All cells are enclosed by a membrane that regulates the entry and exit of materials between the cell interior and its surrounding environment.

  • Etymology:

  • Eu: True

  • Pro: Before

  • Karyo: Nucleus

  • Eukaryotic Cells:

  • Contain a true, membrane-enclosed nucleus.

  • Highly compartmentalized with membrane-enclosed organelles.

  • Feature a plasma membrane, cytoplasm, and linear chromosomes.

  • Larger and structurally more complex.

  • Found in multicellular organisms as well as unicellular organisms.

  • Prokaryotic Cells:

  • Lack a membrane-enclosed nucleus; genetic material (DNA) is distributed throughout the cytoplasm.

  • Lack membrane-enclosed organelles.

  • Smaller and structurally simpler.

  • Unicellular organisms.

  • Contain circular genetic material.

  • Structures include cell wall, capsule, flagella, pili, plasmids, and ribosomes.

• Nucleic Acid Nitrogenous Bases:

  • Purines: Adenine ($A$) and Guanine ($G$) (Mnemonic: "$AG$ is pure").

  • Pyrimidines: Cytosine ($C$), Uracil ($U$), and Thymine ($T$) (Mnemonic: "$CUT$").

Evolutionary Classification and Domains of Life

• Three Domains of Life:

  • All living organisms stem from a single common ancestor and are classified into three primary domains:

  1. Domain Bacteria: Prokaryotic organisms.

  2. Domain Archaea: Prokaryotic organisms.

  3. Domain Eukarya: Eukaryotic organisms.

• Domain Eukarya Subdivisions:

  • Kingdom Animalia

  • Kingdom Plantae

  • Kingdom Fungi

  • Protists (Protista)

• Hand Mnemonic Representation:

  • Thumb: Bacteria

  • Pointer finger: Archaea

  • Middle finger: Animalia (Eukarya)

  • Ring finger: Plantae (Eukarya)

  • Pinky finger: Fungi (Eukarya)

Chemical Context of Life and Chemical Elements

• Matter and Compounds:

  • Matter consists of chemical elements in pure form and in combinations called compounds.

  • Living organisms and their surrounding environments adhere strictly to the basic laws of physics and chemistry.

  • Compound: A substance consisting of two or more different elements joined together by chemical bonds in fixed ratios.

  • A compound's physical and chemical properties depend upon its constituent atoms and how they are bonded together (e.g., formic acid composed of oxygen, carbon, and hydrogen atoms).

• Essential Elements of Life:

  • Four elements make up approximately $96\%$ of total living mass:

  • Carbon ($C$)

  • Hydrogen ($H$)

  • Oxygen ($O$)

  • Nitrogen ($N$)

  • Four elements constitute approximately $4\%$ (or $3.7\%$ detailed mass):

  • Calcium ($Ca$)

  • Phosphorus ($P$)

  • Potassium ($K$)

  • Sulfur ($S$)

  • Trace Elements: Elements required by organisms in minute quantities, constituting less than $0.01\%$ of total mass.

• Detailed Body Mass Breakdown (including water):

  • Oxygen ($O$): $65\%$

  • Carbon ($C$): $18.6\%$

  • Hydrogen ($H$): $9.5\%$

  • Nitrogen ($N$): $3.3\%$

  • Subtotal major essential elements mass: $96.3\%$

  • Calcium ($Ca$): $21.5\%$

  • Phosphorus ($P$): $1.0\%$

  • Potassium ($K$): $0.4\%$

  • Sulfur ($S$): $0.3\%$

  • Sodium ($Na$): $0.2\%$

  • Chlorine ($Cl$): $0.1\%$

  • Magnesium ($Mg$): $0.1\%$

  • Total secondary elements mass: $3.7\%$

  • Trace Elements (listed alphabetically): Boron ($B$), Chromium ($Cr$), Cobalt ($Co$), Copper ($Cu$), Fluorine ($F$), Iodine ($I$), Iron ($Fe$), Manganese ($Mn$), Molybdenum ($Mb$), Selenium ($Se$), Silicon ($Si$), Tin ($Sn$), Vanadium ($V$), Zinc ($Zn$).

Atomic Structure, Energy Levels, and Isotopes

• Subatomic Particles:

  • Protons: Positively charged subatomic particles residing in the atomic nucleus. The number of protons determines an atom's unique identity (atomic number).

  • Electrons: Negatively charged subatomic particles forming a cloud around the nucleus. Electron distribution determines an atom's ability to form chemical bonds.

  • Neutrons: Electrically neutral particles located inside the atomic nucleus.

• Isotopes:

  • Two or more atoms of the same element that differ strictly in their number of neutrons (and thus mass number).

  • Carbon Isotopes:

  • Carbon-12 ($^{12}C$): Abundance of $98.9\%$, containing $6$ protons and $6$ neutrons.

  • Carbon-13 ($^{13}C$): Abundance of $1.1\%$, containing $6$ protons and $7$ neutrons.

  • Carbon-14 ($^{14}C$): Abundance of $<0.1\%$, containing $6$ protons and $8$ neutrons.

  • Radioactive Isotopes:

  • Unstable isotopes that decay spontaneously, emitting subatomic particles and energy.

  • Parent Isotope: Decays into a "daughter" isotope at a fixed, characteristic rate termed the half-life.

  • Applications:

    • Diagnostic tools in medicine acting as radioactive tracers to track specific atoms through metabolic pathways.

    • PET (Positron Emission Tomography) scanners utilize radioactive tracers to monitor tissue growth and metabolic activity within the body.

• Electron Energy Levels and Shells:

  • An atom's electrons differ in their potential energy based on their distance from the nucleus.

  • Energy Level / Electron Shell: An electron's defined state of potential energy.

  • First Shell: Lowest potential energy level, closest to the nucleus.

  • Second Shell: Higher potential energy level.

  • Third Shell: Highest potential energy level in standard atomic shell models.

  • Energy Transitions:

  • Absorbing energy moves an electron outward to a higher energy shell.

  • Losing energy causes an electron to fall inward to a lower energy shell.

Chemical Bonding and Molecular Interactions

• Valence Electrons and Chemical Behavior:

  • The chemical behavior of an atom is determined by the distribution of electrons within its electron shells, primarily governed by the number of valence electrons in its outermost shell.

  • Examples of electron shell fill states:

  • Hydrogen ($H$): $1$ electron.

  • Carbon ($C$), Nitrogen ($N$), Oxygen ($O$).

  • Neon ($Ne$): Has $2$ filled electron shells ($10\,e^-$).

  • Chlorine ($Cl$).

  • Atoms with incomplete valence shells can share or transfer valence electrons with other atoms to achieve stability.

• Covalent Bonds:

  • Molecule: Two or more atoms held together by covalent bonds.

  • Covalent Bond: The sharing of a pair of valence electrons between two atoms.

  • Single Covalent Bond (Single Bond): The sharing of one pair of valence electrons ($H-H$).

  • Double Covalent Bond (Double Bond): The sharing of two pairs of valence electrons ($O=O$).

  • Chemical Formulas:

  • Structural Formula: Graphical representation showing atom symbols and bonds (e.g., $H-H$, $O=O$).

  • Molecular Formula: Abbreviated notation stating exact numbers of atoms (e.g., $H_2$).

• Electronegativity and Bond Polarity:

  • Electronegativity: An atom's structural attraction for shared electrons in a covalent bond.

  • The higher an atom's electronegativity, the more strongly it pulls shared electrons toward itself.

  • Nonpolar Covalent Bond: A bond in which electrons are shared equally between two atoms due to similar electronegativities.

  • Polar Covalent Bond: A bond in which one atom is significantly more electronegative than the other, causing unequal sharing of electrons.

  • Unequal sharing creates partial positive charges ($\delta+$) and partial negative charges ($\delta-$) on the atoms.

  • Example: Water ($H_2O$), where the oxygen atom carries a partial negative charge ($\delta-$) and each hydrogen atom carries a partial positive charge ($\delta+$).

• Ionic Bonds:

  • Formed when two atoms differ so strongly in electronegativity that one atom completely strips an electron away from its bonding partner.

  • The two resulting oppositely charged atoms or molecules are called ions.

  • Cation: A positively charged ion formed by losing electrons (e.g., Sodium ion, $Na^+$).

  • Anion: A negatively charged ion formed by gaining electrons (e.g., Chloride ion, $Cl^-$).

  • Example: Sodium chloride ($NaCl$).

• Weak Chemical Interactions:

  • Hydrogen Bonds:

  • Occur when a hydrogen atom that is already covalently bonded to one electronegative atom is simultaneously attracted to another nearby electronegative atom.

  • Van der Waals Interactions:

  • Weak attractions between adjacent molecules driven by transient, localized charge accumulations.

  • Results from electrons being unevenly distributed by chance in one portion of a molecule at any given moment.

Chemical Reactions and Energetics

• Chemical Reactions:

  • Processes that involve the making and breaking of chemical bonds, leading to changes in the composition of matter.

  • Reactants: The starting materials in a chemical reaction.

  • Products: The resulting materials produced by a chemical reaction.

  • Reversibility: All chemical reactions are theoretically reversible.

• Photosynthesis Reaction Example:

  • Equation:     $6CO_2 + 6H_2O \xrightarrow{\text{Sunlight}} C_6H_{12}O_6 + 6O_2$

  • Reactants: Carbon dioxide ($6CO_2$) and Water ($6H_2O$), powered by sunlight energy.

  • Products: Glucose ($C_6H_{12}O_6$) and Oxygen ($6O_2$).