General Biology: Foundations, Chemistry of Life, and Water

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The Scientific Method and Reasoning in Biology

Deductive and Inductive Reasoning

Biological research relies on logical reasoning to form and test hypotheses. Two main types of reasoning are used:

Deductive reasoning: Uses general premises to make specific predictions. For example, if all mammals have hair and a whale is a mammal, then a whale has hair.
Inductive reasoning: Involves making broad generalizations from specific observations. For example, observing that all swans seen so far are white and concluding that all swans are white.

Hypothesis: A testable and falsifiable statement that explains observations. Multiple hypotheses can be tested, but none can be absolutely proven, only supported or refuted by evidence.

The Scientific Method

Purpose (Question): Identifying the problem or question to be studied.
Hypothesis: Proposing a tentative explanation or answer.
Test (Experiment): Designing and conducting experiments to test the hypothesis.
Analysis: Analyzing the data collected from experiments.
Conclusion: Drawing conclusions based on the analysis.

Experiments often use a control group (no treatment) and an experimental group (treatment applied). The independent variable is changed, and the dependent variable is measured.

Hierarchy of Life

Biological organization is structured from the smallest to the largest units:

Biosphere > Ecosystem > Community > Population > Organism > Organ System > Organ > Tissue > Cell > Organelle > Molecule > Atom

Emergent Properties and Reductionism

Emergent properties: New characteristics that arise at each level of biological organization due to the arrangement and interactions of parts.
Reductionism: Breaking down complex systems into simpler components for study.

Prokaryotic vs. Eukaryotic Cells

Prokaryotic cells: Lack a nucleus and most membrane-bound organelles (e.g., bacteria).
Eukaryotic cells: Have a nucleus and other membrane-enclosed organelles (e.g., plants, animals, fungi, protists).

Evolution

Evolution is the process by which life on Earth has changed over time, accounting for the unity and diversity of life.

Atoms, Elements, and Chemical Bonds

Atoms and Elements

An atom is the smallest unit of an element, retaining its properties. Atoms are composed of:

Protons: Positively charged particles in the nucleus.
Neutrons: Neutral particles in the nucleus.
Electrons: Negatively charged particles orbiting the nucleus.

Atomic Structure and Notation

Atomic number (Z): Number of protons in the nucleus; defines the element.
Mass number (A): Total number of protons and neutrons.
Number of neutrons:

Term	Definition
Atomic number (Z)	Number of protons
Mass number (A)	Number of protons + neutrons
Number of neutrons

Isotopes are atoms of the same element with different numbers of neutrons, resulting in different mass numbers.

Electron Shells and Valence Electrons

Electron shells: Energy levels where electrons are found. The arrangement of electrons determines chemical behavior.
Valence shell: The outermost electron shell; atoms with incomplete valence shells are reactive.

Chemical Bonds

Covalent bonds: Atoms share pairs of electrons. Can be single, double, or triple bonds.
Nonpolar covalent bond: Electrons are shared equally between atoms.
Polar covalent bond: Electrons are shared unequally, resulting in partial charges.
Ionic bonds: Electrons are transferred from one atom to another, creating ions (cations and anions) that attract each other.
Hydrogen bonds: Weak attractions between a hydrogen atom covalently bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom.
Van der Waals interactions: Weak attractions due to transient local partial charges.

Summary Table: Types of Chemical Bonds

Bond Type	Description	Strength
Covalent	Sharing of electron pairs	Strong
Ionic	Transfer of electrons, attraction between ions	Strong (in dry conditions)
Hydrogen	Attraction between H and electronegative atom	Weak
Van der Waals	Transient attractions due to partial charges	Very weak

Water and Its Properties

Polarity of Water

Water (H2O) is a polar molecule due to the unequal sharing of electrons between oxygen and hydrogen atoms, resulting in a partial negative charge near oxygen and partial positive charges near hydrogens.

Hydrogen Bonding in Water

Hydrogen bonds form between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another.
These bonds are individually weak but collectively give water unique properties.

Properties of Water

Cohesion: Water molecules stick together due to hydrogen bonding. This contributes to surface tension.
Adhesion: Water molecules stick to other substances, aiding processes like capillary action in plants.
High specific heat: Water can absorb or release large amounts of heat with little temperature change.
High heat of vaporization: Water requires a lot of energy to change from liquid to gas, helping moderate Earth's climate.
Evaporative cooling: As water evaporates, it removes heat, cooling the surface.

Temperature and Energy

Kinetic energy: Energy of motion; temperature measures the average kinetic energy of molecules.
Thermal energy: Total kinetic energy of all molecules in a body of matter.
Temperature: Average kinetic energy of molecules.

Acids, Bases, and pH

Acid: Substance that increases the hydrogen ion (H+) concentration in a solution.
Base: Substance that decreases the hydrogen ion concentration, often by increasing hydroxide ions (OH-).
Hydronium ion:
pH scale: Measures the concentration of H+ in solution. pH < 7 is acidic, pH > 7 is basic, pH = 7 is neutral.

Summary Table: Key Properties of Water

Property	Description	Biological Importance
Cohesion	Water molecules stick together	Enables transport of water in plants
Adhesion	Water molecules stick to other substances	Helps counter gravity in plant vessels
High specific heat	Resists temperature change	Stabilizes climate and body temperature
High heat of vaporization	Requires much energy to evaporate	Evaporative cooling, climate moderation
Universal solvent	Dissolves many substances	Facilitates chemical reactions in cells

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