Unit 1 Study Notes: Introduction to Biology & Chemistry of Life

Introduction to Biology

Themes & Organization of Biology

Biology is the scientific study of life, organized around several unifying themes. Understanding these themes helps explain the complexity and diversity of living organisms.

• Emergent Properties: New characteristics arise at each level of biological organization due to interactions among components. For example, a cell exhibits properties not found in its individual molecules.

• Reductionism vs. Systems Biology: Reductionism breaks complex systems into simpler parts for study, while systems biology examines interactions within whole systems to understand emergent properties.

• Hierarchy of Biological Organization: Life is structured in a hierarchy from smallest to largest: molecule → organelle → cell → tissue → organ → organ system → organism → population → community → ecosystem → biosphere.

• Negative Feedback Regulation: Biological systems maintain homeostasis through negative feedback, where a change triggers a response that counteracts the initial change (e.g., body temperature regulation).

Example: In an ecosystem, the interaction of plants, animals, and microbes produces emergent properties such as nutrient cycling and energy flow.

Additional info: Positive feedback amplifies changes (e.g., blood clotting), while negative feedback stabilizes systems.

Scientific Method & Scientific Thinking

Steps of the Scientific Method

The scientific method is a systematic approach to inquiry, ensuring that scientific investigations are logical and reproducible.

• Observation: Gathering information about phenomena.

• Hypothesis: A testable explanation for an observation.

• Prediction: A logical outcome expected if the hypothesis is correct.

• Experiment: Testing the prediction under controlled conditions.

• Analysis: Interpreting data to determine if it supports the hypothesis.

• Conclusion: Summarizing findings and their implications.

• Hypotheses vs. Theories: A hypothesis is a specific, testable statement; a theory is a broad, well-supported explanation of natural phenomena.

• Inductive Reasoning: Drawing general conclusions from specific observations.

• Deductive Reasoning: Making specific predictions based on general principles.

• Controlled Experiments: Experiments with variables held constant except for one independent variable.

Example: Testing whether fertilizer increases plant growth by comparing treated and untreated plants under identical conditions.

Additional info: Scientific laws describe patterns; theories explain them. Not all hypotheses are testable (e.g., supernatural causes).

Chemistry of Life

Atoms, Elements, and Isotopes

All matter is composed of atoms, which are the basic units of elements. Understanding atomic structure is essential for studying biological molecules.

• Structure of Atoms: Atoms consist of protons (positive charge), neutrons (neutral), and electrons (negative charge).

• Atomic Number: Number of protons in the nucleus; defines the element.

• Atomic Mass: Sum of protons and neutrons.

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

• Carbon: Has 4 valence electrons, allowing it to form up to four covalent bonds, making it highly versatile in forming organic molecules.

Example: Carbon-12 and Carbon-14 are isotopes of carbon, differing in neutron number.

Additional info: Electrons determine chemical behavior but do not significantly affect atomic mass.

Water & Chemical Bonds

Types of Chemical Bonds and Properties of Water

Chemical bonds hold atoms together in molecules. Water's unique properties are critical for life and result from its molecular structure and bonding.

• Covalent Bonds: Atoms share electrons (e.g., H2O).

• Ionic Bonds: Atoms transfer electrons, forming charged ions (e.g., NaCl).

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules), responsible for water's cohesion.

• Cohesion: Water molecules stick together due to hydrogen bonding, enabling surface tension.

• High Specific Heat: Water absorbs or releases large amounts of heat with little temperature change, stabilizing environments.

• Density of Ice: Ice is less dense than liquid water because hydrogen bonds form a lattice, causing ice to float.

Example: Sweating cools the body because water absorbs heat as it evaporates, a process called evaporative cooling.

Additional info: Water's polarity (unequal sharing of electrons) makes it an excellent solvent for ionic and polar substances.

Energy & ATP

Forms of Energy and ATP Function

Energy is the capacity to do work. Cells use adenosine triphosphate (ATP) as their main energy currency.

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

• Kinetic Energy: Energy of motion (e.g., moving molecules).

• Potential Energy: Stored energy due to position or structure (e.g., chemical bonds).

• ATP Structure: Composed of adenine, ribose, and three phosphate groups.

• ATP Hydrolysis: Breaking the terminal phosphate bond of ATP releases energy for cellular work: $\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P}_i + \text{energy}$

Example: Muscle contraction and active transport use energy released from ATP hydrolysis.

Additional info: ADP (adenosine diphosphate) has less energy than ATP because it has one fewer phosphate group.

Biological Macromolecules

Types, Structure, and Function

Macromolecules are large, complex molecules essential for life. They include carbohydrates, lipids, proteins, and nucleic acids.

• Carbohydrates: Serve as energy sources (e.g., glucose) and structural materials (e.g., cellulose).

• Lipids: Hydrophobic molecules (e.g., fats, oils, phospholipids); not true polymers because they are not made from repeating monomers.

• Proteins: Made of amino acids; have four levels of structure:

  • Primary: Amino acid sequence

  • Secondary: Alpha helices and beta sheets

  • Tertiary: 3D folding

  • Quaternary: Multiple polypeptides

• Nucleic Acids: DNA and RNA store and transmit genetic information. DNA is double-stranded; RNA is usually single-stranded.

• Polymer Formation: Dehydration synthesis joins monomers by removing water; hydrolysis breaks polymers by adding water.

Macromolecule	Monomer	Function
Carbohydrate	Monosaccharide	Energy, structure
Lipid	Fatty acid & glycerol	Energy storage, membranes
Protein	Amino acid	Catalysis, structure, transport
Nucleic Acid	Nucleotide	Genetic information

Example: Saturated fats have no double bonds (solid at room temp); unsaturated fats have double bonds (liquid at room temp). Protein shape is determined by amino acid sequence and interactions.

Additional info: Starch (plants) and glycogen (animals) are storage polysaccharides; glycogen is more highly branched.