Foundations of General Biology: Cells, Chemistry, and Macromolecules

Cell Theory and Organization of Life

Cell Theory

Cell theory is a fundamental concept in biology stating that all living things are composed of at least one cell, and sometimes many cells. Cells are the basic unit of structure and function in living organisms.

• Cell: The smallest unit of life, capable of performing all life processes.

• Multicellular organisms: Composed of many cells that may be specialized for different functions.

Homeostasis

Homeostasis refers to the regulation and maintenance of relatively stable internal conditions in living organisms.

• Example: Regulation of body temperature, pH, and water balance.

Domains of Life

All living things are classified into three major domains based on cellular structure and genetics.

• Bacteria: Single-celled, unicellular organisms without a nucleus (prokaryotes).

• Archaea: Single-celled, unicellular organisms without a nucleus (prokaryotes), often found in extreme environments.

• Eukarya: Organisms with cells that contain a nucleus; includes both single-celled and multicellular organisms (eukaryotes).

• Protists and Plants: Examples of eukaryotes.

Levels of Biological Organization

Life is organized in a hierarchical structure from the largest to the smallest units.

Level	Description
Biosphere	All life on Earth
Ecosystem	Area containing non-living habitat and living things
Community	All living things in an ecosystem
Population	Group of individuals of the same species
Organism	Individual life-form
Organ System	Group of organs working together
Organ	Structure with specific functions
Tissue	Grouping of similar cells
Cell	Functional unit of life
Organelle	Structure within cells (e.g., nucleus)
Molecule	Made of atoms connected by chemical bonds

Emergent Properties

Emergent properties are complex features that arise when simple structures are combined in specific ways. For example, nerve cells can work together to create a nervous system with higher-level functions.

Scientific Method and Heredity

Scientific Method

The scientific method is a systematic approach to investigating natural phenomena.

• Observations: Qualitative (descriptive) or quantitative (numeric).

• Questions: Formulated based on observations.

• Hypotheses: Proposed explanations that must be testable.

• Testing Hypotheses: Making more observations, designing and running experiments.

• Controlled Experiments: Examine the effect of one variable while eliminating others.

• Independent Variable: The variable manipulated by the experimenter.

• Dependent Variable: The variable affected by the independent variable.

Heredity and Evolution

Heredity involves the passing of traits from parents to offspring via DNA. Over long periods and many generations, evolution by natural selection leads to variation and adaptation in life on Earth.

• Heritable Traits: Passed from parents to offspring by DNA.

• Evolution: Change in populations over generations due to natural selection.

Atoms, Elements, and Chemical Bonds

Atomic Structure

Atoms are the basic units of matter, composed of subatomic particles.

• Protons: Found in the nucleus, mass = 1, charge = +1.

• Neutrons: Found in the nucleus, mass = 1, charge = 0.

• Electrons: Very small, charge = -1, orbit the nucleus.

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

• Mass Number: Sum of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons; some are unstable and radioactive.

Electron Shells and Stability

Electrons occupy shells around the nucleus. Atoms are most stable when their outer shells are full.

• 1st shell: up to 2 electrons

• 2nd shell: up to 8 electrons

• 3rd shell: up to 8 electrons

Chemical Bonds

Chemical bonds form when atoms share or transfer electrons to achieve stability.

• Ionic Bond: Complete transfer of electrons from one atom to another.

• Covalent Bond: Sharing of electrons between atoms.

• Polarity: Unequal sharing of electrons leads to partial charges.

• Electronegativity: Attraction an atom has for electrons.

Bond Type	Electron Sharing
Single Bond	1 pair of shared electrons
Double Bond	2 pairs of shared electrons
Triple Bond	3 pairs of shared electrons

Properties of Water

Polarity and Hydrogen Bonds

Water molecules are polar, with oxygen attracting electrons more strongly than hydrogen. This leads to hydrogen bonds, which are weak attractions between molecules.

• Hydrogen Bonds: Weak attractions due to polar covalent bonds.

• Surface Tension: Measure of how difficult it is to break the surface of a liquid.

Cohesion and Adhesion

Cohesion is the tendency of water molecules to stick to each other, while adhesion is their tendency to stick to other substances.

• Cohesion: Responsible for water droplets and surface tension.

• Adhesion: Allows water to move up plant stems and adhere to surfaces.

Temperature Regulation and Solvent Properties

Water has a high capacity for absorbing heat due to hydrogen bonding, stabilizing temperatures in organisms and environments.

• Evaporative Cooling: As water evaporates, it carries away heat, cooling the remaining liquid.

• Universal Solvent: Water dissolves many substances, facilitating chemical reactions in cells.

Acids, Bases, and pH

Water can become acidic or basic depending on dissolved substances. The pH scale measures the concentration of hydrogen ions ($[H^+]$).

• Acids: Increase $[H^+]$ in solution.

• Bases: Decrease $[H^+]$ in solution.

• pH Scale: Ranges from 0 (most acidic) to 14 (most basic); 7 is neutral.

• Each step on the pH scale represents a tenfold change in acidity.

pH Value	Acidity/Basicity
0-6	Acidic
7	Neutral
8-14	Basic

• Buffers: Molecules that resist changes in pH by combining with excess acids or bases.

Organic Molecules and Macromolecules

Organic Compounds

Organic compounds must contain carbon. Carbon's ability to form four chemical bonds allows for a diversity of molecules.

• Isomers: Molecules with the same chemical formula but different structures.

• Hydrocarbons: Compounds containing only carbon and hydrogen; common in fossil fuels.

Functional Groups

Functional groups are specific groups of atoms within molecules that confer particular properties.

• Hydroxyl, Carbonyl, Carboxyl, Phosphate, Amino: All are hydrophilic (water-loving).

• Methyl: Hydrophobic (water-repelling).

Macromolecules: Polymers and Monomers

Most organic molecules in living things are large macromolecules made of repeating monomer units.

• Polymer Formation: Built by dehydration synthesis (removal of water).

• Polymer Breakdown: Occurs by hydrolysis (addition of water).

Carbohydrates

Carbohydrates are made of carbon, hydrogen, and oxygen, usually with the formula $CH_2O$. They serve as energy sources and structural components.

• Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose).

• Disaccharides: Two monosaccharides joined by dehydration synthesis (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose).

• Starch: Energy storage in plants.

• Cellulose: Structural component in plant cell walls; difficult for animals to digest.

Lipids

Lipids are hydrophobic molecules, including fats, oils, and steroids. They function as energy storage and structural components.

• Triglycerides: Composed of glycerol and three fatty acids.

• Fatty Acids: Long hydrocarbon chains; double bonds cause bends (unsaturated fats).

Proteins

Proteins are polymers of amino acids, performing a wide range of functions in cells.

• Amino Acids: 20 different types, each with a unique R-group.

• Peptide Bonds: Link amino acids via dehydration synthesis.

• Globular and Fibrous Proteins: Common shapes.

Levels of Protein Structure

1. Primary Structure: Sequence of amino acids.

2. Secondary Structure: Hydrogen bonds form alpha helices and beta sheets.

3. Tertiary Structure: Interactions among R-groups and water; hydrophobic amino acids cluster inside, hydrophilic outside.

4. Quaternary Structure: Multiple polypeptide chains join to form a functional protein (in some proteins).

Nucleic Acids

Nucleic acids store and transmit genetic information. They are polymers of nucleotides, each consisting of a sugar, phosphate group, and nitrogenous base.

• DNA (Deoxyribonucleic Acid): Double-stranded, bases C-G-T-A, deoxyribose sugar.

• RNA (Ribonucleic Acid): Single-stranded, bases C-G-U-A, ribose sugar.

Feature	DNA	RNA
Strands	Double	Single
Sugar	Deoxyribose	Ribose
Bases	C, G, T, A	C, G, U, A

Additional info: Some explanations and examples have been expanded for clarity and completeness, including the hierarchical organization of life, chemical bonding, and macromolecule structure.