General Biology: Foundations, Chemistry of Life, and Macromolecules

Biological Organization and Energy Flow

Levels of Biological Organization

Biological systems are organized in a hierarchical structure, from the smallest to the largest scale. Understanding these levels helps in studying life from molecules to the biosphere.

• Cells – The basic unit of life.

• Organisms – Individual living entities.

• Populations – Groups of individuals of the same species living in a specific area.

• Communities – Different populations living together in a defined area.

• Ecosystems – Communities plus their physical environment.

Example: A pond ecosystem includes fish (organisms), all fish of one species (population), all living things in the pond (community), and the pond itself (ecosystem).

Energy Flow in Ecosystems

Energy in ecosystems primarily flows from the sun through producers and then to consumers.

• Chemical energy is the primary source of energy for most ecosystems.

• Producers (like plants) convert sunlight into chemical energy via photosynthesis.

Scientific Method and Hypotheses

Controlled Experiments

Controlled experiments are essential for testing scientific hypotheses.

• They involve at least two groups: an experimental group and a control group (which does not receive the experimental treatment).

Scientific Hypotheses

• Must lead to testable predictions.

• Hypotheses are usually narrow in scope, while theories have broad explanatory power.

Chemistry of Life

Elements and Atoms

All matter is composed of elements, which are substances that cannot be broken down by chemical means.

• Element: A pure substance consisting of only one type of atom.

• Atom: The smallest unit of an element, consisting of protons, neutrons, and electrons.

Periodic Table and Atomic Structure

• Atomic number: Number of protons in the nucleus.

• Valence electrons: Electrons in the outermost shell, important for chemical reactivity.

• Unpaired electrons in the valence shell determine an atom's reactivity.

Example: Carbon has 4 unpaired electrons in its valence shell.

Electron Energy Levels

• Electrons can move to higher energy levels (shells) by absorbing energy.

• When electrons lose energy, they move to lower energy levels, closer to the nucleus.

Types of Chemical Bonds

• Ionic bonds: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions.

• Covalent bonds: Formed when atoms share electrons.

• Polar covalent bonds: Unequal sharing of electrons between atoms.

• Nonpolar covalent bonds: Equal sharing of electrons.

Water and Its Properties

• Hydrogen bonds stabilize water molecules and keep ice less dense than liquid water.

• Hydrophobic substances (like vegetable oil) repel water molecules.

pH and Acidity

• pH measures the concentration of hydrogen ions ($[H^+]$) in a solution.

• Each pH unit represents a tenfold change in $[H^+]$.

Example: A decrease in pH from 7 to 5 means the $[H^+]$ increases by 100 times.

Chemical Reactions

• Chemical reaction: The making and breaking of chemical bonds, leading to changes in the composition of matter.

• Reactants: Substances that start a reaction.

• Products: Substances produced by the reaction.

Example equation:

$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

In this equation, $CO_2$ and $H_2O$ are reactants; $C_6H_{12}O_6$ and $O_2$ are products.

Macromolecules and Polymers

Dehydration and Hydrolysis Reactions

• Dehydration reactions assemble polymers by removing water.

• Hydrolysis reactions break down polymers by adding water.

Types of Biological Polymers

• Proteins: Polymers of amino acids.

• Carbohydrates: Polymers of simple sugars (monosaccharides).

• Nucleic acids: Polymers of nucleotides.

Carbohydrates

• Starch can be digested by humans because we have enzymes for alpha glycosidic linkages.

• Cellulose cannot be digested by humans due to beta glycosidic linkages.

Lipids

• Fatty acids can be saturated (no double bonds) or unsaturated (one or more double bonds).

• Phospholipids form bilayers in water due to their hydrophilic heads and hydrophobic tails.

Proteins

• Composed of 20 different amino acids, each with a unique side chain (R group).

• Peptide bonds link amino acids together.

• Protein structure has four levels:

Level	Description
Primary	Sequence of amino acids in a polypeptide chain
Secondary	Alpha helices and beta sheets formed by hydrogen bonding
Tertiary	Three-dimensional folding due to side chain interactions
Quaternary	Assembly of two or more polypeptide subunits

Example: Hemoglobin is a quaternary protein composed of four subunits.

Nucleic Acids

• DNA and RNA are polymers of nucleotides.

• DNA encodes genetic information in the sequence of nucleotides.

• The universal genetic language of DNA is shared by all organisms, indicating common ancestry.

Evolution and Natural Selection

Descent with Modification

• Charles Darwin proposed that species change over time due to natural selection.

• Natural selection favors heritable traits that enhance survival and reproductive success in a given environment.

Example: The evolution of flippers in aquatic mammals from four-limbed land ancestors.

Summary Table: Key Biological Concepts

Concept	Definition/Example
Element	Substance that cannot be broken down by chemical means
Valence Electrons	Electrons in the outermost shell, determine reactivity
Hydrogen Bond	Weak bond between polar molecules, important in water
Dehydration Reaction	Joins monomers by removing water
Hydrolysis	Breaks polymers by adding water
Primary Protein Structure	Sequence of amino acids
Quaternary Protein Structure	Assembly of multiple polypeptide chains

Additional info: Some explanations and examples have been expanded for clarity and completeness, based on standard General Biology curriculum.