General Biology: Foundations, Chemistry, and Biological Molecules

Introduction to Biology

What is Biology?

Biology is the scientific study of life and living organisms, encompassing their structure, function, growth, origin, evolution, and distribution. It covers a wide range of topics from the molecular mechanisms within cells to the interactions of organisms within ecosystems.

Levels of Biological Organization

Hierarchy of Life

Biological organization refers to the different levels at which life can be studied, from the smallest units to the largest systems.

• Atoms and Molecules: The chemical building blocks of matter.

• Cells: The basic unit of life.

• Tissues: Groups of similar cells performing a specific function.

• Organs: Structures composed of different tissues working together.

• Organ Systems: Groups of organs that perform related functions.

• Organisms: Individual living beings.

• Populations: Groups of organisms of the same species in a given area.

• Communities: All the different populations in a specific area.

• Ecosystems: Communities and their non-living environment.

• Biosphere: All ecosystems on Earth.

Example: A forest ecosystem includes trees (organisms), their populations, the animal communities, and the soil, water, and air (non-living environment).

The Scientific Method

Steps of the Scientific Method

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

• Observation: Gathering information about a phenomenon.

• Hypothesis: A testable explanation for an observation.

• Experiment: Testing the hypothesis under controlled conditions.

• Data Collection: Recording and analyzing results.

• Conclusion: Interpreting data to support or refute the hypothesis.

• Communication: Sharing results with the scientific community.

Key Concepts

• Controlled Experiment: An experiment in which only one variable is changed at a time, while all others are kept constant.

• Dependent Variable: The variable being measured or tested.

• Independent Variable: The variable that is changed or manipulated.

• Double Blind Study: An experiment in which neither the participants nor the experimenters know who is receiving a particular treatment, reducing bias.

• Theory vs. Hypothesis: A hypothesis is a specific, testable prediction; a theory is a well-substantiated explanation based on a body of evidence.

• Reading and Analyzing Graphs: Understanding axes, trends, and data points to interpret scientific results.

Example: Testing whether a new drug lowers blood pressure compared to a placebo using a double-blind study.

Chemical Reactions in Biology

What are Chemical Reactions?

Chemical reactions involve the transformation of substances (reactants) into new substances (products) by breaking and forming chemical bonds.

• Reactants: Substances present at the start of a reaction.

• Products: Substances formed as a result of the reaction.

• Writing Reactions: Reactants are written on the left, products on the right, separated by an arrow. Example: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}$

Atoms and Subatomic Particles

Structure of Atoms

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

• Protons: Positively charged particles in the nucleus.

• Neutrons: Neutral particles in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus.

Determining Atomic Structure:

• Atomic Number: Number of protons (defines the element).

• Mass Number: Number of protons plus neutrons.

• Number of Electrons: In a neutral atom, equal to the number of protons.

Example: Carbon has 6 protons, 6 neutrons (mass number 12), and 6 electrons.

Chemical Bonds

Types of Chemical Bonds

Atoms combine to form molecules through different types of chemical bonds:

• Covalent Bonds: Atoms share electron pairs. Can be polar (unequal sharing) or nonpolar (equal sharing).

• Ionic Bonds: Electrons are transferred from one atom to another, creating charged ions that attract each other.

• Hydrogen Bonds: Weak attractions between a hydrogen atom (covalently bonded to an electronegative atom) and another electronegative atom.

Comparison Table:

Bond Type	Strength	Example
Covalent	Strong	H2O (within molecule)
Ionic	Strong (in dry state)	NaCl
Hydrogen	Weak	Between water molecules

Properties of Water

Hydrogen Bonding and Water's Unique Properties

Water's properties are largely due to hydrogen bonding between molecules.

• Cohesion: Water molecules stick together.

• Adhesion: Water molecules stick to other substances.

• High Specific Heat: Water resists temperature changes.

• High Heat of Vaporization: Requires a lot of energy to evaporate.

• Ice Floats: Solid water is less dense than liquid water.

• Solvent Properties: Water dissolves many substances.

Example: Water's high specific heat helps regulate Earth's climate.

pH, Acids, Bases, and Buffers

Understanding pH

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

• pH Scale: Ranges from 0 (acidic) to 14 (basic), with 7 being neutral.

• Acid: Substance that increases $[H^+]$ in solution (pH < 7).

• Base: Substance that decreases $[H^+]$ (pH > 7).

• Neutral: Equal $[H^+]$ and $[OH^-]$ (pH = 7).

• Buffer: Substance that minimizes changes in pH by accepting or donating H+ ions.

Formula:

$\text{pH} = -\log_{10}[H^+]$

Example: Blood contains buffers to maintain a stable pH around 7.4.

Organic Molecules and Polymers

Classes of Organic Molecules

Organic molecules are carbon-based compounds essential for life. The four main classes are carbohydrates, lipids, proteins, and nucleic acids.

1. Carbohydrates

• Monomers: Monosaccharides (simple sugars like glucose).

• Polymers: Polysaccharides (starch, glycogen, cellulose).

• Function: Energy storage and structural support.

• Polymerization Reaction: Dehydration synthesis (removal of water to form bonds).

2. Lipids

• Subunits: Glycerol and fatty acids.

• Types: Fats, oils, phospholipids, steroids.

• Properties: Hydrophobic, energy storage, membrane structure.

• Saturation: Saturated fats (no double bonds, solid at room temp), unsaturated fats (one or more double bonds, liquid at room temp).

3. Proteins

• Monomers: Amino acids.

• Structure: Primary, secondary, tertiary, and quaternary levels.

• Function: Enzymes, structural support, transport, signaling.

• Structure-Function Relationship: The shape of a protein determines its function.

4. Nucleic Acids

• Monomers: Nucleotides (sugar, phosphate, nitrogenous base).

• Types: DNA and RNA.

• Function: Store and transmit genetic information.

Summary Table: Classes of Organic Molecules

Class	Monomer	Polymer	Main Function
Carbohydrates	Monosaccharide	Polysaccharide	Energy, structure
Lipids	Glycerol, fatty acids	Triglyceride, phospholipid	Energy, membranes
Proteins	Amino acid	Polypeptide	Enzymes, structure
Nucleic Acids	Nucleotide	DNA, RNA	Genetic info

Additional info: The type of reaction that builds polymers is called dehydration synthesis, while hydrolysis breaks them down. The sequence of amino acids in a protein (its primary structure) determines its final shape and function.