Introduction to Biology

What is Life?

Biology is the study of living organisms and their interactions with the environment. To be considered alive, an organism must be able to move, grow, reproduce, and spread.

• Characteristics of Life: Acquiring energy, maintaining complexity (multicellular), responding to stimuli, growing, reproducing, and evolving.

• Viruses: Although viruses can spread and evolve, they are not considered fully alive because they lack cellular structure and independent metabolism.

The Scientific Method

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

• Steps:

  1. Observation

  2. Ask a question

  3. Formulate a hypothesis (must be testable)

  4. Make a prediction (if...then statement)

  5. Test/Experiment

  6. Analyze results and draw conclusions

• Variables: Factors that can change in an experiment. Independent variable is manipulated, dependent variable is measured.

• Example: "Hand Soap vs. Hand Sanitizer" experiment: Soap and sanitizer were compared for effectiveness in killing bacteria. Soap reduced bacteria more than sanitizer, but both worked similarly.

Atoms, Molecules, and Chemical Bonds

Atomic Structure

Atoms are the basic units of matter, composed of protons, neutrons, and electrons.

• Protons: Positively charged particles in the nucleus.

• Neutrons: Neutral particles in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus.

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

Chemical Bonds

Atoms combine to form molecules through chemical bonds.

• Ionic Bonds: Transfer of electrons between atoms, resulting in charged ions.

• Covalent Bonds: Sharing of electrons between atoms. Can be polar (unequal sharing) or nonpolar (equal sharing).

• Hydrogen Bonds: Weak attractions between polar molecules, important in water and biological molecules.

Water and Its Properties

Unique Properties of Water

Water is essential for life due to its unique chemical and physical properties.

• Cohesion: Water molecules stick together.

• Adhesion: Water molecules stick to other surfaces.

• Surface Tension: Water forms a "skin" at its surface due to cohesion.

• Solvent: Water can dissolve many substances, making it a universal solvent.

• Specific Heat: Water requires a lot of energy to change temperature, helping regulate climate and body temperature.

• pH Scale: Measures acidity or basicity. Water is neutral (pH 7).

• Buffer: Substances that stabilize pH by accepting or releasing H+ ions.

Carbon and Organic Molecules

Importance of Carbon

Carbon is the backbone of organic molecules, which are essential for life.

• Organic Molecules: Contain carbon atoms.

• Inorganic Molecules: Lack carbon atoms.

• Monomers and Polymers: Monomers are single units; polymers are chains of monomers.

• Dehydration Synthesis: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

• Examples: Proteins, carbohydrates, lipids, and nucleic acids.

Cell Structure and Function

Types of Cells

Cells are the basic units of life. They can be prokaryotic or eukaryotic.

• Prokaryotic Cells: Simple, no nucleus, smaller (e.g., bacteria).

• Eukaryotic Cells: Complex, have a nucleus and organelles (e.g., plants, animals).

Cell Organelles and Their Functions

• Nucleus: Contains DNA, control center of the cell.

• Mitochondria: Powerhouse of the cell, site of ATP production.

• Chloroplasts: Site of photosynthesis in plant cells.

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids and detoxifies.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Digestive organelles, break down waste.

• Vacuoles: Storage organelles, especially large in plant cells.

• Cytoskeleton: Provides structure and aids in cell movement.

• Cell Membrane: Regulates entry and exit of substances, maintains homeostasis.

• Flagella and Cilia: Structures for movement; flagella are tail-like, cilia are hair-like.

Cell Membranes and Transport

Structure of Cell Membranes

All cells are surrounded by membranes composed of a phospholipid bilayer with embedded proteins.

• Fluid Mosaic Model: Describes the flexible, dynamic nature of the membrane.

• Phospholipids: Have hydrophilic heads and hydrophobic tails.

• Proteins: Serve as channels, receptors, enzymes, and structural components.

• Selective Permeability: Membranes control what enters and leaves the cell.

Transport Across Membranes

• Passive Transport: Movement of substances without energy input (e.g., diffusion, osmosis).

• Active Transport: Movement of substances against a concentration gradient, requires energy (ATP).

• Osmosis: Movement of water across a semi-permeable membrane.

• Endocytosis/Exocytosis: Bulk transport into (endocytosis) or out of (exocytosis) the cell.

• Facilitated Diffusion: Passive transport via membrane proteins.

Energy and Enzymes

Energy in Biological Systems

Energy is required for all cellular processes. It exists in various forms and can be transformed.

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

• Second Law of Thermodynamics: Energy transformations increase entropy.

• ATP (Adenosine Triphosphate): Main energy currency of the cell.

• Equation:

Enzymes

Enzymes are biological catalysts that speed up chemical reactions.

• Lock and Key Model: Enzymes are specific to their substrates.

• Competitive Inhibition: Inhibitor competes with substrate for active site.

• Noncompetitive Inhibition: Inhibitor binds elsewhere, changing enzyme shape.

• Denaturation: Loss of enzyme function due to changes in temperature or pH.

• Optimal pH: Most human enzymes work best around pH 7.4.

Photosynthesis

Overview of Photosynthesis

Photosynthesis is the process by which plants convert light energy into chemical energy.

• Location: Chloroplasts in plant cells.

• Equation:

• Stages: Light reactions (convert light to chemical energy), Calvin cycle (uses energy to make glucose).

• Stomata: Openings in leaves for gas exchange.

• Thylakoids: Membrane structures where light reactions occur.

Macromolecules

Types of Biological Macromolecules

Cells are composed of four major types of macromolecules.

• Carbohydrates: Provide energy and structural support.

• Lipids: Store energy, make up cell membranes.

• Proteins: Perform a wide range of functions, including catalysis, structure, and transport.

• Nucleic Acids: Store and transmit genetic information (DNA and RNA).

Table: Comparison of Cell Types

Table: Types of Chemical Bonds

Additional info:

• Some content was inferred and expanded for clarity and completeness, such as definitions and examples of cell organelles, chemical bonds, and the scientific method.

• Tables were constructed to summarize comparisons and classifications mentioned in the notes.