Exam Study Guide Biology

Study Guide: Biology Exam Preparation

Exam Date

  • February 26, 2026

Organelles and Cell System (Flow of Information)

Cells: Definition and Importance
  • Cells are the basic unit of structure and function of all living things.
Cell Theory
  1. All organisms are composed of cells.
  2. All cells come from preexisting cells.
  3. Cells are the smallest structural and functional unit of organisms.
Cell Size
  1. Cells range in size from one millimeter down to one micrometer.
  2. Cells require a large surface area of plasma membrane to efficiently exchange materials.
  3. The surface-area-to-volume ratio necessitates that cells remain small.
    • As cell size increases, volume increases faster than surface area, leading to decreased efficiency in material exchange.
    • Large cells: Small surface area relative to volume.
    • Small cells: Larger surface area to volume ratio advantageous for exchanging molecules.

The Plasma Membrane

  • The plasma membrane is a thin flexible barrier surrounding the cell, controlling the ingress and egress of substances.
  • It is composed of a phospholipid bilayer made of amphipathic molecules.
Structure of the Plasma Membrane
Phospholipid Bilayer
  • Comprised of phospholipids arranged in two layers:
    • Hydrophilic head: Attracted to water, facing outward toward aqueous environments.
    • Hydrophobic tails: Repelled by water, facing inward, shielded from water.
  • Each phospholipid consists of:
    • Glycerol backbone
    • Phosphate group (polar/charged → hydrophilic head)
    • Two hydrocarbon chains (nonpolar → hydrophobic tails)
Membrane Permeability
  • Phospholipid bilayers are selectively permeable, allowing:
    • Some substances to pass easily, while others do not.
  • Proteins in the Membrane:
    • Embedded in the membrane, proteins perform varied roles:
      • Channel proteins: Permit specific molecules to pass.
      • Carrier proteins: Facilitate movement of substances.
      • Pump proteins: Utilize energy to move substances.
Substances That Can Pass Through
  • Easily Pass: Small and nonpolar molecules such as:
    • Oxygen (O₂)
    • Carbon dioxide (CO₂)
  • Require Protein Help:
    • Ions, large molecules, polar molecules.
Amphipathic Definition
  • Amphipathic: Describes molecules that have both hydrophilic (water-loving) and hydrophobic (water-fearing) regions, leading to the automatic formation of bilayers in phospholipids.

Cell Types: Prokaryotic vs. Eukaryotic

Prokaryotic Cells
  • Characteristics:
    • Lack membrane-bound nucleus.
    • Smaller and simpler than eukaryotic cells.
    • Examples: Bacteria, Archaea.
    • Key Features include:
      • Fimbriae: Short appendages aiding in attachment.
      • Flagella: Long projections used for locomotion.
      • Cell wall: Maintains shape, strengthened by peptidoglycan structure.
Eukaryotic Cells

  • Characteristics:

    • Contain a membrane-bound nucleus housing DNA.

    • Larger and more complex than prokaryotic cells.

    • Contain Organelles: Small structures performing specific functions.

    • Key Organelles and their Functions:

    • Nucleus:

      • Command center of the cell, produces RNA.
      • Contains chromatin (DNA bound with proteins).
      • Surrounded by a nuclear envelope with nuclear pores for exchange between nucleoplasm and cytoplasm.

    • Endoplasmic Reticulum (ER):

      • System of membranes continuous with the nuclear envelope.
      • Rough ER: Contains ribosomes; involved in protein synthesis.
      • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies harmful substances.

    • Ribosomes:

      • Synthesize proteins needed for cellular functions.
      • Composed of rRNA; may be free in cytoplasm or bound to ER.

    • Golgi Apparatus:

      • Flattened sacs that process proteins and lipids from ER, packaging them for export or secretion.

    • Vacuoles:

      • Membranous sacs larger than vesicles; store excess materials.
      • Central vacuole in plant cells stores water, nutrients, pigments, and waste, contributing to turgor pressure.

    • Lysosomes:

      • Membrane-bound vesicles containing digestive enzymes; involved in breaking down large molecules, recycling cellular components, and pathogen destruction.

    • Peroxisomes:

      • Similar to lysosomes, involved in fatty acid metabolism and detoxification, converting hydrogen peroxide (H₂O₂) into harmless substances.

Energy Processing

Mitochondria and Chloroplasts

  • Mitochondria:

    • Responsible for ATP production via cellular respiration.
    • Require glucose and oxygen, releasing carbon dioxide.

  • Chloroplasts (in plants):

    • Carry out photosynthesis converting sunlight into chemical energy (glucose).
    • Use carbon dioxide, water, and sunlight, releasing oxygen.

The Cytoskeleton

  • Maintains cell shape and assists in movement of organelles.
  • Composed of three Types of protein fibers:
    1. Microfilaments:
      • Composed of actin, forming a network that maintains cell shape and supports muscle contraction.
    2. Intermediate Filaments:
      • Composed of fibrous proteins that provide structural support and anchor organelles including the nucleus.
    3. Microtubules:
      • Composed of tubulin proteins, providing shape and support; facilitate organelle movement during cell division.
Importance of the Cytoskeleton
  • Facilitates organelle movement and transport (e.g., vesicles from ER to Golgi to membrane).
  • Essential for proper cell division and structural integrity of cells.

Cell Membranes and Permeability

Factors Affecting Membrane Permeability
  • Substances are blocked based on:
    • Size
    • Polarity (charge)
    • Lipid solubility
  • What Passes Easily:
    • Small, nonpolar, and lipid-soluble substances (e.g., O₂, CO₂, N₂, steroid hormones).
  • What Does NOT Pass Easily:
    • Charged ions (e.g., Na⁺, K⁺, Cl⁻) and large polar molecules (e.g., glucose, amino acids) require protein channels or pumps for transport.
Special Case: Water
  • Water is polar but small, allowing it to pass slowly through membranes. The majority move via specialized channels known as aquaporins.
Signal of Polarity
  • Nonpolar Molecules: Mostly consist of carbon (C) and hydrogen (H) with a symmetrical shape, exhibit no charge.
  • Polar Molecules: Exhibit an unequal charge distribution and often include O, N, or phosphate groups.
  • Charged Molecules: Have full charges and cannot pass through hydrophobic regions of the membrane.
Membrane Fluidity
  • Affected by tail saturation:
    • Saturated Tails: Linear, tightly packed, less fluidity.
    • Unsaturated Tails: Bent, more space, increased fluidity.
  • Cholesterol: Regulates fluidity—reducing it at high temperatures and preventing rigidity at low temperatures.

Transport Mechanisms

Passive Transport
  • Diffusion: Movement of molecules from high concentration to low concentration without energy (ATP).
    • Types of Passive Transport:
      • Simple diffusion: Direct passage of small nonpolar molecules.
      • Facilitated diffusion: Requires membrane proteins for larger or polar molecules.
Active Transport
  • Active Transport: Moves substances against the concentration gradient (low to high) using ATP.
    • Examples include sodium-potassium pumps.
Vesicular Transport
  • Exocytosis: Exports bulky materials from the cell via vesicle fusion with the plasma membrane.
  • Endocytosis: Involves membrane folding inward to engulf materials, forming a vesicle that moves into the cytoplasm.
    • Types: Phagocytosis (large particles), Pinocytosis (fluids), Receptor-mediated endocytosis (specific molecules).

Osmosis and Tonicity

Osmosis
  • Defined as the diffusion of water across a selectively permeable membrane from an area of lower solute concentration to one of higher concentration.
Tonicity
  • Describes how a solution influences cell water movement:
  1. Isotonic: Equal solutes inside and outside the cell; no net movement—cell retains its size.
  2. Hypotonic: Lower solute concentration outside; water enters the cell, causing it to swell and possibly burst (lyse).
  3. Hypertonic: Higher solute concentration outside; water exits the cell, leading to shrinkage (crenation).
  • Plant cells resist bursting in hypotonic solutions due to a cell wall.

Enzymes

Definition and Function
  • Enzymes are biological catalysts that increase reaction rates without being consumed or altered by the reaction.
  • They lower the activation energy required for reactions, enabling biochemical processes.
    • Activation energy is necessary to instigate a reaction and can be thought of as an energy barrier a reaction must cross to proceed.
Role in Digestion
  • Enzymatic actions involve specific substrates that bind to the active site of the enzyme:
    • Examples of key enzymes:
      • Amylase: Decomposes carbohydrates/starches.
      • Lipase: Decomposes fats.
      • Protease: Decomposes proteins.
      • Catalase: Breaks down hydrogen peroxide into water and oxygen.
Factors Affecting Enzyme Activity
  • Temperature: Optimal ranges exist, with excessive heat leading to denaturation.
  • pH: Each enzyme has an optimal pH; significant deviations can alter enzyme structure and functionality.
  • Concentration: Enzyme and substrate concentrations affect reaction rates, with maximum production reached at high substrate concentrations (enzyme saturation).
Enzyme Inhibition
  • Competitive Inhibition: Inhibitor resembles substrate and competes for active site access.
  • Non-competitive Inhibition: Binds to an alternative site, altering the enzyme's shape and reducing activity.
Regulation of Enzymes
  • Feedback inhibition occurs when the product of an enzymatic pathway inhibits the enzyme responsible for its synthesis, thus maintaining cellular equilibrium.
General Enzyme Equation
  • Enzyme + Substrate → Enzyme-Substrate Complex → Enzyme + Product
  • Example with catalase:
    • Catalase + H₂O₂ → Catalase + H₂O + O₂
Chemical Reactions in Cells
  • Types:
    • Exergonic Reactions: Release energy (e.g., cellular respiration).
    • Endergonic Reactions: Require energy input (e.g., photosynthesis).
    • Energetic Coupling: The process where an exergonic reaction provides energy for an endergonic reaction using ATP.
Energy Dynamics in Reactions
  • Exergonic Reaction: Reactants have higher energy, and energy is released as products form.
  • Endergonic Reaction: Reactants have lower energy, and energy is absorbed to form products.
Microscope Components
  • Objective Lens: Located on the body tube; varies in magnification (4X to 100X) used for locating and observing specimens.
  • Total Magnification Calculation: Magnifying power of the ocular lens multiplied by the objective lens.

Conclusion

This study guide encapsulates key knowledge necessary for the upcoming Biology examination, detailing crucial structures, functions, processes, and mechanisms inherent in cellular biology and biochemistry, vital for an in-depth understanding of biological systems.