Biology EOC Review Unit 3: Cells, Homeostasis, and Transport

Biology EOC Review Unit 3: Cells, Homeostasis, and Transport

Prokaryotic vs. Eukaryotic Cells

1. Prokaryotes
  • Definition: Prokaryotes are cells that do not have a nucleus or membrane-bound organelles.
  • Characteristics:
      - Lack a nucleus
      - Have a single, circular chromosome
      - Lack membrane-bound organelles
      - Small and simple in structure
      - Generally single-celled organisms
2. Eukaryotes
  • Definition: Eukaryotes are cells that possess a nucleus and membrane-bound organelles.
  • Characteristics:
      - Contain a nucleus
      - Have multiple linear chromosomes
      - Contain membrane-bound organelles
      - Larger and more complex than prokaryotic cells
      - Can be single-celled or multicellular organisms
3. Shared Characteristics of Prokaryotic and Eukaryotic Cells
  • Both types of cells contain:
      - Cell membrane
      - Cytoplasm
      - Ribosomes
      - DNA
      - Cell wall: Present in eukaryotes such as some protists, fungi, and all plants

Cell Organelles

1. Organelles Common in Both Animal and Plant Cells
  • Nucleus: Contains the genetic material/DNA
  • Nucleolus: Produces ribosomes
  • Ribosomes: Responsible for protein synthesis
  • Rough Endoplasmic Reticulum (ER): Ships proteins made by ribosomes located on its surface
  • Smooth Endoplasmic Reticulum (ER): Synthesizes lipids and steroids; detoxifies drugs, alcohol, and toxins
  • Golgi Body: Modifies, sorts, and ships molecules around or out of the cell
  • Cell Membrane: Regulates the trafficking of substances in and out of the cell
  • Cytoplasm: Serves as a medium that stores cell organelles
  • Mitochondria: Produces energy in the form of ATP (adenosine triphosphate)
2. Organelles Unique to Animal Cells
  • Lysosome: Contains enzymes that break down old organelles, bacteria, or food particles
  • Centrioles and Centrosome: Involved in the formation of spindle fibers during mitosis and meiosis
3. Organelles Unique to Plant Cells
  • Chloroplast: Site of photosynthesis and contains chlorophyll
  • Cell Wall: The outermost layer that provides structural support and protection
  • Plasmodesmata: Channels that connect adjacent plant cells, allowing for molecular movement between them
  • Central Vacuole: Stores water, ions, and waste products in plant cells

Cell Membrane

1. Structure of the Cell Membrane
  • The cell membrane consists primarily of phospholipids which form a lipid bilayer.
      - Phospholipid Heads: Polar and hydrophilic
      - Phospholipid Tails: Nonpolar and hydrophobic
  • Proteins embedded in the cell membrane:
      - Facilitate the transport of substances across the membrane
      - Assist in cell-to-cell communication
      - Serve as recognition signals for other cells
  • Cholesterol within the membrane:
      - Provides structural support
      - Regulates membrane fluidity
2. Cell Transport

  • Passive Transport: The movement of materials down the concentration gradient (from high to low concentration) without the use of cellular energy (ATP).
      - Diffusion: Movement of particles directly across the membrane
      - Facilitated Diffusion: Certain molecules pass through specialized protein channels
      - Osmosis: The diffusion of water across the cell membrane, either directly or via aquaporins

  • Active Transport: The movement of materials against a concentration gradient (from low to high concentration) that requires energy (ATP).
      - Protein Pumps: Small molecules or ions move across the membrane through proteins that change shape when energy from ATP is used.
        - Example: Sodium-potassium pump, which moves sodium and potassium ions
      - Bulk Transport: Transports large molecules or clumps of material across cell membranes
        - Endocytosis: Movement of molecules into the cell
          - Phagocytosis: Cell “eating” where vesicles bring in food
          - Pinocytosis: Cell “drinking” where vesicles bring in liquid
        - Exocytosis: Movement of molecules out of the cell

3. Cell Tonicity

  • Hypotonic Solution:
      - Description: A solution with fewer solutes compared to another solution
      - Effect on Animal Cell: Water enters, causing the cell to expand and potentially burst
      - Effect on Plant Cell: Water enters, causing the cell to become turgid (swollen)

  • Isotonic Solution:
      - Description: A solution with equal solute concentrations compared to another solution
      - Effect on Animal Cell: Water molecules move in and out at the same rate
      - Effect on Plant Cell: Cells are flaccid (not turgid or wilted)

  • Hypertonic Solution:
      - Description: A solution with more solutes compared to another solution
      - Effect on Animal Cell: Water moves out, causing the cell to shrivel
      - Effect on Plant Cell: Water moves out, causing the plant to wilt