Biology101 Chapter 3

1. Identify the two cell types and list the characteristics of each. Which characteristics do    
    all cells have in common?
Prokaryotic Cells:

  • No nucleus; DNA is in a nucleoid region.

  • No membrane-bound organelles.

  • Smaller in size (1-10 µm).

  • Example: Bacteria and Archaea.

Eukaryotic Cells:

  • Have a nucleus containing DNA.

  • Contain membrane-bound organelles (e.g., mitochondria, ER).

  • Larger in size (10-100 µm).

  • Example: Animals, Plants, Fungi, and Protists.

Common Characteristics:

  • Plasma membrane.

  • Cytoplasm.

  • DNA as genetic material.

  • Ribosomes for protein synthesis.


2. Compare and contrast animal and plant cell organelles. Which organelles differentiate
    plant cells from animal cells?

     Common Organelles:

  • Nucleus, Endoplasmic Reticulum (ER), Golgi Apparatus, Mitochondria, Ribosomes, Plasma membrane, Cytoskeleton

  • Plant Cell-Specific Organelles:

  • Chloroplasts: Site of photosynthesis.

  • Cell Wall: Provides structure and support.

  • Central Vacuole: Stores water and maintains turgor pressure.

Animal Cell-Specific Features:

  • Lysosomes: Contain digestive enzymes.

  • Centrioles: Involved in cell division.





3. Explain why cells are so small. Does small cell size confer an advantage for cells?
Reason for Small Size:

  • High surface area-to-volume ratio, allowing efficient nutrient uptake and waste removal.

  • Faster communication and transport within the cell.

Advantages:

  • Efficient diffusion of substances.

  • Faster cellular communication and metabolic processes.


4. Describe the structure of the plasma membrane. Why is this an important structure for
    cellular function?

Structure:

  • Phospholipid bilayer with embedded proteins.

  • Hydrophilic heads face outward; hydrophobic tails face inward.

Function:

  • Selective permeability: Regulates entry and exit of substances.

  • Cell communication and signaling.

  • Protection and structural support.



5. List the three types of cytoskeletal elements, describe their shape and function in the
    cell.
Microfilaments (Actin Filaments):

  • Thin, flexible fibers made of actin.

  • Function: Cell shape, muscle contraction, and cell movement.

Intermediate Filaments:

  • Rope-like fibers providing tensile strength.

  • Function: Maintain cell shape and anchor organelles.

Microtubules:

  • Hollow tubes made of tubulin.

  • Function: Cell division (mitotic spindle), intracellular transport, and movement (cilia and flagella).


6. State the function of the centrosome. Explain the difference in function of cilia and
    flagella.
Centrosome:

  • Microtubule-organizing center involved in cell division.

  • Contains two centrioles in animal cells.

Cilia vs. Flagella:

  • Cilia: Short, numerous, coordinated movement. Used for locomotion or moving substances across cell surfaces.

  • Flagella: Longer, fewer in number, propeller-like motion for cell movement (e.g., sperm cells).


7. Define the function of a cell junction, plant cell wall and extracellular matrix.
Cell Junctions:

  • Tight Junctions: Prevent leakage of extracellular fluid.

  • Desmosomes: Provide mechanical strength by anchoring cells together.

  • Gap Junctions: Allow communication and transport between cells.

Plant Cell Wall:

  • Made of cellulose.

  • Provides structural support and protection.

Extracellular Matrix (ECM):

  • Network of proteins (e.g., collagen) outside animal cells.

  • Function: Structural support, adhesion, and communication.


8. Identify the organelles of the eukaryotic cell and state their function.
Nucleus: Stores DNA and controls cell activity.

Endoplasmic Reticulum (ER):

  • Rough ER: Protein synthesis.

  • Smooth ER: Lipid synthesis and detoxification.

Golgi Apparatus: Modifies, sorts, and ships proteins.

Mitochondria: Produces ATP (energy) through cellular respiration.

Chloroplasts (in plants): Photosynthesis.

Lysosomes: Digestion and recycling of cellular waste (mainly in animals).

Vacuoles: Storage of substances; large central vacuole in plants for water storage.


9. Define phagocytosis and autophagy.
Phagocytosis:

  • "Cell eating" – Cell engulfs large particles or microorganisms.

  • Forms a phagosome that fuses with lysosomes for digestion.

Autophagy:

  • Self-eating process where damaged organelles or proteins are degraded.

  • Maintains cellular homeostasis and recycles cellular components.


10. How did mitochondria and chloroplasts evolve into their current roles in the cell?

Endosymbiotic Theory:

  • Mitochondria and chloroplasts originated from ancient prokaryotes engulfed by ancestral eukaryotic cells.

  • Evidence:

    • Double membrane structure.

    • Own DNA and ribosomes similar to bacteria.

    • Replicate independently through binary fission.