AP Bio Unit 3

Unit 3: Cells Cellular Structure, Function & Transport

Driving Questions

• 3.1: What do all cells have in common?

• 3.2: How are prokaryotic cells different from eukaryotic cells?

• 3.3: How do plant cells compare to animal cells?

• 3.4: How do organelles facilitate protein synthesis, processing, and transport?

• 3.5: What is the structure and function of the cell membrane?

• 3.6: How do substances move in and out of a cell?

Cell Theory

• Definition: Explains what cells are based on three principles:

1. All living things are composed of one or more cells.

2. Cells are the smallest functional unit of life.

3. All cells arise from preexisting cells.

Common Structures in All Cells

Four Structures

1. DNA

   • Genetic material coding for proteins.

2. Ribosomes

   • Organelle for protein synthesis; converts amino acids into polypeptides.

3. Cytoplasm

   • Composed of cytosol (water-based solution) and organelles excluding the nucleus.

4. Cell Membrane

   • Phospholipid bilayer encasing the cytoplasm.

Differences between Prokaryotic & Eukaryotic Cells

Prokaryotic Cells

• Characteristics:

  • Lack a nucleus and membrane-bound organelles.

  • Typically small and simple; often unicellular (e.g., bacteria).

Eukaryotic Cells

• Characteristics:

  • DNA contained in a nucleus.

  • Have various membrane-bound organelles.

  • Generally larger and complex; can be unicellular or multicellular (e.g., plants, animals, fungi).

Comparison of Plant & Animal Cells

Unique Structures in Plant Cells

• Chloroplasts

  • Site of photosynthesis.

• Large Central Vacuole

  • Storage of water; aids in maintaining turgor pressure for shape.

• Cell Wall

  • Composed primarily of cellulose; protects cells from osmotic pressure.

Organelles & Protein Synthesis

Key Organelles

1. Nucleus

   • Contains instructions for making proteins.

2. Ribosome

   • Site of protein synthesis.

3. Rough Endoplasmic Reticulum (E.R.)

   • Where proteins are made and initially folded.

4. Golgi Apparatus

   • Modifies, sorts, and ships proteins.

5. Vesicle

   • Transports proteins to various destinations.

Cell Membrane Structure & Function

• Composition:

  • Made up of a phospholipid bilayer.

• Fluid Mosaic Model:

  • Indicates that phospholipids and proteins move and are distributed unevenly throughout the membrane.

• Membrane Components:

  • Membrane Proteins: Include channels, pumps, receptors, enzymes; contribute to various functions.

  • Glycoproteins & Glycolipids: Serve as identification flags for cellular recognition.

  • Cholesterol: Reduces fluidity and permeability, ensuring stability without making the membrane too rigid.

Cell Membrane Permeability

• Selectively Permeable:

  • Allows certain substances to pass while restricting others.

  • Types of Movement:

  • Fast Movement: Unassisted passage of gases and nonpolar molecules.

  • Slow Movement: Small polar molecules require assistance.

  • No Movement: Large polar molecules and ions need transportation assistance.

Types of Transport Across the Membrane

Passive Transport

• Diffusion: Movement from high to low concentration (down the concentration gradient) without energy.

• Osmosis: Special case for water movement affecting cell shape.

• Facilitated Diffusion: Uses transport proteins for polar molecules and ions.

• Examples:

  • Aquaporins: Channel proteins aiding water diffusion.

  • Carrier Proteins: Assist in glucose transport.

Active Transport

• Definition: Requires energy to move substances against their concentration gradient (low to high).

• Examples:

  • Sodium-Potassium Pump: Transports sodium out and potassium into cells, critical for maintaining electrical gradients.

Types of Solutions Affecting Cells

• Isotonic Solution: Balanced solute concentration inside and outside the cell.

• Hypotonic Solution: Lower solute concentration outside; cells swell.

• Hypertonic Solution: Higher solute concentration outside; cells shrink.