AP Biology Unit 2 – Cells: Ultimate Study Notes (CED aligned)

Cell Structure

Prokaryotic vs Eukaryotic Cells

Cell Type Differences

• Prokaryotes:

  • No nucleus

  • No membrane-bound organelles

  • Smaller and simpler

• Eukaryotes:

  • Nucleus present

  • Membrane-bound organelles

  • Larger and more complex

• Cause → Effect

  • Presence of organelles → increased efficiency and specialization

• Tips

  • Always connect structure to function

  • If comparing → mention size + organelles

Organelles and Their Functions

Nucleus and Genetic Control

• Contains DNA

• Controls cell activities

Mitochondria and Energy

• Site of cellular respiration

• Produces ATP

Ribosomes and Protein Synthesis

• Make proteins

• Found free or attached to rough ER

Endoplasmic Reticulum

• Rough ER: protein synthesis

• Smooth ER: lipid synthesis and detoxification

Golgi Apparatus

• Modifies and packages proteins

• Cause → Effect

  • More mitochondria → more ATP production

  • Ribosome presence → increased protein production

• Tips

  • If a cell is active → mention more mitochondria or ribosomes

Cell Membrane Structure

Phospholipid Bilayer

Membrane Structure

• Made of phospholipids

• Hydrophilic heads face outward

• Hydrophobic tails face inward

Membrane Fluidity and Components

Fluid Mosaic Model

• Membrane is flexible

• Contains proteins, cholesterol, carbohydrates

• Proteins:

  • Transport

  • Communication

• Cholesterol:

  • Maintains fluidity

• Cause → Effect

  • Unsaturated lipids → more fluid membrane

  • Cholesterol → stabilizes membrane

• Tips

  • Use term: fluid mosaic model

  • Always mention hydrophobic/hydrophilic

Selective Permeability

What Can Cross

• Small nonpolar molecules pass easily

• Polar and large molecules need help (proteins)

• Cause → Effect

  • Membrane structure → controls what enters/exits

• Tips

  • Phrase: “selectively permeable membrane”

Membrane Transport (Heading 1)

Passive Transport

Diffusion and Facilitated Diffusion

• Diffusion: movement from high → low concentration

• Facilitated diffusion: uses transport proteins

• No ATP required

Active Transport

Movement Against Gradient

• Moves substances from low → high concentration

• Requires ATP

• Uses protein pumps

Osmosis and Tonicity

Water Movement

• Water moves from high → low water potential

Tonicity Effects

• Hypertonic:

  • Higher solute outside

  • Cell shrinks

• Hypotonic:

  • Lower solute outside

  • Cell swells

• Isotonic:

  • No net movement

• Cause → Effect

  • Solute concentration → water movement → cell size change

• Tips

  • “HIPPO”:

    • Hypo = water goes in

  • Always mention water potential or gradient

Surface Area and Cell Size

Surface Area to Volume Ratio

Importance

• Small cells = higher surface area to volume ratio

• Allows faster exchange of materials

• Cause → Effect

  • Increased SA:V → more efficient transport

  • Large cells → slower exchange → need adaptations

• Tips

  • If question mentions size → talk about SA:V ratio

Cell Size Adaptations

Structural Adaptations

• Folding (microvilli) increases surface area

• Long or thin shapes improve exchange

Compartmentalization

Membrane-Bound Organelles

Function of Compartments

• Separate cellular processes

• Increase efficiency

• Prevent interference between reactions

• Cause → Effect

  • Compartmentalization → specialization → efficiency

• Tips

  • Big idea: division of labor in the cell