Transport Across Cell Membranes

• What is the name of the model given to the cell membrane?

  Fluid mosaic
• Describe the Phospholipid bilayer

  Forms a barrier; hydrophobic tails prevent water-soluble substances from passing through.
• Describe the Intrinsic proteins

  These proteins include channel and carrier proteins which transport large molecules and ions across the membrane.
• Describe Extrinsic (peripheral) proteins

  These proteins provide support to the membrane or may be involved in cell signalling.
• Describe Glycoproteins

  proteins with carbohydrate chains attached, These carbohydrate chains also project out into whatever fluid is surrounding the cell
• Describe glycolipids

  • These are lipids with carbohydrate chains attached
  • These carbohydrate chains project out into whatever fluid is surrounding the cel
• Describe Cholesterol

  have hydrophobic tails and hydrophilic heads, Adds stability by reducing membrane fluidity, prevents leakage.
• what are the 5 things that a cell membrane is made up of?

  • Phospholipids
  • Cholesterol
  • Glycolipids
  • Glycoproteins
  • Proteins (Intrinsic and Extrinsic)
• Name different ways of transport

  1️⃣ Simple Diffusion (Passive)

  2️⃣ Facilitated Diffusion (Passive)

  3️⃣ Osmosis (Passive)

  4️⃣ Active Transport (Requires ATP)

  5️⃣ Endocytosis & Exocytosis (Bulk Transport)
• What is simple diffusion

  Movement of molecules from high to low concentration (down the concentration gradient). No ATP required (passive). Only small, non-polar molecules can diffuse (e.g., O₂, CO₂).
• What is Osmosis

  Diffusion of water across a partially permeable membrane. Water moves from high water potential to low water potential. No ATP required.
• What is the water potential for pure water?

  0kPa
• • Adding solutes lowers water potential (more negative Ψ).
  • Water moves from less negative Ψ to more negative Ψ.
• Whats active transport

  Moves substances against the concentration gradient (low to high).Requires carrier proteins and ATP (energy).
• What is Endocytosis & Exocytosis (Bulk Transport)

  Used for very large molecules (e.g., proteins, bacteria).Requires ATP.

  Endocytosis (Into the Cell)

  • Phagocytosis – “Cell eating” (e.g., white blood cells engulf bacteria).
  • Pinocytosis – “Cell drinking” (e.g., absorbing fluids).

  Exocytosis (Out of the Cell)

  • Vesicles fuse with the membrane to release contents (e.g., hormones, neurotransmitters).
• What is co-transport

  Co-transport is a special type of active transport that moves two molecules at the same time
• Using a sodium potassium pump, explain the first step of co-transport

  Sodium-Potassium Pump (Active Transport)

  • Sodium ions (Na⁺) are actively transported out of the epithelial cell into the blood by the Na⁺/K⁺ pump.
  • This lowers the Na⁺ concentration inside the epithelial cell.
• Name the 2nd step in co-transport (NaK)

  Sodium-Glucose Co-Transport (Facilitated Diffusion)

  • Sodium ions (Na⁺) move back into the epithelial cell from the gut lumen down their concentration gradient.
  • Glucose is absorbed along with Na⁺ (co-transport) using a co-transporter protein.
• Name the 3rd step in co-transport (NaK)

  Glucose Moves into the Blood (Facilitated Diffusion)

  • Glucose now moves from the epithelial cell into the blood via a carrier protein (facilitated diffusion).
  • The blood constantly removes glucose, keeping the concentration gradient steep.
• Key Features of Co-Transport

  ✅ Indirect active transport – Uses ATP to create a sodium gradient, but glucose moves by facilitated diffusion.✅ Relies on Na⁺ gradient – Without the Na⁺/K⁺ pump, glucose absorption would not happen.✅ Example in Humans – Absorption of glucose and amino acids in the small intestine.
• Key Exam Points

  ✅ Co-transport uses a sodium gradient to absorb glucose/amino acids.✅ The Na⁺/K⁺ pump maintains the gradient using active transport.✅ Glucose moves into the blood by facilitated diffusion.