Biology 1.2.4 - Cell Transport

Membrane

• made up of a bilayer of phospholipids
• mostly phospholipids, then proteins, cholesterol, and sugars
• Phospholipids are selectively permeable based on their rotation:
• creates an entrance with heads on the outside and tails on the inside

   Proteins in the membrane

• act as doors for material exchange
• provides a passage through the membrane

  Cholesterol in the membrane

• cholesterol keeps the balance of liquid and solid in the membrane

  Carbohydrates in the membrane

• referred to as “membrane sugars” even though they are polysaccharides
• Membrane sugars identify things in the cell
• called glycoprotein when on a protein, called glycolipid when on a lipid

passive transport

• if a molecule passes through the membrane it is called passive transport
• they will pass through transport proteins called channel proteins
• water will try to dilute an area with more molecules inside it - called osmosis

• Goes from hypotonic solution - fewer molecules within it to hypertonic solution - more molecules within it. once this process is complete the solutions are called isotonic meaning they have equal ratios of molecules.
• When a plant cell is within a hypertonic solution during osmosis it collapses - called plasmolysis, also known as wilting
• In a hypotonic solution, an animal cell will burst in lysis, but a plant cell will be saved from the cell wall, but will still have water in it. This state of a cell is called turgid and it is very beneficial for a plant.

Active Transport

• molecules move through cells using energy or ATP
• molecules move through diffusion using active transport, sometimes they need carrier proteins or protein pumps
• The most important carrier protein is the sodium-potassium pump
• endocytosis - brings large substances into the cell
• phagocytosis - larger substances are pulled in for digestion
• pinocytosis - drops of liquid are pulled in for osmoregulation
• exocytosis - takes large substances out of the cell