Cell Membrane - The Basics

• What surrounds all cells?

  Membranes
• What surrounds organelles in eukaryotic cells?

  Membranes
• What is the function of cell-surface membranes?

  They control substance entry and exit
• How are cell-surface membranes described in terms of permeability?

  They are partially permeable
• What processes allow substances to move across the cell-surface membrane?

  Diffusion, osmosis, active transport
• What is another name for the cell-surface membrane?

  Plasma membrane
• What role do membranes around organelles play in a cell?

  They divide the cell into compartments
• How do membranes around organelles affect the cytoplasm?

  They act as barriers to the cytoplasm
• What substances are kept together inside a mitochondrion?

  Substances needed for respiration
• What leaves the nucleus via the nuclear membrane?

  RNA
• Why does DNA remain in the nucleus?

  It is too large to pass through
• What are the main components of cell membranes?

  Lipids, proteins, carbohydrates
• What model describes the arrangement of molecules in the membrane?

  Fluid mosaic model
• What forms the bilayer in cell membranes?

  Phospholipid molecules
• Why is the phospholipid bilayer described as 'fluid'?

  Phospholipids are constantly moving
• What types of proteins are found in the bilayer?

  Channel proteins and carrier proteins
• What do receptor proteins on the cell-surface membrane do?

  They detect chemicals from other cells
• How does insulin interact with liver cells?

  It binds to receptor proteins
• What are glycoproteins?

  Proteins with carbohydrates attached
• What are glycolipids?

  Lipids with carbohydrates attached
• What role does cholesterol play in the membrane?

  It gives the membrane stability
• How does cholesterol affect phospholipids in the membrane?

  It causes them to pack closely together
• Why is cholesterol important for animal cells?

  It helps maintain their shape
• How does temperature affect cell membranes?

  It affects phospholipid movement and permeability
• What happens to membranes at temperatures below 0 °C?

  Membranes become rigid and proteins denature
• What occurs to channel proteins at low temperatures?

  They denature and increase membrane permeability
• What happens to membranes between 0 and 45 °C?

  Membranes are partially permeable
• What happens to the phospholipid bilayer above 45 °C?

  It starts to melt and becomes more permeable
• What effect does high temperature have on channel proteins?

  They denature and lose function
• What are the roles of phospholipids and cholesterol in membranes?

  • Phospholipids:
  • Form a barrier to water-soluble substances
  • Have hydrophilic heads and hydrophobic tails
  • Cholesterol:
  • Provides stability to the membrane
  • Packs phospholipids closely together
• How does temperature affect membrane structure and permeability?

  • Below 0 °C: Membrane is rigid, proteins denature
  • Between 0 and 45 °C: Membrane is partially permeable, phospholipids move more
  • Above 45 °C: Membrane melts, proteins denature, increased permeability
• What is the main purpose of investigating cell membrane permeability?

  To understand how variables affect permeability
• How can beetroot be used to investigate membrane permeability?

  Beetroot cells leak pigment when membranes are permeable
• What are the steps to investigate temperature's effect on beetroot membrane permeability?

  1. Cut five equal pieces of beetroot.
  2. Rinse to remove pigment.
  3. Place in test tubes with water.
  4. Heat at different temperatures.
  5. Use a colorimeter to measure absorbance.
• What tool is used to measure the absorbance of the beetroot solution?

  A colorimeter
• What does a higher absorbance reading indicate in the experiment?

  More pigment has been released
• What should you do before using the colorimeter?

  Allow it to stabilize for five minutes
• Why is distilled water used in the colorimeter cuvette?

  To calibrate the machine to zero
• What is the effect of increasing solvent concentration on cell membrane permeability?

  It increases membrane permeability
• How do solvents affect the structure of cell membranes?

  They dissolve lipids, causing structural loss