Assessment statements

Assessment statement

Obj

Teacher’s notes

2.4.1

Draw and label a diagram to show the structure of membranes.

1

The diagram should show the phospholipid bilayer, cholesterol, glycoproteins, and integral and peripheral proteins. Use the term plasma membrane, not cell surface membrane, for the membrane surrounding the cytoplasm.

Integral proteins are embedded in the phospholipid of the membrane, whereas peripheral proteins are attached to its surface. Variations in composition related to the type of membrane are not required.

Aim 7: Data logging to measure the changes in membrane permeability using colorimeter probes can be used.

2.4.2

Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.

3

2.4.3

List the functions of membrane proteins.

1

Include the following: hormone binding sites, immobilized enzymes, cell adhesion, cell-to-cell communication, channels for passive transport, and pumps for active transport.

2.4.4

Define diffusion and osmosis.

1

Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration.

Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.

2.4.5

Explain passive transport across membranes by simple diffusion and facilitated diffusion.

3

2.4.6

Explain the role of protein pumps and ATP in active transport across membranes.

3

2.4.7

Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.

3

2.4.8

Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.

2

Lecture notes

1. Draw and label a diagram to show the structure of membranes.

  • Phospholipid bilayer annotated to show composition of phosphate heads and fatty acid tails
  • Cholesterol shown between phospholipids, stretching inward from phospholipid surface along side fatty acid tails
  • Glycoproteins shown with carbohydrate chain attached to integral protein and extending outside cell membrane
  • Integral proteins embedded within the phospholipids of the membrane
    • Transmembrane proteins extending fully across phospholipid membrane
  • Peripheral proteins attached to the outside of the phospholipid surface
  • Glycolipid shown with carbohydrate chain attached phospholipid head and extending outside cell membrane
  • Annotated to show membrane thickness of 10 nm

2. Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.

  • Hydrophobic fatty acid tails repel water and form the middle layer of the membrane.
    • fatty acid tails contain only C-H and C-C bonds, which are non-polar
  • Hydrophilic phosphate heads attract water and form the outer layers of the membrane.
    • phosphate heads are ionic and therefore attract water

3. List the functions of membrane proteins including:

  • Hormone binding sites
  • Immobilized enzymes
  • Cell adhesion
  • Cell-to-cell communication
  • Channels for passive transport
  • Pumps for active transport.

4. Define:

  • Diffusion = the passive movement of particles from a region of higher concentration to a region of lower concentration.
  • Osmosis = the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.
    • hypertonic = higher solute concentration
    • hypotonic = lower solute concentration
    • isotonic = equal solute concentrations

5. Explain passive transport across membranes in terms of simple diffusion and facilitated diffusion.

Concentration gradient: Molecules can diffuse across membranes from areas of higher to lower concentration by:

  • Simple diffusion: traveling directly through the membrane if they are small and uncharged, thus avoiding repulsion by the hydrophobic, non-polar tails of phospholipids in the middle of the membrane.
  • Facilitated diffusion: traveling through special transport proteins, if they match the shape and charge requirements to fit through the channels provided by the transport proteins.

6. Explain the role of protein pumps and ATP in active transport across membranes.

Against the concentration gradient: Moves substance from an area where it is in lower concentration to an area where it is in higher concentration.

Protein pumps:

  • Integral transmembrane protein pumps
  • Specific to molecule transported

Requires energy:

  • Usually provided by ATP
  • Often by phosphorylating the protein pump as ATP is hydrolyzed

7. Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus, and plasma membrane.

  • Protein synthesis: rER produces proteins which travel through the lumen of the ER
  • Transport in vesicles: Membranes produced by the rER flows in the form of transport vesicles to the Golgi, carrying proteins within the vesicles
  • Modification: Golgi apparatus modifies proteins produced in rER
  • Transport to membrane: Golgi pinches off vesicles that contain modified proteins and travel to plasma membrane
  • Exocytosis: Vesicles then fuse with plasma membrane, releasing their contents by

8. Describe how the fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis.

  • Lipids move laterally in a membrane, but flip-flopping across the membrane is rare.
  • Unsaturated hydrocarbon tail of phospholipids have kinks that keep the molecules from packing together, enhancing membrane fluidity.
  • Cholesterol reduces membrane fluidity by reducing phospholipid movement at moderate temperatures but it also hinders solidification at low temperatures.

You are watching: SL/HL2 Biology Ferguson. Info created by GBee English Center selection and synthesis along with other related topics.