Topic 1.4:  Membrane Transport

Essential Idea:  Membranes control the composition of cells by active and passive transport.

At SHS, Topic 1.4 is taught in the following class unit(s):

• Eukaryotic Cells (unit 4)
• Cell Membrane Transport (unit 8)
• Neural Structure and Function (unit 42)​

Statements & Objectives:

1.4.U1  Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.

• Describe simple diffusion.
• Explain two example of simple diffusion of molecules into and out of cells.
• Outline factors that regulate the rate of diffusion.
• Describe facilitated diffusion.
• Describe one example of facilitated diffusion through a protein channel.
• Define osmosis.
• Predict the direction of water movement based upon differences in solute concentration.
• Compare active transport and passive transport.  
• Explain one example of active transport of molecules into and out of cells through protein pumps.​

1.4.U2  The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.

• Describe the fluid properties of the cell membrane and vesicles.
• Explain vesicle formation via endocytosis.
• Outline two examples of materials brought into the cell via endocytosis.
• Explain release of materials from cells via exocytosis.
• Outline two examples of materials released from a cell via exocytosis,

1.4.U3  Vesicles move materials within cells.

• List two reasons for vesicle movement.
• Describe how organelles of the endomembrane system function together to produce and secrete proteins (rough ER, smooth ER, Golgi and vesicles).
• Outline how phospholipids and membrane bound proteins are synthesized and transported to the cell membrane.​​

1.4.A1  Structure and function of the sodium-potassium pumps for active transport and potassium channels for facilitated diffusion in axons.

• Describe the structure of the sodium-potassium pump.
• Describe the role of the sodium-potassium pump in maintaining neuronal resting potential.
• Outline the six steps of sodium-potassium pump action.
• Describe the structure of the potassium channel.
• Describe the mechanism of potassium movement through the potassium channel.
• Explain the specificity of the potassium channel.
• Describe the action of the “votage gate” of the potassium channel.

1.4.A2  Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.

• Explain what happens to cells when placed in solutions of the same osmolarity, higher osmolarity and lower osmolarity.
• Outline the use of normal saline in medical procedures.​

1.4.S1  Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Practical 2)

• Define osmolarity, isotonic, hypotonic and hypertonic.
• Calculate the percentage change between measurement values.
• Calculate the mean value of a data set.
• Calculate the standard deviation value of a data set.
• State that the term standard deviation is used to summarize the spread of values around the mean, and that 68% of the values fall within one standard deviation of the mean.
• Explain how the standard deviation is useful for comparing the means and the spread of data between two or more samples.
• Determine the correct type of graph to represent experimental results.
• State that error bars are a graphical representation of the variability of data.
• Accurately graph mean and standard deviation of data sets.
• Determine osmolarity of a sample given changes in mass when placed in solutions of various tonicities.​

1.4.NOS  Experimental design- accurate quantitative measurements in osmosis experiments are essential.

• Define quantitative and qualitative.
• Determine measurement uncertainty of a measurement tool.
• Explain the need for repeated measurements (multiple trials) in experimental design.
• Explain the need to controlled variables in experimental design.​

In the News:

• ​​Mouse impervious to scorpion's sting (2013-10-24)
• ​Scientists create endocytosis on demand by 'hotwiring' cells​ (2017-09-28)​​
• ​​Nobel winners decoded how neurons and cells talk to each other (2013-10-07)
• Nobel prize awarded In medicine (2013-10-07)