How does the plasma membrane control the contents of a cell?
The membrane controls what enters and leaves the cell. This includes using diffusion and osmosis. Sometimes the membrane uses integral proteins as channels and pumps, sometimes the membrane surrounds something which needs moving into or out of the cell.
Learn and test your biological vocabulary for 1.4 membrane transport using these flashards.
These slides summarise the essential understanding and skills in this topic.
They contain short explanations in text and images - good revision for all students.
Read the slides and look up any words or details you find difficult to understand.
A short video tutorial is planned here. How to estimate osmolarity in tissues. (Practical 2)
Potato chips or Carrot disks, or Dandelion stapes the principles are the same.
- Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
- The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
- Know how the structure helps the function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
- Understand why tissues (or organs) waiting to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
- Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Practical 2)
These diagram summaries cover the main sections of topic 1.4 about membrane transport.
Study them and draw your own list or concept map from memory.
A quiz containing five questions covering this topic.
Which of the following best describes exocytosis?
The fluidity of membranes allows materials to be released by exocytosis.
Vesicles move materials within cells to the membrane, e.g. enzymes in cells of a gland.
Sodium channels are made from a protein.
Where in the cell are sodium channel proteins found.
Sodium channel proteins are found spanning the plasma membrane. Their structure helps the function for facilitated diffusion in cells because they allow ions to pass cross the membrane.
If the protein was not a trans-membrane protein then it would not be able to transport ions across the membrane.
This box contains a lung waiting for a transplant operation.
What is special about the solution inside the box which surrounds the tissue?
Tissues and organs must be kept in a solution with the same osmolarity as the cytoplasm of the cells to prevent osmosis. If they were kept in pure water, osmosis would carry water into the cells and they would burst, causing damage to the cells.
The four cells shown below have each been surrounded by a solution for 1 hour.
Which cells have been in a hypertonic solution ?
Cell A is swollen turgid, it is in a hypotonic solution or an isotonic solution.
The cells B, C and D show increasing signs of plasmolysis, and so they must be in hypertonic solutions.
Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Practical 2)
The graph below shows the % change in mass at different concentrations of sucrose.
Which of the following is the best estimate of the molarity of the cytoplasm of these cells?
When a sample of cells show no change in mass, then the net movement of water by osmosis must be zero. This shows the concentration of the cytoplasm of the cells. In this graph it would be about 0.3 mol
Have some fun while revising. try this educational Revision arcade game about membrane transport.