Analysing the movement of substances across the plasma membrane
Learning Outcomes :
At the end, a student is able to:
- state the substances required by living cells,
- state the substances that have to be eliminated from cells,
- explain the necessity for movement of substances across the plasma membrane,
- describe the structure of the plasma membrane
Substances Transported Into (Enter) The Cells :
- Digested food substances :
- Amino acid
- Fatty acid
- Waste products from metabolic processes :
- Carbon dioxide
- Lactic acid
- Excess water
- A cell is surrounded by a plasma membrane that separates it from the outer environment.
- For cellular activities to be carried out, the cell has to move substances into and out of the cell.
- Movement of substances into or out of a cell is important to :
- provide nutrients for metabolism and growth
- supply oxygen for respiration
- regulate solute concentration and suitable pH for maintaining a stable internal environment for optimal enzymatic activities
- maintain an ion concentration gradient required for nerve and muscle cell activities
- secrete useful substances, for example, digestive enzymes and hormones
- eliminate toxic waste products such as urea and carbon dioxide
- The fluid-mosaic model proposes that the plasma membrane consists of protein molecules scattered in a mosaic pattern on a fluid bilayer of phospholipids molecules.
- The phospholipid bilayer have different solubility properties of the two ends of phospholipid molecules.
- There are various types of protein which are either partially or fully embedded in the membrane. Pore proteins forms a channel (allow small molecules, either polar or non-polar, to pass through freely) whereas carrier protein acts as a carrier (attach to specific glucose molecules, before transporting the molecules across the plasma membrane).
- Cholesterol molecules help to stabilise the structure of the plasma membrane.
- The phospholipid bilayer, proteins and other components are not rigid or static but form a dynamic and flexible structure.