General Biology Chapter 5Notes ( Cellular Transport) Day 1
Objectives:
1. Differentiate types of molecular transport across cellular membranes employed by cells.
2. Recognize that these transport systems either require the cell to expend energy (Active transport) or not (Passive transport ).
3. Articulate, using appropriate vocabulary, the meaning of the following Passive cellular transport systems: Simple diffusion, ion channel diffusion, facilitated diffusion and osmosis.
4. Recognize the above passive systems as downhill processes that require no energy expenditure on the part of the cell that is engaged in them.
Notes:
There are essentially two divisions of cellular transport. A system employed by cells that brings molecules into the cellular interior that requires the cell to spend NONE of it’s own energy is referred to as a Passive system. A system that DOES require the cell to spend some of it’s own energy is referred to as an Active system. There are four passive systems that we discuss this chapter and one Active system that we will examine. The four passive systems are said to be downhill systems because they do NOT require the cell to spend any of it’s own energy. They are as follows:
Simple diffusion:
This passive transport system works because of the vibrational energy within all atoms and molecules. Molecules tend to move in space from areas of higher concentration to areas of lower concentration. Consider the perfume that I sprayed in the room. The molecules of perfume started in one corner of the room and diffused through the whole room. Said another way, they diffused from an area of high concentration to an area of low concentration until the molecules of perfume became evenly dispersed throughout the room. Living cells often employ this method to bring certain molecules into or let certain molecules out of themselves. This is not a conscious decision on the part of the cell, but only happens as a physical law. Certain molecules pass through the cellular membrane from areas of high concentration to areas of low concentration until the concentration on both sides of the cellular membranes reaches equilibrium! This type of cellular transport is conducted through the spaces between phosphor-lipid molecules that make up the cell membrane. Recall this fact from chapter four. See the below diagram for a reminder.
Molecules can pass between the gaps in the phosphor- lipid molecules if they are small enough.
Ion channel diffusion:
This process works just like simple diffusion but it pertains to ions which have specific channels that they are permitted to pass through due to specific charges created in the cell membrane. Chloride ions have a specific channel to pass through that sodium ions cannot pass through. Sodium ions can only pass through sodium channels in the cell membrane.
Facilitated Diffusion:
Again, this is another passive system that facilitates very large molecules into and out of the cell through molecular gates created by proteins found integrated in the cell membrane. These integral proteins bend and flex in shape as large molecules pass between them. The shape change in integral proteins does not require energy and is a passive system that works off of a concentration gradient just like the previous two systems. Simply put, it is a method employed by cells to allow larger molecules to pass through the cell membrane.
Osmosis:
Osmosis is just like simple diffusion except that it pertains to water molecules ONLY, hence the movement of water molecules into and out of the cell is referred to as Osmosis. This is a passive process just like the previous three and works by the concentration gradient and is downhill. So, water moves from areas of high concentration to areas of low concentration.