Chapter 4 - Transport Across Cell Membranes Flashcards
Why are phospholipids so important to cell membranes?
They allow lipid soluble molecules to move through the cell whilst remaining impermeable to water soluble substances. They are also self-sealing and remain flexible. For this reason they also enclose all organelles
How is the membrane arranged according to the fluid mosaic model?
The phospholipid membrane is studded with several different types of molecules, particularly channel and carrier proteins for transport and receptor proteins, examples of both intrinsic (go all the way through the bilayer) and extrinsic (only on one side of the bilayer). Glycoproteins and glycolipids may also be present, as antigens for example
What is cholesterol and how does it affect the membrane?
It is a molecule which can “wedge” itself in between the phospholipids in the membrane. It is able to make the entire membrane more rigid and makes it less permeable to water, as well as reducing the ability of molecules within the membrane to slide around as much
What are the different types of transport across membranes?
Simple diffusion, facilitated diffusion, active transport and osmosis
What is the difference between simple and facilitated diffusion?
Simple diffusion describes the process of molecules moving directly across the phospholipid bilayer, typically very small lipids, whereas facilitated diffusion is the movement of typically larger or polar molecules moving into or out of cells through channel or carrier proteins.
Define “diffusion” (A-level)
The net movement of molecules from areas of high concentration to lower concentrations down a concentration gradient. It is a passive process, meaning it doesn’t require metabolic energy
What is water potential?
Water potential is essntially the pressure created by water under certain temperatures compared to pure water. as pure water is 0 and everything else is impure, it must have a lower potential than 0. Water always moves from higher to lower water potentials (less negative numbers to more negative). It is measured in kilopascals and has the symbol psi (the trident)
What is osmosis
Osmosis is the net movement of water molecules across a partially permeable cell membrane, from areas of higher water potential to lower water potential
What is active transport?
Active transport is an active process where the cell moves molecules from areas of low concentration into areas of high concentration, for example mineral ions in the soil into the root cells
What is co-transport of glucose?
The endothelial cells actively transport sodium ions out to reduce its concentration. This makes sodium diffuse into the cell from the ileum through sodium-glucose cotransporters. When it does this it changes the shape of the protein allowing glucose to also diffuse with it. This means glucose is able to diffuse into the cells without being able to diffuse out, and from there it can diffuse into the blood
How can you increase the speed at which transport across membranes happens?
Increase the surface area of the cell or increase the number of transporting proteins
