Movement of Substances Flashcards
Explain the fluid mosaic model
The cell surface membrane is described as fluid because of its components, lipids and proteins which move around within their layer. An excess in unsaturated fatty acid tails makes the membrane more fluid because of the kinks in the tails preventing close-packing of the lipids. The word mosaic describes the scattered pattern of the proteins when viewed from above.
Explain the role of lipids in cell surface membranes.
Lipids that make up the cell surface membrane include phospholipids and cholesterol. A phospholipid molecule has a hydrophilic (water-loving) glycerol-phosphate head and two hydrophobic fatty acid tails. Phospholipids arrange themselves as a bilayer in water. With the hydrophilic glycerol-phosphate heads facing the water and the two hydrophobic hydrocarbon tails away from the water.
State the types of protein in cell surface membrane
Proteins that make up the cell membrane are globular
Integral proteins are partially or fully buried in the phospholipid bilayer. Peripheral proteins are superficially attached on either surface of the phospholipid bilayer
State the role of phospholipids in maintaining membrane fluidity
An excess of unsaturated fatty acid tails in the phospholipids makes the membrane more fluid because the kinks in the tails prevent the close-packing of the lipids. The presence of cholesterol reduces fluidity by reducing the movements of the lipid molecules.
Note that lipid molecules are able to move about more rapidly as compared to proteins.
Define diffusion
It is defined as the net movement of molecules from a region of higher concentration to a region of lower concentration down a concentration gradient, using kinetic energy from the continuous movement of molecules.
State and explain the types of diffusion
Both simple diffusion and facilitated diffusion are passive transport.
- Simple diffusion
- The membrane is fully permeable
Involves small, non-polar molecules such as glycerol, fatty acids, oxygen and carbon dioxide. - Facilitated diffusion
- Diffusion of ions and polar(water-soluble) molecules via specific protein channels or carriers down a concentration gradient.
Carrier proteins are protein-lined pores that are large enough for the molecules to pass through
Channel proteins are globular proteins that can form large pores for diffusion to occur, pores close up when molecules are no longer present
Define osmosis
Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a selectively permeable membrane.
Define active transport
Active transport is defined as the movement of molecules from a region of lower concentration to a region of a higher concentration, against a concentration gradient, using metabolic energy in the form of ATP produced by the cell
State and explain the types of bulk transport
Exocytosis is defined as the process by which cells export products such as enzymes by means of vesicles
Endocytosis is defined as the process by which a cell imports products.
- Phagocytosis - the whole import of solid matter
- Pinocytosis - bulk import of fluids
