B4 Cell Transport Mechanisms Flashcards
1
Q
Cell surface membrane or plasma membrane
A
- entry and exit of molecules in cells
- surrounds cytoplasm of a cell
- partially permeable
- have a specific structure to enable the movement of substances from one place to another.
2
Q
The cell membrane consists of:
A
Proteins, glycoproteins, phospholipids and carbohydrates.
3
Q
The fluid mosaic model
A
- The phospholipid molecules form a double layer (bilayer) that are constantly moving around, giving the membrane a fluid structure.
- the protein molecules are unevenly distributed throughout the membrane forming a mosaic.
-the selective permeability of the cell-surface membrane is related to the type of distribution of specific proteins and phospholipid molecules present in the membrane.
4
Q
Intrinsic proteins
A
Are the proteins which are embedded completely or partly through the lipid bilayer of the membrane.
5
Q
Extrinsic proteins
A
Are the loosely bound proteins that are located outside the membrane.
6
Q
Explain why the model for membrane structure is known as the fluid mosaic model (3)
A
- phospholipid molecules can move freely with respect to one another, this makes the membrane fluid
- proteins are distributed throughout the membrane unevenly and in a mosaic pattern when viewed from above.
- the agreed structure is based upon experimental/chemical evidence and so is classed as a model.
7
Q
Phospholipids
A
- the hydrophobic tails of phospholipid molecules are attracted towards each other
- hydrophilic heads oriented either inwards towards cytoplasm or outwards towards extra cellular fluid forming the phospholipid bilayer.
- allows lipid soluble (non- polar) molecules to pass through by simple diffusion but prevents the passage of small polar molecules (like ions).
8
Q
Cholesterol
A
- decrease’s permeability and increases the stability of the membrane
- more cholesterol = less fluidity of the membrane is
