transport across cell membranes Flashcards
(34 cards)
What is diffusion?
The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.
What factors affect diffusion?
- Temperature
- Concentration difference
How does temperature affect diffusion?
The higher the temperature the higher the rate of diffusion. This is because the particles have more kinetic energy and move at higher speeds.
How does concentration difference affect diffusion?
The greater the difference in concentration between two regions the faster the rate of diffusion, this is because the overall movement from the higher concentration to lower concentration will be larger.
What does diffusion across membranes involves particles passing through?
The phospholipid bilayer.
What does the membrane allow to diffuse across and what does the hydrophobic interior repel?
Allows - Non- polar molecules e.g oxygen
Doesn’t allow - positive or negative ions
What are membranes described as in terms of permeability?
partially permeable
What affects the rate at which molecules or ions diffuse across a membrane?
- Surface area
- Thickness of membrane
How can surface area affect diffusion?
The larger the area of an exchange surface, the higher the rate of diffusion.
How can the thickness of membrane affect diffusion?
The thinner the exchange surface, the higher the rate of diffusion.
What is facilitated diffusion?
Diffusion across a membrane through protein channels.
As most protein channels are specific to one molecule or ion what is known as?
Selectively permeable
What does the rate of facilitated diffusion depend on which simple diffusion doesn’t depend on?
The number of protein channels present. The more protein channels, the higher the rates of diffusion.
What type of process is active transport?
Active process -> requires energy
What is active transport?
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration, up a concentration gradient.
What is the metabolic energy for active transport supplied from?
ATP
Which types of proteins are involved in active transport and what do they do?
Carrier proteins span the membranes and acts as “pumps”
What is the process of active transport?
1- The molecule or ion to be transported binds to receptors in the channel of the carrier protein on the outside of the cell.
2- On the outside of the cell ATP binds to the carrier protein and is hydrolysed into ADP and phosphate.
3- Binding of the phosphate molecule to the carrier protein causes the protein to change shape- opening up the inside of the cell.
4 - The molecule or ion is released to the inside of the cell.
5- The phosphate molecule is released from the carrier protein and recombines with ADP to form ATP.
6- The carrier protein returns to its original shape.
What is the process of active transport known as?
Selective - Specific substances are transported by specific carrier proteins
What is bulk transport?
- Another form of active transport
- Large molecules such as enzymes, hormones, and whole cells like bacteria are too large to move through channel or carrier proteins, so they are moved into and out of cell by bulk transport.
What is endocytosis?
- The bulk transport of material into cells.
What are the two types of endocytosis?
Phagocytosis - For solids
Pinocytosis - For liquids
What is the process for endocytosis?
- The cell-surface membrane first invaginate (bends inward) when it comes into contact with the material to be transported.
- The membrane enfolds the material until eventually the membrane fuses, forming a vesicle. The vesicle pinches off and moves into the cytoplasm to transfer the material for further processing within the cell.
Process of exocytosis.
-Vesicles usually formed by the Golgi apparatus move towards and fuse with the cell surface membrane.
-The contents of the vesicle are then released outside of the cell.