3.2.3 transport across cell membranes

Question 1

What is simple diffusion?

Answer 1

+ the net movement of molecules or ions from a concentrated area to a low concentrated area
+ a form of passive transport
+ energy for diffusion comes from the natural, in built motion of the particles

Question 2

What are the 3 main factors affecting the rate of diffusion?

Answer 2

1. concentration gradient
2. surface area
3. length/ thickness of diffusion pathway

Question 3

What is facilitated diffusion?

Answer 3

+ still a passive process
+ occurs down a concentration gradient
+ however, can only occur at specific points on the plasma membrane
+ requires channel/carrier proteins for the molecule to travel down

Question 4

What are channel proteins?

Answer 4

+ water filled that allow water-soluble ions to pass through them
+ w/o channel proteins, these ions would pass through the membrane at a slow rate
+ highly selective channels that only open when its specific ion is present
+ if the molecules is not present they remain closed

Question 5

What are carrier proteins?

Answer 5

+ intrinsic proteins that span the plasma membrane
+ carry large water soluble substances
+ molecule that uses this protein to diffuse through must bind to the protein
+ this causes the protein to alter its shape, in a way that allows the molecule ti be released from the other side

Question 6

What is active transport?

Answer 6

+ movement of molecules or ions from a region of a low concentration to a region of high concentration using ATP and carrier proteins
+ against concentration gradient
+ carrier proteins are used as a pump
+ requires the binding of ATP to change shape of the protein- cannot occur with channel proteins
+ highly selective process

Question 7

What is the process of active transport?

Answer 7

1. molecule/ion binds to receptors on its specific carrier protein
2. ATP binds to the side of the protein on the inside of the cell
3. ATP is broken down into ADP and an inorganic phosphate molecule causing the carrier protein to change shape
4. carrier protein releases molecule/ion on the other side of the membrane
5. phosphate molecule and ADP released from the protein causing it to return to its original configuration

Question 8

Biological examples of active transport

Answer 8

Plants: absorption of nitrate, magnesium, phosphate ions [root hair cells]

Animals: absorption of small amounts of sugar into villi- occurs after initial diffusion/facilitated diffusion occurs in the small intestine, to ensure the maximum absorption of nutrients

Question 9

What is the sodium-potassium pump example?

Answer 9

+ in some scenarios, more than one ion is transported using the same carrier protein

Question 9

What is osmosis?

Answer 9

+ movement of water molecules from an area of high water potential to a lower water potential through a selectively permeable membrane

Question 9

What is water potential?

Answer 9

+ measured in kilopascals (kPa)
+ pure water (at standard conditions 25*C and 100 kPa) has a WP of 0kPa
+ adding a solute to pure water will lower its water potential
+ the more solute you add the more negative the water potential becomes