Transport Across Cell Membrane

Question 1

Fluid mosaic model explained.

Look in folder for structure of this!! Must learn!

Answer 1

Fluid- phospholipid molecules move relative to each other, providing the membrane with flexibility.
Mosaic- protein molecules vary in size and shape and pattern. (a bit like stones in one)
Model- A scientific suggestion which fits the discoveries and properties presented to date.

Question 2

Phospholipid

Know what it looks like

Answer 2

Lipid soluble molecules can diffuse through.
Large water soluble molecules can’t pass through.
Flexible.
Self sealing.

Question 3

Glycolipid

Know what it looks like

Answer 3

Recognition site e.g. Blood group
Attachment.
Maintains stability.

Question 4

Glycoprotein

Know what it looks like

Answer 4

Recognition site.
Attachment.
Self determination.

Question 5

Carbohydrate

Know what it looks like

Answer 5

Recognition site.
Attachment.
Self determination.

Question 6

Cholesterol

Know what it looks like

Answer 6

Very hydrophobic so reduce lateral movement of phospholipids and other molecules.
Make membrane less fluid amt high temperatures.
Prevent leakage water.

Question 7

Protein(surface)

Know what it looks like

Answer 7

Support.

Receptors e.g. For hormones

Question 8

Channel protein

Know what it looks like

Answer 8

Channel so small water soluble ions through OR bind to and transport molecules across the membrane e.g. Glucose, among acids FACILITATED DIFFUSION AND ACTIVE TRANSPORT.

Question 9

Diffusion

Answer 9

The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower, until even,y distributed.

Net diffusion stops when molecules are evenly distributed.

Question 10

Fick’s law

Answer 10

The rate of diffusion in a given direction across an exchange surface.

Rate of diffusion is proportional to =
surface area X difference in concentration /
Length of diffusion path(membrane thickness)

• increasing surface area or size of concentration gradient will increase rate of diffusion.
• increasing distance (thickness of membrane) over which diffusion takes place will decrease the rate.

Question 11

Factors that affect rate of diffusion:

Answer 11

• Temperature (higher temp,diffuse faster)
• Surface area (larger SA, diffuse faster)
• Concentration gradient(higher gradient, diffuse faster)
• Size of particles (smaller particles, diffuse faster)
• Diffusion medium (solid, slowest. Liquid, faster. Gas, fastest)
• Length of diffusion path (shorter, diffuse faster)

Question 12

Facilitated diffusion

Answer 12

Is when larger molecules (amino acids/glucose) and charges atoms (chloride ions) CANT diffuse directly through the phospholipid bilateral of the cell membrane.
So instead they diffuse through proteins (protein channel/carrier proteins) in the cell membrane.
-normal diffusion rules apply.
-it is a passive process.
-there are so many carrier proteins in membranes because a membrane controls entry and exit of molecules and there needs to be a lot to let them in.
-ions-> channel protein.
-glucose and amino acids-> carrier protein

Question 13

Osmosis definition

Answer 13

The net moment of water molecules from a high to low (more negative) water potential through a SELECTIVELY permeable membrane

Question 14

Osmosis

Answer 14

• Water potential is the potential to give out water by osmosis.
• Water potential is the pressure created by water molecules.
• Pure water is 100% water molecules (no dissolved salutes), so cannot absorb any more water from its surroundings.
• Water potential=kPa=(fork looking symbol)
• As soon as anything is dissolved in water (the solute concentration increases) the water potential becomes negative.
• The more negative the water potential, the more capacity of the solution has to absorb water from its surroundings by osmosis.

Question 15

Hypotonic

Answer 15

The solution has higher water potential than the cells bathed in it.

In an animal cell- water moves into cell. Cell gets bigger. Membrane weak so cell bursts.
In a plant cell- water moves into cell. Contents of cell increase. Cell membrane pushes out on cell wall. Cell is TURGID.

Question 16

Isotonic

Answer 16

Same water potential (no net movement)

In an animal cell- no net osmosis. Cell same size/shape.
In a plant cell- no net osmosis. Incipient plasmolysis. (Contents not longer push on cell wall).

Question 17

Hypertonic

Answer 17

Lower water potential than the cells bathed in it.

In an animal cell- water moves out of cell. Cell shrinks.
In a plant cell- water moves out of cell. Cell contents shrink. Cell membrane pulls away from cell wall. Cell is FLACCID. Plasmolysis is occurring.

Question 18

Active transport definition.

Answer 18

The movement of molecules or ion into or out of the cell from a region of low concentration to a region of higher concentration using ATP and carrier proteins(protein pump).

Question 19

What is ATP?

Answer 19

Need psd for active transport and co transport.
Comes from mitochondria and is regenerated in respiration.
Stands for Adenosine tri phosphate.
When energy is needed it is hydrolysed.

Question 20

What happens during active transport?

Answer 20

• Molecules bind to carrier protein and ATP attaches to the membrane protein on the inside of the cell/organelles.
• Binding of phosphate ion to protein causes the protein to change shape so that access for the molecules is open to the inside of the membrane but closed to the outside.

Should know what this looks like

Question 21

Co-transport and absorption of glucose in the ileum(part of intestine)

MUST KNOW THE STRUCTURE OF THIS DIAGRAM in folder.

Answer 21

1. Sodium ions are actively transported out of the epithelial cells, by the sodium – potassium pump into the blood. This takes place in one type of protein – carrier molecule found in the cell – surface membrane of epithelial cells.
2. This maintains a much higher concentration of sodium ions in the lumen of the intestine than inside the epithelial cells.
3. Sodium ions diffused into the epithelial cells down the concentration gradient through a different type of protein carrier (co-transport) in the cell – surface membrane. As the sodium ions diffuse through this second carrier protein, they carry either amino acid molecules of glucose molecules into the cell with them.
4. Glucose/amino acid’s pass into the blood plasma by facilitated diffusion in using another type of carrier.

Question 22

Recap/summary

Answer 22

Diffusion- high to low concentration. NO carrier proteins or ATP needed.
Facilitated diffusion- high to low concentration. Carrier of channel protein needed. NO ATP needed.
Osmosis- high water potential to low water potential. NO carrier proteins or ATP needed.
Active transport- low to high concentration. Both carrier proteins and ATP needed.
Co transport- low to high concentration. 3 carrier proteins needed. Indirect need for ATP.