Transport across cell membranes

Question 1

What are the functions of Cholesterol in the cell membrane

Answer 1

maintains lipid bilayer during temperature fluctuations e.g. make membrane less fluid at high temperatures

Question 2

What are the functions of Glycoproteins in the cell membrane

Answer 2

they acts as a recognition site which help cells attach to one another to form tissues and allow cells to be recognised as an organism’s own cell

Question 3

What are the functions of Glycolipids in the cell membrane

Answer 3

they act as a recognition site that helps maintain the stability of the membrane and allow cells to attach to one another form tissues

Question 4

What are the functions of Proteins in the cell membrane

Answer 4

imbedded in the cell membrane for mechanical support like hormone receptors and used as channel and carrier proteins for facilitated diffusion

Question 5

What are the functions of the cell membrane

Answer 5

• boundary between the cell cytoplasm and the environment
• controls movement of substances in and out of the cell
• allow different conditions to be established in and out side of the cell

Question 6

Why is membrane permeability different for different for molecules

Answer 6

• some molecules are to large to pass through the channels
• if they have the same charge as the proteins they get repelled
• if they’re polar they will have difficulty passing by the non-polar hydrophobic tails of the phospholipids

Question 7

Describe the structure of a phosholipid

Answer 7

• hydroPHOBIC tails

- hydroPHILIC polar heads

Question 8

Whats is meant by the Fluid Mosaic model of a cell membrane

Answer 8

built up of a mixture of phospholipids and proteins which gives membrane flexibility

Question 9

What is simple diffusion

Answer 9

particles are always in motion due to kinetic energy, net movement of ions is from high to low concentration until distributed equally

Question 10

What is facilitated diffusion

Answer 10

the diffusion of larger molecules through the bilayer with the help of channel and carrier proteins

Question 11

What is a Carrier protein

Answer 11

an ion binds to the protein changing the shape of the protein using its kinetic energy, and opening it up to the otherside of the bilayer

allows for the diffusion of ions like glucose

Question 12

What is a Channel protein

Answer 12

the channel is only open when an ion is present to maintain control of the entry and exit of ions

allow for the diffusion of water soluble ions

Question 13

Define osmosis

Answer 13

the net movement of water molecules from a high to low water potential across a selectively permeable membrane

Question 14

What would happen to a red blood cell in a Hypotonic, Hypertonic and Isotonic solutions

Answer 14

Hypotonic - lysis - water enters cell
Hypertonic - crenation - water leaves cell
Isotonic - stays intact

Question 15

What would happen to a plant cell in a Dilute, Hypotonic, Hypertonic and Isotonic solutions

Answer 15

Dilute - rigidity of cell wall keeps it intact
Hypotonic - cell becomes flaccid - water enters cell
Hypertonic - cell plasmolysis - water leaves cell
Isotonic - stays intact

Question 16

Define Dilute, Hypotonic, Hypertonic and Isotonic solutions

Answer 16

Dilute - Small increase of water potential but same solute concentration

Hypotonic - high water potential (when there’s a greater concentration of solutes on the outside of a cell than the inside so there is influx of solute onto cell)

Hypertonic - low water potential (when there’s a greater concentration of solutes on the inside of a cell than the outside so solute moves out of cell)

Isotonic - when the osmotic pressure in cell and environment is equal

Question 17

What is water potential

Answer 17

the pressure created by water molecules

• high water potential = less negative number
• low water potential = more negative number

Question 18

What is active transport

Answer 18

the movement of molecules against concentration gradient from low to high concentration with the use of ATP and carrier proteins`

Question 19

Why do cells in the intestine have many mitochondria

Answer 19

to produce a lot of ATP for active transport to take place

Question 20

How does the sodium potassium pump work

Answer 20

• sodium binds to the carrier protein on the outside
• ATP binds to the carrier protein
• ATP splits into ADP + Pi
• ADP is released opening the carrier protein to the inside of the membrane
• potassium bids to the carrier protein on the inside
• sodium moves in
• Pi is released and carrier protein opens to outside of the membrane
• potassium moves out to maintain concentration gradient andcharge

Question 21

How is the structure of an epithelial cell in the ileum linked to its function

Answer 21

they have:

• a short diffusion distance
• constant blood flow to maintain concentration gradient
• microvilli, which further increase surface area for diffusion

Question 22

What is co-transported alongside sodium in the small intestine

Answer 22

glucose is co-transported into the epithelial cells, then into the blood capillary alongside sodium by facilitated diffusion

Question 23

Why are there many different protein carriers in the epithelial cells of the small intestine

Answer 23

for facilitated diffusion and active transport to take place at the same time