Book 4- Cell membrane and Transport

Question 1

Cell membranes have a what structure? why?

Answer 1

fluid mosaic because the phospholipids are constantly moving from side to side.

Question 2

What does cholesterol do in the cell membrane?

Answer 2

makes it less acidic

Question 3

What do phospholipids consist of?

Answer 3

A phosphate head which Is hydrophilic, so is positioned outside of the membrane towards water. Two fatty acid tails, which are hydrophobic, meaning they are positioned in-between the phosphate heads away from water.

Question 4

What is the function of the phospholipid bilayer? (3)

Answer 4

1. ) allow lipid soluble substances to enter and leave the cell
2. ) prevent water soluble substances from entering and leaving a cell
3. ) make the membrane flexible

Question 5

4 functions of the cell membrane?

Answer 5

1. ) Transport- molecules cross the membrane via transport proteins or between phospholipids
2. ) Digestion- contain enzymes which can hydrolyse molecules
3. ) Immune response- cell membranes contain specific glycoproteins( antigens). they contain specific protein receptors which can bind to foreign antigens and cause an immune response.
4. ) cell signalling- hormones can bind to receptor proteins causing a signal to be sent to trigger a response.

Question 6

Molecules can cross the phospholipid bilayer if they are what?? (3)

Answer 6

1. ) small
2. ) lipid soluble-dissolve in fats
3. ) Non-polar- so the polar phosphate heads are unaffected

Question 7

Types of transport?

Answer 7

diffusion, facilitated diffusion, active transport, co-transport, osmosis

Question 8

Explain simple diffusion

Answer 8

the net movement of particles from a high conc to a low conc. This does not involve membrane protein and doesn’t require energy. Small, lipid soluble molecules can diffuse through a bilayer.

Question 9

What does facilitated diffusion allow?

Answer 9

Allows the transport of polar molecules across membranes using channel and carrier proteins.

Question 10

Explain facilitated diffusion?

Answer 10

• protein spans the membrane
• ions such as Na+ pass through the protein pore
• a glucose molecule diffuses into carrier protein molecule
• the glucose molecule binds with the carrier protein causing it to change shape.
• the glucose molecule diffuses out of the carrier protein molecule

Question 11

What is active transport?

Answer 11

the movement of molecules or ions through a partially permeable membrane by carrier proteins against a conc gradient. It requires ATP

Question 12

Explain how active transport occurs?

Answer 12

• ATP hydrolase breaks down ATP, releasing energy required for active transport.
• the energy is used to attach the molecule to the carrier protein and to provide energy for the carrier to change shape to move the ion through the membrane
• cells involved possess a lot of mitochondria to provide the ATP via respiration

Question 13

factors which decreases the rate of respiration, therefore will decreases active transport are??

Answer 13

1. ) lowering of temp
2. ) lack of oxygen
3. ) metabolic and respiratory inhibitors eg.cyanide

Question 14

give 2 examples of co transport?

Answer 14

sodium-potassium and sodium-glucose proteins

Question 15

Factors affecting transport?

Answer 15

conc gradient, diffusion distance, molecule size, temperature, number of channel/carrier proteins, surface area

Question 16

What is osmosis?

Answer 16

The net movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane.

Question 17

Pure water has a water potential of what?

Answer 17

0KPa

Question 18

If any substances is added to water it always … its water potential?

Answer 18

reduces

Question 19

Explain a hypotonic solution

Answer 19

Has a low conc of solutes dissolved in it. This increases the wp of the solution. The cell has a lower wp, causing water to move into the cell by osmosis.

Question 20

Explain a isotonic solution

Answer 20

Has the same solute conc and therefore the same wp as the cell, so no osmosis occurs.

Question 21

Explain a hypertonic solution

Answer 21

High conc of solutes dissolved in it. This lowers the wp of the solution. The cell has a higher wp, causing the water to move out of the cell by osmosis.

Question 22

What has happened to a trugid cell?

Answer 22

water enters by osmosis, vacuole swells and pushes against the cell wall