Y12 MS - Transport Across Membranes (Complete)

Question 1

What is shown by A?

Answer 1

Phospholipid
A1 - Hydrophilic phosphate head
A2 - Hydrophobic fatty acid tails

Question 2

What is shown by B?

Answer 2

Glycolipid

Question 3

What is shown by C?

Answer 3

Glycoprotein

Question 4

What is shown by D?

Answer 4

Carbohydrate

Question 5

What is shown by E?

Answer 5

Cholesterol

Question 6

What is shown by G?

Answer 6

Channel protein (intrinsic)

Question 7

What is shown by F?

Answer 7

Extrinsic protein

Question 8

How are the phospholipids arranged in the cell membrane?

Answer 8

In a bilayer
- Hydrophilic phosphate heads face outwards
- Hydrophobic fatty acid tails face inwards

Question 9

Are the phosphate heads and fatty acid tails or phospholipids polar or non-polar?

Answer 9

Phosphate heads - polar
Fatty acid tails - non-polar

Question 10

Why are the fatty acid tails in the cell membrane important?

Answer 10

The fatty acid tails are hydrophobic so prevent water soluble molecules from crossing the membrane
Therefore, a barrier is created between the cytoplasm and the fluid outside of the cell

Question 11

True or false? The membrane is fluid

Answer 11

The membrane IS fluid
The phospholipids move laterally meaning that the cell membrane can is fluid

Question 12

What is the function of channel proteins?

Answer 12

Channel proteins span the membrane (intrinsic) and form water filled channels
This means that small, water soluble molecules are able to diffuse across the channel proteins and into or out of the cell

Question 13

What is the function of carrier proteins

Answer 13

Carrier proteins have a binding site for a specific chemical and transport them across the membrane

Question 14

The cell membrane is ———— —————. What does this mean?

Answer 14

The cell membrane is selectively permeable so only allows some chemicals to cross the membrane

Question 15

The cell membrane is modelled by the fluid mosaic model. What does this mean?

Answer 15

Fluid - the phospholipids are able to move around laterally
Mosaic - the proteins within the phospholipid bilayer form a scattered, mosaic pattern when viewed from above

Question 16

Phospholipids can form a bilayer. What is the other arrangement of phospholipids which can be formed?

Answer 16

A micelle
This is formed when phospholipids are shaken / mixed with water

Question 17

What is the function of glycolipids and glycoproteins?

Answer 17

They are used as cell recognition sites
The pattern of the carbohydrate units act as antigens on the surface of the cell

Question 18

What is the function of cholesterol in the cell surface membrane

Answer 18

Cholesterol decreases the fluidity of the membrane by linking phospholipids together, making the structure more stable so it doesn’t split apart

Question 19

What is diffusion

Answer 19

The net movement of a substance down a concentration gradient

Question 20

What is Ficks Law?

Answer 20

The rate of diffusion is proportional to
(Surface area x concentration gradient) / diffusion distance

Question 21

What are the common adaptations for to increase the rate of diffusion

Answer 21

Large surface area
Short diffusion distance
Maintained diffusion gradient

Question 22

What is simple diffusion in the cell membrane

Answer 22

Where small, non-polar molecules pass across the cell membrane by diffusion (intrinsic proteins not required)

Question 23

What type of molecules can move across the cell membrane by simple diffusion

Answer 23

Small and non-polar e.g oxygen, fatty acids, carbon dioxide, fat-soluble vitamins

Question 24

Where does facilitated diffusion occur in the cell membrane

Answer 24

Intrinsic proteins in the cell membrane facilitate (help) the movement of polar molecules across the membrane
- Uses channel / carrier proteins

Question 25

What are the similarities and differences between simple and facilitated diffusion

Answer 25

Similarities:
- Require a concentration gradient
- Do not need energy (passive processes)
- Result in the movement of a substance across the cell membrane

Differences:
- Simple diffusion involves non-polar molecules whereas …
- Facilitated diffusion requires gated / permanent protein channels whereas …
- Facilitated diffusion is specific whereas …
- Simple diffusion is slower whereas …
- Facilitated diffusion has a maximum rate due to the limited number of proteins whereas …

Question 26

What is osmosis

Answer 26

The passive movement of water from a high water potential to a lower water potential across a selectively permeable membrane

Question 27

True or false? A high water potential means the solution is concentrated

Answer 27

False - high water potential means it is dilute

Question 28

What does an isotonic solution mean

Answer 28

It has the same water potential

Question 29

What happens when animal cells are placed in distilled water and why does this occur

Answer 29

Distilled water has a water potential of 0 so water moves into the cells by osmosis. This results in them swelling and bursting as animal cells do not have a cell wall to keep them rigid

Question 30

What happens to animal cells when they are placed in a concentrated salt solution and why does this happen

Answer 30

The concentrated salt solution will have a lower water potential than inside the cells so water will move out of the cells by osmosis. This will result in the cells shrinking and shrivelling because animal cells do not have a cell wall to keep them rigid

Question 31

What happens when a plant cell is placed in distilled water and why is this

Answer 31

Distilled water has a water potential of 0 so water will move into the cell by osmosis. This will result in the cell stiffening but overall maintaining its shape as plant cells have a cell wall to keep them rigid and prevent them from bursting

Question 32

What will occur when a plant cell is place in a concentrated salt solution and why is this

Answer 32

The concentrated salt solution will have a lower water potential so water will move out of the cell by osmosis. This will result in a process called plasmolysis where the cell body shrinks and pulls away from the cell wall, leaving spaces between the cell membrane and cell wall. This is because the cell wall remains rigid and does not allow the cell to shrink

Question 33

What is active transport

Answer 33

The movement of molecules against a concentration gradient from an area of low to high concentration. This requires energy in the form of ATP made by cell respiration in the mitochondria

Question 34

What does is mean that channel proteins don’t have a fixed shape (unlike channel proteins)

Answer 34

The carrier protein can switch between two shapes, allowing it to open on either side of the membrane

Question 35

How does active transport work

Answer 35

Active transport requires carrier proteins
Carrier proteins are specific to particular molecules or ions
When these molecules or ions bind to the carrier protein, ATP is needed to make the carrier protein change shape to allow the transfer of these substances across the cell membrane
The ATP is hydrolysed (producing ADP, an inorganic phosphate and energy) to release energy in order for this to occur

Question 36

What is co-transport

Answer 36

The coupled movement of substances across a cell membrane by a carrier protein (involving a combination of facilitated diffusion and active transport)

Question 37

What is an example of co-transport

Answer 37

The co-transport of sodium ions and glucose on the cell surface membrane of epithelium cells lining the ileum