Transport Across Membranes

Question 1

Name the 5 ways in which substances are moved across membranes

Answer 1

• Simple diffusion
• Facilitated diffusion
• Osmosis
• Active transport
• Co-transport

Question 2

Define simple diffusion

Answer 2

NET movement of molecules from an area of highER concentration to an area of lowER concentration

Question 3

What is diffusion described as?

Answer 3

A passive, random process

Question 4

Why is diffusion described as a passive, random process

Answer 4

• no external energy source is required (environmentally provided)
• particles move independently from eachother

Question 5

What is meant by the phrase “no net diffusion”

Answer 5

There is no overall change - the same number of particles are diffusing in each direction

Question 6

Do polar molecules diffuse slowly or quickly across lipid bilayers?

Answer 6

Slowly

Question 7

Why do polar molecules diffuse slowly across lipid bilayers?

Answer 7

Diffusion is inhibited by the NON-POLAR fatty acid tails, which repel the polar molecules

Question 8

Which factors affect the rate of diffusion and how?

Answer 8

• Temperature - An increase in temperature increases the kinetic energy of molecules, so rate diffusion increases
• Concentration gradient - The greater the concentration gradient, the greater the rate of diffusion
• Area of exchange surface - Higher area = rate of diffusion increases
• Length of diffusion pathway - A shorter length = rate of diffusion increases

Question 9

What is the difference between simple and facilitated diffusion?

Answer 9

Facilitated diffusion relies on the proteins present in plasma membranes

Question 10

Why is facilitated diffusion used?

Answer 10

Because large and/or polar molecules cannot diffuse across a lipid bilayer fast enough

Question 11

Which two types of membrane protein are involved in facilitated diffusion

Answer 11

• Channel proteins
• Carrier proteins

Question 12

What is a channel protein?

Answer 12

• Span the membrane
• Specific (allowing certain molecules/ions to pass through)
• Allows a specific molecule/ion to passively diffuse through

Question 13

What is a carrier protein?

Answer 13

• Bind with specific molecules (complementary binding site)
• Change shape and release the molecule on the other side (the carrier changes shape)
• Red blood cells move glucose into them in this way
• Passive

Question 14

What is osmosis?

Answer 14

Diffusion of a water molecule across a partially permeable membrane from an area of higher water potential to an area of lower water potential

Question 15

What is water potential (Ψ) ?

Answer 15

• Pressure created by water molecules.
• Measured in kilopascals (KPa)
• Under standard conditions of temperature and pressure (250C and 100KPa) pure water has a water potential of 0KPa.

Question 16

What is a solute?

Answer 16

The thing that is dissolved

Question 17

What is a solvent?

Answer 17

What it is dissolved in

Question 18

What is a solution?

Answer 18

A solute that has been dissolved in a solvent

Question 19

How does adding solute affect water potential?

Answer 19

It lowers the water potential, meaning that water potential is negative.

Question 20

Which solution has the highest solute concentration out of -25KPa and -35KPa?

Answer 20

-35KPa

Question 21

Which terms are used to describe osmosis in animal/plant cells?

Answer 21

• Hypotonic
• Isotonic
• Hypertonic

Question 22

Define Hypotonic

Answer 22

• Less solute
• High water potential outside the cell
• Net osmosis into the cell

Question 23

Define Isotonic (animal/plant cells)

Answer 23

• Same water potential on either side of the cell
• No net osmosis

Question 24

Define Hypertonic

Answer 24

• More solute
• Low water potential outside cells
• Net osmosis out of cells

Question 25

What term describes hypotonic in animal cells?

Answer 25

- Hemolysis - Hemoglobin is released from cells

Question 26

What term describes hypertonic in animal cells?

Answer 26

Crenation

Question 27

What term describes hypotonic in plant cells?

Answer 27

- Turgid - The water inside the cell pushes the cell out but wont burst it due to the cell wall

Question 28

What term describes hypertonic in plant cells?

Answer 28

- Plasmolysed - Cell membrane pulled away from the cell wall - Due to water loss from the cytoplasm and vacuole

Question 29

Which formula is used to calculate the molarity/volume of a solution?

Answer 29

M1V1 = M2V2

Question 30

What does M1 mean?

Answer 30

The molarity of the stock solution

Question 31

What does M2 mean?

Answer 31

The molarity that you want

Question 32

What does V1 mean?

Answer 32

The volume of the stock solution

Question 33

What does V2 mean?

Answer 33

The volume you want

Question 34

How can this formula be rearranged to find the volume of stock solution?

Answer 34

V1 = M2V2/M1

Question 35

Define active transport

Answer 35

The movement of molecules across a plasma membrane against a concentration gradient.

Question 36

Describe the steps in active transport

Answer 36

- Molecules travel through carrier proteins - Molecule binds to a carrier protein and ATP attaches to the membrane protein on the inside of the cell - (the ATP changes the shape of the protein in 1 direction) - The binding of a phosphate molecule to a the protein causes the protein to change shape - This means that molecules can be accessed on the inside of the cell but the membrane is closed on the outside

Question 37

How might more than one molecule be moved at the same time?

Answer 37

- During transmission of nerve impulses - The sodium-potassium pump moves sodium ions out of neurons, while moving potassium ions in

Question 38

Define co-transport

Answer 38

Co-transport utilises energy in the form of an electrochemical gradient, rather than requiring the direct binding of ATP to the transport protein.

Question 39

What is another term for co-transport?

Answer 39

Secondary active transport

Question 40

What is an example of co-transport?

Answer 40

The movement of sodium ions and glucose across the lining of the small intestine (ileum)

Question 41

Describe an example of co-transport

Answer 41

- Sodium ions are actively transported out of the epithelial cell into the blood by a sodium potassium pump i.e. active transport. - Sodium ions are now at a lower concentration in the epithelial cell than in the lumen of the small intestine. - Sodium ions now diffuse down their concentration gradient through a co-transport protein present in the plasma membrane of the epithelial cell. -- Glucose is moved against its concentration gradient at the same time.

Question 42

How many sodiums/potassiums does the sodium potassium pump?

Answer 42

3 sodium ions, 2 potassium ions

Question 43

What factors affect rate of movement across a membrane?

Answer 43

- Concentration gradient (Higher concentration gradient = faster rate) - Temperature (Higher temp = faster rate) - Surface area (Higher SA = Faster rate) - Length of diffusion pathway (Shorter length = faster diffusion) - Number of proteins (More = faster rate)