Bio 4- Transport across cell membrane

Question 1

Where do the hydrophilic heads point?

Answer 1

They point to the outside because they are attracted to water.

Question 2

Where do hydrophobic tails point?

Answer 2

They point into the centre because they are repelled by water.

Question 3

What kind of material can move through the membrane?

Answer 3

Lipid soluble material

Question 4

List 3 functions of phospholipids in the membrane.

Answer 4

• allow lipid-soluble substances to enter + leave the cell
• prevent water soluble substances entering + leaving
• make the membrane flexible

Question 5

What are protein channels?

Answer 5

Water-filled tubes that allow water-soluble ions to diffuse across the membrane.

Question 6

What are carrier proteins?

Answer 6

Proteins that bind to ions/molecules then change shape in order to move the molecules across

Question 7

List 3 functions of proteins in the membrane?

Answer 7

• provides structural support
• allow active transport
• act as channels
• form cell-surface receptors for identifying cells
• help cells adhere together
• act as receptors

Question 8

Where is cholesterol?

Answer 8

Within the phospholipid bilayer

Question 9

Is cholesterol hydrophobic or hydrophilic?

Answer 9

very hydrophobic

Question 10

What does cholesterol do?

Answer 10

Prevents water loss + dissolved ions

Question 11

List 3 functions of cholesterol

Answer 11

• reduces movement of molecules
• makes the membrane less fluid
• prevents water leakage.

Question 12

what is osmosis?

Answer 12

The diffusion of water locales across a partially permeable membrane; from an area of high water potential to an area of low water potential

Question 13

What is water potential?

Answer 13

The likelihood of water molecules to diffuse out of or into a solution

Question 14

What type of water has the highest water potential?

Answer 14

Pure water

Question 15

What does isotonic mean?

Answer 15

When solutions have the same water potential

Question 16

What are three things that effect the rate of osmosis?

Answer 16

• water potential
• exchange surface thickness
• surface area

Question 17

If the water potential is high what happens to the rate of osmosis?

Answer 17

Its faster

Question 18

If the exchange surface is thick what happens to the rate of osmosis?

Answer 18

Its slower

Question 19

If the surface area is large what happens to the rate of osmosis?

Answer 19

Its faster

Question 20

What proteins are involved in active transport?

Answer 20

Carrier proteins

Question 21

How are carrier proteins involved in active transport?

Answer 21

A molecule attaches to the carrier proteins, the protein changes shape and moves the molecule across the membrane releasing it to the other side

Question 22

Name the two main differences between active transport and facilitated diffusion

Answer 22

1) active transport moves solutes from low to high conc button facilitated diffusion its from high to low
2) active transport requires energy but facilitated diffusion doesn’t

Question 23

Name the two factors that effect active transport.

Answer 23

• carrier proteins

- number of proteins

Question 24

Where is glucose absorbed in?

Answer 24

In the bloodstream in the small intestine

Question 25

why can’t glucose diffuse out of the ileum?

Answer 25

The conc of glucose is too low for the glucose to diffuse out into the blood

Question 26

Explain how glucose is absorbed by co-transport in the ileum?

Answer 26

1) sodium ions are actively out of the ileum epithelial cells into blood by the sodium-potassium pump which creates a conc gradient. There’s now a higher conc of Na+ in the ileum than in the cell
2) Na+ diffuses from the ileum into epithelial cell down a conc gradient. They do this via the sodium-glucose co-transport proteins
3) the co-transport carries glucose into the cell with Na, the conc of glucose inside the cell increases
4) Glucose diffuses out of the cell into the blood down a conc gradient through a protein channel by facilitated diffusion

Question 27

What is diffusion?

Answer 27

The net movement of particles from an area of higher conc to an area of low conc

Question 28

Is diffusion passive or active?

Answer 28

Passive

Question 29

What is facilitated diffusion?

Answer 29

Diffusion where carrier proteins and protein channels are used because some large particles diffuse very slowly through the phospholipid bilayer because they are so big

Question 30

Why do charge molecules need to diffuse through facilitated diffusion?

Answer 30

Charge particles would diffuse very slowly in simple diffusion because they are water soluble and the centre of the bilayer is hydrophobic

Question 31

What do large or charge particles diffuse through?

Answer 31

Carrier proteins or channel proteins

Question 32

Is facilitated diffusion active or passive?

Answer 32

Passive

Question 33

What are carrier proteins?

Answer 33

Large molecules across membranes, down their conc gradient

Question 34

How do carrier proteins work?

Answer 34

1) a large molecule attached to a carrier protein
2) the protein changes shape
3) releases the molecule on the opposite side

Question 35

What are channel proteins?

Answer 35

Proteins that form pores in the membrane for charged particles

Question 36

List the three factors that effect the rate of diffusion

Answer 36

• conc gradient
• thickness of exchange surface
• surface area