Section 2: Chapter 4: Transport across cell membranes

Question 1

What is the function of phospholipids in the membrane?

Answer 1

• Lipid-soluble substances can enter and leave.
• Prevents water-soluble substances to enter or leave.
• Makes membrane flexible.

Question 2

What 2 places are proteins found in the phospholipid bilayer?

Answer 2

1) surface of the bilayer.

2) Spanning the bilayer (protein channels and carrier proteins).

Question 3

What are the functions of proteins in the cell-surface membrane?

Answer 3

• Structural support.
• Protein channels - transporting water-soluble substances.
• Carrier proteins - active transport.
• Cell-surface receptors.

Question 4

What are the functions of cholesterol in the cell-surface membrane?

Answer 4

• Strength.
• Limits phospholipid movement by pulling together fatty acid tails.
• Hydrophobic - prevents water leaking.

Question 5

What are the functions of glycolipids in the membrane?

Answer 5

• Recognition sites.

- Stability.

Question 6

What are glycolipids made up of?

Answer 6

A carbohydrate covalently bonded with a lipid.

Question 7

What are the functions of glycoproteins in the membrane?

Answer 7

• Recognition sites.

- Help cells attach to each other.

Question 8

What is the fluid-mosaic model of the cell-surface membrane?

Answer 8

• Fluid - phospholipid molecules make the membrane flexible.

- Mosaic - proteins embedded in the bilayer.

Question 9

What are the two types of diffusion?

Answer 9

Simple and facilitated.

Question 10

Is simple diffusion a type of passive or active transport?

Answer 10

Passive.

Question 11

Define diffusion.

Answer 11

Net movement of molecules from high to low concentration.

Question 12

Explain facilitated diffusion.

Answer 12

• Still passive and down conc. gradient.
• Protein channels form hydrophilic channels for water-soluble ions to pass through.
  
  • Ions bind to the protein, causing it to change shape and open on other side of membrane.
• Carrier proteins - mol (eg/ glucose) binds to it, changing it’s shapes the mol can be released onto other side of membrane.

Question 13

What type of molecules can be transported via simple diffusion?

Answer 13

Small, non-polar molecules eg/ oxygen.

Question 14

Is facilitated diffusion a type of passive or active transport?

Answer 14

Passive.

Question 15

What molecules do protein channels let through?

Answer 15

Water-soluble molecules.

Question 16

What molecules do carrier proteins let through?

Answer 16

Glucose etc.

Question 17

Define osmosis.

Answer 17

Movement of water from high to low Ψ through a selectively permeable membrane.

Question 18

What is the Ψ of water?

Answer 18

0.

Question 19

What units is water potential measured in?

Answer 19

KiloPascals - kPa.

Question 20

How would you find the water potential of cells or tissues?

Answer 20

Place the tissue in a series of solutions of different Ψ. No net gain or loss of water = tissue same Ψ as solution.

Question 21

What will happen to a cell if placed in a hypertonic solution?

Answer 21

The cell is plasmolyzed, it will shrink and shrivel up.

Question 22

What is an isotonic solution?

Answer 22

Ψ is the same in the cell as in the solution.

Question 23

What will happen to a cell if placed in a hypotonic solution?

Answer 23

The cell will become turgid and eventually burst.

Question 24

What is a hypertonic solution?

Answer 24

Ψ of solution lower (more negative) than cell.

Question 25

What is a hypotonic solution?

Answer 25

Ψ of solution is more positive (closer to 0) than in the cell.

Question 26

Define active transport.

Answer 26

Movement of molecules or ions from low to high concentration using ATP and carrier proteins.

Question 27

What type of proteins are used in active transport?

Answer 27

Carrier proteins.

Question 28

Describe the process of active transport.

Answer 28

• Carrier protein spans membrane and binds to specific molecule/ion using it’s receptor site.
• Inside the cell, ATP binds to the protein, causing it to change shape and open to otherside of membrane.
• Mol released on other side of membrane.
• When ATP binded to protein, it splits into ADP and phosphate. This phosphate is released from the protein at the end of AT, so protein can go back to original shape and bind to another mol.

Question 29

How are membranes adapted for transport?

Answer 29

• Microvilli on epithelial cells in ileum - increases SA for carrier proteins.
• Increased number of carrier and channel proteins.

Question 30

What type of transport is used in absorbing glucose and amino acids into the blood?

Answer 30

Co-transport.

Question 31

Describe co-transport.

Answer 31

1) Sodium ions AT from ep cells → blood. Via protein-carrier mol.
2) higher conc. of sodium in lumen than ep cells.
3) Sodium ions → ep cells. Down conc. gradient. Via co-transport protein.
4) Amino acids/glucose carried in with sodium in step 3.
5) Amino acids/glucose → blood plasma. Fat diffusion. Via protein carrier.

Sodium ions down conc. gradient.
Glucose against.