Chapter 4

Question 1

What are the functions of phospholipids in the cell surface membrane?

Answer 1

Allow lipid soluble substances to enter and leave the cell
Prevent water soluble substances to enter and leave the cell
Make the membrane flexible and self sealing

Question 2

How does the structure of phospholipids make it suitable for its function?

Answer 2

It forms a bilayer so that the hydrophilic phosphate head is points to the outside of the membrane
The hydrophobic tails point into the membrane, repelling water

Question 3

What are the different proteins in the cell surface membrane?

Answer 3

Glycoproteins
Protein channels
Carrier proteins

Question 4

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

Answer 4

Provide structural support
Protein channels allow water soluble substances to enter the cell
Carrier proteins allow active transport of substances across the cell
Act as receptors for hormones and cells
Help cells adhere together

Question 5

What is the purpose of cholesterol in the cell surface membrane?

Answer 5

Add strength to the membrane
Reduce the movement of other molecules in the membrane
Make the membrane less fluid at high temperatures
Prevent leakage of water and ions

Question 6

What are the functions of glycolipids in the cell surface membrane?

Answer 6

They act as recognition sites
Help maintain stability of membrane
Help cells attach to others to form tissue

Question 7

What are the functions of glycoproteins in the cell surface membrane?

Answer 7

Act as recognition sites

Help cells attach to others to form tissue

Question 8

What molecules cannot pass through the cell surface membrane?

Answer 8

Molecules:
Insoluble in lipids
Too large
Of the same charge of protein channels
Polar

Question 9

Why can’t molecules insoluble in lipids pass the membrane?

Answer 9

They cannot pass through the phospholipid bilayer

Question 10

Why can’t molecules of the same charge as the channels pass the membrane?

Answer 10

They are repelled by the same charge from the protein channels

Question 11

Why can’t polar molecules pass the membrane?

Answer 11

They can’t pass through the non-polar hydrophobic tails in the phospholipid bilayer

Question 12

Why is the cell surface membrane called a fluid-mosaic model?

Answer 12

Fluid- the individual phospholipid molecules can move so the membrane is flexible
Mosaic- molecules are different sizes, shapes and patterns

Question 13

Why does diffusion occur?

Answer 13

Particles concentrated together will distribute themselves evenly

Question 14

Define diffusion

Answer 14

The net movement of molecules/ions from a region of high concentration to a low concentration until evenly distributed

Question 15

What is Fick’s Law?

Answer 15

Concentration gradient x surface are

/ diffusion distance

Question 16

What is facilitated diffusion?

Answer 16

Diffusion requiring the assistance of channel and carrier proteins

Question 17

How is facilitated diffusion similar to simple diffusion?

Answer 17

Goes down a concentration gradient
Doesn’t require ATP
Is a passive process

Question 18

How is facilitated diffusion different to simple diffusion?

Answer 18

It is the transport of charged molecules, molecules too large and non-polar molecules
It happens at specific protein molecules on the membrane

Question 19

How are protein channels involved in facilitated diffusion?

Answer 19

Allow water soluble ions to pass through as they form hydrophilic channels. The ions bind with the proteins causing it to change shape so that it is opened into the cell

Question 20

How are carrier proteins involved in facilitated diffusion?

Answer 20

The molecule binds to the protein, changing the shape so that it is open into the cell

Question 21

What is osmosis?

Answer 21

The net movement of water from a region of high concentration to a lower concentration through a partially permeable membrane

Question 22

Define a solute

Answer 22

A substance that is dissolved in a solvent

Question 23

Define a solvent

Answer 23

A substance with the ability to hold dissolved subtances

Question 24

What is a solution?

Answer 24

The solute and solvent together in a substance

Question 25

How is water potential represented and measured?

Answer 25

By the Greek letter psi (looks like a trident)

Measured in units of pressure (kiloPascals - kPa)

Question 26

How will the addition of a solute to pure water affect the water potential?

Answer 26

It will lower the water potential

Question 27

What must the water potential of a solution always be?

Answer 27

Less than zero- a negative value

Question 28

What is the water potential of pure water?

Answer 28

0

Question 29

How can the water potential of a cell or tissue be measured?

Answer 29

Placing them in a series of solutions of different, known water potentials. Where there is no net gain or loss of water from the cell or tissue, it has the same wp as the solution

Question 30

What is ATP used for in active transport?

Answer 30

Directly move molecules

Individually move molecules by co-transport

Question 31

How does active transport differ from passive forms of transport?

Answer 31

Metabolic energy from ATP is needed
Substances moved against concentration gradient
Carrier proteins needed
It is very selective- only some substances transported

Question 32

How can diffusion across cells be increased?

Answer 32

Epithelial cells have microvilli to increase surface area

Or increase number of proteins in the membrane

Question 33

How is diffusion involved in digestion?

Answer 33

Carbs and proteins are constantly digested so there is a concentration gradient compared between ileum and blood

Question 34

How is active transport involved in digestion?

Answer 34

By co-transport, where glucose or amino acids are taken into the cells with sodium ions which move down their concentration gradient