Chapter 3 Cell Membrane and Transport

Question 1

What is the function of the cell membrane?

Answer 1

Controls the exchange of materials between the cell and its environment.

Question 2

What are the characteristics of a phospholipid?

Answer 2

A phospholipid has a glycerol and two fatty acids with a phosphate. The phosphate end is the head which is hydrophilic. The glycerol and fatty acids make up the tail which is hydrophobic.

Question 3

Define hydrophilic

Answer 3

Polar ; a molecule that can interact with water molecules because of its charge.

Question 4

Define hydrophobic

Answer 4

Non-polar ; a molecule that cannot interact with water molecules because it has no charge.

Question 5

What two types of proteins are embedded in the cell membrane?

Answer 5

Intrinsic proteins

Extrinsic proteins

Question 6

What are the function of intrinsic proteins?

Answer 6

Transporting water soluble substances across the bilayer by forming channels.

Question 7

What is the function of cholesterol in the cell membrane?

Answer 7

It limits the movement of the phospholipids giving the membrane stability. It stops the cell leaking water because it is hydrophobic.

Question 8

What is the structure and function of glycoprotein in the cell membrane?

Answer 8

A carbohydrate attached to a protein. It is a receptor site for chemicals and hormones

Question 9

What is the structure and function of glycolipids in the cell membrane?

Answer 9

A branching carbohydrate attached to a phospholipid. It is a receptor site for chemicals/hormones.

Question 10

Why is the model of membrane structure called the ‘fluid-mosaic’ model?

Answer 10

The phospholipid molecules are constantly moving and therefore fluid.
The proteins embedded in the bilayer vary in shape, size and pattern like a mosaic.

Question 11

What is exocytosis?

Answer 11

The active process of a vesicle fusing with the cell membrane, releasing the molecules it contains. Used for cell secretions.

Question 12

What is endocytosis?

Answer 12

The active process of the cell membrane engulfing material, bringing it into the cell in a vesicle.

Question 13

What are the two types of endocytosis?

Answer 13

Phagocytosis

Pinocytosis

Question 14

What is phagocytosis?

Answer 14

The active process of the cell membrane engulfing large particles, bringing them into the cell in a vesicle, and breaking them down by releasing digestive enzymes.

Question 15

What is pinocytosis?

Answer 15

The active process of the cell membrane engulfing droplets of fluid, bringing them in a vesicle.

Question 16

How is the cell membrane selectively permeable?

Answer 16

The cell surface membrane is selectively permeable to water and some solutes depending if they are lipid soluble or water soluble.

Question 17

How do lipid-soluble substance move through the cell membrane?

Answer 17

Lipid soluble substances such as vitamin A and Oxygen dissolve into the phospholipids and diffuse across the membrane. The bilayer is hydrophobic so lipid soluble molecules can move through easily.

Question 18

How do water-soluble substances move through the cell membrane?

Answer 18

Water soluble substances such as glucose cannot diffuse through the phospholipids and must pass through intrinsic protein molecules which form water filled channels across the membrane.

Question 19

Define diffusion

Answer 19

The passive movement of a molecule or ion down a concentration gradient, from a region of high concentration to a region of low concentration.

Question 20

What is Fick’s law of diffusion?

Answer 20

Rate of diffusion= Surface area x difference in conc. / distance

Question 21

What 4 factors effect diffusion?

Answer 21

Concentration gradient
Distance
Surface area
Thickness of membrane

Question 22

Define facilitated diffusion

Answer 22

The passive movement of molecules or ions down a concentration gradient by protein carriers.

Question 23

What are the factors that effect facilitated diffusion?

Answer 23

Surface area
Thickness of membrane 
Distance
Concentration gradient
Saturation of proteins

Question 24

Define active transport

Answer 24

The movement of molecules or ions against a concentration gradient using ATP

Question 25

What factors effect active transport?

Answer 25

Surface area
Thickness of membrane 
Distance
Concentration gradient 
Saturation of proteins
ATP

Question 26

Define Osmosis

Answer 26

The ent passive movement of water molecules across a semipermeable membrane from a region of high water potential to a region of low water potential.

Question 27

Define water potential

Answer 27

The tendency for water to move into a system; water moves from a region of high water potential to low water potential.

Question 28

What is the water potential of pure water in kPa?

Answer 28

Zero (0) kPa

Question 29

Define solute potential

Answer 29

A measure of the osmotic strength of a solution. It is the reduction in water potential due to the presence of solute molecules

Question 30

What is the water potential equation?

Answer 30

Water potential= pressure potential + solute potential

Ψ= Ψp+ Ψs

Question 31

Define pressure potential

Answer 31

The pressure exerted by the cell wall contents on the cell wall

Question 32

Define turgid

Answer 32

A plant cell wall that holds as much water as possible. Further entry of water is prevented as the cell wall cannot expand further.

Question 33

Define plasmolysis

Answer 33

The retraction of the cytoplasm and cell membrane from the cell wall as it loses water

Question 34

Define incipient plasmolysis

Answer 34

Cell membrane and cytoplasm are partially detached from the cell wall due to insufficient water to make the cell turgid.

Question 35

What is the pressure potential at incipient plasmolysis?

Answer 35

0kPa

Question 36

Define haemolysis

Answer 36

If water moves into red blood cells by osmosis, without the cell wall they burst.

Question 37

Define hypotonic

Answer 37

The water potential of the external solution has a high water potential (less negative) than the solution inside the cell.
Water moves into the cell by osmosis

Question 38

Define hypertonic

Answer 38

The water potential of the external solution is lower (more negative) than the solution inside the cell.
Water moves out of the cell by osmosis

Question 39

Define isotonic

Answer 39

The water potential of the external solution is equal to the water potential of the solution inside the cell.
There is no net movement of water