Transport across cell membranes

Question 1

Channel Proteins in the cell membrane does what?

Answer 1

• Helps molecules be transported through the membrane by Facilitated Diffusion

Question 2

Why is the cell-surface membrane described as a fluid-mosaic?

Answer 2

• the phospholipid molecules in the bilayer are constantly moving about giving a fluid structure
• the protein molecules are unevenly distributed throughout the membrane forming a mosaic

Question 3

How are phospholipids arranged in a membrane?

Answer 3

• hydrophilic heads of phospholipids oriented either inwards towards the cytoplasm or outwards towards the watery extra-cellular fluid
• hydrophobic tails are oriented towards each other away from water.

Question 4

What passes through a membrane during simple diffusion?

Answer 4

-very small molecules e.g, carbon dioxide and oxygen

Question 5

What does a phospholipid bilayer prevent from going through?

Answer 5

• water soluble ions and polar molecules

Question 6

Intrinsic and Extrinsic Protein

Answer 6

intrinsic - spans the whole membrane

extrinsic - doesn’t span the whole membrane

Question 7

Cholesterol in the cell membrane does what?

Answer 7

• provides strength and regulates fluidity of fatty acid chain

Question 8

What is facilitated diffusion

Answer 8

• Diffusion aided by Carrier and Channel Proteins without the use of energy

Question 9

Rate of Diffusion equation (Fick’s Law)

Answer 9

Surface Area x Concentration Difference/Diffusion Distance

Question 10

Carrier Proteins in the cell membrane does what?

Answer 10

• Helps molecules be transported through the membrane by facilitated Diffusion and active Transport

Question 11

How do carrier proteins work?

Answer 11

• the carrier protein has a complementary shape to the polar molecule being transported
• they bind which causes the carrier protein to change shape and transport molecules across the membrane

Question 12

What is diffusion?

Answer 12

• the net movement of molecules from a high concentration to a low concentration until the molecules are equally distributed

Question 13

Glycoproteins and Glycolipids Function

Answer 13

involved in cell to cell recognition and able to act as receptors

Question 14

Factors that decrease Active Transport

Answer 14

• Lowering of temperature
• Lack of Oxygen
• Metabolic and Respiratory Inhibitors

Question 15

What is Osmosis?

Answer 15

Diffusion of water through a selectively permeable membrane

Question 16

What is Water Potential?

Answer 16

The potential tendency of water molecules to leave a solution by osmosis

Question 17

What is Active Transport?

Answer 17

• the movement of ions or molecules across a cell membrane against the conc gradient through carrier proteins and requiring energy.

Question 18

What factors increase Rate of Diffusion?

Answer 18

Increased Surface Area

Increased Concentration Difference

Decreased Diffusion Distance

Question 19

What happens to red blood cells in a isotonic solution?

Answer 19

• the solution has the same water potential as the cell so there is no net movement of water.

Question 20

Cell turgor during osmosis?

Answer 20

• as water enters the cell, the vacuole enlarges and the vacuole, cytoplasm and cell membrane exert an outward turgor pressure on the cell wall

Question 21

What happens to red blood cells in a hypertonic solution?

Answer 21

• the cell has a higher water potential than the solution so water moves out of the cell and into the solution which makes the cell shrivel and become flaccid.

Question 22

What happens to red blood cells in a hypotonic solution?

Answer 22

• the cell has a lower water potential than the solution and so water moves into the cell which causes swelling and eventually bursting of the cell

Question 23

What is an epithelial cell?

Answer 23

cells in the body specialised for the absorption or transport of important molecules

Question 24

Intestine Epithelial cell adaptations? (2)

Answer 24

• folded cell surface membrane into microvilli to increase surface area
• numerous mitochondria to provide ATP for the release of energy. (active transport)