2.5.2- Diffusion Across Membranes

Question 1

Define what facilitated diffusion is.

Answer 1

Movement of molecules from
An area of high to low concentration of that molecule, across a partially permeable membrane via protein channels or carriers.

Question 2

What does the abbreviation “ATP” stand for?

Answer 2

Adenosine triphosphate

Question 3

Describe the role of ATP within cells

Answer 3

To provide cellular energy to drive the biochemical processes to sustain life

Question 4

What are substances that can pass across cellular membranes without using any of the cells metabolic energy and only use the kinetic energy of the molecules called?

Answer 4

Passive processes.

Question 5

All molecules have ________ _________ and can move freely and randomly when in gas and liquid media.

Answer 5

Kinetic energy

Question 6

Explain what will naturally happen to molecules in gas or liquid media when there is a high concentration of the certain molecule in an area.

Answer 6

They will dump into each other as they randomly move about and will spread further from each other and will move so they’re in lower concentration, until they’re evenly dispersed.

Question 7

When molecules are evenly dispersed but are still moving randomly, there is no net diffusion and they have reached _______

Answer 7

Equilibrium

Question 8

Define what diffusion is.

Answer 8

Momentum of molecules from an area of high concentration of that molecule to low- possible across a membrane.

Question 9

Explain how come molecules, that are small, e.g. Oxygen and CO2 can pass through the cellular membrane

Answer 9

Via simple diffusion

Question 10

How can day soluble molecules like steroid hormones, pass through the membrane- even if they’re larger?

Answer 10

They an diffuse through the membrane as they dissolve in the lipid bilayer- they’re still moving down the concentration gradient.

Question 11

Explain why it is a ‘special case’ how water can pass through the bilayer by unfacilitated diffusion.

Answer 11

Water is polar and insoluble in the phospholipid bilayer so it would be thought the membrane was impenetrable by water

Question 12

Why can water in fact move move through the membrane via direct diffusion?

Answer 12

It is present in such high quantities, it allows direct diffusion

Question 13

Explain how membranes where very high water movement rates are required are adapted to change to this.

Answer 13

Aquaporins- specific water channel proteins- are present to cross through the membrane without the challenge of passing through the lipid environment

Question 14

Explain how the concentration gradient is maintained in cells, despite diffusion into the cells- in general terms.

Answer 14

Many of the molecules that enter cells then go into organelles- hence, the concentration gradient is maintained and more molecules can enter the cell

Question 15

Explain how the oxygen concentration is Maintained within cells.

Answer 15

Oxygen diffuses to cytoplasm and then to mitochondria for aerobic respiration

Question 16

Explain how the CO2 concentration is maintained within palisade mesophyll cells of a plant leaf.

Answer 16

CO2 diffuses into cytoplasm then to chloroplasts for use in photosynthesis.

Question 17

Factors what alter the kinetic energy of molecules will them effect…

Answer 17

The rate of diffusion

Question 18

List the five factors that will alter the kinetic energy of molecules, hence, altering the rate of diffusion

Answer 18

~Temperature
~diffusion distance 
~surface area 
~size of diffusing molecule
~concentration gradient

Question 19

Describe the type of molecules that will pass through the lipid bilayer via protein channels

Answer 19

Small and polar molecules

Question 20

Explain why polar molecules are insoluble in lipids.

Answer 20

They have an electrical charge, hence, are unable to interact with the hydrophobic rails of the lipid bilayer.

Question 21

What is the average diameter of a protein channel?

Answer 21

0.8nm

Question 22

Cholesterol in membranes reduces the permeability of the membrane to…

Answer 22

Small and water soluble molecules

Question 23

Why can a glucose molecule not diffuse through a protein channel in a membrane?

Answer 23

They are too large

Question 24

Describe the type of molecule that a transmembrane protein carrier carries.

Answer 24

Molecules that are too large to pass through a protein channel

Question 25

Protein channels and protein carriers in the membrane are ________ proteins.

Answer 25

Integral

Question 26

Explain how a protein channel passes mater across the membrane.

Answer 26

They open to allow the molecule in, adapt shape and then open on the other side to allow the molecule out.

Question 27

There are specific transmembrane carrier proteins for…

Answer 27

Different types of molecules

Question 28

Neurone plasma membranes have many channels specific to _______ or ________ ions.

Answer 28

Sodium

Potassium

Question 29

Why are there so many sodium or potassium ion channels in the plasma membrane of neurones?

Answer 29

Due to the diffusion of these ions in and out f the neurone axon is crucial for nerve impulse conduction

Question 30

Explain how the plasma membrane of epithelial cells that line airways are specialised for their function.

Answer 30

They have chloride ion channels that play a crucial role in regulating the composition of mucus to trap particles and pathogens.