[4.2-4] diffusion, osmosis, active transport

Question 1

what is the definition of simple diffusion?

Answer 1

the passive net movement of particles from an area of high concentration to an area of low concentration

Question 2

does simple diffusion need energy?

Answer 2

• no. passive means no energy from ATP hydrolysis is required
• the only energy used is the in-built kinetic energy of the molecules themselves

Question 3

what particles does simple diffusion work for?

Answer 3

not:

• large
• charged
• polar
• water-soluble

Question 4

what is the definition of facilitated diffusion?

Answer 4

a specialised form of diffusion where a specific channel protein is required to enable each specific molecule to move through the cell membrane

Question 5

in what ways is facilitated diffusion similar to simple diffusion?

Answer 5

• movement is still passive ie. no extra energy from ATP hydrolysis needed
• still from high to low concentration

Question 6

what gives the cell membrane its selectively permeable nature?

Answer 6

the presence / absence of specific channel proteins

Question 7

what is a selectively permeable membrane?

Answer 7

a membrane that is permeable to water molecules, and a few other small molecules, but not to larger molecules

Question 8

what is the definition of osmosis?

Answer 8

the movement of water from an area of less negative water potential to an area of more negative water potential across a selectively permeable membrane

Question 9

what does ‘net’ mean in terms of osmosis?

Answer 9

it means ‘overall’ so there will be no further osmosis, even if there is movement of water molecules

Question 10

what is the sign for water potential?

Answer 10

ψ

Question 11

what does ‘kPa’ relate to in terms of osmosis?

Answer 11

• pure water = 0 kPa
• kPa measures pressure exerted by solution
• pressure differences lead to movement

Question 12

how is the concentration of a solution measured in terms of negativity?

Answer 12

• dilute solution = ‘less negative’
• more concentrated solution = ‘more negative’
• value becomes more negative as solution becomes more concentrated

Question 13

how does negative value relate to the movement of water by osmosis?

Answer 13

• water moves from hypotonic ψ (less negative) to hypertonic ψ (more negative)
• isotonic is when there is equal ψ

Question 14

what is the definition of active transport?

Answer 14

the movement of particles from an area of low concentration to an area of high concentration using ATP and carrier proteins

Question 15

describe the active transport of a single molecule or ion [7]

Answer 15

1. carrier proteins span the cell membrane and bind to the molecule or ion to be transported on one side of it
2. molecule of ion binds to receptor sites on the carrier protein
3. inside of the cell/organelle, ATP binds to the protein, causing it to split into ADP and a phosphate molecule
4. protein molecule changes shape and opens to the opposite side of the membrane
5. molecule or ion is released to the other side of the membrane
6. phosphate molecule is released from the protein which causes the protein to revert to its original shape, ready for the process to be repeated
7. the phosphate molecule then recombines with the ADP to form ATP during respiration

Question 16

what is the role of the sodium-potassium pump?

Answer 16

• sodium ions are actively removed from the cell/organelle
• potassium ions are actively taken in from the surroundings
• this process is essential to a number of important processes in the organism eg. the creation of a nerve impulse