Transport

Question 1

What factors affect diffusion rate?

Answer 1

Temperature
Concentration difference
surface area
thickness of membrane

Question 2

What is facilitated diffusion ?

Answer 2

Diffusion across a membrane through protein channels

Question 3

What is meant by the term ‘selectively-permeable’?

Answer 3

Protein channels in facilitated diffusion are specific to to one molecule or ion

Question 4

What affects the rate of facilitated diffusion ?

Answer 4

Temperature
Concentration gradient
Membrane surface area and thickness
Number of channel proteins present

Question 5

What is active transport?

Answer 5

Movement of ions or molecules from an area of low concentration to high concentration, using energy supplied by ATP and carrier proteins.

Question 6

Whats the first stage in active transport ?

Answer 6

The molecule or ion binds to receptors in the channel of the carrier protein.

Question 7

What happens after the molecule binds in active transport?

Answer 7

On the other side of the carrier protein the ATP binds and is hydrolysed into ADP and phosphate.

Question 8

What does binding of the phosphate molecule to the carrier protein cause in active transport ?

Answer 8

The protein changes shape and opens up on the side that the molecule or ion needing to be moved is on.

Question 9

Why is bulk transport used ?

Answer 9

Large molecules like enzymes, hormones and whole cells like bacteria are too large to use channel or carrier proteins

Question 10

What is endocytosis ?

Answer 10

Bulk transport of materials into a cell, by the membrane folding around the membrane until it fuses around it and forms a vesicle that can then be moved around the cell to where it is needed.

Question 11

What is phagocytosis ?

Answer 11

Bulk transport of solids

Question 12

What is pinocytosis ?

Answer 12

Bulk transport of liquids

Question 13

What is exocytosis ?

Answer 13

Bulk transport of materials out of a cell by vesciles ususally formed by the golgi apparatus move towards the the cell surface membrane and fuse then are released.

Question 14

What is water potential ?

Answer 14

The pressure exerted by water molecules as they collide with a membrane or container, measured in pascals or kilopascals.

Question 15

What water potential does pure water have ?

Answer 15

0 kilopascals, the highest value

Question 16

What does the presence of a solute do to water potential ?

Answer 16

It lowers the water potential below zero, the more concentrated the solution the more negative the water potential is.

Question 17

When two solutions of different concentrations are separated by a partially permeable membrane, what will happen ?

Answer 17

Only the water can move, so water from the solution with the higher water potential (less concentrated) will move into the solution with the lower water potential (more concentrated).

Question 18

What happens in cytolysis?

Answer 18

When animal cells are placed in a solution that has a higher water potential than inside the cell, water moves into the cell by osmosis which increases the hydrostatic pressure. Cell surface membranes are not very thick and cannot stretch very much so the pressure will eventually cause the cell to break and burst.

Question 19

What happens in crenation?

Answer 19

When animal cells are placed in a solution with a lower water potential than inside the cell, water moves out of the cell by osmosis and causes the cell to become shrunken and shrivelled.

Question 20

What is turgor?

Answer 20

In plant cells when the water potential is higher outside of the cell and water moves in, the hydrostatic pressure pushes the membrane against the cell wall.

Question 21

What happens in plasmolysis?

Answer 21

When a plant cell is placed in a solution with a lower water potential than inside the cell, water moves out of the cell by osmosis, causing reduction in the volume of the cytoplasm meaning it pulls away from the cell wall.