Chapter 2- Transport across membranes

Question 1

List and describe examples of diffusion.

Answer 1

1. Diffusion of oxygen and carbon dioxide in the alveoli.
2. Diffusion of mineral salts into root hair cells.
3. Diffusion of perfume in air.

Question 2

Define facilitated diffusion.

Answer 2

Facilitated diffusion is defined as the passive transport of molecules passing through and biological membrane via a transport protein. Usually, only polar molecules require facilitated diffusion.

Question 3

List three proteins which aid in facilitated diffusion and explain how they function.

Answer 3

1. Channel proteins (opens up a channel).
2. Carrier proteins (opens and closes | binding site | changes shape).
3. Transmembrane proteins.

Question 4

Define osmosis.

Answer 4

Osmosis is defined as the net movement of water molecules from a region of less negative water potential to a region of more negative water potential. Osmosis happens across a biological membrane.

Question 5

What is water potential?

Answer 5

Water potential is the tendency of water to move from one region to another.

Question 6

Describe the process of osmosis in root hair cells.

Answer 6

1. There is a thin film of water surrounding the cell. Mineral salts dissolve in this film and gets diluted, becoming less negative.
2. Mineral salts move into the concentrated cell sap via osmosis.
3. Cell sap gets diluted.
4. Mineral salts move into cells inside via osmosis using the same method until it reaches the xylem.

Question 7

Describe what happens to an animal cell in hypertonic solution.

Answer 7

1. Water moves out of the cell via osmosis as it is less negative.
2. The cell shrinks in size as it loses water.
3. Little spikes start to appear on the cell.
4. The cell is crenated.
5. It will become dehydrated and hence die after a while.

Question 8

Describe what happens to an animal cell in hypotonic solution.

Answer 8

1. Water moves into the cell via osmosis as it is more negative.
2. The cell starts to swell as water enters.
3. The cell eventually bursts as water keeps entering.
4. The cell is said to have become lysed.

Question 9

Describe what happens to a plant cell in hypertonic solution.

Answer 9

1. Water moves out of the cell via osmosis as it is less negative.
2. The vacuole decreases in size.
3. Cytoplasm and cell membrane start to shrink away from the cell wall.
4. The cell becomes plasmolysed / flaccid.

Question 10

Describe what happens to a plant cell in hypotonic solution.

Answer 10

1. Water moves into the cell via osmosis as it is more negative.
2. Vacuole increases in size and pushes other cell contents to the wall.
3. The cell will become turgid.
4. The cell wall then exerts an opposing force, stopping water from entering the cell. The cell does not burst.

Question 11

Define active transport.

Answer 11

Active transport is defined as the process in which energy is used to move particles of a substance against its concentration gradient. This can only happen in living cells as they respire and hence produce energy.

Question 12

State two examples of active transport.

Answer 12

1. Lumen to epithelial walls in the ileum.

2. Root hair cells.

Question 13

Define endocytosis and exocytosis.

Answer 13

1. Endocytosis is defined as the absorption of large molecules into a cell by engulfing it in a membranous vesicle.
2. Exocytosis is defined as the secretion of large molecules out of a cell by releasing it from a membranous vesicle.

Question 14

List an example of endocytosis and exocytosis each.

Answer 14

1. Feeding by amoeba or paramecium.
2. Engulfing of bacteria by WBCs via phagocytosis.
3. Secretion of proteins from the Golgi body.

Question 15

Define diffusion.

Answer 15

Diffusion is the net movement of particles down a concentration gradient, from a region of higher concentration to a region of lower concentration. Diffusion can occur anywhere.