Movement of Substances

Question 1

Define

The process of diffusion

Answer 1

Diffusion is the net movement of particles from a region of high concentration to a region of low concentration

Question 2

What are factors that affect rate of diffusion?

4 factors

Answer 2

1. Concentration gradient
2. Size of particles
3. Temperature
4. Distance

Question 3

How is facilitated diffusion different from simple diffusion?

Answer 3

Facilitated diffusion allows for faster movement of particles down the concentration gradient, involving the use of proteins in the cell membrane to facilitate diffusion

Question 4

Define

The process of facilitated diffusion

Answer 4

Facilitated diffusion is the movement of specific particles down a concentration gradient via transport proteins across the membrane

Question 5

What are the two main types of transport proteins in facilitated diffusion?

Answer 5

1. Channel proteins
2. Carrier proteins

Question 6

Describe

The process of facilitated diffusion using channel proteins

Answer 6

Charged ions such as Na+, Ca+ and K+ cannot easily diffuse through the lipid part of the membrane as the fatty acid chains are non-polar. Channel proteins have pores (lined with polar groups) that allow entry and exit of these ions.

Channel proteins are very specific and only allow one type of ion to pass through

Question 7

Describe

The process of facilitated diffusion using carrier proteins

Answer 7

Carrier proteins facilitate the diffusion of larger polar molecules such as glucose and amino acids. When these molecule attaches itself to a carrier protein at a specific site, it causes the protein to change its shape, thus delivering the molecule to the other side of the membrane

Question 8

What are aquaporins?

Answer 8

Specific channel proteins that moves water in and out through osmosis

Question 9

Define

Osmosis

Answer 9

Osmosis is the net movement from a region of higher water potential to a region of lower water potential across a partially permeable membrane

Question 10

What are hypertonic, isotonic and hypotonic solutions?

Answer 10

Hypertonic: Solution is of high concentration/lower water potential than cell
Isotonic: Solution is of the same concentration as the cell
Hypotonic: Solution is of low concentration/higher water potential than cell

Question 11

What happens to cells in hypertonic solutions?

Answer 11

Animal cells: Water potential in cell is higher, hence water leaves cell through osmosis. Cell shrinks in size and becomes crenated

Plant cells: Water potential in cell sap is higher, hence water leaves cell through osmosis. As cell wall is rigid, cell membrane shrinks and pulls away from cell and cell becomes plasmolysed. The cell becomes flaccid

Question 12

What happens to cells in hypotonic solution?

Answer 12

Animal cells: Water potential in cell is lower, hence water enters the cell through osmosis. Cell expands and beomes lysed (bursts)

Plant cells: Water potential in cell is lower, hence water enters the cell through osmosis. Cell expands but cell wall prevents cell from bursting, hence becoming turgid. Water in the vacuole will exert a pressure on the cell wall, known as turgor pressure.

Question 13

Define

The process of active transport

Answer 13

The net movement of solutes against a concentration gradient across a membrane via protein pumps with the use of energy

Can only be carried out by living cells

Question 14

Describe

The process of endocytosis

Answer 14

In this process, the cell wraps a segment of the surface membrane around the molecule in brings it into the cytosol within a vesicle (endosome). Requires energy.

Question 15

Describe

The process of exocytosis

Answer 15

Secretory vesicles carry their contents to the cell membrane and fuse, before releasing their contents outside of the cell. Requires energy.