Diffusion

Question 1

What is diffusion?

Answer 1

The net movement of molecules or ions from a region of a high concentration gradient to a region with a low concentration gradient down a concentration gradient

Question 2

What is a concentration gradient?

Answer 2

The differencce between the concentration of molecules in two places. A high concentration gradient and a low concentration gradient.

Question 3

What does a partially permeable membrane do?

Answer 3

It allows the movement of small molecules such as oxygen, carbon dioxide and water to pass through easily.

Question 4

How is the movement of a molecule across cell membranes? Why?

Answer 4

Passive. Because cells do not need to use energy to move the molecules.

Question 5

SUPPLEMENT- name the factors that influence the efficiency of diffusion

Answer 5

.distance molecules have to travel: cell membranes are very thin
.concentration gradient: cells use substances that diffuse as quickly as possible, keep low concentration inside cytoplasm. molecules keep diffusing because cell is maintaining a steep concentration gradient
.the surface area: some cells have cell membranes folded to give large surface to allow many molecules to cross by diffusion
.temperature: molecules move faster and collide more often as temperature increases. diffusion faster at warmer temperatures

Question 6

How does gas exchange surfaces in mammals?

Answer 6

In the alveoli, oxygen diffuses across a very thin layer of cells into blood and carbon dioxide diffuses in the opposite direction.

Question 7

How does gas exchange surfaces in plants?

Answer 7

It occurs inside the leaves. The spongy mesophyll cells provide a large surface area for the exchange of gases. The air between the cells in the plant is where the gass diffuses.

Question 8

Where is diffusion more efficient? Why?

Answer 8

Through air. This is because diffusion is 300.000 times faster through the air than through water.

Question 9

What is a solution made up of?

Answer 9

A solute (dissolves solvent) and a solvent (dissolves in a solute).

Question 10

What is the definition of “soluble”?

Answer 10

Something which dissolves in a solvent.

Question 11

Is the cell membrane partially permeable?

Answer 11

Yes!!

Question 12

What is osmosis?

Answer 12

Osmosis is the diffusion of watewer from a dilute solution into a more concentrated solution through a partially permeable membrane.

Question 13

SUPPLEMENT- what is water potential?

Answer 13

is a way of thinking about the ability of water to move by osmosis. influenced by how much water is available, also pressure exerted on water in plant cells by cell wall. a dilute solution (lot of water molecules) has high water potential. a concentrated solution (fewer water molecules) has low water potential

Question 14

Why do water molecules enter the plant cells?

Answer 14

Because there is a water potential gardient so that water molecules can diffuse into the cells by osmosis.

Question 15

What happens when water enters a cell?

Answer 15

It swells up and as the water pushes against the cell wall, it develops a turgid pressure.

Question 16

What happens when the cell is full with water?

Answer 16

The cell becomes turgid, this is because the cell wall stops the cell bursting.

Question 17

What happens when a plant cell loses water?

Answer 17

It becomes wilt (the opposite of firm and turgid)

Question 18

SUPPLEMENT- define the term flaccid

Answer 18

we say a cell is flaccid when they are no longer firm and become limp. this happens when plant cells are placed into a concentrated sugar or salt solution, and water passes out of the cells by osmosis. as water passes out, the sap vacuole starts to shrink.

Question 19

What is Active Transport?

Answer 19

It is the movement of ions or molecules in or out of a cell through the cell membrane against a concentration gradient, using energy released during respiration.

Question 20

SUPPLEMENT- describe the role of carrier proteins and respiration in active transport

Answer 20

carrier proteins span the cell membrane and provide means by which ions and molecules can enter or leave a cell by active transport.
first, molecule or ion combines with a carrier protein. energy from respiration enables carrier protein to change its shape to carry ion or molecule to inside of membrane. molecule or ion is released to inside of membrane and carrier protein reverts to original shape

Question 21

SUPPLEMENT - when does a cell become plasmolysed?

Answer 21

a cell becomes plasmolysed when more water leave the cells and the cytoplasm starts to move away from the cell wall

Question 22

SUPPLEMENT - what happens with animal cells when they swell?

Answer 22

animal cells have no cell wall to stop them swelling so they burst

Question 23

SUPPLEMENT - state what effect each of the following would have on active transport, in each case give reasons for your answer

a- a lack of oxygen
b- an increase in temperature
c- the presence of poison, such as cyanide

Answer 23

a- any factor that affects rate of respiration will also affect rate of active transport, so lack of oxygen would reduce respiration rate and active transport

b- an increase in temp. would increase rate of respiration, so would also have same effect on active transport

c- presence of poison can stop respiration, so active transport would stop altogether

Question 24

SUPPLEMENT - describe the active uptake of glucose by epithelial cells in villi and in kidney tubes

Answer 24

epithelial cells lining villi in small intestine and kidney tubules absorb glucose by active transport. these cells have high rate of respiration to provide energy for active transport