Substance movement

Question 1

What is diffusion?

Answer 1

Net movement of particles from area of higher concentration to area of lower concentration passively down a concentration gradient

Question 2

What is simple diffusion and give an example?

Answer 2

Diffusion directly across cell membrane

e.g O2 and CO2

Question 3

What type of molecules can simply diffuse and why?

Answer 3

Small = means they can pass through spaces between phospholipids
Non-polar = means they can dissolve in hydrophobic cell membrane core

Question 4

What is facilitated diffusion?

Answer 4

Diffusion across cell membrane via channel or carrier proteins

Question 5

How do carrier proteins work?

Answer 5

1) large molecule attaches to carrier protein
2) causes carrier protein to change shape
3) carrier protein releases molecule on opposite side of membrane

Question 6

How do channel proteins work?

Answer 6

Form pores in cell membrane which ions can travel through

Question 7

Describe the factors affecting diffusion rate?

Answer 7

Temperature = higher means particles have more ke diffusing faster

Conc gradient = steeper conc faster rate of diffusion

Membrane thickness = particles travel shorter distances through thin surfaces diffusing faster

Surface area = large SA means more particles can cross membrane at once diffusing faster

Carrier/channel proteins = more proteins faster rate of facilitated diffusion

Question 8

what is active transport?

Answer 8

Movement of particles from area of lower concentration to area of higher concentration requiring energy from ATP to move particles against a concentration gradient

Question 9

How does active transport occur via carrier proteins?

Answer 9

1) molecule or ion binds to carrier protein

2) ATP binds to carrier protein

3) Hydrolysis of ATP to ADP and Pi causes carrier protein to change shape releasing molecule or ion on opposite side of membrane

4) Pi released from carrier protein causing protein to return to its original shape ready to be used again

Question 10

What factors affect active transport rate and how?

Answer 10

Temperature = higher temps particles have more ke travelling faster

Membrane thickness = particles travel shorter distances faster through thin exchange surfaces

Carrier protein numbers = more proteins faster rate of active transport

Respiration rate = more respiration more ATP available for active transport

Question 11

What is bulk transport?

Answer 11

Movement of large molecules e.g enzymes and hormones in and out of the cell using another form of active transport

Question 12

What are the 2 types of bulk transport?

Answer 12

Endocytosis = transports materials into cells
Exocytosis = transports materials out of cells

Question 13

What is endocytosis?

Answer 13

Large or many molecules at once are transported into cells

cell-surface membrane engulfs materials forming vesicles which then move into cytoplasm where materials can be processed

Question 14

What are the 2 forms of endocytosis?

Answer 14

Phagocytosis = uptake of solid materials
Pinocytosis = uptake of liquid materials

Question 15

What is exocytosis?

Answer 15

Large or many molecules at once are transported out of cells

Vesicles (formed by Golgi apparatus) move towards and fuse with cell-surface membrane where materials are released outside the cell

Question 16

What is water potential?

Answer 16

Pressure exerted by H2O molecules on membrane or container surrounding a solution (measured in kPa)

Question 17

What is a solution with a high water potential?

Answer 17

Solution has high water concentration with little dissolved solute

Question 18

What is a solution with a low water potential?

Answer 18

Solution has low water concentration with lot’s of dissolved solute

Question 19

What does the kPa value tell you about water potential?

Answer 19

Pure water = Ψ of 0 kPa

value decreases (more negative) as more solute is added

Question 20

What is osmosis?

Answer 20

Diffusion of H2O molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential

Question 21

What happens to animal cells in a hypotonic solution?

Answer 21

• hypotonic solution has a higher Ψ than cell
• water molecules move into the cell
• cell swells and bursts

Question 22

What happens to animal cells in a isotonic solution?

Answer 22

• isotonic solution has the same Ψ as cell
• no net movement of water into or out of cell
• cell stays the same size

Question 23

What happens to animal cells in a hypertonic solution?

Answer 23

• hypertonic solution has a lower Ψ than cell
• water molecules move out of the cell
• cell shrinks

Question 24

What happens to plant cells in a hypotonic solution?

Answer 24

• hypotonic solution has a higher Ψ than the cell.
• water molecules move into the cell
• cell swells and becomes turgid

Question 25

What happens to plant cells in a isotonic solution?

Answer 25

- isotonic solution has the same Ψ as the cell - no net movement of water into or out of the cell - cell stays the same size

Question 26

What happens to plant cells in a hypertonic solution?

Answer 26

- hypertonic solution has a lower Ψ than the cell - water molecules move out of the cell - cell shrinks and becomes plasmolysed

Question 27

What factors affect rate of osmosis and how?

Answer 27

Temperature = higher temps H20 molecules have more ke diffusing faster Ψ gradient = steeper gradient faster rate of osmosis Membrane thickness = H2O molecules travel shorter distances faster through thin exchange surfaces SA = larger SA means more H2O molecules cross membrane at once making osmosis faster