Transport in cells

Question 1

Define simple diffusion

Answer 1

Simple diffusion is the net movement of a substance from a region of higher concentration to a region of lower concentration down a concentration gradient until equilibrium is reached

Question 2

What is simple diffusion caused by

Answer 2

Constant random motion of all particles

Question 3

What are the factors affecting diffusion and how do they affect diffusion

Answer 3

• Concentration gradient =
• Distance /
• Sa:V =
• Particle size /
• Temperature =
• Medium (Fastest in gas, slowest in solid)

Question 3

What does simple diffusion result in

Answer 3

Equilibrium

Question 4

Define facilitated diffusion

Answer 4

Facilitated diffusion is the diffusion of ions and water-soluble molecules across the cell membrane using transport proteins, down a concentration gradient

Question 4

What are the characteristics of facilitated diffusion

Answer 4

• Passive process –> no energy required
• Quantity of transport proteins is a limiting factor

Question 4

How are channel proteins used in facilitated diffusion

Answer 4

• Provides a hydrophilic channel across the membrane for ions or hydrophilic molecules to enter/leave the cell
• Specific for molecules that can move across membrane

Question 5

What are the transport proteins used in facilitated diffusion

Answer 5

• Channel proteins
• Carrier proteins

Question 6

Define water potential

Answer 6

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

Question 6

Define osmosis

Answer 6

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

Question 7

How are carrier proteins used in facilitated diffusion

Answer 7

• Diffusing substances bind temporarily to carrier protein
• Causes carrier protein to change shape
• Changes in shape are triggered by the binding and release of substances

Question 8

What happens when too much water leaves an animal cell

Answer 8

Cell shrinks and crenates

Question 8

What happens when too much water enters an animal cell

Answer 8

Cell swells and may lyse

Question 9

What happens when too much water enters a plant cell

Answer 9

Cell swells and become turgid

Question 10

What happens when too much water leaves a plant cell

Answer 10

Cell shrinks and becomes plasmolysed

Question 11

Describe what happens when a plant cell is placed in a diluted solution

Answer 11

• Diluted solution has higher water potential than plant cell
• Water moves into plant by osmosis
• Vacuole swells, pushing cytoplasm and cell membrane against cell wall
• Cell become turgid
• Cell does not lyse because of cell wall

Question 12

Define turgor pressure

Answer 12

Turgor pressure is pressure exerted by the vacuole on the cell wall

Question 12

Define full plasmolysis

Answer 12

Full plasmolysis is when cell membrane has completely withdrawn from cell wall and this is irreversible

Question 12

Describe what happens when a plant cell is placed in a concentrated solution

Answer 12

• Concentrated solution has lower water potential than plant cell
• Water moves out of cell by osmosis
• Vacuole decreases in size, pulling cytoplasm and cell membrane away from cell wall
• Cell becomes plasmolysed
• Space between cell wall and cell membrane will be filled with surrounding solution
• Plant starts to wilt

Question 13

Define active transport

Answer 13

Active transport is the movement of ions or molecules across a cell membrane from a region of lower concentration to a region of higher concentration against a concentration gradient, with the expenditure of energy from ATP molecule in cell

Question 14

What are the characteristics of active transport

Answer 14

• Allows a cell to maintain internal concentration of solutes regardless of surrounding concentration
• Requires use of specific carrier proteins

Question 15

Explain how the sodium-potassium pump works

Answer 15

• Animal cell needs to maintain a high concentration of potassium ions and a low concentration of sodium ions
• Cell maintains this by pumping potassium ions in and sodium ions out
• Carrier protein used is the sodium-potassium pump
• ATP required for carrier protein to change shape
• 3 sodium ions are exchanged for 2 potassium ions

Question 16

Define bulk transport

Answer 16

Bulk transport is the transport of materials into or out of a cell by enclosing it within a vesicle

Question 17

What are the characteristics of bulk transport

Answer 17

• Allows large molecules or large quantities of molecules to enter/leave a cell without passing through membrane
• Active process as it requires expenditure of energy by ATP molecule in cell

Question 18

Define endocytosis

Answer 18

Endocytosis is when substances are taken into a cell when ATP provides energy for the inward folding of cell membrane to form vesicles that separate from the membrane

Question 19

What is one example of endocytosis

Answer 19

Phagocytosis

Question 20

Define phagocytosis

Answer 20

Phagocytosis is the process of engulfing foreign particles

Question 21

Define exocytosis

Answer 21

Exocytosis is when ATP provides energy for substances in secretory vesicles to move towards and fuse with cell membrane, releasing vesicle contents outside the cell

Question 22

Is a membrane required for exocytosis

Answer 22

Yes

Question 23

What substances move by active transport

Answer 23

Ions and water soluble molecules

Question 24

What substances move by simple diffusion

Answer 24

Small and uncharged substances

Question 25

What substances move by facilitated diffusion

Answer 25

Ions and water soluble molecules

Question 26

Is a membrane required for endocytosis

Answer 26

Yes

Question 27

Is a membrane required for osmosis

Answer 27

Yes