1.4 Membrane Transport

Question 1

Active transport

Answer 1

movement of substances across membranes using energy in the form of ATP

Question 2

Concentration gradient

Answer 2

a gradient resulting from an unequal distribution of ions across the cell membrane

Question 3

Diffusion

Answer 3

passive movement of particles from a region o higher concentration to a region of lower concentration.

Question 4

Endocytosis

Answer 4

the process in which the cell takes in materials from the outside by infolding of the membrane to form a vesicle

Question 5

Exocytosis

Answer 5

the process in which the cell releases materials to the outside by discharging them as membrane-bounded vesicles that pass through the cell membrane.

Question 6

Facilitated diffusion

Answer 6

diffusion through a membrane that requires protein

Question 7

Hypertonic

Answer 7

a more concentrated solution relative to another fluid

Question 8

Hypotonic

Answer 8

a less concentrated solution relative to another fluid

Question 9

Osmoregulation

Answer 9

control of the water balance of a living organism

Question 10

Osmosis

Answer 10

passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration

Question 11

Secretion

Answer 11

when material is released from the cell

Question 12

Semi-permeable membrane

Answer 12

membrane that allows some substances to diffuse but not others

Question 13

Transport pumps

Answer 13

proteins in the plasma membrane that use ATP to move substances across the membrane

Question 14

Vesicles

Answer 14

a bubble-like membranous structure that stores and transports cellular products

Question 15

Passive transport

Answer 15

movement of substances down the concentration without energy

Question 16

What factor can affect the rate of diffusion?

Answer 16

Temperature- an increase in temperature gives an increase gives an increase in kinetic energy which increases the rate of diffusion.

Question 17

When does simple diffusion occur? e.g….

Answer 17

when substances are able to move between the phospholipid molecules of the bilayer e.g carbon dioxide,
oxygen, steroid hormones

Question 18

why is facilitated diffusion different than simple diffusion?
Two examples

Answer 18

It involves the the channel proteins which let the solute pass through e.g larger particles which can not move through the hydrophobic layer can travel through it, ions

Specific carrier proteins that combine with solute molecules and change shape to let them through the membrane. Does not require energy. e.g Glucose, amino acids.

Question 19

How do potassium channels work?

Answer 19

Potassium channels are voltage gated. Voltages across the membranes are due to an unequal distribution of + and - ions inside and outside of the cell.
During a nerve impulse there are more positive charges inside the cell. This causes the potassium channels to change shape and open. Potassium ions diffuse rapidly out of the cell down their concentration gradient
An extra globular sub unit moves into the open channel returns to it’s normal shape.

Question 20

What makes this channel specific for potassium ions?

Answer 20

The width of the pore is 0.3 mm and the amino acids which line it are specific for potassium. ?

Question 21

what does the term osmolarity mean?

Answer 21

The total concentration of the cell or solutes in the cell

Question 22

What happens in active transport

Answer 22

a particle collides with a specific protein pump in the cell membrane.
the protein pump is activated by ATP, uses the energy released to change shape
the particle being transported is released on the other side of the membrane.
ADP and P are released from the protein pump and this causes it to revert back to it’s original shape, ready to receive another particle.

Question 23

The sodium-potassium pump

Answer 23

restores and maintains unequal distributions of Na+ and K+ inside and outside of the axon.

Question 24

How are sodium and potassium actively transported using the carrier protein?

Answer 24

• The interior of the pump is open to the inside of the axon; three sodium ions enter the pump and attach to their binding sites
• ATP transfers a phosphate group from from itself to the pump, this causes the pump to change shape and the interior is then closed.
• The exterior of the pump opens to the outside of the axon and the three sodium ions are released.
• Two potassium ions from outside can then enter and attach to their binding sites
• Binding of potassium causes release of the phosphate group; this causes the pump to change shape again so that it is again only open to the inside of the axon
• the interior of the pump opens to the inside of the axon and the potassium ions are released.

Question 25

How is the rate of active transport affected by temperature?

Answer 25

As the temperature increases the rate of active transport increases as the particles have more kinetic energy, however once the proteins have reached a certain temperature they will begin to denature. Therefore the rate of active transport will then decrease.

Question 26

what types of molecules are transported using endocytosis and exocytosis?

Answer 26

macromolecules(very large molecules) that are too big to cross the plasma membrane directly

Question 27

How does the fluidity of membranes allow materials to be exchanged through endocytosis and exocytosis?

Answer 27

The phospholipids are able to move around each other, this means that when two membranes come close together the phospholipids can move between and around each other, allowing the membranes to fuse.