Membranes - Diffusion , Osmosis, and Active Transport

Question 1

Define diffusion

Answer 1

The net movement of particles from an region of higher concentration to a region of lower concentration

Question 2

Is diffusion active or passive?

Answer 2

Passive

Question 3

Define passive transport

Answer 3

Movement of substances that does not require energy

Question 4

Define osmosis

Answer 4

The movement of water from a region of high water potential to a region of low water potential across a partially permeable membrane

Question 5

Define facilitated diffusion

Answer 5

Diffusion across a plasma membrane through protein channels

Question 6

Is facilitated diffusion passive?

Answer 6

Yes

Question 7

Is osmosis passive or active?

Answer 7

Passive

Question 8

Define active transport

Answer 8

The movement of molecules from an area of low concentration of that molecule to an area of high concentration of that molecule. This movement requires ATP

Question 9

What sort of molecules tend to move via diffusion across a membrane?

Answer 9

small molecules (e.g. gases)
lipid soluble molecules
non-polar molecules

Question 10

How does water tend to move across membranes?

Answer 10

Through aquaporins (via osmosis)

Question 11

Why can steroid hormones easily cross a membrane by simple diffusion?

Answer 11

They are lipid soluble
- They are non-polar

Question 12

Which 2 factors affect the rate of diffusion?

Answer 12

Temperature

Concentration difference

Question 13

What effect does an increase in temperature have on the rate of diffusion?

Answer 13

It increases the rate of diffusion

Question 14

What effect does a greater difference in concentration of two regions have on the rate of diffusion?

Answer 14

It increases the rate of diffusion

Question 15

Why does a higher temperature increase rate of diffusion?

Answer 15

higher temperature means particles have more kinetic energy and move at higher speeds

Question 16

Why is it easier for oxygen to diffuse across a membrane than water?

Answer 16

oxygen molecules are small and non-polar whereas water molecules are polar
the hydrophobic interior of the phospholipid bilayer repels the charged molecules
water is only partially charged so is still able to diffuse through the membrane, though only slowly

Question 17

What 4 factors affect the rate of diffusion across a membrane?

Answer 17

temperature
concentration gradient
surface area
thickness of membrane

Question 18

An increase in surface area of an exchange surface has what effect on rate of diffusion?

Answer 18

increases rate of diffusion

Question 19

An increase in membrane thickness has what effect on the rate of diffusion?

Answer 19

Decreases rate of diffusion

Question 20

Why are membranes containing protein channels selectively permeable?

Answer 20

Most protein channels are specific to one molecule or ion
- Therefore only these specific molecules/ions are able to move across the membrane

Question 21

What does facilitated diffusion allow to move across a membrane?

Answer 21

larger molecules
lipid insoluble molecules
small charged particles

Question 22

Give an example of a small charged particle that moves across membranes via facilitated diffusion

Answer 22

Na+

Question 23

Give an example of a large molecule that moves across membranes via facilitated diffusion

Answer 23

Glucose or amino acids

Question 24

What happens to carrier proteins when a specific molecule binds to them?

Answer 24

They change shape

Question 25

How do protein channels allow charged particles to move through the membrane?

Answer 25

They provide a hydrophilic channel for charged particles

Question 26

What are the 5 factors which affect the rate of facilitated diffusion?

Answer 26

temperature concentration gradient membrane surface area membrane thickness number of channel proteins

Question 27

Which type of movement of particles requires ATP?

Answer 27

Active transport Bulk transport

Question 28

What does active transport require to occur?

Answer 28

ATP Carrier proteins

Question 29

Why is active transport considered to be selective?

Answer 29

specific substances are transported by specific carrier proteins

Question 30

Define endocytosis

Answer 30

the bulk transport of material into cells

Question 31

Define pinocytosis

Answer 31

the bulk transport of liquids into cells

Question 32

Define phagocytosis

Answer 32

the bulk transport of solids into cells, most commonly the process by which white blood cells engulf pathogens

Question 33

Define exocytosis

Answer 33

the bulk transport of materials out of a cell

Question 34

Does bulk transport require ATP?

Answer 34

Yes

Question 35

Why would a molecule be moved by bulk transport?

Answer 35

It is too big for channel or carrier proteins

Question 36

Name 3 things which are moved by bulk transport

Answer 36

Enzymes, hormones, bacteria

Question 37

Outline how phagocytosis occurs

Answer 37

the cell surface membrane invaginates when it comes into contact with a bacterium the membrane then enfolds around the bacterium forming a vesicle around it the vesicle then pinches off and moves into the cytoplasm towards lysosomes

Question 38

Outline how exocytosis occurs

Answer 38

vesicles are usually formed by the golgi apparatus vesicles move towards and fuse with the cell surface membrane contents of the vesicle are then released outside of a cell

Question 39

Name an example of exocytosis

Answer 39

Excretion

Question 40

Why are ions only able to cross a membrane through a protein channel?

Answer 40

protein channels provide a hydrophilic channel through the membrane ions cannot pass through membranes without them due to the hydrophobic centre of the phosphoplipid bilayer

Question 41

What is the effect of a higher surface area to volume ratio on the rate of diffusion?

Answer 41

It increases the rate of diffusion

Question 42

What is the symbol of water potential?

Answer 42

Ψ

Question 43

What are the units of water potential?

Answer 43

kPa

Question 44

What is water potential?

Answer 44

The pressure exerted by water molecules as they collide with a membrane or container

Question 45

What is the Ψ of pure water?

Answer 45

0

Question 46

Why does water potential decrease as solute is added?

Answer 46

when a substance is dissolved in water the kinetic energy of the water is lowered because water molecules aggregate around the solute movement of water molecules is partially impeded so a lower pressure is exerted

Question 47

What is a hypertonic solution?

Answer 47

having a higher concentration of solute relative to another solution

Question 48

What is an isotonic solution?

Answer 48

having the same concentration of solute relative to another solution

Question 49

What is a hypotonic solution?

Answer 49

having a lower concentration of solute relative to another solution

Question 50

What is the usual water potential in animal cells?

Answer 50

About 50kPa

Question 51

What would be the effect of placing a red blood cell in a hypotonic solution?

Answer 51

net movement of water into the cell cell swells and bursts causing haemolysis cell contents lost, haemoglobin released

Question 52

What would be the effect of placing a red blood cell in a hypertonic solution?

Answer 52

net movement of water out of the cell cell shrinks and shrivels becomes darker in colour as haemoglobin is more concentrated crenation

Question 53

What would be the effect of placing a plant cell in a hypotonic solution?

Answer 53

net movement of water into cell cell becomes turgid protoplast pushed against cell wall

Question 54

What would be the effect of placing a plant cell in a hypertonic solution?

Answer 54

net movement of water out of cell contents shrink cell plasmolysed protoplast completely pulled away

Question 55

When a plant cell is placed in a hypertonic solution, what fills the space between the cell wall and the protoplast?

Answer 55

the external solution with a more negative water potential

Question 56

Why do plant cell walls not burst from osmosis?

Answer 56

they have strong cellulose walls - which are able to resist the hydrostatic pressure

Question 57

What happens to the volume of cytoplasm when a plant cell is placed in a hypertonic solution?

Answer 57

volume of cytoplasm decreases

Question 58

Define precision

Answer 58

the closeness of two or more measurements to each other

Question 59

Define accuracy

Answer 59

the closeness of a measured value to a standard or known value

Question 60

Define repeatbility

Answer 60

if you repeat the experiment, how close are you results to other results you have collected

Question 61

Define reproducility

Answer 61

if someone else repeats the experiment how close are their results to yours

Question 62

Describe the routes that water molecules take through the cell surface membrane

Answer 62

diffuse between phospholipids - move through aquaporins