2.1.5 - Biological Membranes (set B- movement of molecules across membranes )

Question 1

Define the process active transport?

Answer 1

The movement of molecuels or ions into or out of a cell from an area of low concentration to an area of high concentration (against a concentration gradient) across a partially permeable membrane, it requires energy in the form of ATP (from respiration) so it is therefore an active process

• membrane is selectively permeable

Question 2

What are two things active transport requires?

Answer 2

• metabolic energy, in the form of ATP from respiration
• carrier proteins

Question 3

Explain the role of carrier proteins in active transport and the role they play?

Answer 3

Carrier proteins span the membranes and act like a ‘pump’ and is complementary in shape to the molecule they transport - molecules are ‘pumped’ in one direction across the membrane

Question 4

Explain the general process of active transport?

Answer 4

1) moelcule/ion binds to receptors in channel of carrier protein

2) ATP binds to carrier protein and is hydrolysed into ADP and phosphate

3) binding of phosphate molecule to carrier protein causes the protein to change shape

4) molecule/ion is released to inside of cell

5) phosphate molecule is released and recombines with ADP to form ATP

6) carrier protein returns to its original shape

Question 5

Explain why active transport is a selective process?

Answer 5

The carrier proteins involved are complementary to the molecule they transport - once the molecule collides with the protein, it is transported across the membrane and released the other side - cannot be transported back since the carrier protein is no longer complementary to it

Question 6

Explain what happens during the binding of the phosphate molecule during the process of active transport?

Answer 6

Phosphate molecule binds to carrier protein which causes the protein to change shape, opening up the the inside of the cell - means the molecule/ion is released to the inside of the cell

Question 7

Explain what happens when the phosphate molecule is released during active transport - what effect does this have on the carrier protein?

Answer 7

Phosphate molecule is released from the carrier protein and recombines with ADP to form ATP

• carrier protein returns to its original shape

Question 8

Explain what happens when ATP binds to the carrier protein in active transport?

Answer 8

ATP binds to the carrier protein on the inside of the cell - and is hydrolysed into ADP and phosphate (ADP + P) which releases energy

• phosphate molecule remains bound to the protein (phosphorylating it)

Question 9

Explain why active transport requires energy?

Answer 9

Active transport requires energy for the process by transporting molecules against a concentration or electrochemical gradient

• opposite direction to diffusion

Question 10

Define the process bulk transport?

Answer 10

Another form of active transport, which moves substances (eg enzyme,hormones or whole cells like bacteria) that are too large to move through channel or carrier proteins - there are two types excotysosis and endocytosis

Question 11

Give the two types of bulk transport?

Answer 11

• exocytosis
• endocytosis

Question 12

Explain the importantce of the phosphate molecule binding to the protein reference energy?

Answer 12

Phosphate molecule binds to the protein phosphorylating it - provides the energy required for carrier proteins to change shape (conformational change)

Question 13

Define the bulk transport exocytosis?

Answer 13

the bulk transport of material out of a cell using a vesicle (usually formed from the golgi apparatus) which fuses with the cell surface membrane & the contents are released

Question 14

Define the bulk transport endocytosis - give the name of both types?

Answer 14

the bulk transport of material into a cell by the fusing of a vesicle with the cell surface membrane - two types phagocytosis and pinocytosis

Question 15

Define phagocytosis?

Answer 15

Movement of solids during process of endocytosis

Question 16

Define pinocytosis?

Answer 16

Movement of liquids during process of endocytosis

Question 17

Briefly explain the process of exocytosis?

Answer 17

1) cell forms a vesicle around the material that needs to be expelled from the cell

2) vesicle is transported to the cell membrane along the cytoskeleton

3) vesicle membrane fuses with the cell membrane and released the contents from the cell

Question 18

Give and explain three factors that affect the rate of active tranport?

Answer 18

• rate of respiration - releases ATP molecules which increases the rate of active transport
• number of carrier proteins - more carrier proteins, faster the rate of active transport
• speed of individual carrier proteins - faster they work faster the rate of active transport

Question 19

Give two examples of substances moved by active transport?

Answer 19

• uptake of glucose by epithelial cells in the villi of the small intestine
• uptake of mineral ions from soil water by root hair cells in plants

Question 20

Give three uses of active transport?

Answer 20

• reabsorption of useful molecules and ions into the blood after filtration into the kidney tubules
• loading of sugar from the photosynthesising cells of leaves into the phloem tissue for transport around the plant
• loading of inorganic ions from the soil into root hairs

Question 21

Define the process diffusion?

Answer 21

The net movement of particles from a region of higher concentration to a region of lower concentration (down a concentration gradient) until there is a concentration equilibrium - due to the random movement and collisions of particles

• passive process - no ATP required

Question 22

Explain why diffusion is slower over larger distances - reference particles and kinetic energy?

Answer 22

Particle move at high speeds and constantly collide - slowing their overall movement, over larger distances they collide more

Question 23

Give 2 factors and explain how they affect the rate of diffusion?

Answer 23

• temperature - higher temp increase rate of diffusion due to particles having more kinetic energy, so they move faster
• concentration difference/gradient - greater difference between two regions, the larger movment from high concentration to lower concentration - faster rate of diffusion

Question 24

Define simple diffusion?

Answer 24

the process by which molecules, atoms, or ions diffuse directly through a membrane down their concentration gradient without the assistance of transporter protein

• passive process, no ATP required

Question 25

Outline the process of simple diffusion?

Answer 25

Small, non-polar molecules (oxygen,carbon dioxide) are able to diffuse through spaces between phospholipids

Question 26

Give two factors which affect the rate at which molecules or ions diffuse across membranes?

Answer 26

• surface area - larger areas for gas exchange - faster diffusion
• thickness of membrane - thinner the exchange surface - faster diffusion

Question 27

Define facilitated diffusion?

Answer 27

passive movement of molecules down a concentration gradient (high concentration to low concentration) across a membrane, and involves special carrier & channel proteins in
the membrane

Question 28

Explain what type of molecule’s are involved in facilitated diffusion?

Answer 28

larger polar molecules e.g. amino acids
and glucose, or ions such as sodium ions (Na+)
and chloride ions (Cl-)

• which can’t diffuse directly through the phospholipid layer of membrane - require specific proteins

Question 29

Outline the role of channel proteins in facilitated diffusion?

Answer 29

Form water filled pores in the memrbane for charged particles (smaller ions and polar moelcules) to diffuse through

• down concentration gradient
• different protein facilitate diffuse of different particles

Question 30

Explain how channel proteins control the exchange of ions?

Answer 30

Channel proteins are ‘gated’ - part of protein on inside surface of membrane can move - opening or closing the pore

• controls exchange of ions

Question 31

Outline the role of carrier proteins in facilitated diffusion?

Answer 31

Moves larger molecules (polar molecules and ions)
- down concentration gradient
- different proteins facilitate diffusion of different molecules
- proteins change shape when specific molecule binds

Question 32

Explain the changing of shape of carrier proteins?

Answer 32

Can switch between two shapes

• causes the binding site of carrier protein to open to one side of membrane first, and then open to other side of membrane when protein switches shape

Question 33

Explain 2 factors which affect the rate of facilitated diffusion?

Answer 33

• concentration gradient - high concentration gradient, faster the rate of diffusion until equilibrium is reached
• number of channel and carrier proteins - once all proteins in the membrane are in use, maximum rate of diffusion is reached

Question 34

Outline some similarities and differences between simple and facilitated diffusion

Answer 34

• Simple diffusion involves much smaller molecules which are non-polar - facilitated involves larger and polar molecules
• both passive - rely on kinetic energy of moelcules
• simple moves oxygen and carbon dioxide - facilitated moves glucose, amino acids and ions

Question 35

Define water potential?

Answer 35

the pressure exerted by water molecules as they collide with a membrane or container - measured in Pa or kPa

• Pure water has a ψ of 0 kPa

Question 36

Define the process osmosis?

Answer 36

the net random movement of water molecules from an region of high water potential to a region of low water potential (down a water potential gradient) across a partially permeable membrane

• passive process

Question 37

Give 3 factors which affect the rate of osmosis - explain them?

Answer 37

• thinner the exchange surface the shorter the pathway the water molecules have to travel - increases rate of osmosis
• greater surface area of the partially permeable membrane the more area
  water molecule have to cross the membrane - increases the rate of osmosis
• water potential gradient

Question 38

Define hypotonic solution?

Answer 38

solution with MORE water in it than solute, compared to another solution

• higher water potential outside the cell

Question 39

Define hypertonic solution?

Answer 39

solution with MORE solute in it than water, compared to another solution

• lower water potential outside the cell

Question 40

Define isotonic solution?

Answer 40

Two solutions/cells that have the same water potential

-equal water potential inside and outside of cell

Question 41

Explain the idea of water potential - give an exmaple?

Answer 41

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

• cell cytoplasm contains dissolved sugars, salts ext so water potential is more negative - less water molecules that are free to move

Question 42

Outline what happens when an animal cell is placed in a hypotonic solution (more dilute)?

Answer 42

• Water enters the cell by osmosis (high
WP to low WP) via the partially permeable membrane

• increases the hydrostatic pressure inside the cell

• Cell-surface membrane cannot withstand
the pressure increase - cell burst (cytolysis)

Question 43

Outline what happens when an animal cell is placed in a hypertonic solution (more concentrated)?

Answer 43

• Water leaves the cell by osmosis (high WP to low WP) via the partially permeable
membrane

• lowers the hydrostatic pressure inside the cell - cell shrinks and shrivels

• The cell is CRENATED

Question 44

Outline what happens when a plant cell is placed in a hypertonic solution (more concentrated)?

Answer 44

• Water leaves the cell by osmosis (high WP to low WP) via the partially permeable membrane

• lowers the hydrostatic pressure inside
the cell - cell surface membrane pulls away from cell wall due to pressure difference

• The cell is now PLASMOLYSED.

Question 45

Outline what happens when a plant cell is placed in a hypotonic solution (more dilute)?

Answer 45

• Water enters the cell by osmosis (high
WP to low WP) via the partially permeable membrane

• increases the hydrostatic pressure inside the cell - cell-surface membrane pushes up against the cell wall (does not burst, due to cell wall)

• Cell is now TURGID.