Diffusion, Osmosis and Active Transport

Question 1

What are the factors that affect diffusion? (4)

Answer 1

• Conc. gradient
• Surface area
• Diffusion pathway (length)
• Temp.

Question 2

What can molecules cross with simple diffusion? (4)

Answer 2

• Nonpolar barriers
• Smaller and less polar the molecules - faster diffusion
• Small polar molecules take longer
• Big molecules and charged ions will not pass

Question 3

What is facilitated diffusion - channel proteins? (3)

Answer 3

• Allows charged ions to pass
• Down a concentration gradient
• Fluid filled channel
• Selectively permeable

Question 4

What is facilitated diffusion - carrier proteins? (4)

Answer 4

• Larger substances
• Intrinsic globular protein
• Specific protein for specific molecules
• Shape of protein changes after binding - opens at the other side

Question 5

What is facilitated diffusion affected by?

Answer 5

All factors and no. protein channels

Question 6

Rate of diffusion and surface area experiment. Method? (5)

Answer 6

1) Cut agar block into different sized cubes - Agar cubes contain indicator so they turn pink with a presence of an alkali
2) Immerse cubes in sodium hydroxide for 10 mins.
3) Remove cubes and pat dry
4) Measure the distance of sodium hydroxide travelled with a ruler
5) Calculate rate of diffusion (cm/min)

Question 7

Method of active transport (carrier proteins)? (5)

Answer 7

1) Molecule binds to receptors on the outside
2) ATP binds to protein on the inside and is hydrolysed to ADP
3) Phosphate binds to protein to change its shape
4) Molecule is released inside
5) Phosphate forms ATP and protein changes back to normal

Question 8

What is bulk transport?

Answer 8

Molecules that are too large to move through channel or carrier proteins are taken by bulk transport.
E.g. enzymes, hormones and whole cells (bacteria)

Question 9

Endocytosis method? (6)

Answer 9

• Liquids = pinocytosis
• Solids = phagocytosis
  1) Cell surface invaginates (bends inwards)
  2) Substance enfolded
  3) Vesicle formed
  4) Moved into cytoplasm

Question 10

Exocytosis method?

Answer 10

Secretory vesicles pinch off the golgi apparatus are moved to membrane and contents are released out

Question 11

How is water potential calculated?

Answer 11

Solute + pressure potential = water potential

Question 12

Osmosis definition?

Answer 12

The passive movement of water through a partially permeable membrane down a water potential gradient

Question 13

What is water’s water potential? (3)

Answer 13

0 kPa

• highest value
• others all negative

Question 14

What causes hydrostatic pressure? (3)

Answer 14

• Closed system
• Higher volumes
• Higher pressure

Question 15

In animal cells what does higher and lower water potential outside of the cell do to the cell?

Answer 15

Higher = swell and burst
Lower = shrivell and shrink

Question 16

Definition of hypertonic

Answer 16

Higher water potential INSIDE of the cell.

Net movement of water OUT of cell

Question 17

Definition of isotonic

Answer 17

Same water potential inside and outside of cell.

No net movement

Question 18

Definition of hypotonic

Answer 18

Higher water potential OUTSIDE of cell.

Net movement of water INTO the cells.