2 — movement of substances

Question 1

Diffusion answering technique

Answer 1

1. X is a partially permeable membrane
2. Size of c molecules is too large thus cannot/small enough to pass thru x.
3. Net movement of c molecules from a to b by diffusion, from a region of higher concentration to a region of lower concentration, down a concentration gradient.
4. Link back to qs.

Question 2

Factors of rate of diffusion

Answer 2

Concentration gradient (CG) steeper = faster
Diffusion distance shorter = faster
SA:V greater = faster
- RHCs: long & narrow protrusion
- microvilli: finger-like projections
- RBCs: circular biconcave shape

Question 3

Concentration gradient definition

Answer 3

Difference in concentration betw 2 regions

Question 4

Definition of diffusion

Answer 4

Net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient

Question 5

Definition of osmosis

Answer 5

Net movement of water molecules from a region of higher water potential to a region of lower potential down a concentration gradient thru a partially permeable membrane

Question 6

Definition of active transport

Answer 6

Process in which energy (released by mitochondria) is used to move the particles of a substance across a membrane against its concentration gradient from a region of lower concentration to higher concentration

Question 7

Factors affecting rate of osmosis

Answer 7

Water potential gradient
Osmosis distance
SA:V

Question 8

Define water potential

Answer 8

measure of the tendency of water molecules to move from one place to another

Question 9

Answer formula for osmosis

Answer 9

1. State presence of partially permeable membrane
2. State the size of the molecule, can pass thru anot
3. Net movement of water molecules from x to y by osmosis, down a water potential gradient, thru a partially permeable membrane.
4. Link back to result of experiment

Ratio of final weight/initial weight = 1 -> No change in weight of X -> no net movement of water molecules from x to y by osmosis, down a water potential gradient, thru a partially permeable membrane -> link back to result of experiment

Question 10

Explain how a desert plant absorbs mineral salt and water into the roots. [6]

Answer 10

Mineral salt:
- Lower concentration of mineral salt in the soil than in the cell sap of the root hair cell. [1]
- Active transport of mineral salt against concentration gradient into the cell,[1]
- which require energy released from the oxidation of glucose in mitochondria during cellular respiration. [1]

Water
- Concentrated cell sap of root hair cell has lower water potential than the soil [1]
- due to concentrated mineral salt solution. Net movement of water molecules into the root hair cell [1]
- via osmosis across partially permeable cell membrane. [1]

Question 11

Answ formula for effect on animal cells in different WPs

Answer 11

1. State water potential of solution: higher/lower/same
2. State wp -> high/low
3. YES/NO: net movement of water molecules from x to c (higher region to lower region conc/n) Down a WP gradient, thru the partially permeable cell membrane by osmosis
4. State changes in cell: shape + size + mass.

In < WP solution than
cytoplasm of animal cell: expands and burst, ^mass
Plant cell: cell more turgid & firm; vacuole ^ in size & mass

In = WP solution than
RBCs/plant cells: remains the same in shape, size, mass

In > WP solution Than
RBC: crenated; shrink in size & hv tiny spikes on cell surface membrane, >mass
Plant cell: cell flaccid & plasmolysed, cell membrane & cytoplasm shrink away from cell wall; size of vacuole & mass decreases
(Need mention that cell wall can withstand the pressure to prevent the cell from bursting)

Question 12

What causes the plants to wilt

Answer 12

Rate of evaporation of water from leaf cells ^ than rate of water absorption from root hair cells -> net movement of water molecules out of plant cells -> lose turgidity -> plant wilts

Question 13

Importance of maintaining turgor

Answer 13

• Turgor is essential in maintaining shape of soft tissues in plants
• Turgor pressure: exerted by the water in vacuole
• It keeps herbaceous (non-woody) plants firm & upright
• Loss of turgidity will cause plant cells to be flaccid & plasmolysed -> plant wilts

Question 14

CAQ: observational changes in potato strips: investigation of osmosis

Answer 14

Longer, bent -> water entered hence solution shld hv ^water conc

Shrink in size -> solution PS is in has higher conc of solute particles, water moves out

No change in size -> dilute solute solution but solute particles size shld be too big hence cannot diffuse.

Question 15

Where AT occurs

Answer 15

Occurs only in respiring living cells, where there r abundance of mitochondria to release large amt of energy thru oxidation of glucose

Question 16

Applications of AT

Answer 16

• ^ conc/n of dissolved mineral salts in root hair cells’ cell sap compared to the soil -> RHC absorb dissolved mineral salts by active transport -> decreases WP of cell sap of cells -> WP lower than surrounding soil -> net movement of water molecules from soil into cell sap via osmosis down the WP gradient
• ^ conc/n of glucose & amino acids in small intestine epithelial cells compared to lumen of the small intestine -> absorbed via AT

Question 17

Answ formula for AT

Answer 17

State concentration of x (higher) in where vs y (lower) in where -> net movement of y to x across a membrane, against its conc gradient, from a region of lower conc to a region of higher conc.

Question 18

Explain how a desert plant absorbs mineral salt and water into the roots. [6]

Answer 18

Mineral salt:
Lower concentration of mineral salt in the soil than in the cell sap of the root hair cell. [1] Active transport of mineral salt against concentration gradient into the cell,[1] which require energy released from the oxidation of glucose in
mitochondria during cellular respiration. [1]

Water
Concentrated cell sap of root hair cell has lower water potential than the soil [1] due to concentrated mineral salt solution.
Net movement of water
molecules into the root hair cell [1] via osmosis across partially permeable cell membrane. [1]

Question 19

Compare and contrast between diffusion and osmosis. [4]

Answer 19

Similarities:
Both involve net movement of molecules down concentration gradient [1]
Slow and passive process / does not require energy [1]

Differences:
Osmosis is for water molecules only whereas diffusion is for other
molecules [1]
Osmosis requires a partially permeable membrane, whereas for diffusion is with/without a partially permeable membrane. [1]

Question 20

Describe and explain how a typical plant cell will respond when soaked
in distilled water. [5]

Answer 20

Higher water potential in distilled water compared to cell sap of plant cell [1]
Net movement of water molecules down the water potential gradient
from distilled water into plant cell [1] Via osmosis [1]
The cell swells and becomes turgid [1]
The cell wall can withstand the pressure to prevent cell bursting [1]

Question 21

Root hair cells have a high ion concentration. Explain how this is maintained and its importance.

Answer 21

RHCs contain many mitochondria which are sites of aerobic respiration where glucose is oxidised to release energy for active transport of mineral salts into root hair cells.
Thus, the cell sap in their vacuole has a high ion concentration. The cell membrane of RHCs prevent cell sap from diffusing out, maintaining a high ion concentration.
The RHCs constantly maintain a low water potential to allow the osmosis of water from surrounding soil solution.

Question 22

Explain how the decrease in mass of potato cylinder A occurred. [2]

Answer 22

There is higher water potential in the cell sap of
potato cells compared to the concentrated sugar
solution [1].
Net movement of water molecules out of the cell
sap of potato cells through osmosis [1].

Question 23

Describe and explain how a red blood cell may appear if it has been placed in the
distilled water for 30 minutes. [2]

Answer 23

Red blood cell bursts [1].
Net movement of water molecules entering the
red blood cell by osmosis as it has a lower water potential than distilled water and the cell membrane cannot withstand the pressure [1]