2 — movement of substances Flashcards
Diffusion answering technique
- X is a partially permeable membrane
- Size of c molecules is too large thus cannot/small enough to pass thru x.
- 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.
- Link back to qs.
Concentration gradient definition
Difference in concentration betw 2 regions
Definition of diffusion
Net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient
Definition of osmosis
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
Definition of active transport
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
Define water potential
measure of the tendency of water molecules to move from one place to another
Answer formula for osmosis
- State presence of partially permeable membrane
- State the size of the molecule, can pass thru anot
- Net movement of water molecules from x to y (CELL SAP OF PLANT CELL) by osmosis, down a water potential gradient, thru a partially permeable membrane.
- 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
Eg
Cell B: Higher water potential in the sugar solution than in the cell sap of the plant cell, net movement of water molecules from the
sugar solution into the plant cell sap through osmosis, making the plant cell turgid;
Cell C: Higher water potential in the cell sap of the plant cell than in the sugar solution, net movement of water molecules from the cell
sap of the plant cell into the sugar solution through osmosis, making the plant cell plasmolysed and flaccid;
Explain how a desert plant absorbs mineral salt and water into the roots. [6]
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]
Answ formula for effect on animal cells in different WPs
- State water potential of solution: higher/lower/same
- State wp -> high/low
- 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
- State changes in cell: shape + size + mass.
In higher 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 lesser 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 and detached from cell wall; size of vacuole & mass decreases
(Need mention that cell wall can withstand the pressure to prevent the cell from bursting)
Eg. [3]:
The plant cell will be flaccid and appears plasmolysed. [1] The volume of the large central vacuole and cytoplasm will be greatly reduced/ shrunk in size. [1] The cell membrane will be detached from the cell wall. [1]
What causes the plants to wilt
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
Importance of maintaining turgor
- 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
CAQ: observational changes in potato strips: investigation of osmosis
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.
Where AT occurs
Occurs only in respiring living cells, where there r abundance of mitochondria to release large amt of energy thru oxidation of glucose
Answ formula for AT
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 by active transport.
EG
- ^ 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
Compare and contrast between diffusion and osmosis. [4] + between the 3 types of movement of substances [3]
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]
[3]:
Both osmosis and diffusion are passive processes which do not require energy while active transport is a process which requires
energy; [1]
Osmosis only involves water molecules while diffusion and active transport involve any molecules; [1]
Osmosis involves movement of water molecules down a water potential gradient while diffusion involves movement of molecules down a concentration gradient while active transport involves the movement of molecules against a concentration gradient [1]
