ch 4 Flashcards
define diffusion
it is the movement of molecules from an area of their high concentration to the area of their low concentration (down the conc. gradient )
define active transport
it is the movement of molecules from an area of low conc to an area of high conc (against the conc gradient)
describe how active transport is active
it needs much mitochondria , high respiration so high supply of oxygen and glucose
what factors affect diffusion [4]
-temperature -> as temp increases, the molecules gain heat energy and move faster so kinetic energy increases so diffusion becomes faster
-conc. gradient -> when it increases diffusion increases
-distance-> as distance increases , diffusion increases
-surface area -> when surface area of cell membrane increases, diffusion increases
factors affecting active uptake
energy-> more conc of glucose and oxygen , so more production of energy so more active uptake
define osmosis
its the movement of water molecules from HWP to LWP through a semi-permeable membrane
what happens to an animal cell when placed in pure water [5]
-water moves by osmosis from HWP to LWP through semi-permeable membrane
-from outside the cell to inside
-cell gains water (endosmosis)
-cell increases in size and volume
-cell swells then ruptures
what happens to an animal cell when placed in conc salt soloution [5]
–water moves by osmosis from HWP to LWP through semi-permeable membrane
-from inside the cell to outside
-cell loses water (exosmosis)
-cell decreases in size and volume
-cell shrinks
what happens to an animal cell when placed in soloution with the same conc as its cytoplasm [2]
-no conc gradient, so no osmosis occurs
-cell remains unchanged
compare diffusion and osmosis [2]
-diffusion is movement of any molecule but osmosis is only movement if water molecules
-diffusion doesnt need semi permeable membrane while osmosis does
what happens to a plant cell when placed in dilute solution [5]
-cell gains water (endosmosis)
-water crosses the cell wall, cell membrane and cytoplasm to reach the vacuole
-vacuole expands , swells with water
-the cytoplasm gets compressed to form a turgid cell
-the expanded vacuole also exerts a pressure on the cell wall called turgid pressure this condition is called turgidity
what happens to a plant cell when placed in concentrated salt solution [7]
-cell loses water (exosmosis)
-the vacuole shrinks and cell becomes flaccid
-the shrinked cell vacuole pulls on the cytoplasm , which pulls on the elastic cell membrane
-cell membrane seperated from the rigid cell wall and a gap is created between them
-the gaps are filled with the conc solution , this is called partailly plasmolysed cell
-the vacuole loses more and more water so shrinks more
-cell membrane is pulled more till it gets completely torn off from the cell wall, this is called fully-plasmolysed cell
why do plants die as a result of irrigation with sea water [3]
-sea water has high conc. of salts and LWP
-therefore water moves by osmosis from plant roots to the outside
-so plants wilts and die
how is osmosis useful to plants? [2]
- osmosis helps plants to absorb water from the soil by root hair
-osmosis helps plant cells to absorb water and become turgid with high turgid pressure to support the plant
