2.4.5-2.4.9~osmosis Flashcards
what are all cells surrounded by
a cell membrane which is partially permeable
how can water move in and out of cells
osmosis
osmosis definition
net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane
water concentration gradient
water moves down the concentration gradient
water potential of pure water at atmospheric pressure
0KPa
partially permeable
allows small molecules through but not larger molecules
water potential
tendency of water to move out of a solution
water potential of solution
lower than 0KPa (negative value)
diffusion of plant cell in pure water/dilute solution
water will enter the plant cell through its partially permeable cell surface membrane by osmosis, as the pure water/dilute solution has a higher water potential than the plant cell
volume of plant cell as water enters vacuole
increases
pressure in plant cell
expanding protoplast pushes against cell wall and pressure builds
what prevents cell from bursting
inelastic cell wall
cell wall effect on pressure
pressure created by cell wall stops too much water from entering and prevents cell from bursting
turgid
when a plant cell is fully inflated with water and has become rigid and firm
importance of turgidity
turgidity is important as effect of all the cells in a plat being firms is to provide support and strength for the plant which makes it stand upright with its leaves held out to catch sunlight
if plants do not receive enough water
cells cannot remain turgid and plant wilts
severity of effects on osmosis in animal cells
more severe than in plant cells as don not have a cell wall
animal cells if water leaves by osmosis
water will leave the cell through its partially permeable cell surface membrane by osmosis and the cell will shrink and shrivel up
environment where water leaves cell by osmosis
hypertonic
what is a hypertonic environment
solution outside of the cell has a higher solute concentration than inside the cell
what happens if you put an animal cell in water or dilute solution (higher water potential than the cell)
water enters the cell through the partially permeable cell surface membrane by osmosis, the cell will continue to gain water by osmosis until cell membrane is too far stretched and the cell bursts
cytolysis
water gained by osmosis causes the cell membrane to be stretched so far and the cell bursts
why does an animal cell bust
no cell wall to withstand the increased pressure
environment where cell gains water due to osmosis
hypotonic
what is a hypotonic environment
the solution outside the cell has a lower solute concentration than the inside if the cell
isotonic environment
solution outside of the cell has the same solute concentration as the inside of the cell
what happens if animal cell is in isotonic environment
the movement of water molecules into and out of the cell occurs at the same rate and there is no change to the cells –> no net movement if water
similarity of cell wall in animal and plant cell
-present composed of a phosopholipid bilayer
-partially permeable
difference of cell wall in animal and plant cell
-plant cell is fully composed of cellulose and is fully permeable
-animal cell has no cell wall
similarity of osmosis of water into and out of the cell for animal and plant cells
can occur
plant cell placed in solution with lower water potential
-water leaves cell through partially permeable cell surface membrane by osmosis
-volume of the cell decreases
-protoplast shrinks and pulls away from cell wall
-cell is plasmolysed
animal cell placed in solution with lower water potential
-water leaves cell through partially permeable cell surface membrane by osmosis
-volume of cell decreases
-cell shrinks and shrivels up
plant cell placed in solution with higher water potential
-water enters cell through partially permeable cell surface membrane by osmosis
-volume of cell increases
-protoplast expands and pushes against cell wall
-cell wall withstands increased pressure created
-pressure increases until cell is turgid
-cell is fully inflated with water and no more can enter
animal cell placed in solution with higher water potential
-water enters cell through partially permable cell surface membrane by osmosis
-volume of cell increases
-no cell wall to withstand increased pressure created
-cell membrane eventually stretched too far and cell bursts
how is it possible to investigate water potential
immersing plant tissue in solutions of different water potentials and then using the results to estimate water potential of the plant tissue itself
most common osmosis practical to investigate water potential
potato cylinders in a range of solutions with different water potentials (at lease 5 different concentrations usually required)
required practical 3 - investigating water potential method
-cut the required number of potatoes ensuring they are all cut to the same length
-blot potatoes dry to remove excess moisture
-record initial mass of potato and record
-leave in solution of set length of time (30mins) in a water bath (30 degrees)
-remove and blot dry to remove excess liquid
-measure and record the length and mass of each potato
what analysis is used in investigating water potential practical
percentage change in mass for each potato cylinder
positive percentage change in mass
potato has gained water by osmosis so solution has a higher water potential than the potato
potato cells when positive percentage change in mass
cells are turgid as water exerts turgor pressure on the cell walls
negative percentage change in mass
solution had a lower water potential than the potato so water molecules will move out of the potato cells by osmosis
negative percentage change in mass effect on cells
cells are flaccid and may be plasmolysed (cell membrane is pulled away from cell wall)
no percentage change in mass
no net movement of water in or out of the potato cells as the solution has same water potential to the cytoplasm inside the potato cells–> so no concentration gradient
how do you identify the concentration of sucrose solution from a graph
the point at which the line of best fit crosses the x-axis
what does plotting data allow you to see
relationship between two variables
what is qualitative data
non-numerical data
what is discrete data
numerical data that can only take certain values
what is continuous data
numerical data that can take any value in a range
type of graph for qualitative and discrete data
bar charts or pie charts
type of graph most suitable for continuous data
line graphs or scatter graphs
axis independent variable be plotted on graph
x
axis dependent variable should be plotted
y
