Osmosis + investigating the effects of osmosis on plant tissue required practical Flashcards
Define osmosis
Osmosis is the net movement of water molecules from an area of high water concentration (a dilute solution) to an area of lower water concentration (a concentrated solution) across a partially permeable membrane
In terms of concentration of water, what does a dilute sugar solution contain
Dilute sugar solutions contain a high concentration of water (the solvent) and a low concentration of sugar (the solute)
In terms of concentration of water, what does a concentrated sugar solution contain
Concentrated sugar solutions contain a low concentration of water (the solvent) and a high concentration of sugar (the solute)
What is a partially permeable membrane
A partially permeable membrane is a membrane that allows only certain substances to pass through
e.g. the membrane allows water molecules to pass through but not sugar molecules
State the difference between diffusion and active transport
In diffusion all particles move freely down concentration gradients.
In osmosis only water (solvent) molecules move across a partially
permeable membrane from a dilute solution to a concentrated solution.
Describe what will happen in this image
https://bam.files.bbci.co.uk/bam/live/content/zpfb2nb/small
There is a higher concentration of water on the left hand side and a lower concentration of water on the right hand side.
Therefore the water now
diffuses from the left hand side to the right hand side.
Describe the concentration of the cytoplasm
The cytoplasm of cells is a relatively concentrated solution. It contains a relatively low concentration of water.
How can the cytoplasm become more concentrated
If a cell uses up water in its chemical reactions, the cytoplasm becomes more concentrated
How can the cytoplasm become too dilute
The cytoplasm becomes too dilute when more water is made in chemical reactions
What happens if we place an animal cell in water
If an animal cell is placed in water, then osmosis will take place. Water will move by osmosis from outside the cell to inside the cell (from an area of higher water concentration to an area of lower water concentration)
The water moving in will cause the cell expand. The cell could even burst
What happens if we place an animal cell in a very concentrated solution
If we place an animal cell in a very concentrated solution, the water will move out of the cell by osmosis (the water will move from an area of higher water concentration to an area of lower water concentration). This will cause the cell to shrink, shrivel up and no longer survive.
What happens if we place a plant cell in water
If we place a plant cell in water, then water will move by osmosis from outside the cell to inside the cell . This will cause the cell to expand. The cell wall prevents the plant cell from bursting. Instead the cell becomes swollen. The cell has become turgid
What happens if we place the plant cell into a concentrated solution
If we place the plant cell into a concentrated solution, then water moves out of the cell by osmosis. This causes the cell to shrink. The cell has become flaccid
What happens if we place the plant cell into a concentrated solution
If we place the plant cell into a concentrated solution, then water moves out of the cell by osmosis. This causes the cell to shrink. The cell has become flaccid.
Describe how to investigate the effects of osmosis on plant tissue
Cut up a potato into identical cylinders of the same size
Measure the mass of each cylinder using a balance.
Place each cylinder into a test tube and add different concentrations of sugar solutions in each of the test tubes.
Ensure that one of the test tubes is filled with distilled water. (the reason that distilled water is used is because distilled water contains no dissolved substances and dissolved substances could affect teh rate of osmosis) r
Leave the potato cylinders overnight to allow osmosis to take place.
Next remove the potato cylinders and gently roll them on a paper towel to remove any surface moisture
Measure the mass of the cylinders again.
If the cylinders have drawn in water by osmosis, they would have increased in mass
If water has been drawn out they would have decreased in mass
Calculate the percentage change. By calculating percentage change you can compare the effect of the sugar solution on cylinders that didn’t have the same initial mass. An increase in mass will give a positive percentage change and a decrease in mass will give a negative percentage change
How to calculate percentage change
percentage change = change in value/original value x 100
A potato cylinder has a starting mass of 1.56g. This increases by 0.25g. Calculate the percentage increase
percentage change = change in value/original value x 100
% change = 0.25/1.56 x 100
% change = +16.03% to 2dp
A potato cylinder has a starting mass of 1.32g.
This decreases by 0.19g
Calculate the percentage decrease
percentage change = change in value/original value x 100
% change = -0.19/1.32 x 100
% change = -14.39% to 2d.p.
Describe the graph
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=640,f=auto/uploads/2020/08/Osmosis-Analysis_2.png
supposed to be a curved line
This graph shows that in water, the potato cylinder gains mass as water moves into it by osmosis. (arrow at the top of the graph)
However, in a concentrated sugar solution, the cylinder loses mass as water moves out of the cell by osmosis. (arrow at the bottom of the graph - line at the end)
As the concentration increases, the percentage change in mass decreased
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=640,f=auto/uploads/2020/08/Osmosis-Analysis_2.png
what does the point at which the line of best fit crosses the x-axis show
The point at which the line of best fit crosses the x-axis is the concentration of sugar inside the potato as this is where there would be no change in mass of the potato.
Where the line crosses the x axis there is no change in mass. This is because the concentration outside the cell is the same as the concentration inside the cell, so no overall osmosis takes place.
The point at which the line crosses the x axis is the concentration inside the cell.
What is the dependent variable in this experiment
The dependent variable is the variable that you measure
The dependent variable is the mass of the potato
What is the independent variable in this experiment
The independent variable is the variable you change
The independent variable is the concentration of the sugar solution.
What are the control variables in this experiment
The control variables are the volume of the solution, the temperature of the solution, the time, the type of sugar used)
Tube A has distilled water
Tube B 1.0 conc.
Tube C 2 conc.
Tube D. 3 conc.
Which potato cylinder would you expect to be shortest after 24 hours.
Explain your answer
The potato cylinder in tube D, because this type contains the most concentrated sugar solution so this cylinder will have lost the most water by osmosis
