Onion incipient plasmolysis experiment
Summary
TLDRThis educational script explains the concept of solute potential in plant cells through an experiment involving plasmolysis. It describes the process of placing onion cells in solutions with varying sucrose concentrations, observing the cells' turgid state and the onset of plasmolysis. The experiment aims to determine the solute potential by identifying the concentration at which 50% of cells exhibit incipient plasmolysis. The results are recorded, tabulated, and graphed to find the sucrose concentration corresponding to a solute potential of -1450 kPa.
Takeaways
- 🌿 **Concept of Water Potential**: The script explains the concept of water potential, which is zero for pure water and negative for solutions with solutes like salts and sugars.
- 🔬 **Plant Cell Structure**: It describes the structure of a plant cell, including the cell wall, cell membrane, cytoplasm, and nucleus.
- 💧 **Osmosis and Water Movement**: The process of osmosis is explained, where water moves from an area of higher water potential to an area of lower water potential.
- 🌱 **Turgidity and Plasmolysis**: The script discusses the states of turgid cells, where the cell is full of water, and plasmolysed cells, where water has left the cell causing the cell membrane to pull away from the cell wall.
- 📉 **Pressure Potential**: It introduces pressure potential, which is the force exerted by the cell membrane against the cell wall, and how it changes with the cell's water content.
- 📊 **Experimental Setup**: The script outlines an experiment where plant cells are placed in solutions of varying sucrose concentrations to observe the degree of plasmolysis.
- 🔍 **Observation and Data Collection**: It details the method of observing cells under a microscope and counting the number of turgid versus plasmolysed cells at different sucrose concentrations.
- 📈 **Data Analysis**: The process of plotting the results on a graph with sucrose concentration on the x-axis and the percentage of plasmolysed cells on the y-axis is described.
- ⚖️ **Incipient Plasmolysis**: The term 'incipient plasmolysis' is defined as the concentration at which 50% of cells show plasmolysis, which is used to determine the solute potential of the cell.
- 🔑 **Solute Potential Calculation**: The script concludes with calculating the solute potential of the cell by referencing a table that correlates solute potential with sucrose molarity.
Q & A
What is the significance of measuring the degree of incipient plasmolysis?
-Measuring the degree of incipient plasmolysis is significant as it helps determine the solute potential of a cell by observing the point at which 50% of cells in a sample exhibit plasmolysis.
What is meant by 'incipient plasmolysis'?
-'Incipient plasmolysis' refers to the point at which 50% of cells in a sample start to show signs of plasmolysis, which is the separation of the cell membrane from the cell wall due to water loss.
Why is the water potential of pure water considered to be zero?
-The water potential of pure water is considered to be zero because it serves as a reference point, with no solutes to create a gradient for water movement.
How does the presence of solutes within a cell affect its water potential?
-The presence of solutes within a cell lowers its water potential because solutes create a concentration gradient, making the inside of the cell have a water potential that is less than zero.
What is the relationship between water potential and osmosis?
-Water moves by osmosis from a region of higher water potential to a region of lower water potential, which typically means from outside the cell to inside when the cell's water potential is lower.
What is the term for the pressure exerted by the cytoplasm against the cell wall?
-The pressure exerted by the cytoplasm against the cell wall is called turgor pressure, which is a result of water entering the cell and causing the cytoplasm to expand.
What happens to the cell when it is placed in a solution with a higher solute potential than the cell's?
-When a cell is placed in a solution with a higher solute potential, water moves out of the cell by osmosis, leading to a decrease in cytoplasm volume and plasmolysis.
How is the solute potential of a cell determined in the experiment described?
-The solute potential of a cell is determined by finding the concentration of a sucrose solution that causes 50% of the cells to undergo incipient plasmolysis.
What is the independent variable in the experiment described in the script?
-The independent variable in the experiment is the concentration of the sucrose solution, which is varied to observe its effect on cell plasmolysis.
How are the results of the experiment recorded and analyzed?
-The results are recorded by counting the number of cells that show signs of plasmolysis at various sucrose concentrations and then plotted on a graph to determine the concentration at which 50% plasmolysis occurs.
What is the significance of the solute potential value of -1450 kiloPascals mentioned in the script?
-The solute potential value of -1450 kiloPascals is the water potential at which 50% of the cells in the experiment show incipient plasmolysis, indicating the solute potential of the cells used in the study.
Outlines
🌿 Understanding Solute Potential and Osmosis
The paragraph introduces the concept of solute potential by explaining the process of incipient plasmolysis in plant cells. It begins with a visual representation of an onion cell, highlighting the cell wall, cell membrane, cytoplasm, and nucleus. The discussion then moves to water potential, explaining that pure water has a water potential of zero. The presence of solutes like salts, sugars, or proteins inside the cell lowers the water potential, causing water to move into the cell by osmosis. This results in a turgid cell with increased cytoplasmic volume and pressure potential. The paragraph also describes scenarios where cells are placed in solutions with different solute potentials, leading to either water influx or efflux, and the resulting cell states, such as plasmolysed cells. The concept of solute potential and pressure potential is introduced, and their relationship is summarized in an equation.
🧪 Measuring Incipient Plasmolysis in an Experiment
This section delves into an experimental approach to determine the solute potential by observing incipient plasmolysis. It describes an experiment where cells are exposed to varying concentrations of sucrose solution, and the percentage of cells undergoing plasmolysis is recorded. The independent variable in the experiment is the concentration of the sucrose solution, starting from distilled water (0 M) to 1 M. The dependent variable is the percentage of cells showing signs of plasmolysis. The experiment involves observing cells under a microscope and counting the number of turgid and plasmolysed cells. The results are then tabulated and graphed to visualize the relationship between sucrose concentration and the percentage of plasmolysed cells. The paragraph concludes with the identification of the sucrose concentration at which 50% of cells show plasmolysis, which is defined as incipient plasmolysis.
📊 Determining Solute Potential from Experimental Data
The final paragraph focuses on interpreting the experimental data to determine the solute potential. It explains that the solute potential is identified when 50% of the cells in a sample are plasmolysed, which is referred to as incipient plasmolysis. The paragraph describes how to plot the experimental results on a graph with sucrose concentration on the x-axis and the percentage of plasmolysed cells on the y-axis. The point where 50% plasmolysis is achieved is marked, and it is noted that this corresponds to a sucrose concentration of 0.5 M. The solute potential at this concentration is then referenced from a table, which shows a solute potential of -1450 kPa for a 0.5 M sucrose solution. This value represents the solute potential at the point of incipient plasmolysis, and the units are clarified as kilopascals.
Mindmap
Keywords
💡Plasmolysis
💡Solute Potential
💡Water Potential
💡Osmosis
💡Turgidity
💡Pressure Potential
💡Sucrose Solution
💡Incipient Plasmolysis
💡Concentration
💡Graph
💡KiloPascals
Highlights
Practical determination of solute potential by measuring incipient plasmolysis.
Introduction to key terms: cell wall, cell membrane, cytoplasm, and nucleus.
Explanation of water potential in pure water being zero and in cells containing solutes.
Osmosis as the movement of water from higher to lower water potential.
Definition of turgid cells and the role of pressure potential.
Description of plasmolysis and its visual indicators in cells.
Concept of incipient plasmolysis and its significance in determining solute potential.
Experimental setup involving different sucrose solution concentrations.
Methodology for observing and counting cells under a microscope for plasmolysis.
Results from the experiment showing the percentage of cells undergoing plasmolysis at various sucrose concentrations.
Graphical representation of the relationship between sucrose concentration and cell plasmolysis.
Identification of the sucrose concentration at which 50% plasmolysis occurs, indicating incipient plasmolysis.
Conversion of the incipient plasmolysis concentration to solute potential in kiloPascals.
Importance of solute potential in understanding cell water relations.
Practical application of the experiment in teaching and understanding osmotic principles.
Use of a phone camera to document results, demonstrating adaptability in experimental recording.
Discussion on the variability in solute potential among different cells and its impact on the experiment.
Transcripts
so this is a practical determination of
a solute potential by measuring the
degree of incipient plasmolysis so one
of the top four things to really think
about where we find for students and
it'd be useful to start off with what do
we mean by a few terms so if we've got
cells so let's draw a plant cell and
onion cell and let's have cell wall and
then inside that we're gonna have cell
membrane I'll do it in red so in this
instance the cell membrane is right up
against the cell wall and inside there
that's our cytoplasm and we might have a
nucleus or something inside there okay
and if we put that into some water it's
a water the water potential if it's pure
water water potential equals zero
and a cell any Cell will have some stuff
dissolved in it won't have some salts
and sugars or protein proteins or
thing's dissolved in there so the what
potential will be less inside the cell
so that be minus something and these
will be kiloPascals and water will move
by osmosis from a region of higher water
potential to lower water potential so
from zero to the minus number so water
will move in by osmosis
and then that cell in this condition
will be turgid there will be an
expansion of the cytoplasm in volume
somar volume because there's more water
and that membrane will press up against
the wall and that pressing up against
the wall is called pressure potential
so there is the solute potential inside
solute potential and pressure potential
there and you've got a little equation
where the the overall kind of potential
of the cell is solute potential plus the
pressure potential there might be
another situation where we've got
similar sort of cell rubbish drawing of
a cell wall but we might put that into a
strong salt solution or sugar solution
so what potential of the solution is you
know - lots so let's call that - 500 may
be the solute potential of the cell the
cell might be say let's call it minus
300 and in that case osmosis goes from
region of higher to lower water
potential
so osmosis will happen the other way so
water will leave the cell and when that
happens the volume of the cytoplasm
decreases and so the cytoplasm is less
in volume and pulls away the membrane
away from the cell wall
so the cell will look like that we can't
really say the cytoplasm is shrink till
the membrane is shrink we need to say
them the membrane is pulled away from
the moved away from the wall and the
volume of the cytoplasm is less this is
called allows mala SACEUR plasma lized
cell personalised there is a situation
in between here where this is just about
to start pulling away from there so you
can imagine this water potential goes
down and down and down and down until
it's equal to the solute potential and
then this is just about to move away so
our pressure potential is zero at that
point we call that incipient plasmolysis
the problem with this is that all of
these cells have got different solute
potentials so some will start to pull
away before others so when when do you
actually measure it and our definition
that we're going to use is when 50% of
the cells look personalised so if 50%
are plasma lized
in any sample any tissue that we look at
that is going to be equal to our
incipient plasmolysis
so we set up this experiment and we look
we have one two three four five six six
pots we actually use petri dishes and
these our independent variable is the
sucrose solution and it's the
concentration of it concentration it's a
concentration of sucrose solution and we
start off with distilled water so not
pointe-noire molar and then we have not
point to not point four nine point six
nine point eight and one point not these
are our concentrations of sucrose
solution and then we're going to look
down the microscope and see what the
cells look like today's our count how
many look like this
turgid and how many like that plasma
lized and then we're going to process
the results and so what we do next is if
i get rid of that and show you first
view down the microscope this is our
distilled water naught point naught
point naught molar sucrose so naught
point naught molar sucrose and we look
down there and ya to me they all look
turgid i can't find any that show any
plasmolysis at all so we count those or
a section of those I think the result
something you use the accounted a
quarter of the view which is roughly
about about 30 cells and we decided that
all 30 were turgid so our percentage
plasma lized is zero percent and then we
go through the different now this is not
point two molar sucrose and when I
looked at a quarter this so again
there's about 30 cells of Surfing
there's 29 cells and
decided that I could only really found
one that was plasma lized I can't know
this quarter here 9001 one showed some
plasmolysis and it gained through the to
the concentrations these are actual
results produced by our students using a
phone down the other microscope always a
good idea so nor point four I decided
that we could see a couple of a couple
of cells in the quarter that started to
show some plasmolysis so for example
this cell here this left quarter that we
starting to show some plasmolysis there
we are as well so a couple of those
cells so two out of 29 accounted then as
we got to not point six count to thirty
cells and 25 of them were showing some
signs of plasmolysis not by a molar
Ageha
counted 29,028 of them was showing
plasmolysis and finally at one molar all
of those cells that I counted in the
quarter you know 100% of them were
personalized so we'd make those into a
table we'd make those into a table and
that is the table that we would we come
up with we can see our independent
variable concentration of sucrose from
zero to one and the percentage of cells
plasma lized so just rounded it to the
nearest percent now then plot a graph
and you've got some graph paper in your
lab book to do this a graph of the
independent variable versus dependent
and that is the graph that we we come up
with but that's not the end of the
process we need to remember our
definition our definition was
50% plasmolysis and that's going to be
our incipient plasmolysis our solute
potential so we need to on this graph
draw a line across from 50% so the line
across from 50% and down down here
handily for us that's going to be not
0.5 molar sucrose so that is the
concentration where we've got incipient
plasmolysis but actually in our lab book
we've got a table we look further back a
table showing that solute potentials at
different molarities and so per hour nor
point 5 molar not 0.5 molar our solid
potentially is minus 1450 so minus 1450
so that equals minus 1450 and the units
will be kiloPascals should be small okay
they're killing us and thousands of
Pascal's so that is our solute potential
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