Onion incipient plasmolysis experiment

Summary

This 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

00:00

🌿 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.

05:02

🧪 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.

10:04

📊 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.

Keywords

💡Plasmolysis

Plasmolysis is the process where the cell membrane pulls away from the cell wall due to the loss of water from the cell. This occurs when the cell is placed in a hypertonic solution, meaning the solution has a higher solute concentration than the cell's cytoplasm. In the video, plasmolysis is used to determine the solute potential of the cell by observing when 50% of the cells in a sample show signs of membrane separation from the cell wall, which is termed incipient plasmolysis.

💡Solute Potential

Solute potential, also known as osmotic potential, is the component of water potential in a solution that is attributable to the presence of solutes. It is a measure of the energy status of water in a solution relative to pure water, which is set at zero. In the context of the video, solute potential is crucial for understanding how cells respond to different concentrations of solutes, as it influences the movement of water into or out of the cell.

💡Water Potential

Water potential is a measure of the potential energy of water in a solution or a living organism. It is a negative value that indicates the difference in energy between the solution and pure water. In the video, water potential is discussed in relation to osmosis, where water moves from an area of higher water potential (like pure water) to an area of lower water potential (like a cell with solutes).

💡Osmosis

Osmosis is the movement of water across a selectively permeable membrane from an area of higher water potential to an area of lower water potential. This process is essential for maintaining cell turgor and is a key concept in the video, where it is used to explain how cells behave in solutions of varying solute concentrations.

💡Turgidity

Turgidity refers to the state of a cell when it is fully hydrated and the cell membrane is pressed tightly against the cell wall. This occurs when the cell's water potential is higher than that of the surrounding solution, leading to water influx by osmosis. In the video, turgid cells are contrasted with plasmolyzed cells to illustrate the effects of different solute concentrations on cell hydration.

💡Pressure Potential

Pressure potential is the positive pressure exerted by the cell contents against the cell wall when the cell is turgid. It is part of the overall water potential of the cell and contributes to the cell's ability to maintain its shape and structure. The video explains that when cells are turgid, the pressure potential is positive, but it decreases as the cell loses water and undergoes plasmolysis.

💡Sucrose Solution

A sucrose solution is a type of hypertonic solution used in the video to create different solute concentrations for the experiment. By varying the concentration of sucrose, the presenter demonstrates how cells respond to different water potentials, which is essential for determining the solute potential at incipient plasmolysis.

💡Incipient Plasmolysis

Incipient plasmolysis is the point at which 50% of the cells in a sample have begun to show signs of plasmolysis. This term is used in the video to define the solute potential at which cells are just starting to undergo plasmolysis, which is a critical measure for understanding cell water relations.

💡Concentration

Concentration in the context of the video refers to the amount of solute (like sucrose) dissolved in a solution. It is a key independent variable in the experiment, with different concentrations of sucrose solution used to observe changes in cell behavior, particularly the onset of plasmolysis.

💡Graph

A graph is a visual representation used in the video to plot the relationship between the concentration of sucrose solution and the percentage of cells undergoing plasmolysis. The graph helps to illustrate the point of incipient plasmolysis, which is determined by the intersection of a line representing 50% plasmolysis with the curve showing cell response to different concentrations.

💡KiloPascals

KiloPascals (kPa) are units of pressure used to express water potential and solute potential in the video. The solute potential at incipient plasmolysis is given in kiloPascals, providing a quantitative measure of the cell's water potential under different conditions.

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