Experiment #: 3

Skills Being Tested: analysis and interpretation

Date: Monday 24/01/22

Title: Osmosis

Aim: to determine the effect of Sodium Chloride Concentration on Plant Cell

Apparatus & materials: ruler, scape, hand towel, potato strips, petri-dishes, NaCl solutions

(0.25M, 0.5M, 1.0M, 2.0M, 3.0M), electronic balance

Method: 1) Sodium Chloride solutions were placed in labelled petri-dishes as follows:

Petri-dish NaCl (g) Volume of water Concentration of salt

A 1.80 125 0.25

B 3.60 125 0.50

C 7.25 125 1.00

D 14.5 125 2.00

E 21.75 125 3.00

F 0.00 125 0.00

2) Twelve strips of potato of equal length were prepared then each strip was measured to

confirm and record their length.

3) Two strips were placed into each petri dish and ensured they were submerged.

4) Strips were left in the solutions for 40 minutes

5) The strips were removed from the solutions, dried with a hand towel then their final length

was measured.
Results:

Table showing data collection before and after potato strips were in solution.

Petri-dish NaCl Initial length Final length Length change

A 0.25 40.0 40.3 0.33

B 0.50 49.0 45.0 -4.00

C 1.00 31.6 30.0 -1.67

D 2.00 45.3 39.7 -5.67

E 3.00 35.7 33.3 -2.33

F 0.00 38.0 41.0 3.00

Discussion: Osmosis is the passage of water molecules from a region where they are in high

concentration to a region of lower concentration through a partially permeable

membrane. The osmotic relationships of plant cells are described in terms of

water potential. Water potential is measured by the tendency of water molecules

to move from one place to another. It is represented by the Greek letter psi (𝚿).

Water always moves from a region of higher water potential to one of lower

water potential. The higher the water potential the greater the tendency to leave

a system. Under standard conditions pure water water has the highest water

potential which is defined by zero (0). All solutions have lower water potential

than pure water and therefore have negative values. The more concentrated a

solution is, the more negative its water potential will be.

In petri-dish F, the average change in length of the potato strips is seen to

have increased. This is because the potato strips were submerged in pure water.

Since pure water has a greater water potential than the contents inside the potato

cell, water molecules move across the semipermeable membrane and into the
cell via osmosis. Due to this influx of water the cell becomes turgid and thus

increases in size. Similarly the potato strips in petri-dish A also experienced an

increase in size therefore it can be said that the 0.25M salt solution has a greater

water potential than the potato cell which causes a net movement of water

molecules inside the cell thus increasing its size.

In contrast the other potato strips experienced a decrease in their size. For

example in petri-dish B and D the potato strips experienced a decrease of -4.00

mm and -5.67mm respectively in their size. This is because water molecules in

the cytoplasm of the potato cell are at a higher concentration and thus have a

higher water potential than in the salt solutions in the petri-dishes. Therefore

water will leave the potato, travel across the cell membrane and enter into the

salt solution. The decrease in water molecules in the potato cell results in loss of

volume and in turn the cell becomes flaccid.

The overall trend of the graph showed that the greater the solute

concentration the more the size of the cell decreases. This summaries that the

potato strips exposed to a salt solution with higher solute concentration/lower

water potential than the water potential of the cell itself results in a greater

change in size. However there were exceptions in this experiment. The results

of the potato strips from both peri-dish B and D did not follow this trend. Their

values increase instead of decreasing which would suggest a random error to

have taken place.

been taken from different potatoes.

2) Water is lost to the environment due to evaporation.

Precaution: 1) Take measurements of potato strips at least 3 times to minimize inaccurate

readings.

2) Ensure that scale is zeroed before taking measurements.

Source of error: 1) The length of change was averaged and rounded and thus the result is not

totally precise due to estimation.

2) The potatoes that were used in the experiment were different types.

Reflection: Osmosis is very important to the life of living organisms in many different

ways. Firstly plants wouldn’t exist without osmosis and without plants, no other

life could exist as they are a vital link of the entire food chain of the planet. Plants

also depend on osmosis to move water from their roots to their leaves. Given that

osmosis is very important to cells, this experiment can provide the investigator

understanding of the relationship between osmosis and plant cells in real life

situations. It provides a useful model for understanding concentration and the

movement of water across membranes by simulating how cells react to their

environment and if placed in a new environment osmosis can facilitate the

changes needed in order for the cell to maintain homeostasis. The pressure within

and outside each cell is also maintained by osmosis as this process ensures a

balance of fluid volume on both sides of the cell wall. If fluid volume outside the

cell is more than the fluid volume within, such pressure could lead the cell to
 cave in. This experiment can also be used to investigate the water potential of

different plant cells and solutions with different concentrations.

My takeaway from this experiment is that osmosis helps cells respond

accordingly to their environment which is important for their survival. From

doing this experiment I learned a new term, ‘water potential’, and how it relates

to the osmotic relationship between plant cells and the concentration of solutions.

One way of improving this experiment is to have more controlled variables.

So for example, the initial length of the potato strips could have all been cutdown

to the same lengths. Measuring techniques can also be improved instead of one

person being assigned to take measurements, there could be multiple people

taking measurements and comparing their readings.

Conclusion: From the experiment it was found that the Sodium Chloride affects the size

of plant cells and most likely their water potential. As illustrated by the table,

in solutions where more NaCl was presented, there was a general reduction in

the potato strips plant cells, due to the volume of water inside the cells being

lost to the hypertonic environment.

Skills Being Tested: analysis and interpretation

Date: Monday 24/01/22

Title: Osmosis

Aim: to determine the effect of Sodium Chloride Concentration on Animal Cell

Apparatus & materials: 6 eggs, hand towel, 6 beakers, NaCl solutions (0.25M, 0.5M, 1.0M,

2.0M, 3.0M), electronic balance

Method: 1) Sodium Chloride solutions were placed in labelled beakers as follows:

Beakers NaCl (g) Volume of water Concentration of salt

A 1.80 125 0.25

B 3.60 125 0.50

C 7.25 125 1.00

D 14.5 125 2.00

E 21.75 125 3.00

F 0.00 125 0.00

2) Six eggs were placed in vinegar to dissolve their shells. Afterwards they were measured to

confirm and record their weight.

3) One egg was placed into each beaker containing a different at solution and ensured that

they were fully submerged.

4) Eggs were left in their solutions for 120 minutes.

5) The eggs were removed from the solutions, dried with a hand towel then their final weight

was measured.
Results:

Table showing Data Collection Before and After Eggs were Placed in Solution.

Beaker NaCl Initial weight Final weight (g) Weight change

A 0.25 75.13 71.01 -4.12

B 0.50 68.25 71.94 3.69

C 1.00 78.08 82.20 4.12

D 2.00 78.06 77.00 -1.06

E 3.00 86.59 83.59 -3.00

F 0.00 77.68 83.75 6.07

Discussion: Osmosis is the passive process in which water moves through a selectively

permeable membrane from the side of the membrane with a high concentration

of water to the side with a low concentration of water. The egg that was placed

in beaker F with pure water showed the greatest difference in weight. This

increase in mass of the egg in pure water is due to the movement of water

molecules into the animal cells via osmosis. Water molecules in the beaker are

at a higher concentration than water molecules in the cytoplasm of the animal

cells and so move along the concentration gradient and into the cells. As more

water molecules are present in cells, the final mass of the egg will be greater

than the first. Similarly the shell-less eggs that were placed in beakers B and C

also increased in weight after being removed from their solution. These

solutions can be described as hypotonic. A hypotonic solution is any external

solution that has a low solute concentration and high water concentration

compared to intracellular solute concentration. In hypotonic solutions there is a

is placed into a hypotonic solution will swell and expand until it eventually

bursts. The egg in beaker F gained the most mass, meaning it was placed in the

most hypotonic solution. Since the concentration of the solution was 0.0M then

this solution is the most hypotonic solution used in the lab.

The shell-less eggs that were placed in beakers A, D and E all experienced a

decrease in their weight after being removed from their different solutions. A

hypertonic solution is any external that has a higher amount of dissolved

substance/solute concentration compared to the inside of the cell. When an

animal cell is placed in a hypertonic solution, there will be a net movement of

water molecules across the cell membrane to outside of the cell. Thesis can

cause the cell to become smaller and even shrivel, resembling a raisin. The

solutions in beakers A, D and E can be referred to as hypertonic because these

cells experienced a decrease in their weight. The egg in beaker A lost the most

mass, meaning it was placed in the most hypertonic solution. Since this egg was

placed in the 0.25M salt solution it can be said this was the most hypertonic

solution used in the lab.

Precaution: 1) Ensure the scale is tearded before using the electronic balance.

2) Take the masses of NaCl and the eggs at least 3 times to ensure accuracy.

Limitation: 1)

Source of error: 1)
Reflection: Osmosis factors heavily in each of these processes and is an important force

for keeping every single cell in your body healthy. Cells utilize osmosis to reach a

state of equilibrium or homeostasis.Through the process of osmosis, nutrients get

transported to cells and waste materials get moved out of them. In this lab we

tested samples of egg tissue to see how much water they absorb or release in salt

solutions of varying concentrations. This gives us an indirect way to measure the

osmotic concentration within living cells. Osmosis is hard to see without a

microscope but by carrying out this experiment we created our own model of a

cell, using shell-less chicken eggs. By doing this we can see what happens when

we manipulate the osmotic balance in the cell. The purpose of this experiment is

to observe an egg as a model to understand the concept of osmosis.

Knowing that there are different types of cells and certain cells behave in

different environments is important in our world for many reasons. The cell is the

most basic unit of life and knowing about it will help us answer many different

questions. If someone knows about the cell and how it works they could find a

way to counteract viruses and illnesses, thus creating medicine and cures.Without

knowledge of the cell, we wouldn’t know about how we get our energy, how

osmosis works or its importances to life on Earth.

Conclusion: In the pure water, and in more dilute solute solutions, animal cells will gain

weight from the water that is soaked into the cell. In contrast when animal cells

are placed in more concentrated solute solutions, the cell will lose mass as the

water moves out of it. As is seen from the table, there is generally a decrease in

mass when a potato is placed in water containing NaCl solution.