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Introduction:

Biology is the study of living things, how they work, and their reactions to other organisms

and their non-living environment. But, to know how organisms work and survive, you have

to look at their parts. The basis of the living organism, the smallest living part of the

organism, its building block, is the cell. The basic cell may not seem like much, but make up

everything in that organism. Going one step further into the study of the organism is to

know the parts of the cell, and most importantly its membrane. The cell membrane is the

wall between the cell and its environment. It is its fortress and its gate. It allows for the

absorption of what is good and nourishing and permits the rejection of harmful materials. In

order to gain a deeper understanding of the topic of membranes and how they react in the

cell, we performed a series of labs. These labs showed us why cells are microscopic, how

and why they gain and lose size and color, and how materials are transported through the

membrane, with and without the help of the cell.

Lab 1: Diffusion and Osmosis – Kinetic Energy of Molecules

Lab 2: Diffusion of a Solid in a Solid

Lab 3: Semi-Permeable Membrane (Artificial)

Lab 4: Semi Permeable Membrane – Purple Onion Cells (Biological)

Lab 5: Ferd’s Potato Dilemma

Lab 6: What Are Amoebas Not the Size of Lake Erie

Lab 7: Active Transport

Lab 1: Diffusion and Osmosis – Kinetic Energy of Molecules

Purpose, Observations and Conclusion

The purpose of this lab was to confirm the idea that molecules are in a constant state of

motion. To test for this, we observed carmine powder, a red powdery dye, under a

microscope while mixed with water. If molecules are in a constant state of motion, and

carmine particles are mixes with water under a cover slip, then the dyes would disseminate

and one would be able to see the random motion of the individual particles. Under the

microscope, one was able to see the movement of the molecules as they spread around

under the cover slip. This action took place because everything is in a constant state of

random motion.

Lab 2: Diffusion of a Solid in a Solid

Purpose

The purpose of this activity was to determine if the

molecules that make up a solid are able to diffuse in another

solid. To study this, we placed three drops of a gel dye into

a gel AGAR substance and watched the diffusion take place.

If molecules are in constant motion, and two soluble solids

are brought together, then the solids will diffuse together.

Observations

We observed the dyes spreading out from their initial “drop

zone.” They formed rings of dye that eventually began to

touch each other. In time, the colors began to mesh together

and the entire dish became one murky color.

Conclusion

In this lab, the three drops of gel dye in the Petri dish of AGAR at first stayed in the place

they were dropped. After a few minutes, the solid dyes began to diffuse into the AGAR. In

an hour, the dyes were completely diffused in the Petri dish, with all of the colors meshing

together. This occurred because all molecules are in constant motion. This allowed the

dyes to move across the concentration gradient to an area in the AGAR where there was a

low concentration of dye. This experiment followed the expected "molecules will travel

from high concentration to low concentration. This was able to happen because the

Lab 3: Semi Permeable Membrane

Purpose

The purpose of this activity is to discover whether or not liquid substances are able to diffuse

between artificial membranes. To perform this, we used a tube of a semi permeable

membrane and created a bag, then filled it with a glucose and starch solution. We then pu

that bag in a beaker filled with an iodine solution. We then looked to see if there were any

changes of any sort to indicate a transfer across the membrane. If only certain smaller

molecules are able to pass through a semi permeable membrane, and I create two solutions

with solutes of differing molecular size while having them separated only by a membrane,

then the smaller molecules will travel across the membrane due to the random movement of

molecules.

Results

Original Contents Original Color Final Color Benedict’s Color

Bag Glucose and Starch Clear Tint of blue Mustard green

Beaker H2O and Iodine Pale yellow Clear Rust

Control H2O Clear Clear Clear Blue

There was a visible color change in the solutions after sitting overnight and when testing for

simple carbohydrates. The color changes in the Bag and the Beaker show a presence of

glucose.

Conclusion

In this activity, after sitting overnight, there was a visible difference in color between the two

solutions. The beaker was initially a yellow color and became clear. The glucose solution in

the membrane was initially clear, but then became a tinted blue color. This gave us the

indication that something moved across the membrane, but the color change alone was

inconclusive as to what specifically moved across the membrane. To determine the

presence of the glucose solution, we used Benedict’s solution. We tested samples from the

beaker and the bag and both turned out positive. This correlates with the final color as the

iodine solution color was not as strong and the bag solution had a tinted blue color instead of

being clear. The starch and glucose solution diffused into equilibrium overnight; the glucose

left the membrane and the starch stayed in, but the iodine bonded with the starch and was

trapped in the bag as the beaker solution became clearer.

Lab 4: Observing Osmosis in Purple Onion Cells

Purpose

We performed this lab to determine and observe how osmosis works through living organic

matter via membranes. This lab had us slice up an onion and peel off its skin. Once the

purple skin was on a slide and under a microscope, a series of higher concentrated solutions

of saltwater were washed over it. If water will leave its hypotonic environment in a cell to

reach equilibrium with a hypertonic environment through osmosis, and we rinse onion cells

with varying degrees of hypertonic solution, then water of the cell stored in the vacuole

should leave the cell, resulting in a smaller vacuole.

Results

After each rinse of a higher hypertonic salt solution,

the purple vacuole got smaller when we looked at it in

the cell. It kept shrinking. To make sure this was due

to the salt water, we rinsed it with pure water, and the

vacuole began to return to its normal size. The cell

wall did not change shape, but the vacuole shrunk,

resulting in a larger looking cytoplasm.

In order from top cluster to bottom, Original, 5%

solution, 10% solution, 15% solution, and after 3 H2O

washes.

Conclusion

In the activity, the vacuoles in the cell initially

dominated the cell size and were full of water. With

the addition of salt to the cell in the form of different

concentrations of salt water, the vacuole shrunk,

indicating water loss. This was most prevalent in the

highest 15% concentration solution. The result

implies that the addition of salt to the cells made water

move out of the vacuole, shrinking it it in the cell.

This happened because the salt water was hypertonic

and the vacuole hypotonic. The water left the cell to create equilibrium. The only way for

water to diffuse to create equilibrium is through osmosis.

Lab 5: Ferd’s Potato Dilemma

Purpose

This lab was to match Molarity to specific beakers left for us by the puzzler. Using what we

knew about osmosis and membrane function, we were left with various unlabeled beakers of

glucose solution and we had to determine which beaker belonged to which Molarity. The

only way to do this is through what we learned about what water does in the purple onion

cell lab. Water would leave the high water environment and would enter the low water

environment. Therefore: If we set potato pieces in different concentrations of glucose

solution, and water will leave the potato to go to the lower concentration of water in the

solution, the potato pieces in the highest glucose solution will have the smallest mass after

soaking overnight. This lab explored the terms isotonic, hypertonic, and hypotonic.

Results

The potato pieces looked rather comfortable resting in their little solution baths.

Mass b/f soaking

Mass after soaking

Gain or loss Difference in mass

Quotient in mass

0 Mol Soln (H2O) 4.12 4.88 G .76 1.18 .4 Mol Soln 3.8 3.41 L -.30 .897 Mystery Soln A 3.81 3.19 L -.62 .83 Mystery Soln B 4.21 3.39 L -.82 .8 Mystery Soln C 4.31 4.81 G .5 1.11 Mystery Soln D 4.63 3.41 L -1.22 .737

Conclusion

In this lab, we used our knowledge of membranes and

osmosis to match up the mystery solutions to the beakers

A, B, C, and D. It turns out that Beaker A was .6 Mol

Solution, Beaker B was .8 Mol Solution, Beaker C was .2

Mol Solution, and Beaker D was the 1 Mol Solution. To

determine this, we looked at what happened to the

constants of the 0 Mol and the .4 Mol solutions before

and after soaking. The 0 Mol solution gained mass as the

water saturated the potato, but the .4 Mol solution lost

mass as the water left the potato to enter the solution and

create equilibrium. Using the knowledge that the higher the Molarity, the lower the mass of

the soaked potato and calculating the greatest difference between potato masses, we

determined that is the highest Molarity is D because it had the greatest loss. Then came B

with the second greatest loss, and then C and so on. All of this was due to the osmosis

between hypertonic and hypotonic solutions and the transfer of water between them over

the membranes of cells. The ratios of the masses were also used to confirm the conclusions.

The lowest ratio meant the greatest loss in weight and the greatest Molarity.

Lab 6: Why Are Amoebas Not the Size of Lake Erie?

Purpose

The purpose of this lab was to figure out why amoebas are not large. We observe that large

organisms are made of large cells, but why is it inefficient, evolutionarily speaking, to have

really large cells? Should a large cell not be able to gain resources faster than a small one?

This lab dealt with surface area and the diffusion of liquid to determine this. If the rate of

absorption is determined by the ration of surface area to volume, and we cut cubes of gel of

three different sizes, then the one with the largest difference in ratio will absorb liquid the

fastest. Large objects have a very large volume compared to their surface area, but the

smaller one gets, the larger the surface area is in comparison, so if it really is better to have

small cells, this lab will prove so by the speed of the color change in the gel made with

phenol red.

Results

Cube Cube Dimensions Surface Area Volume Ration SA/Vol

A 1cmx1cmx1cm 6cm2 1cm3 6:1

B 2cmx2cmx2cm 24cm2 8cm3 3:1

C 3cmx3cmx3cm 54cm2 27cm3 2:1

The smaller cubes changed color completely at a faster rate than the larger cube. The larger

cube had a pink center for a long while whilst the other two became clear.

Conclusion

In this lab, we tested the diffusion rate of molecules and how having smaller cells is

beneficial in an evolutionary sense. The smaller cell is able to absorb nutrients and water

much more quickly than a larger cell, meaning it can get what it needs to where it needs in a

short amount of time. On a smaller scale, a very small cube 1/100 of a cm in length would

have a surface area to volume ratio of 600000:1, meaning it would be very fast at letting a

solution past its membrane and wholly into the cell. Although the cube 3cm in length had

the largest surface area, the ratio is what matters. This lines up with our hypothesis that a

smaller cube would be faster at fully absorbing the vinegar in this experiment.

Lab 7: Active Transport

Purpose

This lab was performed to study active transport. We took yeast in a sodium carbonate

solution and added neutral red, the filtered it and performed a series of tests to determine if

active transport took place. If neutral red is a solute that cannot normally diffuse in a yeast

cell, and yeast cells are capable of active transport, then the yeast cells will undergo a color

change and no neutral red would filter through the paper.

Results

The yeast and sodium carbonate solution with neutral red filtered to a pale honey-colored

liquid, leaving clumps of red yeast particles on the paper. This implies that the yeast

absorbed the neutral red and the filtrate is the sodium carbonate. Then we took the yeast

mixture and filled three test tubes equally with it. In the first we added sodium hydroxide, in

the second, ammonium hydroxide, and the

third we boiled. The results were that the

first test tube stayed a red color. The second

turned a yellowish orange color and the third

boiled one turned a bright orange-yellow.

Conclusion

This lab had four major sub experiments in

it. What happened in the test tubes are as

follows: The first test tube stayed red,

meaning that the NaOH was not accepted

into the cell. The neutral red would have

turned yellow if it did because it would be

more basic. It was still acidic, so it stayed

red. The second tube had the NH4Oh pass

through the membrane, but that was due to

diffusion as the neutral red turned yellow, making the solution more basic. The third boiled

tube, although it changed color, is also not active transport because active transport requires

energy from the cell, not external help. Also, the high heat just broke down the membranes,

meaning that active transport is impossible – there is no membrane! This leaves us with the

first experiment. The neutral red was absorbed into the cell as seen by the leftover red yeast

cells. If one looked under a microscope, they would see no red dye in the filter. Since there

is not red dye in the filter paper or in the filtrate, it was fully absorbed in the cells. Active

transport! The yeast pumped the dye in!

Summary Discussion

This chapter was all about membranes and their importance to the cell. Membranes use two

different types of transport to bring things into and out of the cell, either active transport or

passive transport. This depends on whether or not the cell uses energy to transport the molecule

across the membrane. This transport can happen by osmosis, the transfer of water, or diffusion,

the transfer of everything else.

To establish that diffusion actually takes place, one wonders how exactly molecules move on

their own into and out of the cell without any energy used by the cell. We assumed that this is

because all molecules are in a constant state of random motion. This is a nice theory, but how

did we test it? Well, we took come carmine powder, sprinkled it in water, put it on a slide, and

watched it move all by itself via small, random vibrations. The powder moved from areas high

concentration of dye to areas of low concentration of dye. These insentient particles were able

to do this without any help. They completely leveled out. What was observed is the proof for

what is called a Brownian movement; the tendency of molecules to evenly distribute themselves

in a solution.

This random movement is the basis of diffusion. This process can be seen in the drops of dye in

the solid dye dissolving in the solid gel lab. It can also be seen in the semi permeable membrane

lab.

We also see in these labs that the surroundings of a cell can affect what goes across the

membrane. In the onion cell lab, we saw that the hypertonic solution around the onion cell

made the hypertonic vacuole lose its water via osmosis to help create a more isotonic

environment. This was proven by the shrinking of the cell vacuoles.

The same thing can also be seen in Ferd’s potato dilemma. The water in the cells of the potato

left to join the solution. Since water was moving across the membrane, it was again osmosis.

We know that the glucose did not enter the potato and we are sure water left as the mass of the

potato shrunk. Therefore nothing could have entered and it is only logical to assume that water

left the cell to equalize the solution.

What If a molecule was unable to get into a cell by diffusion? What if it had to get from low

concentration to high? This can happen as seen in the active transport lab. The red dye was fully

absorbed in the yeast cells. This would not happen in regular passive transport – the diffusion

would only take place until equilibrium is reached. In this experiment, equilibrium is passed up.

All of the red dye is in the cell, none in the filter paper, and none in the filtrate. This is

undeniable evidence that shows active transport is at work in the cell.

One could wonder why cells are not larger than they are. Would it not make more sense for a

cell with a larger surface area to work more efficiently? It is not as seen in the cell size lab. The

efficiency of diffusion within a cell all depends on its ratio of volume to surface area. Think about

it. If a cell has 54cm2 of surface area, it has to spread all of that amongst 27cm

3 of volume. If it

only has 6cm2 of surface area, then it only has 1cm

3 of volume to spread molecules to. For piece

of volume to piece of volume, there is more surface area to go around in a smaller cell. The size

of cells being what they are, the ratio of surface area to cell volume is exceedingly high, making it

very friendly towards diffusion. This is seen in the lab with the smallest cube losing its color

much faster in the vinegar solution than the large cube did.