DIFFUSION IN AGAR CELLS

Ahmad Kamal, Syanaz Bazil 000592-0049

DIFFUSION IN AGAR CELLS

RESEARCH QUESTION: Does different volumes of the blocks which are

1cm3,8cm3,∧27cm3, affect the volume of sodium hydroxide solution

diffused into the agar blocks when the volume of the sodium

hydroxide solution, concentration of the agar block,

concentration of the sodium hydroxide solution, shape of the agar

block, and time taken for the diffusion are the same?

INTRODUCTION:

Diffusion is a process that can be defined as the net movement of

particles from are of higher concentration to lower

concentration. Diffusion occurs in all living things, ranging

from unicellular organism to multicellular organism. It is a very

important process as materials like nutrients, water, oxygen,

carbon dioxide, and cellular waste are transported between the

cells and the environment inside the organism1. In this

experiment, the cell is represented by the agar block. The

immersion of the agar block into the sodium hydroxide solution is

to demonstrate the process of diffusion that occurs inside the

living organism. The rate of diffusion that occurs highly

dependent on the size of the cell, specifically their area and

their volume. So the experiment is designed to find out the

relations between the volume of the agar cell and the rate of

1 http://www3.nd.edu/~hgberry/biology2012/mod7/7.02Agar_Cube_Lab.docx

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http://www3.nd.edu/~hgberry/biology2012/mod7/7.02Agar_Cube_Lab.docx


diffusion. The agar already contained phenolphthalein indicator,

which changes from colorless to pink when there is presence of

sodium hydroxide solution. The volume of the region not

penetrated by the sodium hydroxide solution is the region that

doesn’t turn the color from colorless to pink. The differences in

the volume of the region not penetrated by the sodium hydroxide

solution is used to measure the rate of diffusion of each

different sizes of cube cell. As the organism gets bigger in

size, the surface area will increase, however the volume increase

faster than the surface area. Size of cell of every organism

depends on the efficiency of the material to move in and out by

diffusion2.

HYPOTHESIS

As the volume of the agar block increase, the volume of the

sodium hydroxide solution diffused into agar block decreases.

This can be justified because when the length of each agar block

which has the shape of cube increases, the volume will definitely

be larger. Hence, when the volume of the agar block gets larger,

there will be a greater distance for the sodium hydroxide

2 http://teachers.saschina.org/khorner/files/2012/08/Diffusion-and-Cell-Size-Lab.pdf

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http://teachers.saschina.org/khorner/files/2012/08/Diffusion-and-Cell-Size-Lab.pdf

http://teachers.saschina.org/khorner/files/2012/08/Diffusion-and-Cell-Size-Lab.pdf


solution to be diffused into the cell, thus resulting in bigger

region not penetrated by the sodium hydroxide solution. So for

the same initial amount of sodium hydroxide solution, the largest

agar block will have the least volume of sodium hydroxide

solution penetrated into the agar block. The results can be

measured by measuring the volume of sodium hydroxide solution

penetrated. This can be done by subtracting the region of agar

block not penetrated subtracted from the initial volume of the

agar block. 1% phenolphtalein is added initially to the agar

block so that any presence of a base (sodium hydroxide) will be

detected thus, changing the appearance from colourless to pink.

VARIABLE:

Variables Ways of manipulating/controlling/

measuring variable

Independe

nt

Volume of the block of

agar

Different dimensions of the

blocks are being cut using

a ruler and knife into 3

types of blocks. This can

be done by having a piece

of paper with dimensions 3

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cm x 3cm x 3cm, 2 cm x 2 cm

x 2 cm, and 1 cm x 1 cm x 1

being put on the agar. When

it is done being cut, the

volume of each block is

calculatedDependent The volume of the

sodium hydroxide

solution that

penetrated the agar

block

The volume of the region

not penetrated by the

sodium hydroxide solution

is measured and recorded,

which is shown by the part

where there is not a pink

colour, inside the block.

This is done by cutting the

agar block in half by using

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a knife and the volume not

penetrated by sodium

hydroxide solution is

calculated after measuring

the sides of the agar block

by using a ruler. So, the

volume of sodium hydroxide

solution that penetrated

the agar block can be

calculated by subtracting

the volume of the agar cube

not penetrated from the

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initial volume of the agar

cube.Controlle

d

Volume of sodium

hydroxide solution

The sodium hydroxide

solution used to immerse

the agar blocks contains

the same volume which is

200 ml inside a 500 ml

beaker.Concentration of sodium

hydroxide solution

The same concentration of


which is 0.5 M is used and

received from the lab

assistantTime taken to immerse

the cubes in the

solution

The same time taken to

immerse the cubes in the


which is 10 minutes is

fixed. Time is controlled

using a stopwatchShape of the agar block The same shape of each

block (cubes) in order for

the solution to be diffused

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uniformly is fixedConcentration of the

agar block

The same concentration of

the agar block by preparing

a 20 g agar powder is

fixed, mixed with 500 ml ofdistilled water, resulting

in the concentration to be

0.04 g¿cm3

Table 1: Independent, dependent, controlled variables and methods

to measure/manipulating/controlling them

MATERIALS

MATERIALS QUANTITY VOLUME/SIZE

Agar powder, 10 g 3 10 g

Distilled water,

500 ml

- 500 ml

Phenolphtalein

indicator solution,

1%, 5 ml

1 5 ml

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1%, 1g

Phenolphtalein in

100 ml 95% ethyl

alcohol

- 100 ml

Sodium hydroxide

solution (NaOH)

- 200 ml

Dilute hydrochloric

acidTable 2: Materials and its quantity and volume/size

APPARATUS

APPARATUS QUANTITY VOLUME/SIZE

Beaker 3 500 mlElectronic balance 1 -Bunsen burner 1Tripod stand 1Wire Gauze 1Lighter 1Measuring cylinder 1 500 mlMeasuring cylinder 1 10 ml1 Metric ruler 11 knife 1

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1 spoon 1 `2 Square mould for

casting gel

2

Tissue paper 1Table 3: Apparatus and its quantity and volume/size

METHODOLOGY 3

Procedure4

1. 10 g of the agar powder is mixed with 500 ml of the

distilled water

2. The mixture is heated until it is almost boiled. It is then

to be stirred frequently until the solution is clear.

3. When the solution is clear, it is being removed from heat. 5

ml of 1% phenolphthalein solution is added and then stirred.

4. If the mixture is still pink, a few drops of dilute

hydrochloric acid is added until the colour disappeared.

5. Agar is then poured into a square mould and it is cooled

down.

6. When the agar has been solidified, 3 cm x 3cm x 3 cm cube, 2

cm x 2 cm x 2 cm cube, and 1 cm x 1 cm x 1 cm is cut.

3 MARA College Banting Biology SL Students’ Handbook Year 2 13th edition. 2013. Pages 91-93. Print

4 @_@

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7. 200 ml of 0.5 M sodium hydroxide solution is poured into the

500 ml beaker. The time when it is being poured is noted all

of the cubes of agar is immersed into the solution. It is

lead to be soaked for 10 minutes while it is also being

stirred gently.

8. A spoon is used to remove the cubes after 10 minutes and it

is dried by using filter paper.

9. The cubes are then cut and the depth of the pink colour is

measured by using a ruler.

DATA COLLECTION AND PROCESSING

QUALITATIVE DATA

1. The agar block is colourless at first, but it started to

change its colour when it is immersed in the beaker

containing 200 ml of sodium hydroxide solution.

2. The agar block with the smallest volume (1cm3 ) turns its

colour from colourless to pink faster than other agar

blocks.

3. After the agar blocks are immersed in the sodium hydroxide

solution and being cut, it appears that there is still

region not penetrated by the sodium hydroxide solution for

the 8cm3∧27cm3blocks.

4. The region not penetrated by sodium hydroxide solution is

observed to follow the original shape of the agar block.

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5. The agar block with the biggest size and largest volume

which is 27cm3, has the least penetration of the pink colour after immersed by the hydroxide solution, followed by

8cm3 and 1cm3 agar block.

QUANTITATIVE DATA

Dimensi

on(cm)

Initial volume of

the agar block

before being

immersed in NaOH

solution (±0.1cm3¿

Trial Height,

±0.3cm

Width

±0.3cm

Length

±0.3cm

3 x 3 x

3

27.0 1 2.1 1.8 1.82 2.1 1.9 2.0

3 1.8 1.8 1.82 x 2 x

2

8.0 1 0.8 0.6 0.62 0.8 0.5 0.73 0.7 0.9 0.6

1 x 1 x

1

1.0 1 0.0 0.0 0.02 0.0 0.0 0.03 0.0 0.0 0.0

Table 4: Height, width, length of the region not penetrated

by the sodium hydroxide solution and their trials

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Dimensi

on(cm)

Initial

volume

of the

agar

blocks

before

being

immersed

in NaOH

solution

(

±0.1cm3¿

Trial

Height

,

±0.3cm

Width

±0.3c

m

Lengt

h

±0.3c

m

Volume not

penetrated

by NaOH

solution

of the

agar block

(±0.1cm3¿)

Volume

penetrated

by NaOH

solution

of the

agar block

(±0.1cm3 ¿

3 x 3 x

3

27.0 1 2.1 1.8 1.8 6.8 20.22 2.1 1.9 2.0 8.0 19.0

3 1.8 1.8 1.8 5.8 21.22 x 2 x

2

8.0 1 0.8 0.6 0.6 0.3 7.72 0.8 0.5 0.7 0.3 7.73 0.7 0.9 0.6 0.4 7.6

1 x 1 x

1

1.0 1 0.0 0.0 0.0 0.0 1.02 0.0 0.0 0.0 0.0 1.03 0.0 0.0 0.0 0.0 1.0

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Table 5: Dimension of the blocks, initial volume of the blocks,

volume not penetratd of the block and volume penetrated by the

block

1. The initial volume of each agar block before being immersed

in NaOH solution is found by multiplying the dimensions of

the blocks (cube)

Initial volume (cm3¿ = height x width x length

Eg: For 3 x 3 x 3 block, 3 cm x 3 cm x 3 cm = 27.0cm3

2. The volume not penetrated by NaOH solution in the agar block

can be calculated using the formula

Volume not penetrated by NaOH solution = length of the white

region x width of the white region x height of the white

region

Eg: For 27cm3 volume of agar block = 1.8 cm x 1.8 cm x 1.8

cm = 5.832 cm3≈5.8cm3

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3. The volume of agar block penetrated by NaOH solution can be

calculated by subtracting the initial volume with volume not

penetrated by NaOH solution measured before

Eg: For 27cm3 volume of agar block,

Volume of agar block penetrated by NaOH solution, trial 1 =

27.000-6.804 = 20.196 cm3≈20.20cm3

4. The mean (average) of volume penetrated by NaOH solution can

be calculated by taking the average of the 3 trials

∑ ofTrial1+Trial2+Trial3totalnumberoftrials

e.g for27cm3 volume penetrated =

20.196cm3+19.020cm3+21.168cm33 = 20.128cm3≈20.13cm3(2d.p)

5. Uncertainty of average of volume of penetration of the agar

block (standard deviation):

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The uncertainty of the average time taken can be calculated

by using the standard deviation formula :

SD=√∑ (x−x)2

N−1

Where x = data

X = the mean or average

N= number of values

∑ ¿sum across the values

Example calculations:

S.D = √ (20.196−20.130 )2+(24.02−20.130)2+(21.168−20.130 )2

3−1

= ±2.84727 ≈ 2.847

6. Fraction of penetration can be calculated by the formula:

Fraction of penetrated block =

Meanof thevolumeofpenetrationInitialvolumeoftheblock x 100%

7. Percentage of penetration

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Percentage of penetration of sodium hydroxide solution can

be calculated by using the formula :

Meanof thevolumeofpenetrationInitialvolumeoftheblock x 100%

For the cube with volume of 27 cm3= 20.1327 x 100% = 74.5556 %

≈74.56%

8. Standard error percentage = StandarddeviationMeanof thevolumeofpenetrationx

100%

= 2.8520.13x 100% = 14.158% ≈ 14.16%

9. The rate of diffusion can be calculated by using this

formula:

Rate of diffusion =Percentageofpenetrationt

Where t stands for the time taken to immerse the blocks of

agar in sodium hydroxide solution

Eg: For agar block which has the volume 27cm3,

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rate of diffusion = 74.5610=7.456 % /min≈7.46% /min

10. Standard Error can be calculated using the formula:

Eg: For agar block which has the volume 27cm3

Standard error = StandarderrorpercentagePercentageofpenetrationx rate of diffusion

= 7.4674.56x 7.46 = 0.7464

Presentation of Data Processing:

Dimensi

on (cm)

Initial

volume

of the

agar

block,

(±0.1cm3

)

Tria

l

Volume

not

penetrat

ed by

NaOH

solution

of the

agar

block (

±0.1cm3¿

)

Volume

penetrated

by NaOH

solution

of the

agar block

(±0.1cm3 ¿

Average

Volume

penetrated

, cm3

(±0.01cm3)

Standard

deviation

(±0.001cm3

)

3 x 3 x 27.0 1 6.8 20.2 20.13 2.847

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3 2 8.0 19.0

3 5.8 21.2

2 x 2 x

2

8.0 1 0.3 7.7 7.68 0.050

2 0.3 7.7

3 0.4 7.6

1 x 1 x

1

1.0 1 0.0 1.0 1.00 0.000

2 0.0 1.0

3 0.0 1.0

Table 6: Dimensions of the agar block, initial volume of theagar block, average volume of agar block penetrated,

percentage of penetration of sodium hydroxide solution, andstandard deviation.

Dimensi

on

Initial

volume of

the agar

block,

(±0.1cm3)

Percentage

of

penetration

,% (±

Standard

Error of

volume

Standard

error

percentage,

%(± 0.1 %)

Rate of

diffusion,

%/min

(±

Standard

Error

rate)

Standard

error for

rate of

diffusion

(± 0.001 %

min-1)

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penetrated)

3 x 3 x

3

27.0 74.56 14.16 7.46 0.7464

2 x 2 x

2

8.0 96.00 0.65 9.60 0.065

1 x 1 x

1

1.0 100.00 0.00 10.00 0.000

Table 7 : Dimensions of the agar block, standard errorpercentage, rate of diffusion, standard error rate

GRAPH

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0 5 10 15 20 25 300

2

4

6

8

10

12

Rate of diffusion against volume of the agar block, %/min

Volume of the agar block (cm3)

Rate of diffusion of sodium hydroxide solution, %/min

Graph 1: Rate of diffusion of sodium hydroxide solution against

volume of the agar block

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CONCLUSION AND EVALUATION

1. The aim of the experiment is to figure out the relationship between the different size of the agar blocks which have dimensions 1 cm x 1 cm x 1 cm, 2 cm x 2 cm x 2 cm, and 3 cm x 3 cm x 3 cm with volume 1cm3,8cm3,27cm3 and the volume ofsodium hydroxide solution diffused into the agar block.

2. Based on the results plotted on the graph, the volume of theagar block and the rate of diffusion in %/min shows a negative correlation. From the data obtained from the experiment, we can see that the agar block with the highest volume in cm3 has the lowest rate of diffusion of sodium hydroxide solution expressed in %/min. On the other hand theagar block with the lowest volume in cm3 has the highest rate of diffusion of sodium hydroxide solution.

3. This is coherent with the hypothesis formed at the beginningof the experiment. It indicates that as the volume of the agar block increases, the rate of diffusion of sodium hydroxide solution decreases. This is why the volume of the agar block when it has a small volume, it has full penetration percentage of sodium hydroxide solution represented by the pink colour. The reason would be because it takes a longer time to penetrate into the agar cube as ithas now longer distance for it to go towards the centre, in order to completely diffuse the agar block. The pink colour appeared as the agar block is initially being put a few drops of phenolphthalein indicator in order to detect the presence of sodium hydroxide solution.

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4. From the experiment, we can see that the largest the surfacearea to volume ratio, the greater the rate of diffusion. Thereason that can explain this situation is because the as a cell increases in size, both its volume and surface area will increase. However, the volume will increase faster thanthe surface area of the cell. This is best demonstrated by the example- A 1cm3 of agar block will have 6cm2 total surface area.

Thus, the total surface area volume over volume ratio would be 6:1

- An 8cm3 of agar block will have 24cm2 total surface. Then, the total surface area over volume ratio would be 3: 1

- An 27cm3 of agar block will have 54cm2 total surface. So,the total surface area over volume ratio would be 2:1

5. The rate of a cell when it produces heat and consume resources is directly proportional to its volume whereas rate of uptake and removal is proportional to surface area. Hence, this will create problems as the rate of a cell when it produces a heat and consume resources faster than it is able to uptake new substances. Plus, a larger volume, will causes more distances in order for things to diffuse into it.

6. This is the reason as why that multicellular organisms doesn’t rely on diffusion, unlike unicellular organism whichhas a larger total surface area over volume ratio compared to multicellular organism, for example humans. This however can be overcome as humans have alveolus in their lungs, which has large surface area over volume ratio in order for it to have a higher rate of diffusion.

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7. From the graph, it appears that the agar block with the highest volume has a longest error bar as compared to the others. This can be seen as the standard error for the rate of diffusion is the highest when the volume is 27cm3, which is 0.7464 % min-1. The standard error decreases as the volume of the agar block decreases, as for 8cm3 agar block, the standard error is 0.065 % min-1. On the other hand, the lowest would be 0.000 which indicates that the data does notdeviate from the original value. The higher the value for standard error (represented by the error bar above), the wider the spread of data, which implies lack of precision and may lead to high inaccuracy. Nevertheless, the standard error did not reach ± 1 SE, which means that the standard errors’ value are small. This will indicate that the data isstill valid and standard error can approximate to zero.

LIMITATIONS AND RECOMMENDATION

No Limitations Recommendations to overcome thelimitation

1 The time when the blocks are falling are not the same, thus affecting the rate of diffusion of sodium hydroxide.

Ensure that the blocks fall at the exact same time or initially place the blocks inside the beaker before pouring the sodium hydroxide solution.

2 The agar block that is being cut is not uniform in shape as it is cut onlyby using knife and ruler.

Create a cutter that is uniformin shape to ensure uniform cutting so that the agar blocksis being cut with exact

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measurement3 The cube shape of the agar

block is not efficient because of the distance ofthe diffusion of sodium hydroxide solution into the agar is different as compared to other shapes, such as sphere.

Design a much more efficient shape, such as sphere as its distances from the outer to thecenter is the same. This will uniformly distribute the penetration of sodium hydroxidesolution into the agar cell.

4 The agar blocks are not properly dried by the filter paper thus causing the diffusion to still occur, which produces inaccurate recording of the volume of sodium hydroxide solution penetrated

The agar blocks are dried immediately to make sure that there is no excess solution that is still diffusing into the agar block.

5 Contaminants such as alkali surrounding the agar which will cause the phenolphthalein that is dropped in the agar to be changed from colourless topink, and bacteria existing around the agar which could affect it since agar is a food for bacteria.

Check to make sure that there is no contaminants at the apparatus and materials before the experiment starts by cleaning them using water to rinse and

6 The fan in the lab causes the windy surrounding, which will end up affecting the rate of diffusion of the sodium hydroxide solution into the agar block

The fan inside the lab is turned off while conducting theexperiment

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7 Fast stirring of the sodium hydroxide solution after the agar block is being immersed causes heatto be produced, thus affecting the rate of diffusion

The stirring is done slowly, carefully and at a uniform rate. This can also be done by using a magnetic stirrer, as ithas a stirrer which has a knob that will make sure that the solution will be stirred at a constant rate.

Table 8: Limitations of the experiment and recommendations to overcome the limitations

REFERENCE

1. MARA College Banting’s International Baccalaureate, Biology SL Handbook, 2012

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DIFFUSION IN AGAR CELLS

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