Biomolecules: Practical 1- Food test

Apparatus

• 6 test tubes
• 1 250cm3 beaker
• 1 tripod stand and wire gauze
• 2 10cm3 measuring cylinders
• benedicts sol, iodine sol, ethanol sol, dilute sodium hydroxide, copper (11) sulphate,
• hot water supply
• distilled water
• sol1: glucose sol
• sol 2: egg albumen
• sol 3: starch suspension
• sol 4: oil
• Unknown A and B

Procedure:

Iodine test for starch

1. Add 2 cm3 of sol 3 to clean test tube, followed by a few drops of iodine sol
2. Record your observations and conclusions

Biuret's Test for Proteins

1. Add 2 cm3 of sol 2 to a clean test tube, together with 2cm3 of dilute sodium hydroxide sol. Stir to mix the contents
2. Using a pipette, add copper (ll) sulphate drop by drop, mixing the contents after the addition of each drop.
3. Record observations.

Benedict's Test for Reducing Sugar

1. Pour about 2 cm3 of sol 1 into a test tube and add ane qual volume of Benedict's sol. Shake the mixture
2. Heat the test tube in the boiling water bath for 4 minutes.
3. Record observations.

Ethanol Emulsion Test for Fats

1. Add 2 cm3 of sol D to a clean test tube together with 2 cm3 of ethanol.
2. Record your observations of the contents after shaking test tube vigorously for 1 minutes.
3. Add 2 cm3 of water to the test tube and mix.
4. Record observations.

Solution	Benedict Test		Iodine Test			Biuret’s Test			Ethanol Emulsion Test
	Observations	Conclusions		Observations	Conclusions		Observations	Conclusions		Observatons	conclusions
1	An orange precipitate was obtained	Moderate amount of reducing sugar is present		X	X		x	X		X	X
2	X	X		X	X		The mixture turned violet	Protein is present		X	X
3	X	X		The mixture turned blue black	Starch is protein		X	X		X	X
4	X	X		X	X		X	X		A white emulsion was obtained	Lipid is present
A	A brick-red precipitate is was obtained	Large amounts of reducing sugar is present		The mixture remained brown	No starch is present		The mixture remained blue	No protein is present		The mixture remains clear	No lipid is present.
B	The mixture remained blue	No reducing sugar is present		The mixtured turned blue black	Starch is present		The mixture turned violet.	Protein is present		A white precipitate	Lipid is present

Practical #2- Leek Experiment

Practical: Estimationg of the osmotic concentration of leek cells

Aim: to estimate the approximate osmotic concentration of leek stem cells

Apparatus:

• Razor blade
• White tile
• 5 petrid dishes
• Dorceps
• Distilled water
• 1%, 2%, 4%, 7%, 10% salt solution
• Chinese leeks
• Stop watch
• Vernier calipers
• Thread
• Labels
• Electronic balance
•  

Procedure

1. Cut the inflorescence stalk of the Chinese leek tp obtain a length of 3.0cm

2. Cut the strip longitudanally as shown in the diagram below to obtain 4 equal quarters. Repeat till you have obtained 6 strips.

Using length

3. Measure the length of the inner surface of thw strip and record the length

4. Place one strip in a petri dish of distilled water, one each in 1%,2%, 4%, 7%, 10% salt solution.

5. After 25 minutes, record the length of the inner surface and weight. Record the results in a table and suse the data to plot the graph. Explain how the length was measured.

Discussion Questions:

At which concentrations are the salt solution isotonic to the leek cells?

There is no percentage change of length. This means that the water potential of the cell sap is similar to that of its surroundings

Explain the gain or loss in the length of the stems.

The epidermal layer has a waxy surface and thicker wall. Hence it takes in less water then the outer layer where the walls are thinner. Thus the strip bend inwards.

Texture of a Potato strip in different environments

Hypotonic: high water potential, hard, rigid, coarse

Hypertonic: low water potential, soft limp, smooth

                 

Gain in mass: water potential

                                    Net movement

                                    Across partially permeable membrane

                                    Osmosis

Instead of measuring the change in length of the stem, is there another variable you can measure as an indication to osmosis?

Thickness (but length is still better)

Suggest a way to improve this experiment.

• Experimental errors:
• Repeat à take the average to reduce the random error à reliable results
• Eg: use 3 leeks instead of one
• Using longer leeks will yield more reliable results
• Cut off the ends à they might have dried out
• Do the experiment with more solutions of different concentrations, and at equal intervals
• Water evaprates from petri dish à cover with petri dish cover
• Using thread to measure à a lot of error (mass is more accurate)
• Measure curvature instead à graph paper 

Practical #1- Beetroot experiment

Aim: To investigate the factors affecting the cellular homeostasis of beetroots cells

Apparatus:

Apparatus

 
Procedure

• Set up a boiling water-bath with the bigger beaker. When the water starts to boil, turn off the Bunsen burner.
• Use a ruler and scalpel to cut the cylinder of beetroot into 25 discs of 2mm each.
• Take 5 discs of beetroot and cut them further into smaller pieces.
• Rinse the beetroot discs and pieces until the water is colourless.

Label and prepare 5 test tubes as follows:

Tube	Content
A	4ml of water
B	4ml of 25% alcohol
C	4ml of 50% alcohol
D	4ml of hot water (90 degree C – 100 degree C)
E	4ml of water with chopped beetroot

• Place 5 discs of betroot in A-D and all the chopped beetroot in tube E using the forceps.
• Leave the tubes to stand in your test tube rack for 15 minutes.
• Shake the tubes gently after 15 minutes and hold it agasint the white tile to note the colour. Record your observations in a table.
• Use a colouring meter to record the percentage of transmission of light.
• Decant a small amount of liquid from each tube into a cuvette to measure the percentage of transmission.
• Dispose the content of the tubes after the exeriment. Do not throw the beetroot into the sink.

Results:

Tube	Contents of tubes	% Of transmission of light	Description of liquid in tube
A	4ml of water	86.7	The liquid was colourless at first but turned a hue of pink after 15 minutes.
B	4ml of 25% alcohol	80.03	The liquid was colourless at first but turned pale pink after 15 minutes.
C	4ml of 50% alcohol	33.6	The liquid was colourless at first but turned dark pink after 15 minutes.
D	4ml of hot water (90 degree C – 100 degree C)	5.43	The liquid was colourless at first but turned very dark pink after 15 minutes.
E	4ml of water with chopped beetroot	20.73 (very low-supposed to be the second highest) (72.0)	The liquid was colourless at first but turned a dark shade of pink after 15 minutes. (turned light pink)

*Note: Use the same colour but to vary the range, use workds like ‘darker’, ‘dark’, ‘light’ etc

Discussion Questions

1.     Why was it necessary to wash the beetroot slices thoroughly befure using them in this experiment?

- The cell wall and cell membranes of the beetrot had been punctured causing the betalain to leak out. Hence to ensure a fair experiment, it has to be rinsed.

2.     Identify the independent and dependent variables in this experiment

-        Independent variable: Concentration of alcohol, temperature, surface area

-        Control set-up: Test tube A

-        Dependent Varable: Percentage of light transmission (colour of liquid)

3.     Construct a suitable table with appropriate headings and units to tabulate data

- See above for results

4.     Explain with reference to the tabulated data the effect of different solutions in tubes A-C on the readings obtained in the experiment. Make reference to the knowledge you acquired from the lessons on cellular homeostasis.

-        Temperature --> denature proteins

-        Cell membrane and Tonoplast --> becomes more porous

-        Alcohol: interaction with the lipid layer (phospholipid bilayer) and hence the cell membrane and tonoplast becomes more porous.

5.     Suggest an explanation for the observations of tube D and E.

- Beetroot in D was submerged in hot water bath. When expoded to heat the beetroots cell is disrupted. The molecules start to move faster causing the membrane and pigment insde to become denatured. The lipids in the membrane becomes more fluid, as the temperature is high, ths the membranes become more gragile. Coils of protein will break aparat and start vibrating. Holeswill tart to form and the cell membrame will be destroyed. The betalina pigments will then leak out. Thsus the percentage of light transmissio of tube D is 5.43%. For tube E there was a larger surface area for diffusion to occur among the membranes, thus more betalain pigments leaked out. The rate of diffusion from internal to ecternal environment increased as a result to a larger surface area exposed. Thus E has a reading of 20.73%.