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Unit 8: Lipid Isolation - Practice Quiz

BTY114 — Cell Biology Laboratory 60 Questions
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1 What is the main purpose of isolating lipids from an egg sample?

Isolation of egg lipids Easy
A. To increase the amount of egg protein
B. To remove all water from the laboratory
C. To separate lipids from other egg components
D. To produce more egg carbohydrates

2 Which part of an egg is especially rich in lipids?

Isolation of egg lipids Easy
A. Egg yolk
B. Egg white
C. Chalaza
D. Eggshell

3 What type of solvent is commonly used to dissolve lipids during extraction?

Isolation of egg lipids Easy
A. Salt solution
B. Sugar solution
C. Organic solvent
D. Distilled water

4 Why is an egg sample commonly homogenized before lipid extraction?

Isolation of egg lipids Easy
A. To remove the egg color
B. To freeze the sample
C. To break up the sample evenly
D. To increase particle size

5 What is the main role of a solvent in egg lipid isolation?

Isolation of egg lipids Easy
A. It stains the eggshell
B. It changes lipids into sugars
C. It creates new proteins
D. It dissolves selected lipids

6 Which laboratory tool is commonly used to mix an egg sample with an extraction solvent?

Isolation of egg lipids Easy
A. Test-tube rack
B. Balance pan
C. Thermometer
D. Vortex mixer

7 What is centrifugation used for during lipid isolation?

Isolation of egg lipids Easy
A. Changing lipid charge
B. Measuring lipid color
C. Separating sample layers
D. Heating the solvent

8 After extraction and centrifugation, where may the lipid-containing solvent be found?

Isolation of egg lipids Easy
A. In the balance display
B. In a separated liquid layer
C. On the outside of the centrifuge
D. Only inside the tube cap

9 What does decanting mean in a lipid isolation procedure?

Isolation of egg lipids Easy
A. Grinding a solid sample
B. Measuring sample temperature
C. Heating a glass tube
D. Pouring off a liquid layer

10 Why should the layers in an extraction tube not be mixed after separation?

Isolation of egg lipids Easy
A. To increase the sample temperature
B. To keep the phases separate
C. To make the tube heavier
D. To dissolve the glass

11 Which class of lipid is abundant in egg yolk?

Isolation of egg lipids Easy
A. Cellulose fibers
B. Phospholipids
C. Mineral crystals
D. Nucleic acids

12 What is lecithin commonly classified as?

Isolation of egg lipids Easy
A. A nucleic acid
B. A phospholipid
C. A simple sugar
D. A structural protein

13 What is the purpose of filtering an egg extract?

Isolation of egg lipids Easy
A. To remove insoluble particles
B. To create additional lipids
C. To measure the sample mass
D. To increase solvent acidity

14 Why may the extracted solvent be evaporated after lipid extraction?

Isolation of egg lipids Easy
A. To produce more solvent
B. To destroy all lipid molecules
C. To leave the lipid residue
D. To remove the centrifuge tube

15 Which safety practice is important when handling organic solvents?

Isolation of egg lipids Easy
A. Use appropriate protective equipment
B. Heat the solvent in an open hand
C. Store the solvent beside food
D. Taste a small solvent sample

16 Why should an organic solvent be kept away from flames?

Isolation of egg lipids Easy
A. It may be flammable
B. It may become magnetic
C. It may form a protein
D. It may freeze immediately

17 What observation may indicate the presence of an extracted lipid residue?

Isolation of egg lipids Easy
A. A bright metal crystal
B. A blue flame
C. A dry paper tear
D. A translucent greasy spot

18 Which property makes many lipids different from water?

Isolation of egg lipids Easy
A. They are always gases
B. They are generally hydrophobic
C. They are strongly metallic
D. They are made only of salts

19 What should be recorded when determining the amount of isolated lipid?

Isolation of egg lipids Easy
A. The size of the pipette tip
B. The number of tube labels
C. The color of the laboratory wall
D. The mass of the lipid residue

20 Why should the sample and extraction containers be labeled?

Isolation of egg lipids Easy
A. To prevent centrifugation
B. To increase lipid solubility
C. To change the solvent color
D. To identify samples correctly

21 Why is an organic solvent such as ethanol or acetone used during the isolation of egg lipids?

Isolation of egg lipids Medium
A. It converts lipids into amino acids
B. It increases the density of proteins
C. It prevents all solvent evaporation
D. It dissolves lipids more effectively than water

22 What is the main purpose of homogenizing the egg yolk before solvent extraction?

Isolation of egg lipids Medium
A. To permanently remove all water from the yolk
B. To increase contact between yolk material and solvent
C. To separate cholesterol from every phospholipid
D. To chemically destroy the lipid molecules

23 During egg-lipid extraction, the mixture forms two visible layers after standing. What is the best next step before collecting the extract?

Isolation of egg lipids Medium
A. Mix the layers continuously until they disappear
B. Identify the layers and remove the lipid-containing layer
C. Heat the mixture until the layers become solid
D. Discard both layers and repeat with water

24 Why should the egg sample be mixed thoroughly with the extraction solvent but not shaken violently for a prolonged time?

Isolation of egg lipids Medium
A. Limited mixing is required because solvents cannot contact suspended material
B. Thorough mixing improves extraction, while excessive shaking may form stable emulsions
C. Violent shaking chemically changes every lipid into a sugar
D. Gentle mixing prevents all lipids from dissolving in the solvent

25 A persistent emulsion forms between the aqueous and organic phases. Which treatment is most appropriate for improving phase separation?

Isolation of egg lipids Medium
A. Increase shaking speed immediately
B. Add a small amount of saturated salt solution
C. Add a large volume of distilled water
D. Add concentrated protein solution

26 Why is a drying agent sometimes added to the organic lipid extract before solvent evaporation?

Isolation of egg lipids Medium
A. To hydrolyze triglycerides into glycerol
B. To increase the water content of the extract
C. To remove residual water from the organic layer
D. To neutralize all phospholipid head groups

27 What observation most strongly suggests that lipid material remains after the extraction solvent has evaporated?

Isolation of egg lipids Medium
A. A translucent or greasy residue remains
B. A blue solution forms without a reagent
C. A crystalline salt disappears completely
D. A clear gas-filled tube is produced

28 Why should the extraction solvent be evaporated in a fume hood or other approved ventilated area?

Isolation of egg lipids Medium
A. Airflow is required to dissolve proteins in the sample
B. Many organic solvents produce harmful or flammable vapors
C. Ventilation prevents the lipids from becoming phosphates
D. The hood changes the solvent into a nonpolar compound

29 A student obtains a very low lipid yield after extraction. Which procedural change would most directly improve recovery?

Isolation of egg lipids Medium
A. Use less solvent and shorten the mixing time
B. Discard the sample before separating the phases
C. Perform a second extraction of the remaining sample
D. Replace the solvent with an equal volume of water

30 Why is it useful to record the mass of the empty collection container before evaporating the solvent?

Isolation of egg lipids Medium
A. The container mass identifies the lipid classes present
B. The lipid mass can be calculated by subtracting container mass
C. The measurement prevents all solvent from evaporating
D. The container mass determines the yolk protein sequence

31 An extracted residue weighs , and the original yolk sample weighed . What is the approximate percentage lipid recovery by mass?

Isolation of egg lipids Medium
A.
B.
C.
D.

32 Which result would most likely indicate that nonlipid contaminants remained in the isolated egg-lipid fraction?

Isolation of egg lipids Medium
A. The residue is unusually dark and does not dissolve in the lipid solvent
B. The sample mass decreases as the solvent evaporates
C. The residue is pale and dissolves readily in the lipid solvent
D. The extract forms a separate organic layer before evaporation

33 Why can proteins interfere with the isolation of egg lipids from yolk?

Isolation of egg lipids Medium
A. They prevent the organic solvent from having any density
B. They convert phospholipids directly into carbohydrates
C. They always evaporate before the solvent is added
D. They can bind lipids and retain them in insoluble complexes

34 A student accidentally collects the wrong phase from a two-layer extraction. What is the most likely consequence?

Isolation of egg lipids Medium
A. The lipid yield decreases and more water-soluble material is collected
B. The solvent automatically changes into a drying agent
C. The sample becomes pure lipid after additional water is added
D. The lipid yield doubles because both phases contain identical lipids

35 Which control would best help determine whether the extraction solvent itself contributes to the measured residue?

Isolation of egg lipids Medium
A. Evaporate the same volume of unused solvent in a clean container
B. Add extra egg yolk to the completed lipid extract
C. Replace the egg yolk with an equal mass of protein
D. Measure the pH of the solvent after centrifugation

36 Why might centrifugation be used after mixing egg yolk with an extraction solvent?

Isolation of egg lipids Medium
A. To compact insoluble debris and clarify the extract
B. To increase the boiling point of the organic solvent
C. To convert neutral lipids into charged molecules
D. To prevent the formation of any separate liquid phase

37 Which change would most likely cause an underestimation of the isolated lipid mass?

Isolation of egg lipids Medium
A. Discarding part of the organic layer during transfer
B. Using a preweighed dry collection container
C. Repeating the extraction with fresh solvent
D. Allowing the solvent to evaporate completely

38 Why should the collection container be dry before the final lipid residue is weighed?

Isolation of egg lipids Medium
A. A dry container chemically converts triglycerides to sterols
B. Water is required to volatilize all lipid molecules
C. Residual water would falsely increase the measured mass
D. Dry glass prevents phospholipids from dissolving

39 A student uses only water to extract yolk lipids and observes little oily material. What is the best explanation?

Isolation of egg lipids Medium
A. Water poorly dissolves most neutral lipids
B. Water prevents all phospholipids from existing
C. Water destroys the yolk before lipid extraction
D. Water is more nonpolar than triglycerides

40 Which practice most improves the reliability of comparing lipid yields between different egg samples?

Isolation of egg lipids Medium
A. Estimate residue mass by visual appearance only
B. Use equal sample masses and identical extraction conditions
C. Evaporate one sample while cooling another
D. Use different solvent volumes for every sample

41 During a Folch-type extraction of egg yolk, the homogenate is mixed with chloroform and methanol, followed by addition of aqueous salt solution. Which phase should contain most neutral lipids and phospholipids after complete phase separation?

Isolation of egg lipids Hard
A. The upper aqueous methanol-rich phase
B. The lower chloroform-rich phase
C. The original unfractionated homogenate
D. The interfacial protein precipitate

42 A student obtains a persistent cloudy interface instead of two clear phases during egg-lipid extraction. Which intervention is most appropriate before collecting the lipid fraction?

Isolation of egg lipids Hard
A. Add more water and immediately decant the upper phase
B. Evaporate the mixture until the interface disappears
C. Add a small amount of salt solution and centrifuge
D. Add concentrated acid to hydrolyze all lipids

43 Why is methanol included with chloroform during extraction of egg-yolk lipids rather than using chloroform alone?

Isolation of egg lipids Hard
A. It converts triglycerides into fatty acids
B. It selectively precipitates cholesterol from solution
C. It increases the density of the aqueous phase
D. It disrupts lipid–protein and lipid–membrane interactions

44 An extraction uses an excessive volume of aqueous buffer relative to chloroform. Which outcome is most likely?

Isolation of egg lipids Hard
A. Improved recovery of all hydrophobic lipids
B. Greater carryover of water-soluble contaminants
C. Selective removal of cholesterol from the organic phase
D. Complete conversion of phospholipids to triglycerides

45 A dry mass measurement gives a much higher apparent lipid yield when the organic extract is dried rapidly without a final desiccation step. What is the most likely explanation?

Isolation of egg lipids Hard
A. Proteins are chemically converted into triglycerides
B. Cholesterol polymerizes during rapid drying
C. Residual solvent and water remain in the weighed residue
D. Phospholipids become denser during solvent evaporation

46 Why should the egg-yolk sample be homogenized thoroughly before solvent extraction?

Isolation of egg lipids Hard
A. To reduce mass-transfer limitations and expose lipid-containing structures
B. To hydrolyze phospholipids before they enter the solvent
C. To remove cholesterol by mechanical precipitation
D. To increase the melting point of its triglycerides

47 A sample is accidentally overheated during solvent evaporation. Which lipid class is most vulnerable to oxidative deterioration under these conditions?

Isolation of egg lipids Hard
A. Short-chain alkanes
B. Fully saturated wax esters
C. Cholesterol crystals only
D. Highly unsaturated fatty-acid-containing lipids

48 A student collects the upper phase after a chloroform–methanol–water extraction, believing it contains the lipids because it appears cloudy. Which correction is most appropriate?

Isolation of egg lipids Hard
A. The aqueous phase should be boiled to release triglycerides
B. The lower chloroform-rich phase should generally be collected
C. The interface should be discarded because it contains all lipids
D. Both phases should be discarded because lipids remain insoluble

49 Which procedural change would best reduce oxidation during isolation of egg lipids intended for fatty-acid analysis?

Isolation of egg lipids Hard
A. Increase extraction temperature above the solvent boiling point
B. Use prolonged exposure to bright light
C. Minimize air exposure and keep samples cool
D. Leave the extract open while stirring overnight

50 A lipid extract remains in the interfacial layer after phase separation. Which explanation is most scientifically plausible?

Isolation of egg lipids Hard
A. Amphipathic phospholipids and denatured proteins stabilize an emulsion
B. Water cannot form hydrogen bonds with proteins
C. All neutral lipids are intrinsically insoluble in chloroform
D. Cholesterol forms a permanent aqueous salt

51 If the final egg-lipid extract is intended for thin-layer chromatography, why should the sample be redissolved in a small volume of a compatible volatile solvent?

Isolation of egg lipids Hard
A. To produce a concentrated, narrow application band
B. To convert all lipids into charged ions
C. To prevent the stationary phase from adsorbing lipids
D. To increase the boiling point of the mobile phase

52 A TLC analysis of an egg-lipid extract shows severe streaking from the origin. Which adjustment is most likely to improve separation?

Isolation of egg lipids Hard
A. Replace the lipid solvent with distilled water
B. Apply a smaller amount of a more dilute extract
C. Use a permanently wet development chamber
D. Increase the sample spot diameter substantially

53 A recovery experiment adds a known amount of a lipid standard to egg yolk before extraction. The measured recovery is 72%. What does this value primarily indicate?

Isolation of egg lipids Hard
A. The extraction and measurement procedure has incomplete recovery
B. The organic solvent contains no dissolved contaminants
C. The standard was completely destroyed before extraction
D. The egg yolk contains exactly 72% lipid by mass

54 Why is a procedural blank important when determining the mass of isolated egg lipids gravimetrically?

Isolation of egg lipids Hard
A. It converts phospholipids into measurable carbohydrates
B. It identifies the fatty-acid composition without chromatography
C. It estimates residue contributed by solvents and laboratory materials
D. It increases the amount of lipid extracted from the yolk

55 An extract is washed repeatedly with water, and the final lipid yield decreases substantially. Which mechanism best explains the loss?

Isolation of egg lipids Hard
A. Neutral triglycerides become ionic in pure water
B. Chloroform is chemically transformed into methanol
C. Some amphipathic phospholipids partition into the aqueous or interfacial fraction
D. Water permanently destroys all sterol molecules

56 A researcher wants to compare lipid yields from eggs stored under different conditions. Which design feature is essential for interpreting differences in yield?

Isolation of egg lipids Hard
A. Pool all samples before extraction
B. Measure only the volume of the organic phase
C. Use a different extraction solvent for every sample
D. Normalize yield to the mass of the original yolk sample

57 Why might saponification before extraction cause an apparent decrease in recoverable neutral lipid mass?

Isolation of egg lipids Hard
A. Phospholipids become insoluble in every organic solvent
B. Cholesterol is converted directly into glucose
C. All fatty acids are volatilized at room temperature
D. Esterified triglycerides are converted into soaps and glycerol

58 A student uses an uncalibrated balance to compare lipid yields between samples, although all extracts were processed identically. Which conclusion is most defensible?

Isolation of egg lipids Hard
A. Relative comparisons may be useful, but absolute yields are uncertain
B. Identical processing proves the absolute lipid mass is accurate
C. The extracted lipids must have identical compositions
D. The balance error necessarily cancels all biological variation

59 Which observation most strongly suggests that protein contamination remains in a dried egg-lipid extract?

Isolation of egg lipids Hard
A. The residue dissolves readily in chloroform and leaves no visible film
B. The residue mass decreases after complete solvent evaporation
C. The extract produces a sharp single band for every lipid standard
D. The residue is unusually dark, nonuniform, and poorly soluble in nonpolar solvent

60 A protocol calls for transferring the organic phase with a glass Pasteur pipette while avoiding the interface. Why is this precaution especially important for egg-yolk extractions?

Isolation of egg lipids Hard
A. The interface chemically converts chloroform into a lipid solvent
B. The interface contains only pure water and no biological material
C. The interface can contain emulsified lipids and denatured yolk proteins
D. The interface prevents all evaporation from the organic phase
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