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

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

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

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 freeze the sample
B. To remove the egg color
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 dissolves selected lipids
B. It changes lipids into sugars
C. It stains the eggshell
D. It creates new proteins

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. Vortex mixer
D. Thermometer

7 What is centrifugation used for during lipid isolation?

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

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

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

9 What does decanting mean in a lipid isolation procedure?

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

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

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

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 increase solvent acidity
B. To create additional lipids
C. To measure the sample mass
D. To remove insoluble particles

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

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

15 Which safety practice is important when handling organic solvents?

Isolation of egg lipids Easy
A. Use appropriate protective equipment
B. Store the solvent beside food
C. Heat the solvent in an open hand
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 become magnetic
B. It may form a protein
C. It may be flammable
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 translucent greasy spot
D. A dry paper tear

18 Which property makes many lipids different from water?

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

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 mass of the lipid residue
C. The color of the laboratory wall
D. The number of tube labels

20 Why should the sample and extraction containers be labeled?

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

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 dissolves lipids more effectively than water
C. It increases the density of proteins
D. It prevents all solvent evaporation

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

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

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

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

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

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

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

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

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

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. The hood changes the solvent into a nonpolar compound
C. Ventilation prevents the lipids from becoming phosphates
D. Many organic solvents produce harmful or flammable vapors

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

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

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

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

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

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 lipid yield doubles because both phases contain identical lipids
C. The sample becomes pure lipid after additional water is added
D. The solvent automatically changes into a drying agent

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

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

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

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

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

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

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

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

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 prevents all phospholipids from existing
B. Water destroys the yolk before lipid extraction
C. Water poorly dissolves most neutral lipids
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. Use different solvent volumes for every sample
B. Estimate residue mass by visual appearance only
C. Evaporate one sample while cooling another
D. Use equal sample masses and identical extraction conditions

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 interfacial protein precipitate
B. The original unfractionated homogenate
C. The lower chloroform-rich phase
D. The upper aqueous methanol-rich phase

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

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

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

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

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

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

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

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

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 interface should be discarded because it contains all lipids
C. Both phases should be discarded because lipids remain insoluble
D. The lower chloroform-rich phase should generally be collected

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

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

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. Cholesterol forms a permanent aqueous salt
C. All neutral lipids are intrinsically insoluble in chloroform
D. Water cannot form hydrogen bonds with proteins

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

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. Use a permanently wet development chamber
B. Replace the lipid solvent with distilled water
C. Apply a smaller amount of a more dilute extract
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 standard was completely destroyed before extraction
B. The egg yolk contains exactly 72% lipid by mass
C. The extraction and measurement procedure has incomplete recovery
D. The organic solvent contains no dissolved contaminants

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

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

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. Water permanently destroys all sterol molecules
C. Chloroform is chemically transformed into methanol
D. Some amphipathic phospholipids partition into the aqueous or interfacial fraction

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

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

Isolation of egg lipids Hard
A. Cholesterol is converted directly into glucose
B. Phospholipids become insoluble in every organic solvent
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. Identical processing proves the absolute lipid mass is accurate
B. The balance error necessarily cancels all biological variation
C. Relative comparisons may be useful, but absolute yields are uncertain
D. The extracted lipids must have identical compositions

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

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

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