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

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

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

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

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

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

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

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

Isolation of egg lipids Easy
A. It changes lipids into sugars
B. It creates new proteins
C. It stains the eggshell
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. Vortex mixer
B. Test-tube rack
C. Balance pan
D. Thermometer

7 What is centrifugation used for during lipid isolation?

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

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

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

9 What does decanting mean in a lipid isolation procedure?

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

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 keep the phases separate
C. To dissolve the glass
D. To increase the sample temperature

11 Which class of lipid is abundant in egg yolk?

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

12 What is lecithin commonly classified as?

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

13 What is the purpose of filtering an egg extract?

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

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

Isolation of egg lipids Easy
A. To destroy all lipid molecules
B. To produce more solvent
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. 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 freeze immediately
B. It may form a protein
C. It may be flammable
D. It may become magnetic

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

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

18 Which property makes many lipids different from water?

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

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

Isolation of egg lipids Easy
A. The number of tube labels
B. The size of the pipette tip
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 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 increases the density of proteins
C. It dissolves lipids more effectively than water
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 permanently remove all water from the yolk
C. To separate cholesterol from every phospholipid
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. Mix the layers continuously until they disappear
B. Discard both layers and repeat with water
C. Heat the mixture until the layers become solid
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. Limited mixing is required because solvents cannot contact suspended material
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. Add a small amount of saturated salt solution
B. Add concentrated protein solution
C. Increase shaking speed immediately
D. Add a large volume of distilled water

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

Isolation of egg lipids Medium
A. To neutralize all phospholipid head groups
B. To hydrolyze triglycerides into glycerol
C. To increase the water content of the extract
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 translucent or greasy residue remains
B. A clear gas-filled tube is produced
C. A blue solution forms without a reagent
D. A crystalline salt disappears completely

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

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

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. Discard the sample before separating the phases
B. Perform a second extraction of the remaining sample
C. Use less solvent and shorten the mixing time
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 container mass determines the yolk protein sequence
C. The measurement prevents all solvent from evaporating
D. The lipid mass can be calculated by subtracting container mass

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 pale and dissolves readily in the lipid solvent
B. The residue is unusually dark and does not dissolve in the lipid solvent
C. The extract forms a separate organic layer before evaporation
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 prevent the organic solvent from having any density
B. They always evaporate before the solvent is added
C. They convert phospholipids directly into carbohydrates
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 doubles because both phases contain identical lipids
B. The solvent automatically changes into a drying agent
C. The lipid yield decreases and more water-soluble material is collected
D. The sample becomes pure lipid after additional water is added

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. Measure the pH of the solvent after centrifugation
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 increase the boiling point of the organic solvent
C. To compact insoluble debris and clarify the extract
D. To convert neutral lipids into charged molecules

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. Repeating the extraction with fresh solvent
C. Allowing the solvent to evaporate completely
D. Using a preweighed dry collection container

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. Residual water would falsely increase the measured mass
C. Dry glass prevents phospholipids from dissolving
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 is more nonpolar than triglycerides
B. Water poorly dissolves most neutral lipids
C. Water destroys the yolk before lipid extraction
D. Water prevents all phospholipids from existing

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. Use equal sample masses and identical extraction conditions
C. Estimate residue mass by visual appearance only
D. Evaporate one sample while cooling another

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 original unfractionated homogenate
C. The lower chloroform-rich phase
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 a small amount of salt solution and centrifuge
B. Add concentrated acid to hydrolyze all lipids
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 selectively precipitates cholesterol from solution
C. It converts triglycerides into fatty acids
D. It increases the density of the aqueous phase

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. Greater carryover of water-soluble contaminants
C. Improved recovery of all hydrophobic lipids
D. Selective removal of cholesterol from the organic phase

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

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 increase the melting point of its triglycerides
C. To hydrolyze phospholipids before they enter the solvent
D. To remove cholesterol by mechanical precipitation

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. Cholesterol crystals only
B. Short-chain alkanes
C. Highly unsaturated fatty-acid-containing lipids
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. Both phases should be discarded because lipids remain insoluble
B. The lower chloroform-rich phase should generally be collected
C. The interface should be discarded because it contains all lipids
D. The aqueous phase should be boiled to release triglycerides

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. Increase extraction temperature above the solvent boiling point
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. Water cannot form hydrogen bonds with proteins
B. All neutral lipids are intrinsically insoluble in chloroform
C. Amphipathic phospholipids and denatured proteins stabilize an emulsion
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 prevent the stationary phase from adsorbing lipids
B. To convert all lipids into charged ions
C. To increase the boiling point of the mobile phase
D. To produce a concentrated, narrow application band

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

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 standard was completely destroyed before extraction
C. The organic solvent contains no dissolved contaminants
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 identifies the fatty-acid composition without chromatography
B. It estimates residue contributed by solvents and laboratory materials
C. It increases the amount of lipid extracted from the yolk
D. It converts phospholipids into measurable carbohydrates

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. Some amphipathic phospholipids partition into the aqueous or interfacial fraction
B. Chloroform is chemically transformed into methanol
C. Neutral triglycerides become ionic in pure water
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. Normalize yield to the mass of the original yolk sample
C. Measure only the volume of the organic phase
D. Use a different extraction solvent for every 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. Esterified triglycerides are converted into soaps and glycerol
C. Cholesterol is converted directly into glucose
D. All fatty acids are volatilized at room temperature

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. The balance error necessarily cancels all biological variation
C. The extracted lipids must have identical compositions
D. Identical processing proves the absolute lipid mass is accurate

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 residue dissolves readily in chloroform and leaves no visible film
C. The residue is unusually dark, nonuniform, and poorly soluble in nonpolar solvent
D. The extract produces a sharp single band for every lipid standard

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