Unit 4: Isolation of Organelles - Practice Quiz

1 Which plant organelle is isolated in this experiment?

2 Which plant tissue is commonly used to isolate chloroplasts?

3 What is the main purpose of homogenizing leaf tissue?

4 Which instrument is commonly used to homogenize leaf tissue?

5 Why is an isolation buffer used during chloroplast isolation?

6 Which condition is usually maintained to reduce chloroplast damage?

7 What is the purpose of filtering the homogenate?

8 Which technique separates cell components based partly on their size and density?

9 What is the pellet formed during centrifugation?

10 Where are chloroplasts usually found after centrifugation?

11 What is the liquid above the pellet called?

12 Why should centrifuge tubes be balanced?

13 Which pigment gives chloroplasts their characteristic green color?

14 Which structure surrounds a chloroplast?

15 What is the main role of chloroplasts in plant cells?

16 Why should isolated chloroplasts be handled gently?

17 Which observation suggests that a chloroplast fraction contains chlorophyll?

18 What should be done with the supernatant when the chloroplast pellet is needed?

19 Which method can be used to examine isolated chloroplasts?

20 What is the purpose of resuspending the chloroplast pellet?

21 Why is an ice-cold isolation buffer commonly used during chloroplast isolation?

22 What is the main purpose of using an isotonic buffer during chloroplast isolation?

23 A leaf homogenate is filtered before centrifugation. What is the primary purpose of this step?

24 During differential centrifugation, intact chloroplasts are mainly separated because they differ from soluble cytoplasmic components in their:

25 If the centrifugation speed is too low during the chloroplast pelleting step, what is the most likely result?

26 Why should leaf tissue be homogenized gently rather than vigorously during chloroplast isolation?

27 A chloroplast preparation appears brown rather than green. Which problem is most likely indicated?

28 Which observation most directly suggests that isolated chloroplasts remain intact?

29 Why might sorbitol or sucrose be included in a chloroplast isolation buffer?

30 A researcher accidentally uses distilled water instead of an isotonic buffer. What is the likely effect on chloroplasts?

31 What is the main advantage of separating chloroplasts on a density gradient rather than using only one centrifugation step?

32 If a chloroplast pellet is accidentally discarded with the supernatant, what is the most direct consequence?

33 Why is chlorophyll absorbance sometimes measured in an isolated chloroplast preparation?

34 A sample has high chlorophyll content but poor photosynthetic activity. Which explanation is most plausible?

35 Which modification would most likely reduce contamination of a chloroplast pellet by cell debris?

36 Why should the supernatant be removed carefully after chloroplast centrifugation?

37 A buffer contains a reducing agent during chloroplast isolation. What is its likely purpose?

38 Which result would best indicate that a chloroplast preparation contains substantial broken chloroplasts?

39 A student wants maximum chloroplast yield but is less concerned about purity. Which approach is most appropriate?

40 Why are chloroplast isolation procedures often performed under dim or indirect light?

41 A leaf homogenate is centrifuged first at low speed to remove cell debris and nuclei, followed by a higher-speed spin intended to pellet chloroplasts. Which change would most directly improve chloroplast recovery without greatly increasing nuclear contamination?

42 Why is an isotonic sorbitol or sucrose-containing isolation buffer essential when isolating intact chloroplasts from leaf tissue?

43 An isolated chloroplast preparation has high chlorophyll recovery but very low ferricyanide-dependent oxygen evolution. Which explanation is most consistent with these results?

44 A researcher wants to distinguish intact chloroplasts from broken chloroplasts after isolation. Which assay is most directly informative?

45 During homogenization, a sample is processed for twice as long as recommended. The final pellet is green but contains many small membrane fragments. What is the most likely primary cause?

46 Why are chloroplast isolation procedures commonly performed at low temperature and with rapid handling?

47 A chloroplast preparation is contaminated with mitochondria. Which additional purification strategy would best exploit the difference in organelle buoyant density while preserving intact chloroplasts?

48 A protocol uses EDTA in the isolation buffer, but the preparation is intended for assays requiring intact chloroplast envelopes. Which concern is most appropriate?

49 A green band appears at an unexpected interface in a density gradient. Microscopy shows mostly small vesicles rather than intact chloroplasts. Which interpretation is most defensible?

50 Which result would provide the strongest evidence that a chloroplast fraction is both enriched and relatively pure?

51 A protocol gives poor chloroplast yield from mature leaves but acceptable yield from young leaves. Which tissue property most plausibly explains the difference?

52 If the homogenate is filtered through a mesh that is too fine, what trade-off is most likely?

53 A student resuspends the chloroplast pellet by vigorous vortexing and obtains low intactness in the final sample. Which modification is most appropriate?

54 A preparation has low total chlorophyll recovery but a high proportion of intact chloroplasts among the recovered particles. Which procedural change would most likely increase yield while preserving quality?

55 Why can excessive centrifugation force reduce the quality of an isolated chloroplast fraction even when it increases the apparent pellet size?

56 A chloroplast suspension shows rapid loss of photosynthetic activity only when illuminated during storage. Which control is most important for identifying the cause?

57 A chloroplast fraction exhibits substantial activity of a cytosolic enzyme marker. Which conclusion is most justified before changing the isolation protocol?

58 A researcher compares two protocols. Protocol A gives 80% intactness and 40% chlorophyll recovery; Protocol B gives 50% intactness and 70% recovery. For an assay requiring intact envelope transport, which protocol is preferable?

59 A green pellet is observed after the first low-speed centrifugation, indicating that chloroplasts sedimented with the debris. Which adjustment is most rational as a first test?

60 Which observation most strongly suggests osmotic rupture rather than mechanical fragmentation during chloroplast isolation?