1a: The Theory of Endosymbiosis proposes the origin of both mitochondria and chloroplasts in modern photosynthesizing eukaryotic cells. What was proposed to have occurred in the evolution of these two organelles?  Select all that apply.  a. Mitochondria are part of the endomembrane system and as such created by infoldings of the plasma membrane. b. Photosynthetic cells were engulfed (ingested) by the host cell. c. Chloroplasts are part of the endomembrane system and as such created by infoldings of the plasma membrane. d. Aerobic bacteria were engulfed (ingested) by the host cell.
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1a: The Theory of Endosymbiosis proposes the origin of both mitochondria and chloroplasts in modern photosynthesizing eukaryotic cells. What was proposed to have occurred in the evolution of these two organelles?
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Select all that apply.ÂÂ
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a. Mitochondria are part of the endomembrane system and as such created by infoldings of the plasma membrane.
b. Photosynthetic cells were engulfed (ingested) by the host cell.
c. Chloroplasts are part of the endomembrane system and as such created by infoldings of the plasma membrane.
d. Aerobic bacteria were engulfed (ingested) by the host cell.
1b: Which statement is not true of mitochondria and chloroplasts?
Select one:
a. Both mitochondria and chloroplasts contain DNA.
b. Mitochondria are only found in animal cells, and chloroplasts are only found in plant cells.
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c. Ribosomes are present in both mitochondria and chloroplasts.
d. They grow and divide independently in the cell.
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1c: Which if the following apply to lysosomes?
Select one or more:
a. Lysosomes are only found in plant and fungal cells. They are not found in animal cells.
b. The pH of the lysosome lumen is maintained via proton pumps in the membrane.
c. Lysosomes are produced from merging vesicles which bud from mitochrondria.
d. Lysosomes have a single membrane that is continuous with the nuclear membrane.
1d: What is an important role of the Golgi
Select one:
a. It is studded with ribosomes for protein synthesis. Proteins move into the lumen and are then sent to the smooth ER.
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b. Receives vesicles from the ER containing protein destined for export from the cell
c. Lipid synthesis
d. Connects with the nuclear membrane to receive mRNA destined for ribosomes.
The Correct Answer and Explanation is :
1a: The Theory of Endosymbiosis
Correct answers:
b. Photosynthetic cells were engulfed (ingested) by the host cell.
d. Aerobic bacteria were engulfed (ingested) by the host cell.
Explanation:
The endosymbiosis theory explains the origin of mitochondria and chloroplasts in eukaryotic cells. According to this theory, mitochondria originated when ancestral eukaryotic cells engulfed aerobic bacteria. Similarly, chloroplasts arose when ancestral eukaryotic cells engulfed photosynthetic cyanobacteria. Both events involved symbiotic relationships where the engulfed cells provided energy (via aerobic respiration or photosynthesis), while the host cell provided nutrients and protection. Over time, these engulfed bacteria evolved into organelles. Mitochondria and chloroplasts are not part of the endomembrane system; they have double membranes, their own DNA, and replicate independently, supporting their endosymbiotic origin.
1b: Which statement is not true of mitochondria and chloroplasts?
Correct answer:
b. Mitochondria are only found in animal cells, and chloroplasts are only found in plant cells.
Explanation:
This statement is incorrect because mitochondria are present in almost all eukaryotic cells, including both plant and animal cells, as they are the sites of cellular respiration. Chloroplasts are found in photosynthetic organisms like plants and algae. Both organelles share features supporting their endosymbiotic origin: they contain their own DNA, ribosomes, and grow/divide independently within the cell.
1c: Lysosomes
Correct answers:
b. The pH of the lysosome lumen is maintained via proton pumps in the membrane.
Explanation:
Lysosomes are acidic organelles responsible for breaking down cellular waste, macromolecules, and pathogens. The lumen’s low pH is actively maintained by proton pumps, which transport H⁺ ions into the lysosome. They have a single membrane but are not continuous with the nuclear membrane. Lysosomes are primarily found in animal cells, not plant cells.
1d: Important role of the Golgi
Correct answer:
b. Receives vesicles from the ER containing protein destined for export from the cell.
Explanation:
The Golgi apparatus modifies, sorts, and packages proteins received from the rough endoplasmic reticulum (ER) for export or transport to other parts of the cell. It plays a central role in the secretory pathway. Ribosome-studded protein synthesis occurs in the rough ER, not the Golgi. Lipid synthesis occurs in the smooth ER.