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Difficulty: MediumIdentifying Core Claims and Hypotheses

### Origin of Eukaryotic Organelles

Eukaryotic cells contain membrane-bound organelles, such as mitochondria, that are absent in prokaryotes. Two hypotheses have been proposed to explain the origin of these organelles.

Hypothesis 1
Mitochondria evolved from free-living, aerobic prokaryotes that were engulfed by a larger, anaerobic host prokaryote. Instead of being digested, the engulfed cells entered a symbiotic relationship with the host cell. Over time, the engulfed prokaryotes lost their independent functions and became dependent organelles.

Hypothesis 2
Eukaryotic organelles developed through the invagination (folding inward) and subsequent pinching off of the ancestral host cell's own plasma membrane. This compartmentalization isolated specific enzymes and genetic material, allowing specialized functions to evolve within separate membrane-bound structures.

According to Hypothesis 2, eukaryotic organelles originated directly from which of the following cellular components?

  1. The plasma membrane of the ancestral host cellAnswer
  2. B
    Free-living prokaryotes that were engulfed by a host cell
  3. C
    The nuclear membrane of a pre-existing eukaryotic cell
  4. D
    Lipid droplets suspended in the cytoplasm of a prokaryote

Answer

The plasma membrane of the ancestral host cell
Hypothesis 2 explicitly states that organelles developed through the folding inward (invagination) and subsequent pinching off of the ancestral host cell's own plasma membrane. Therefore, according to Hypothesis 2, the organelles originated from the plasma membrane of the ancestral host cell.

Step-by-Step Solution

1
Locate the description of Hypothesis 2 in the passage.
Identify the mechanism proposed by Hypothesis 2 for the origin of eukaryotic organelles.
To understand the core claim of Hypothesis 2.
2
Analyze the text of Hypothesis 2 to find where it states organelles came from.
The text states that organelles developed through the folding inward (invagination) and pinching off of the ancestral host cell's own plasma membrane.
To identify the specific cellular component that served as the origin.

Key Concept

Identifying Core Claims and Hypotheses
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Topics

Identifying Core Claims and Hypotheses

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