Yeast are

Options

A. a) aerobic and prokaryotic
B. b) anaerobic and prokaryotic
C. c) facultative aerobic and eukaryotic
D. d) facultative anaerobic and eukaryotic

Answer

### Step-by-Step Solution:

1. **Understanding Yeast**: Yeasts are unicellular organisms that belong to the kingdom Fungi. They are classified as eukaryotic because their cells contain a nucleus and other organelles.

2. **Economic Importance**: Yeasts play a significant role in various fermentation processes, which are crucial for producing food products such as bread and alcoholic beverages (e.g., ethanol).

3. **Respiration Characteristics**: Yeasts are primarily facultative anaerobes. This means they can perform both aerobic respiration (using oxygen) and anaerobic respiration (without oxygen). When oxygen is available, they utilize aerobic respiration; otherwise, they can switch to anaerobic respiration.

4. **Analyzing Options**:
- **Option A**: "Aerobic and prokaryotic" - This is incorrect because yeasts are eukaryotic, not prokaryotic.
- **Option B**: "Anaerobic and prokaryotic" - This is also incorrect for the same reason; yeasts are eukaryotic.
- **Option C**: "Facultative aerobic and eukaryotic" - This is correct as it accurately describes yeast.
- **Option D**: "Facultative anaerobic" - This is incorrect because yeasts can switch to aerobic respiration when oxygen is present.

5. **Conclusion**: The correct classification of yeast is "facultative aerobic and eukaryotic."

### Final Answer:
Yeast are facultative aerobic and eukaryotic organisms.

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