Correct Option
The correct option is (c) 1 and 3 only.
Explanation
Yeast is a unicellular eukaryotic fungus capable of facultative anaerobic respiration. It plays a critical role in fermentation processes by breaking down carbohydrates in the absence of oxygen.
Statement-wise Analysis
- Statement 1 is Correct: Yeasts are single-celled (unicellular) organisms belonging to the Kingdom Fungi. Unlike many other fungi which are multicellular and filamentous, yeast exists as individual cells.
- Statement 2 is Incorrect: When yeast respires anaerobically (fermentation), it breaks down glucose to produce ethanol (alcohol) and carbon dioxide. Lactic acid is produced during anaerobic respiration in human muscle cells or by bacteria such as Lactobacillus, not by yeast.
- Statement 3 is Correct: Yeast can survive and generate energy in the absence of air (oxygen). This ability to perform anaerobic respiration is the basis for its use in the baking (CO2 raises dough) and brewing (ethanol production) industries.
Key Takeaway: The anaerobic respiration of yeast is known as alcoholic fermentation (yielding ethanol and CO2), which is distinct from lactic acid fermentation (yielding lactic acid) seen in muscle cells and curd-forming bacteria.