Explanation:

- Yeast is a microorganism from the fungi kingdom, often used in baking and brewing. It ferments sugars, producing carbon dioxide and alcohol. This feature makes it the 'sugar eating fungus'.

Yeast -

- Ketchup doesn't involve fermenting sugar. It's a condiment made from tomatoes, vinegar, and spices.

- Vinegar is an acidic liquid produced from the fermentation of ethanol by acetic acid bacteria, not from fungi.

- Baking powder is a leavening agent used in baking. It releases carbon dioxide once mixed with liquid but doesn't involve living organisms like yeast.

Yeast is indeed what you were thinking, and it is correctly referred to as the 'sugar eating fungus'.