$(a)$ $A$ product is formed in our muscles due to the breakdown of glucose when there is a lack of oxygen. Name the product and also mention the effect of the build-up of this product.
$(b)$ Differentiate between fermentation in yeast and aerobic respiration on the basis of end products formed.

(N/A) The product formed is lactic acid.
The accumulation of lactic acid in the muscles leads to muscle cramps.
$(b)$ In yeast,fermentation results in the production of ethanol and carbon dioxide. In contrast,aerobic respiration results in the production of carbon dioxide and water. Additionally,the amount of energy $(ATP)$ released during fermentation is significantly lower than that released during aerobic respiration.