Lack of oxygen in muscles often leads to cramps among cricketers. This results due to

What role does bile play in digestion?

$(a)$ Draw the structure of a nephron and label the following on it: Glomerulus,Bowman's capsule,Renal artery,Collecting duct.
$(b)$ What happens to glucose that enters the nephron along with the filtrate?

What is the advantage of having a four-chambered heart?

Give reasons for the following:
$(a)$ Rings of cartilage are present in the trachea.
$(b)$ Mucus is secreted along with $HCl$ in the stomach.

$(a)$ $A$ 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.