The blood leaving the tissues becomes richer in

$(a)$ $A$ 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.

Explain the three pathways of breakdown of glucose in living organisms.

Choose the function of the pancreatic juice from the following:

The volume of glomerular filtrate produced is $180 \, L$ per day,but the volume of urine excreted is just $1-2 \, L$. Give a suitable reason for this statement.

$(a)$ What is the nature of food coming from the stomach?
$(b)$ Mention any two structural modifications in the small intestine which help in the absorption of food.