The chemical process involved in the removal of harmful metabolic wastes from the body is called excretion.

$(a)$ $A$ 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.

$(a)$ What is the role of mucus in the stomach?
$(b)$ How is the exit of food from the stomach regulated?
$(c)$ Where does food enter from the stomach?

State the function of the following in the alimentary canal:
$(i)$ Liver $(ii)$ Gall bladder $(iii)$ Villi.

Choose the correct path of urine in our body.

Name the components of blood which transport:
$(i)$ Food,carbon dioxide and nitrogenous wastes
$(ii)$ Oxygen