Why do ventricles have thicker walls than atria?

$(a)$ Name the hormone which is released into the blood when its sugar level rises. Name the organ which produces this hormone and its effect on blood sugar level. Also,mention the digestive enzymes secreted by this organ with one function of each.
$(b)$ Explain the need for chemical communication in multicellular organisms.

During the respiration of an organism $A$,one molecule of glucose produces two $ATP$ molecules,whereas in the respiration of another organism $B$,one molecule of glucose produces $38$ $ATP$ molecules.
$(a)$ Which organism is undergoing aerobic respiration?
$(b)$ Which organism is undergoing anaerobic respiration?
$(c)$ Which type of organism,$A$ or $B$,can convert glucose into alcohol?
$(d)$ Name one organism which behaves like $A$.
$(e)$ Name two organisms which behave like $B$.

Which is the correct sequence of air passage during inhalation?

Differentiate between an autotroph and a heterotroph.

$(a)$ Name the following:
$(i)$ Part in which urine is produced.
$(ii)$ Part which stores the urine.
$(iii)$ Part which connects $(i)$ and $(ii)$.
$(iv)$ Part from which urine is passed out.
$(b)$ Name the factors on which the amount of water reabsorbed along the tubular part of the nephron depends.