Question

Select the correct sequence of organs in the alimentary canal of cockroach starting from the mouth.
A) Pharynx \to $ Oesophagus$ \to $Crop $ \to $ Gizzard$ \to $ ileum $ \to $Colon$ \to $Rectum B) Pharynx \to $Oesophagus$ \to $Gizzard$ \to $crop$ \to $ileum$ \to $colon$ \to Rectum C) Pharynx $$$$$ \to Oesophagus$\to$ Gizzard$\to$ ileum$\to$ crop$\to$ colon$\to$Rectum
D) Pharynx $$$$$ \to $Oesophagus$ \to $ileum$ \to $Crop$ \to $Gizzard$ \to $Colon$ \to $ Rectum

Answer 1

Alimentary canal of a cockroach is divided into three parts; foregut, midgut and hindgut and along with it, there are two pairs of salivary gland present in them.

Complete answer:
i. Foregut
The food particle is ingested with the help of the mouth which leads to a small tube-like structure called the pharynx. It leads to another tube-like structure which is quite large called the oesophagus. This opens into a large sac-like structure called crop (Here, the food is stored prior to digestion). This leads to a small cup-like structure present beneath it, known as the gizzard or proventriculus. A gizzard is lined by thick cuticular layer and inside this layer, six chitinous teeth-like structures are present, which helps in cutting, grinding and mastication of food. In fact, the whole foregut is lined by a cuticular layer. At the junction of foregut and midgut, there are 6-8 thread-like structures present called hepatic cecum which secretes digestive enzymes.
ii. Midgut
It is the coiled tube-like structure and it is the main site of digestion. At the junction of midgut and hindgut, 100-150 fine thread-like structures are present called malpighian tubules. They act as the excretory organ.
iii. Hindgut
Their hindgut is divided into three parts; a narrow Ileum, a broad colon and sac-like rectum. The digested food is then discharged from the rectum.
Hence, the correct answer is option A.

Note: Students may get confused between ileum $\&$ilium and between malpighian tubule $\&$malpighian body.
Ileum: It is the part of the alimentary canal which helps in further digestion of food coming from the stomach. It is also involved in the absorption of nutrients like fat, carbohydrates and proteins.
Ilium: It is a hip bone divided into three-parts; ilium, ischium and pubis. Malpighian tubule: It is the excretory organ, it helps in the removal of nitrogenous substances.
Malpighian body: It is involved in the excretion in mammals. It is formed by the bowman capsule enclosing the glomerulus.