Question

Modified part of___________ is the gizzard of the grain eater birds.
a)Oesophagus
b)proventriculus
c)true stomach
d)small intestine

Answer 1

Hint: In the birds, the digestive system consists of a modified part of the esophagus known as the crop and the modified part of the stomach and the small intestine which opens into the cloaca. The crop is the modified part of the esophagus present in the birds.

Complete answer:
 The digestive system of the bird consists of the esophagus crop, proventriculus, the gizzard, small intestine, large intestine, and the anal opening. The crop is the modified part of the esophagus and is used to store the food for the later use. The modified part of the stomach is also known as the gizzard. The proventriculus is a part of the stomach where the digestive juices are released and the process of digestion starts. In the gizzard of the birds, the food is grinded down to small components. The stones and pebbles eaten by the birds help in the grinding of food present in the stomach.

Additional Information: The crop in the birds acts as a storage organ for food materials. It helps in sending the food material slowly to the stomach so that food can settle down easily. The crop is also used to feed the young ones. Birds also produce crop milk. The food is passed onto the proventriculus to the gizzard and major digestion occurs in the stomach. The kidney of the birds secretes the waste products and transfers into the small intestine. The undigested food gets mixed up in the small intestine with the waste of the kidneys and then is excreted out through the anal opening.
So, the answer is ‘true stomach’.

Note: The birds have only one opening for the excretion of the waste material. They do not have a separate opening for the urine excretion which leads to the mixing up of food and urine waste product in the small intestine.