Digestion within a digestive tract is (a) Incomplete (b) Extracellular (c) The same as absorption (d) An irreversible process
Hint: In the animal kingdom the digestive tract is mainly divided into the incomplete or complete digestive tract in which the incomplete digestive tract consists of a single opening while the complete digestive tract has two openings. It is also divided based on the digestion of food outside or inside the cell where the digestion within the digestive tract takes place outside the cell.
Complete Answer: Digestion within the digestive tract is a type of Extracellular digestion where the food gets broken down into smaller absorbable components chemically and this type of digestion takes place outside the cell. The organism which shows Extracellular digestion has a more advanced alimentary canal as compared to the gastrovascular cavity for digestion. After the breakdown of food, the nutrient gets absorbed into the bloodstream with the help of gut epithelia and undigested material gets removed from the anus. It is a complex type of digestion that takes place with the help of glands and organs. It is most common in fungi, higher algae and some animal groups.
Additional Information: The incomplete digestive tract consists of a single opening where the mouth shows dual function like intake of food and also the elimination of faeces. It is common in cnidarian and flatworm whereas in the complete digestive tract the intake of food takes place by mouth and elimination of faeces takes place with the help of the anus. Intracellular digestion takes place inside the food vacuole of a cell where the food gets broken down into smaller pieces with the digestive enzyme present inside the lysosome.
So, the correct answer is option b) 'Extracellular'.
Note: Extracellular digestion helps the small living organism to feed on higher organisms like saprophytic fungi which feed on the dead and decaying matter of plant and animal, where the digestive enzyme of higher organism get secreted by fungi which further broken down into simple and soluble material.