Ch 14Digestion and Absorption — Class 11 Biology, concept-first.

Every living organism, from the simplest single-celled protist to a complex multicellular animal, must take in nutrients from its surroundings to survive.

The human alimentary canal is a single, continuous, muscular tube some eight to ten metres long in the adult when fully stretched out, though it is coiled compactly to fit inside the abdominal and tho…

Humans, like other mammals, are heterodont — they possess more than one distinct type of tooth within the jaw, each shaped for a different mechanical task in reducing food to a size and texture suitab…

Digestion depends not only on the mechanical breakdown of food but, far more importantly, on a sequence of chemical secretions poured into the alimentary canal at successive points along its length.

Digestion is not simply a matter of the right enzyme meeting the right substrate at the right time; food must also be actively and continuously moved along the alimentary canal, and mixed thoroughly w…

The chemical breakdown of food into absorbable molecules is carried out by a series of digestive enzymes, each secreted at a particular point along the alimentary canal and each specific to one class…

Carbohydrates form the largest single component of a typical diet, chiefly as starch (in cereals, pulses and root vegetables) together with smaller amounts of the disaccharides sucrose (cane sugar) an…

Dietary protein — from pulses, milk, eggs, meat and fish — must be broken down all the way to its constituent amino acids before it can be absorbed, since intact protein molecules and even most peptid…

Fat digestion differs fundamentally from the digestion of carbohydrate and protein in one crucial respect: fat is not water-soluble, whereas the digestive enzymes that must act on it are dissolved in…

Not every component of the food that is eaten can be digested and absorbed. A typical diet, particularly one rich in vegetables, fruit and whole grains, contains a substantial amount of indigestible p…

The digestive system described through this chapter functions correctly only when it is both supplied with an adequate and balanced diet and free of disease or dysfunction in any of its component orga…