Ivan Petrovich Pavlov (b 1849) - a physiologist most famous for his work on the “conditioned reflex” for which he won the Nobel Prize in 1904…. His work started originally as an examination of the regulation of digestive enzymes and contributed greatly to our understanding of the digestive

system.

Digestion of food items is quite varied by species:

Most organisms have ways to metabolize

CarbohydratesLipids & FatsProteinsNucleic Acids

However, some organisms have some specialized materials that they can digest as well.

Waxes – indigestible in humans and most other organisms. But in organisms that can digest waxes the caloric value is similar to that of fats and oils.

The Wax Moth – which can feed on and consume waxes in the environment, such as in a bee hive (honeycomb).

The Honey Guide (from the southern African continent) – a bird that has the ability to digest wax due to symbiotic bacteria in its gut that will break down the wax.

Wood as a food?

Wood occurs in a variety of different forms, and as such it can be of caloric value to some species.

The major constituant of wood is CELLULOSE, and it occurs in wood as well as in many other structural elements in a variety of plants.

The common garden snail can digest cellulose from wood and other plant matter. However, it does not appear to have its own digestive enzymes capable of breaking down cellulose. Instead, it uses a variety of micro-organisms to digest the celulose.

After further study, it now appears that virtually all organisms that can digest cellulose, do so through the aid of bacteria. The only exception appears to be the silverfish.

The silverfish – an insect that appears to be able to digest cellulose WITHOUT the aid of micro-organisms to break down the material.

Ruminants – mammals that digest plant-based food by initially softening it within the animal's first stomach, then regurgitating the semi-digested mass, known as “cud”, and chewing it again.

The process of re-chewing the cud to further break down plant matter and stimulate digestion is called "ruminating".

Ruminating mammals include cattle goats, sheep, giraffes, bison, yaks, water buffalo, deer, camels, alpacas, llamas, wildebeest, and antelope.

Halocynthia – a tunicate…. commonly called the “red sea squirt”

The reason for the change in optimum ezymatic temperature appears to be an effect only of the length of the experiment. Therefore, it is most likely that the 50 hour mark is showing a more accurate representation of optimum temperatures in this enzyme in this species in nature.

Why would this be so???

The effects of changes in diet on rats. The major change is seen in the actual caloric content of the food. The top graph shows food that has lowered caloric value per gram whereas the top shows increased caloric value per gram.

In the experimental section, the dashed line is showing the energy content of the food consumed per day whereas the solid line is showing weight of the food consumed.

Can you make correlations to human dietary choices?

Lafayette B. Mendel – biochemist who discovered numerous properties of vitamins and proteins that has developed into our modern concept of nutrition. His

work was accomplished between 1910 and 1930.

The Food Pyramid

A two-headed calf born possibly from exposure to an endocrine disrupting compound.