The purpose of digestion is to break down the food ingested, into simpler substances or compounds that can be absorbed into the body and made available for cell function. Large insoluble food molecules are converted into small, soluble ones that can be transported into the blood stream and delivered to cells throughout the body.
2. What is the name given to mammals that eat only meat?
Mammals that eat only meat are called carnivores. E.g. dogs, cats
3. What is the name given to mammals that eat only plant material?
Mammals that eat only plant material are called herbivores. E.g. cows, koalas
4. What is the difference between a fore-gut fermenter and a hind-gut fermenter? Give examples of mammals in each category.
In foregut fermenters, microbial fermentation takes place in the foregut, known as the rumen in ruminants. The stomach of the ruminant consists of four chambers which are the rumen, reticulum, omasum and abomasum (‘true stomach’). The microbes in the rumen produce sugars and short chain fatty acids during the digestion of cellulose, using most of the dietary glucose and protein from the plant material. They then regurgitate the ‘cud’ from the rumen and continue chewing in order to increase the surface area and allow for further microbial fermentation. By the time the ingested food reaches the abomasum, majority of the nutrients have been metabolised and some of the microbes in the rumen have been ingested, providing amino acids for the host and hence increasing their nutrient uptake. Foregut fermenters digest food more efficiently than hind gut fermenters as fermentation takes place before digestion which allows them to extract maximum nutrition from their diet. Examples of fore-gut fermenters are cattle, cows and sheep.
Mammals cannot digest cellulose as they lack the essential enzymes, especially cellulose
Microbial fermentation is a slow process and requires times and space in order to occur
In majority of herbivores, the large intestine is expanded to house microorganisms
Downside of hindgut fermentation is that many of the by products of fermentation cannot be absorbed so far down the alimentary canal Cows and deers are fore-gut fermenters and use symbiotic bacteria (microflora) for the digestion of cellulose(e.g. e.g. elephant, horse, guinea pig, rabbit, herbivorous reptiles, e.g. tortoise and herbivorous birds)
In hind gut fermenters; microbial fermentation takes place in an enlarged caecum, which accounts for its longer overall digestive tract. Since microbial fermentation is a slow process and requires time and space in order to occur, its caecum is much larger and longer than that of the foregut fermenters in order to accomodate the microbes. The process of fermentation is the same as that of foregut fermenters, except since the caecum is located after the stomach and small intestine, most of the food reaches the caecum undigested. Hence the microbes cannot be digested by the host as a source of amino acids because they are in the large intestine where protein digestion no longer occurs. The digested food is then excreted along with the microbes, which means their nutrient uptake is not as high as fore-gut fermenters. However, they are able to eat their own faeces as the food making the faeces has been digested by the microbes, making it of nutritional value. Examples of hind-gut fermenters include rabbits, possums and koalas
5. What is the purpose of a cow ‘sitting quietly chewing’
Cows spend most of their time ‘sitting quietly chewing’ because their teeth have flat surfaces that are efficient for grinding food. Grinding increases the surface area for the digestive enzymes to breakdown the cellulose. When chewing, the cows are a regurgitating a lump of food called ‘cud’. This mechanical digestion physically breaks down the large food particles to increase the surface area for microbial fermentation. By chewing their food twice, they are able