Question 1 Describe how a large surface area is achieved in the digestive system of Platyhelminthes, sharks, crustacean, mammals. Question 2 Describe the four chambers of the cow's stomach and explain the unique functions of each chamber in the digestion of plant material. The four chambers of a cow's stomach are the rumen, reticulum, omasum, and abomasum, each with a specialized function in the digestion of plant material through fermentation. Ruminants are a group of mammals that includes giraffes, deer, cattle, bison, sheep, goats, and antelopes. They are characterized by the presence of a rumen, a specialized part of the digestive tract. The rumen is a fermentation vat where symbiotic bacteria and protists break down complex plant carbohydrates into simpler molecules. This process, called foregut fermentation, allows ruminants to extract nutrients from plant matter that other animals cannot. This is the largest chamber and acts as a fermentation vat. Microbes here break down complex carbohydrates like cellulose into volatile fatty acids (VFAs), which the cow can absorb for energy. The papillae increases the SA for the housing the microbes. Reticulum: This chamber is connected to the rumen and helps with particle sorting. Its textured, honeycomb interior helps trap larger, less-digested particles. Heavy or dense material (and even ingested foreign objects) tends to settle here. It also plays a role in regurgitation for further chewing (cud-chewing). Larger particles are directed back to the mouth for further chewing, ensuring that only suitably broken-down feed passes forward. Omasum: This chamber is responsible for absorbing water (primary roles), electrolytes, and some VFAs from the ingesta. The folded structure acts like pages in a book, filtering out larger particles such as the fermented material from the rumen, preventing larger particles from entering the abomasum. (has pockets that it uses to hold the food so it can absorb the water) Abomasum: This is the "true" stomach of the cow, where digestive enzymes and acids break down food further. This is most similar to a monogastric stomach. Question 3 Describe cellulose digestion in rabbits Rabbits, as herbivores, consume a diet rich in cellulose—a complex carbohydrate found in plant cell walls. However, like many mammals, rabbits lack the endogenous enzymes necessary to break down cellulose directly. To overcome this, they rely on a specialized digestive process known as hindgut fermentation, which involves symbiotic microorganisms to facilitate cellulose digestion. Hindgut Fermentation Process: 1. Ingestion and Initial Digestion: After a rabbit consumes plant material, the food passes through the stomach and small intestine, where easily digestible nutrients like simple sugars, proteins, and fats are absorbed. 2. Fermentation in the Cecum: o The remaining fibrous material moves into the cecum, a large, blind-ended pouch located at the junction of the small and large intestines. o The cecum houses a diverse community of microorganisms, including bacteria, protozoa, and fungi, which produce enzymes capable of breaking down cellulose into simpler compounds. o Through fermentation, these microbes convert cellulose into volatile fatty acids (VFAs) such as acetic, propionic, and butyric acids, which rabbits can absorb and utilize for energy. 3. Formation of Cecotropes: Not all nutrients are absorbed during the initial passage through the cecum. To maximize nutrient uptake, rabbits produce specialized fecal pellets called cecotropes. Cecotropes are soft, mucus-coated pellets rich in B vitamins, microbial protein, and residual VFAs. 4. Cecotrophy (Reingestion of Cecotropes): Rabbits instinctively consume cecotropes directly from the anus, usually during periods of rest. By reingesting cecotropes, rabbits pass the nutrients through the digestive system again, allowing for further absorption in the small intestine.
