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Lecture 8

BIO2242: Lecture 8 notes

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BIO2242 – LECTURE 8 What does this animal eat? Food types – vegetation: They have a protective cell wall which makes it difficult to digest Vegetation as food: The energy you want to get is bound up in molecules of cellulose, and there are no vertebrates that can produce cellulose themselves. Many plants produce secondary chemicals that inhibit the digestion of many materials within the cell. Vegetation is low food quality and low assimilation efficiency, so it takes a long time to get the energy out of the plant and a lower proportion of the amount of food that you eat is able to be incorporated into your own body. Protective cell well: In order to break the protective cell wall, most herbivores have complex dentitions. Selenodont = half-mooned shaped, crescent shaped on each tooth. In herbivores, the two jaws come down at the same time, so the teeth on the upper and lower jaws meet at the same time. Herbivores have reduced temporalis muscles (muscles at the top, that pull upwards) and large massatar muscles, which are muscles that pull to the side. They chew by moving their lower jaw sideways. Difficult to digest: The sheep is a foregut fermenter, it has an enlarged stomach, with many compartments, it has a very long midgut, a relatively large hindgut with a lot of foldings. The pony is a hindgut fermenter, it has a small stomach, mid gut is relatively long but the hind gut is huge. Great expansion of the length of the gut which allows longer digestion time and allows them to hold more food. Cellulose fermentation: The cellulose, the main constitute in plant’s cell walls, need to be broken down with enzymes that vertebrates don’t have. This is how we create carbon dioxide, water and energy: We need a fuel into that, so glucose is that fuel that goes into the chemical reaction. If you had starch, these are glucose molecules that are joined together, and we need get to glucose out of it, so we need amylase to take the starch, which breaks down the separate glucose molecules, and the glucose then goes into the reaction to extract energy from that (ATP). In cellulose, it has a similar but different chemical bond. We want to get glucose out of it but vertebrates don't have the enzyme. So we have to use the bacteria that produce the enzyme, cellulase, that then, breaks down into glucose. The glucose is then fermented to produce short chain fatty acids, where SCFA then go into the oxidative-productive process to produce energy. Bacteria produce cellulase -> SCFA which are molecules that go into the chemical reaction to break down ozygen. Cellulose fermentation II: They enlarge the region of the gut to be able to fit more bacteria and food in. Herbivores digestive strategies: Some of them get their energy from the microbial cell wall, so they are fermenting the cellulose on the outside of the cell. And this happens in the foregut hence foreut fermenters. The other type is, instead of concentrating on fermenting the cell wall, we break open each cell, which leaks the cell contents and digest those cell contents. And so, they do ferment but only a small amount in the hindgut, hence hindgut fermenters. Foregut fermenters: There are many foregut fermenters that ruminate. Rumination means that they take a piece of grass and they chew it and they swallow it. This starts a softening process
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