Research Paper: Digestive System of Mammals

A mammal’s digestive system depends on the food that their main diets consist of. Mammals are classified into three categories: carnivores, herbivores and nectar-feeding animals. This report will be focusing on the differences in each separate digestive system.

Herbivore
An herbivore is the term specified to a group of animals that feed on plants alone. Because of this eating regime, their digestive system is adapted in order to cater for the animals’ needs. One of the major features of the digestive system is teeth. The teeth of an herbivore consist mainly of incisors, molars and premolars in order to cut, bite, crush and grind their food. The canines, which are used for tearing flesh, are very small, as the herbivore does not need it when consuming plants. In some cases, the canines are non-existent. The molars are a distinctive feature of some herbivores due to the protrusions on the surface known as cusps, which help to grind and chew food over a long period of time. Plants contain cellulose, which can only be broken down after much crushing and grinding. Because of this characteristic, some animals replace their upper incisors with pads known as the horny pads. The lower incisors are able to bite against this bad in order to properly cut plants.

Other adaptations of herbivores and how they “digest” cellulose include a vast range of characteristics. Some herbivores have a longer caecum, a pouch that is to be considered the beginning of the large intestine. This caecum consists of bacteria and protozoa that contain cellulase, which is essential in breaking down cellulose. Without this bacteria, the animal would not be equipped to digest the cellulose that make up the cell wall of plant cells. These plant cells contain nutrients essential for the animal’s survival, and the bacteria helps to digest the cellulose to glucose and convert some of the other sugars to nutrients necessary for the herbivore. The herbivore and bacteria have a symbiotic relationship where the bacteria have a constant environment containing the correct food and features a bacterium needs to survive.

A third characteristic that allows the herbivore to digest their food is the stomach. Some animals, like kangaroos, have two stomachs in order to properly digest their food. Other herbivores, known as Ruminants, have a complex stomach consisting of four chambers in order to properly digest their food. The first chamber is known as the rumen, which moistens the cellulose and breaks it into smaller pieces. From there it travels into the reticulum, where certain bacteria containing cellulase are able to break down the cellulose and produce small balls called ‘cud’. This cud is regurgitated into the mouth of the carnivore to be re-chewed into finer particles. After this, the cud is swallowed once again before it is able to enter the third chamber, known as the omasum. The omasum is where the water is absorbed and the coarse particles are filtered. The final chamber is known as the abomasum is similar to the stomach of other mammals, where digestion finally takes place. The food finally enters the intestines and digestion is complete. Carnivore A carnivore, like other animals, has a unique digestive system that has adapted due to its specific diet. A carnivore is the term given to mammals that only eat meat, such as lions and vultures. The teeth of a carnivore are slightly different to that of a herbivore. One of the main differences is the utility of the canines. Canines are essential in tearing flesh off of animals, which is a carnivore’s primary energy source. Molars and premolars are also utilised, but have been modified during evolution (known as the carnassial teeth). The fourth upper premolar and first lower molar teeth are adapted to shear flesh. The tips of the teeth end in sharp points that slide past one another, acting like scissors in order to shear flesh. The vertical movement of the jaw is another adaption common in all carnivores that help the carnassial teeth to function. The carnivorous digestive system consists of a long tube that travels from the mouth all the way to the anus known as the alimentary canal. The canal is considered to be ‘outside’ the body and entry to the blood is entry to the internal environment of the cells. Unlike herbivores, carnivores have a short caecum that has no fundamental use. Nectar Feeder The digestive system of a nectar feeder is relatively different to that of both carnivores and herbivores. The teeth, tongue, stomach and intestines are the major features that make the digestive system so distinct. The teeth are small, needle-like structures set into a narrow, pointed jaw that is suitable for biting into flowers. There is no need for large, strong teeth that is able to crush, tear and bite. The tongue is specialised for collecting nectar and pollen. It is covered in small protrusions known as papillae that traps the pollen and nectar. As well as the projections on the tongue, there are also projections on the roof of the mouth. The nectar is trapped by the papillae at the tip of the tongue whilst the pollen is collected by the compound papillae in the middle of the tongue. The tongue then presses itself to the roof of the mouth and the nectar and pollen then travel down the pharynx and into the oesophagus. The stomach is another feature that has adapted to the nectar feeder’s diet. Like herbivores, the stomach is split into chambers; except where herbivores have four chambers, nectar feeders have two. The main chamber and the smaller chamber have been dubbed the diverticulum. The stomach also acts as a storage chamber for both nectar and pollen. Nectar does not require digestion except for the breaking down of disaccharides and monosaccharides. Pollen is digested in the intestines. The stomach has a ridged wall that is lined with epithelial cells, which produce mucus. However, the stomach cannot break down proteins due to a lack of pepsinogen. Nectar feeders do not have a caecum, thus causing the large intestine and small intestine to merge until it is almost impossible to differentiate between them.

Investigation Report: Theories About the Xylem and Phloem Transpiration and Translocation Transpiration is the process in which water and nutrients are transported from the roots to the small pores on the underside of leaves xylem. From there it changes to vapour and is evaporated into the atmosphere. Guttation is a process in that makes up transpiration. It is a term given to the loss of liquid water from uninjured leaves and stems of the plant, primarily through water stomata. The process of transpiration and the rate at which it occurs depends mainly on the conditions in which the plant lives. These conditions include temperature, humidity, sunlight availability and intensity, precipitation, soil type and saturation, wind, land slope, and water use and diversion by people. Translocation is the term given to the movement of moisture from leaves to other tissues throughout the plant by the phloem. Plants produce carbohydrates (sugars) in their leaves through the process of photosynthesis. However, other features of the plant that do not use photosynthesis also need these carbohydrates, thus the method of translocation is put to use. These features are known as sinks and include flowers, roots, stems, fruits and underdeveloped leaves. The Transpiration Stream The transpiration stream is the uninterrupted flow of water and nutrients that are transported from the roots to the rest of the plant via the xylem. The moisture travels to the leaves where it is evaporated. It is driven by capillary action or root pressure. The Role of Stomata and Guard Cells The stomata are tiny openings that are used for gas exchange. Carbon dioxide and oxygen enter the stomata where it is used in photosynthesis and respiration. Oxygen produced by photosynthesis exits through the same opening. Guard cells are cells that surround each stoma and control and regulate the rate of transpiration by opening and closing the stoma. When the water potential is lower in the adjacent cell than that in the cell of the sap of the guard cell, water cells move into the adjacent cell via osmosis. Formation of the Xylem to the Phloem Xylem is one of the two transport tissues in vascular plants. Xylem transports water throughout the plant and provides nutrients to the different structures. They are transported via two structures known as the tracheids and vessel elements. Tracheids and vessel elements can be distinguished by their distinctively long shape. Vessel elements are shorter and are connected together in long tubes to create vessels. Phloem is the second transport tissue in vascular plants. The phloem is responsible for transporting the carbohydrates (sugars), mRNAs and proteins from photosynthetic leaves to sink tissues.

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