Image Source – Attribution: By Leysi24 (Own work) [CC BY-SA 3.0 via Wikimedia Commons
Firstly, dismantle the human torso model in the science laboratory and describe what you know about each part of the alimentary canal and associated glands and organs. Draw and label a detailed diagram, showing each of the organs above. Then complete the “Cut-and-Paste your Guts” activity, identifying each organ from it’s description and pasting each description into your book, in the order that food would pass through, on it’s 12 hour journey through the 7 metres of the digestive system.
Next, match the skulls (noting the teeth structure and position of eye sockets) with the corresponding herbivore, omnivore and carnivore digestive systems. Describe the diet of each organism, explaining your reasoning in terms of teeth structure, size of stomach and length of intestines, any enlarged organs and corresponding diet.
Horses are hindgut fermenters, while sheep are foregut fermenters.
Obtaining and transporting nutrients is a vital function for all multicellular organisms and different species have evolved some interesting ways of gaining, storing and digesting their nutrients. Amongst herbivores, for example, almost all have cellulose digesting bacteria within their gut that live symbiotically, assisting with the break down of vegetation. Some are classified as “hindgut fermenters”, which have microbes and fermentation in their hindgut, the caecum and proximal colon. These animals are less effecient at digesting their food and can sometimes be observed practising coprophagy (eating faeces).
Other herbivores are “foregut fermenters”, or ruminants, which have pouches with microbes in the stomach. These microbes consume glucose from cellulose but produce fatty acids that the animal can use for energy. Microbes can also be digested further along the digestive tract as they are also a source of protein. Forgut fermentation, or rumination, is a slower digestive process, but has the advantage of providing more nutrients and wasting less energy. Foregut fermenters include:
- Kangaroos and Wallabies
Good information about different types of digestive systems from a UK Veterinary site, Comparative Digestion.
The image above shows a villus from the cross section of the small intestine. These tiny, finger-like projections increase the surface area of the organ to allow greater absorption of nutrients. Each villus has capillaries into which the nutrients (glucose and amino acids) are absorbed and a lacteal, which absorbs lipids (fats and oils) and drains into the lymph ducts. Goblet cells in the epithelium secrete mucin, which dissolves in water to form mucous. The absorptive cell, or microvilli, are also in the epithelium and function to absorb nutrients.
This week we started the study of how organisms obtain their nutrients by looking at the mammalian digestive system. We discussed the comparison between carnivores and herbivores in terms of their skeletal structure, teeth and alimentary canal. Scientists can determine the diet of long-dead organisms by looking at their teeth. The relative size and structure of incisors, canine and molar teeth will indicate whether an organism is better adapted to a diet of meat or plant materials. Here is an interesting article about the study of teeth and diet in ancient humans.
This Friday we will complete Activity 5.5 “Different digestive systems in mammals” (page 45) which will enable you to predict certain features of the digestive system of a mammal, if you are provided with information about it’s diet and body size. You will also be able to interpret diagrams of digestive tracts from different mammals. In general, herbivores have much larger and more complex digestive systems, with fermentation chambers to allow the break down of tough cellulose and fibrous materials. Carnivores have shorter and simpler digestive systems as their diet is more energy-dense and nutrient-rich than food of plant origin. The exception may be honey-eaters, which do not require a complex system for digestion, as their food is already energy dense and in a form easily absorbed into the blood stream.
This diagram shows the important chemical enzymes that aid digestion in mammals. Remember that mechanical digestion does not change the food chemically, it just increases the surface area to volume ratio of the food to allow the enzymes to work better. Bile is actually an emulsifier (like detergents) – it breaks the lipids down into smaller globules to allow the lipases (enzymes that act on fats and oils) to work better. So bile works mechanically rather than chemically – the product is the same chemically as the reactants.
These pitcher plants and other ‘carnivorous’ plants produce digestive enzymes that can break down the flesh of small invertebrates, such as flies, spiders and ants. Often they grow in soil that is deficient in specific inorganic nutrients, such as nitrates and phosphoros, and can get these essential elements from the dead animals that are attracted by sweet and sticky liquids.
The main things to remember about enzymes are:
- Enzymes are proteins and biological catalysts.
- They are not used up in the reaction – only a small amount of enzyme is needed for each reaction.
- They do not change the amount of product formed
- They speed up a reaction, but do not change the direction of the reaction.
- They are very specific to their substrate and are often named according to the chemicals they work on.
- Enzymes, being proteins, are sensitive to heat, pH and heavy metal ions. When heat is applied the proteins are ‘denatured’ and no longer work.
In the human body there are several different enzymes including:
- Amylase which works on starch
- Maltase which works on maltose
- Sucrase which works on sucrose
- Lipasewhich works on lipids (Fats) and
- Pepsin which works on polypeptides (Proteins)
More about Enzymes from Wikipedia here. Award-winning Enzyme Investigation here. Andrew Douch, a Biology teacher from Wanganui Secondary College, has produced many Biology podcasts, for students to learn about different topics – here is a link to his “Enzymatic” podcast. Andrew has also included some notes about enzymes here. Experiment with enzymes in liver here.
Today we discussed the digestive systems of other animals, including flatworms, earthworms, cockroaches and birds. How is the diet, size and structure of the animal related to their digestive systems? What is the function of a ‘gizzard’ and ‘crop’ in earthworms and birds?
Today we are looking at the different digestive systems of mammals and investigating the relationship between diet, nutritional requirements and the structure and function of digestive systems. You will learn the meaning of the terms fermentation, hind-gut and fore-gut fermenters, ruminants, caecum and colon.
Check out the MyStudiyo Quiz “Heterotrophs are Consumers” at http://www.mystudiyo.com/ch/a86690/go