Why Cellulose Is Essential for Herbivores and Ruminants
Cellulose makes up about 30% of the wall of the plant cell and it serves as the connection between the cells and the tissues. The main substance found as a structural component in the cell wall of the plant is cellulose by which plants remain stiff and upright. As a fibre, it has great importance in the diet. But it cannot be digested by humans because the digestive system of humans is assisted by it. It helps the food to push the waste out of the body. In animals, microbes secrete cellulose to digest it. The digestion of cellulose occurs in a four-chambered stomach. Cellulose is the most abundant organic polymer found on the earth which occurs naturally.
What is Cellulose?
Cellulose is a complex polymeric carbohydrate molecule that comprises thousands of glycosidic linkages in the form of a linear chain. The chain is unbranched and straight consisting of linked D-Glucopyranose bonded by hydrogen bonds producing a substance which in its pure form is insoluble and inert.
Structure of Cellulose
A large number of organisms ranging from the bacterium Acetobacter xylinum synthesize cellulose from the forest trees. A good amount of cellulose is produced by A. Xylinum and also this bacteria is used in the study of cellulose biosynthesis. The protein named enzyme cellulose synthase present in the membrane synthesizes cellulose as well as catalyzes the glucose polymerization from UDP- glucose into the product of cellulose.
There are many bacteria, Dictyostelium disodium, and higher plants from which genes for cellulose synthesis can be identified. From the Cellulose which is present in plants to the bacterial cellulose, all are arranged similarly from the microfibrils as chains of polysaccharides and ribbon bundles of microfibrils.
Reasons Why Humans Cannot Digest Cellulose
In the human body, cellulose cannot be digested due to a lack of appropriate enzymes to break the beta acetal linkages. The human body does not have the digestive mechanism to break the monosaccharide bonds of cellulose. Although cellulose is indigestible then also it helps in the smooth working of the intestinal tract.
But, it plays a vital role in the human body because it is an excellent source of fibre. Every kind of sugar can be digested by the enzymes secreted from the human mouth, liver, and stomach except cellulose. There are some foods like fermented food, grains, and vegetables that are hard to digest or are indigestible.
Cellulose Digestion in Herbivores
Utilizing the symbiotic gut bacteria, cellulose can be digested by herbivores with the help of monogastric digestion. Herbivores are less efficient than ruminants in the case of extracting energy from the digestion of cellulose. Here, cellulose is digested by microbial fermentation.
Herbivores eat plant materials as their food and the cell walls in plants contain cellulose. By these, the cellulose breaks into absorbable substances. Then it gets absorbed into the body and provides nutrition.
Cellulose Digestion In Termites
Termites are also unable to digest the cellulose then also they feed cellulose present within the wood. Some microorganisms live in the gut of termites. These microorganisms are named mastigophorans. Termites break down the wood and microorganisms produce the by-product which can be digested by both the organisms and termites.
Termites rely on their celluloses. It is believed because they have the strong activity of cellulose in the midgut. Acetic acid and other acids are released at the time of the digestion of wood cellulose.
Cellulose Digestion in Ruminants
In ruminates, the place of digestion of cellulose is the four-chambered stomach and it is digested with the help of bacteria and enzymes present there. The first compartment is the rumen where the plant material is stored temporarily and later it gets processed and also gets exposed to bacteria in the initial stage. Anaerobic bacterial digestion occurs as bacteria can break down the cellulose. The presence of several compartments in the stomach helps in the process. After the partial digestion in the stomach, they chew their cud. This process helps in further breaking the material.
The monosaccharide glucose is produced by the breakdown of the plant fibre by Ruminococcus bacteria. A further breakdown can occur with the help of glucose. In ruminants, the symbiotic relationship can be seen in which the digestion of fibre is enabled without encoding for more enzymes in their genomes for this process.
Importance of a Balanced Diet For humans
A balanced diet is referred to as a diet that provides the essential nutrients required by the human body to work effectively. A Balanced diet should include carbohydrates, vitamins, minerals, starches and fibre, protein, healthy fats, and antioxidants. Without a balanced diet, the body is more inclined to various kinds of disease, infection, and low performance in various physical and mental aspects of life. Some more benefits of having a balanced diet are-
Improves Immune System- A healthy balanced diet improves one's immune system and helps them fight acute and chronic diseases. That's why people who eat healthily and exercise every day get sick less than people who consume a lot of junk food and sit on their couches.
Reduce Weight- A balanced diet not only helps to control body weight but when applied with exercise can help one lose weight drastically. A balanced diet is healthy and tasty as this can be adapted in o e's lifestyle. Balanced diets are way more sustainable and practical than diets for weight loss.
Mental Health- A balanced diet helps one to maintain mental stability. In times of stress and work, food is the first thing people ignore, and getting the right combination of nutrients can help to reduce symptoms of chronic anxiety and depression. One should look after mental health as it is important for healthy survival and good life.
Good for Growth- A balanced diet is essential for essentially kids and adolescents as the body nutrient requirement is most at those times. It is also important to get the right nutrients so that cells are created and sustained and the body grows in the proper place.
Improves Skin Glow- A healthy balanced diet provides the glow on one's face that everyone looks for with artificial products. Consuming a balanced diet will contribute to healthy skin and hair which will enable one to look younger and more confident.
People who do not receive a sufficient amount of healthy food suffer later in their old age and are more prone to suffer from diseases like Alzheimer's, etc. Those are some of the reasons why one should follow a balanced diet. A balanced diet with a sufficient amount of exercise can turn around anyone's life and save them from multiple severe diseases like diabetes and blood pressure problems.
FAQs on How Cellulose Supports Digestion in Animals
1. Why is cellulose important in an animal's diet?
Cellulose is a vital component in the diet of many animals. For herbivores like cows and sheep, it is a primary source of energy after being broken down by symbiotic microorganisms. For animals that cannot digest it, including humans, cellulose functions as insoluble dietary fibre. This fibre is crucial for maintaining a healthy digestive system, as it adds bulk to stool, aids in the smooth movement of food through the gut, and helps prevent constipation.
2. How do grass-eating animals like cows digest cellulose?
Grass-eating animals, known as ruminants, have a specialised digestive system to break down cellulose. The process involves:
A multi-chambered stomach, with the first chamber called the rumen, which houses billions of symbiotic microorganisms (bacteria and protozoa).
These microorganisms produce the enzyme cellulase, which breaks down the complex cellulose into simpler sugars.
The animal regurgitates partially digested food (cud) and chews it again to further break down plant fibres, a process called rumination.
This allows for maximum nutrient extraction from tough plant material.
3. Why can't most animals, including humans, digest cellulose?
Most animals, including humans, cannot digest cellulose because they lack the specific enzyme called cellulase. Cellulose is a polysaccharide made of glucose units linked by strong chemical bonds known as beta-glycosidic bonds. The digestive enzymes produced in the human gut can only break alpha-glycosidic bonds (found in starch). Without cellulase, these beta-bonds remain intact, and cellulose passes through the digestive tract undigested.
4. What is the main difference between cellulose digestion in ruminants and non-ruminant herbivores?
The main difference lies in the location of microbial fermentation. Ruminants (like cows, goats) are foregut fermenters, meaning cellulose is digested in the rumen before reaching the small intestine. This allows for efficient absorption of nutrients from the fermented material. In contrast, non-ruminant herbivores (like horses, rabbits) are hindgut fermenters. They have a large cecum and colon where microbial digestion occurs after the small intestine, which is generally less efficient for nutrient absorption from fibre.
5. What are the end products of cellulose digestion in animals that can break it down?
In herbivores capable of digesting cellulose, the microbial fermentation process breaks it down into several key products. The primary energy-yielding end products are Volatile Fatty Acids (VFAs), such as acetate, propionate, and butyrate. These VFAs are absorbed directly through the rumen or cecum wall and used as the main source of energy for the animal. Other by-products include gases like methane (CH₄) and carbon dioxide (CO₂).
6. What is the role of the cecum in cellulose digestion?
The cecum is a large pouch connected to the junction of the small and large intestines, particularly prominent in non-ruminant herbivores like rabbits and horses. It functions as a fermentation vat, similar to the rumen in cows. The cecum houses a population of symbiotic bacteria that produce cellulase to break down cellulose. This process of hindgut fermentation allows these animals to extract energy from fibrous plant matter that would otherwise be indigestible.
7. Do any animals use cellulose for structural support like plants do?
While cellulose is overwhelmingly associated with plant structure, a rare exception exists in the animal kingdom. A group of marine invertebrates called tunicates (or sea squirts) are known to produce cellulose, which is referred to as tunicin. This tunicin forms a major part of their tough outer covering or 'tunic', providing them with structural support and protection. However, this is a very specific adaptation and not a characteristic of other animals.
8. Can the efficiency of cellulose digestion be improved in livestock animals?
Yes, the efficiency of cellulose digestion in livestock like cattle and sheep can be influenced and improved through several agricultural practices. This includes optimising their diet by balancing fibrous feeds with more easily digestible nutrients, using feed additives that support a healthy microbial population in the rumen, and processing feeds (like chopping or grinding) to increase the surface area available for microbial action. Research also explores manipulating the rumen microbiome to enhance its digestive capabilities.
