Answer of Question of Nutrition & Digestion
All animals require a balanced diet containing both fuels (mainly carbohydrates and ipids), and structural and functional components (proteins, minerals, and vitamins). For every multicellular animal, certain amino acids, lipids, vitamins, and minerals are essential” dietary factors that cannot be produced by the animal’s own synthetic machinery. Animal proteins are better-balanced sources of amino acids than are plant • proteins, which tend to lack one or more essential amino acids. Undernourishment and protein malnourishment are among the world’s major health problems, affecting millions of people.
Autotrophic organisms (mostly green plants), using inorganic compounds as raw materials, capture the energy of sunlight through photosynthesis and produce complex organic molecules. Heterophic organisms (bacteria, fungi, and animals) use the organic compounds synthesized by plants, and chemical bond energy stored therein for their own nutritional and energy needs.
A large group of animals with very different levels of complexity feed by filtering out minute organisms and other particulate matter suspended in water. Others feed on organic detritus deposited in the substrate. Selective feeders, on the other hand, have evolved mechanisms for manipulating larger food masses, including various devices for seizing, boring, tearing, biting, and chewing. Fluid feeding is characteristic of endoparasites, which may absorb food across the general body surface, and of ectoparasites, herbivores, and predators that have developed specialized mouthparts for piercing and sucking.
Digestion is the process of breaking down food mechanically and chemically into molecular subunits for absorption. Digestion is intracellular in protozoan groups and sponges. In more complex metazoans it is supplemented, and finally replaced entirely, by extracellular digestion, which takes place in sequential stages in a tubular cavity, the alimentary canal. The mouth receives food, mixes it with lubricating saliva, then passes it down the esophagus to regions where the food may be stored (crop), or ground (gizzard). or acidified and subjected to early digestion (vertebrate stomach). Among vertebrates, most digestion occurs in the small intestine. Enzymes from the pancreas and intestinal mucosa hydrolyze proteins, carbohydrates, fats, nucleic acids, and various phosphate compounds. The liver secretes bile, containing salts that emulsify fats. Once foods are digested, their products are absorbed as molecular subunits (monosaccharides, amino acids, and fatty acids) into the blood or lymph vessels of the villi of the small intestine. The large intestine (colon) serves mainly to absorb water and minerals from the food wastes as they pass through it. It also contains symbiotic bacteria that produce certain vitamins.
Most animals balance food intake with energy expenditure. Food intake is regulated primarily by a hunger center iocated in the hypothalamus. In mammals, should caloric intake exceed requirements for energy, the excess calories normally are dissipated as heat in specialized brown fat tissue. A deficiency in this response is one cause of human obesity.
Several gastrointestinal hormones coordinate digestive functions. They include gastrin, which stimulates acid secretion by the stomach; cholicystokinin (CCK), which stimulates gallbladder and pancreatic secretion; and secretin, which stimulates bicarbonate secretion from the pancreas and inhibits gastric motility.
Answers to the Questions
Q.1. Differentiate between nutrition and digestion.
Ans. Nutrition is the study of the sources, actions, and interactions of nutrients
required in the bodies of organisms. Nutrition includes all of those processes by which an animal takes in (obtaining food), digests, absorbs, stores, and uses food nutrients to meet its metabolic needs.
Digestion is the chemical and/or mechanical breakdown of large complex non diffusible food into particles that can diffuse into cells.
Q.2. How do autotrophs and heterotrophs differ?
Ans. Organisms need some necessary chemicals for growth, maintenance, and energy production, which they obtain from the environment. In nature these substances (organic) are not found as such in free form. Organisms have to synthesize these organic substances.
Autotrophs, (self nourishing), the green plants and photosynthetic protists, can synthesize all their needed complex substances from simple inorganic substances, such as carbon dioxide, water, nitrates, phosphates etc. usually in a process called photosynthesis.
Heterotrophs are the organisms which cannot synthesize their organic molecules from simple inorganic chemicals and as such have to obtain these substances from other organisms. Heterotroph organisms are the animals, fungi and most bacteria.
Q.3. What do you mean by calorie and Calorie? What is the calorific value of
carbohydrate, lipid, and proteins?
Ans. A calorie (gm calorie) is the amount of energy required to raise the temperature of one gram of water to 1°C.
A Calorie or kilocalorie or kilogram calorie (Kcal) is equal to 1000 calories. The average calorific value of carbohydrates is 4.1 Calories per gm, of lipid it is 9.3 Calories (Kcal) and that of proteins is 4.4 Calories per gram.
Q.4. What are macronutrients and micronutrients? OR
What are essential and nonessential/minerals? Give example.
Ans. Generally speaking a macronutrient is an essential nutrient for which an animal has a large minimal requirement (greater than 100 mg). The heterotrophs require carbohydrates, lipids and proteins, in their diet along with minerals, such as sodium, chloride, calcium, phosphorus, and magnesium.
Micronutrients are dietary elements essential only in small quantities e.g., iron, chlorine, copper, vitamins etc.
Some of these dietary substances are termed essential nutrients. These are classified, as: essential amino acids (methionine, Valine, Threonine, phenylalanine, Leucine, Isoleucine, tryptophan, and lysine), essential fatty acids, vitamins, and minerals. These essential substances must be present in the diet.
Q.5. Give an account of physiological roles of each of the following:(a) Carbohydrates (b) Lipids (c) Proteins.
Ans. A nutritionally adequate diet satisfies three needs: (a) provides fuel (chemical energy) for metabolic reactions; (b) supplies adequate organic raw materials animals use in biosynthesis, and; (c) supplies essential nutrients, substances the animal cannot synthesize from any raw materials.
(a) Carbohydrates are the major dietary source of energy, mostly obtained
from plants. Carbohydrates in the body as polysaccharides (glycogen), disaccharides (Lactose, maltose, sucrose), and monosaccharides (glucose, fructose, glyceraldehyde) play important roles, such as build up of carbon chain structures for synthesis of organic compounds; reserve storage energy etc., apart from energy provision. Cellulose, a polysaccharide, although is not digested in most animals (except herbivores such as horses, koalas, termites etc, who have cellulose digesting microbes in their digestive tracts), assist in passage of food in alimentary canal by providing fibrous “roughage” reducing the chances of cancer of the colon.
(b) Lipids are the most concentrated source of food energy. Natural fats or triglycerides are present in fats, oils, meat, nuts, many seeds etc. Many animals require on!y specific types of lipids, e.g., many animals require unsaturated fatty acids, such as linoleic acid, linolenic acid, and arachidonic acid; precursor molecules for synthesis of sterols (cholesterol). Cholesterol is part of cell membrane. Lipids in some vertebrate insulate the body and thus maintain a constant temperature.
(c) Proteins are organic compounds built of 20 kinds of monomers called amino acids. The sources are meat/flesh of other animals, milk, beans and nuts etc.
Biosynthesis and interconversion of macronutrients
As heterotrophs, animals cannot make organic molecules from raw inorganic materials. To synthesize these molecules an animal must obtain precursors from its diet. When a source of organic carbon (such as sugar) and a source of organic nitrogen (such as amino acids) is available, the animal can fabricate a great variety of organic molecules with the help of enzymes to rearrange the
molecular skeletons of the precursors acquired from digested food. For e pie,
a single type of amino acid can supply nitrogen for the synthesis of severai other types of amino acids that may not be present in the food. (The body cannot however synthesize eight essential amino acids). Also, animals synthesize fats from carbohydrates, and carbohydrates from proteins or fats. In vertebrates liver is the site of these resyntheses..Fig. 5.1.
Q.6. What are macrominerals and microminerals? Give their physiological role in animals.
Ans. Minerals that are required in large amounts are called macrominerals or essential minerals.Micromlnerals or Trace Minerals are minerals which animals need in very small quantities. These are usually needed for enzyme activity. Following are the physiological roles of the minerals.
Q.7. What are vitamins? Give their physiological roles in the bodies of vertebrates.
Ans. Vitamins are organic molecules required in the diet in amounts that are quite small compared with the relatively large quantities of essential amino acids and fatty acids animals need. Tiny amounts of vitamins may suffice, from about (0.01)
to 100 mg per day, depending on the vitamin. •
Although requirements for vitamins are modest, these molecules are absolutely essential in a nutritionally adequate diet. Deficiencies can cause severe problems.
So far, 13 vitamins essential to humans have been identified (see table). The compounds are grouped into two categories: water-soluble vitamins and fat-soluble vitamins. Water-soluble vitamins include the B complex, which consists of several compounds that generally function as coenzymes in key metabolic processes. Vitamin C (ascorbic acid) is also water-soluble. Ascorbic acid is required for the production of connective tissue. The fat-soluble vitamins are A, D, E, and K
Q.8. What are some animal strategies for getting and using food?
Ans. Most animals ingest other organisms, dead or alive, whole or by the piece. (Exceptions are certain parasitic animals, such as tapeworms, which absorb organic molecules directly across their outer body surface.). Diets vary Hervivores, including, gorillas, cows, hares, many snails, and sponges, eat autographs (plants, algae, and autotrophic bacteria) Carnivores, such as sharks. hawks, spiders, and snakes, eat other animals. Omnivores consume both animals, and autographs. Cockroaches, crows, raccoons, and humans, who evolved as hunters and gatherers, are examples of omnivores.
The feeding mechanism by which animals obtain their food very. Animals may be: (a) suspension feeders, (b) substrate feeders or deposit feeders. (c) fluid feeders, (d) herbivores, and (e) carnivores or predators.
(a) Suspension Feeders
Suspension feeding is the removal of suspended food particles from the surrounding water by some sort of capture, trapping or filtration structures. This feeding strategy involve three steps: (1) moving water past the feeding structure, such as gills, baleen etc., (2) removal of nutrients from water (3) transport of nutrients to the mouth of digestive tract. This type of feeding is found in sponges, ascidians, brachiopods, ectoprocts, entoprocts, phoronids, most bivalve molluscs, many crustaceans, polychaetes, gastropods, and baleen whales etc.
(b) Deposit Feeders
Deposit feeders are animals that obtain their nutrients from the sediments of sot t-bottom habitat (mud or sand) or moist soft soil. Animals swallow large quantities of sediment, digest and absorb nutrients in it, and remains pass out the anus. It occurs in many polychaetes, some snails, some sea urchins, and earthworms.
(c) Fluid Feeders
These animals make their living by sucking nutrient-rich fluids from a living host. Feeding on this fluid is called fluid feeding. This feeding mechanism is characteristic of some parasites, such as butterflies, moths and aphids which suck plant juices, intestinal nematodes, ectoparasites, such as leeches, ticks, mites, lampreys, and certain crustaceans, pollen and nectar feeding birds, and vampire bat (Desmodus), the only sanguinivorous mammal.
These are animals that feed upon herbs or plants. Herbivory requires the ability to bite and chew large pieces of plant matter, such as teeth in vertebrates. Many molluscs have a radula; a muscularized belt-like rasp armed with chitinous teeth, polycheates have sets of chitinous teeth on proboscis or pharynx. Herbivory is also found in almost every group of arthropods.
Predators are carnivorous animals which capture and devour live prey. Many ciliate protozoa, cnidarians, nemerteans, polychaete worms, gastropods, octopuses, squids, crabs, sea-stars, and many vertebrates are predators.
Q.9. What do you mean by digestion? How do intracellular and extracellular digestion differ?
Ans. Digestion is the process of chemical and/or mechanical breakdown of non diff usable, complex food substances into diff usable form. In protists and sponges, cells take in whole food particles inside directly from the environment by diffusion, active transport and/or endocytosis and break them down with enzymes to obtain nutrients. This process is called intracellular Intracellular digestion provides all or some of the nutrients in protozoa, sponges, cnidarians, platyhelminths, rotifers, bivalve molluscs and primitive chordates. Extracellular Digestion is the enzymatic breakdown of larger pieces of food into smaller diffusable molecules usually in a special organ or cavity.
Q.10. How do you continuous and discontinuous feeding differ?
Ans. Many slow moving, or sessile animals, such as tube worms and barnacles continuously strain small food particles from the water all the time. Such animals are called continuous feeders, and their mode of feeding is called continuous feeding. Usually the animals are small and the food is abundant around them.
Discontinuous feeders are active, sometimes highly mobile animals with digestive specializations. They take in large meals that is either ground up, or stored, or both. Herbivores and carnivores are discontinuous feeders, and their mode of feeding is called discontinuous feeding.
.11. What protists and animals utilize surface nutrient absorption?
- Some highly specialized animals directly absorb nutrients from the external
medium across their body surfaces. This medium may be nutrient rich sea water, fluid in other animals, digestive tracts, or body fluid of other anitnals. For
example, some free living protists, such as Chilomonas, absorb all of their nutrients across their body surface. The endoparasitic protozoa, cestode worms, endoparasitic gastropods, and crustaceans, all of which lack digestive systems, absorb nutrients across their body surface.
0.12. How do incomplete and complete digestive tracts differ? Which animals possess each one?
Ans. In primitive, multicellular animals, such as cnidarians, the gut is a blind (closed) sac called a gastrovascular cavity. Same is the case of planarians and trematodes (liver flukes). Their digestive gut has only one opening which is both entrance and exist, thus it is an incomplete digestive tract. Whereas a complete digestive tract has an opening for ingress, called mouth, and an opening for egress called anus at the opposite end of the digestive tube. A complete digestive tract permits the one way flow of ingested food without mixing it with previously ingested food or waste. Complete digestive tract (present in aschelminths, annelids, molluscs, arthropods, echinoderms and chordates etc.) also has the advantage of progressive digestive processing in specialized regions along the system.
Q.13. What is the function of diverticulae in bivalve molluscs?
Ans. The stomach of a bivalve mollusc contains a crystalline style, gastric shield, and diverticulated region. These diverticulae are blind-ending sacs that increase the surface area for absorption and intracellular digestion. A progressive passage of Feeding