25-1 copyright 2010 mcgraw-hill australia pty ltd powerpoint slides to accompany biology: an...

25-1Copyright 2010 McGraw-Hill Australia Pty Ltd PowerPoint slides to accompany Biology: An Australian focus 4e by Knox, Ladiges, Evans and SaintSlides prepared by Karen Burke da Silva, Flinders University

Chapter 25: Animal and human nutrition


What nutrients do animals need?• Animals are heterotrophs

– cannot synthesise organic compounds from inorganic molecules

– rely on other organisms for nutrients

• Nutrients– organic compounds

carbohydrates, lipids

– chemical compounds amino acids, fatty acids vitamins, minerals


Plants as food• Plant tissues

– mostly carbohydrate monosaccharides, disaccharides, starches cellulose, pectin

– some lipid (mostly unsaturated fatty acids)– little protein– minerals depend on soil

• Composition may change seasonally and with locality


Animals as food• Animal tissues

– mostly protein– some lipid (saturated fatty acids, unsaturated fatty acids

in fish)– little carbohydrate

• Carnivores can produce glucose from proteins and other materials– gluconeogenesis


Fig. 25.2: Composition of some foods


How much food do animals require?• Nutrient requirements depend on

– age– reproductive state– metabolic rate

• Metabolic rate varies with– level of activity– body mass– environmental conditions


Basal metabolic rate• Endotherms

– metabolic rate in inactive animal in thermoneutral environment (within thermal comfort zone)

• Ectotherms– metabolic rate in inactive animal is temperature-

dependent


Metabolic rate and body mass• Relationship between metabolic rate and body

mass– mass-specific metabolic rate

metabolic rate per unit body mass

– small animals require more energy per unit body mass than do large animals

• Relationship between body mass and quality of food– small animals eat higher-quality (more energy-rich) food

than do large animals


Fig. 25.4: Nutritional quality and body mass


The digestive process• Food must be broken down into molecules small

enough to enter cells– digestion

• Process of digestion– physical

mechanical activity of teeth or gizzard

– enzymatic chemical action of enzymes


Enzymatic digestion• Digestive enzymes usually have low specificity

– act on types of substrates (e.g. proteins) rather than on specific bonds

• Sequential breakdown– complex molecules are broken down into successively

simpler ones as they pass through the gut


Control of digestive secretion in humans• Nervous control

– saliva: is under nervous control and contains salivary enzymes

• Hormonal control– gastrin: stimulates release of hydrochloric acid and

pepsinogen in stomach– secretin: stimulates release of bile from gall bladder– cholecystokinin: stimulates release of trypsinogen from

pancreas

Question 1:

If acid and enzymes in the stomach can digest meat and other foods, why is the stomach lining itself not digested?

a) Digestion of foods does not take place until food exits the stomach

b) Very little hydrochloric acid is produced in the stomach

c) The stomach secretes a layer of mucus forming a layer that coats the stomach lining

d) The pH level in the stomach is nearly neutral so there is no need to worry about the lining


Box 25.1: Stomach ulcers and the Nobel Prize

• Australians Robin Warren and Barry Marshall won the Nobel Prize for discovering role of Heliobacter pylori in gastric ulcers

• Marshall infected himself deliberately



Intracellular and extracellular digestion• Intracellular digestion

– food taken into the cell for digestion is exposed to enzymes while enclosed in a vacuole

• Extracellular digestion – food digested externally is exposed to mechanical and

chemical (enzyme) digestion outside the cells– breakdown products are taken into the cells after

digestion


Digestive systems• Single-celled organisms and sponge cells engulf

food that they digest in intracellular vacuoles– phagocytosis

• Multicelled organisms have specialised organs and tissue for digestion– vary in complexity from blind-ending digestive cavities to

digestive systems with associated secretory organs

Fig. 25.8: Amoeba feeding



Simple digestive cavities• A simple sac-like gut with specialised digestive

tissue is found in cnidarians (corals, sea anemones and allies)– waste expelled through mouth– water dilutes action of enzymes

• A similar gut is found in platyhelminthes (flatworms)– convoluted gut increases surface area for absorption– decreases distance travelled by diffusing nutrients


Fig. 25.10: Gastrovascular cavity of Hydra


Two openings: one-way movement of food• Food passes through gut in one direction

– waste is eliminated at terminal anus

• Regional specialisation of gut, allowing sequential secretion of enzymes

• Food moved along gut by – body movements – ingestion of more food– peristalsis in animals with muscular gut wall

Question 2:

What are the advantages of a one-way digestive tract?

a) It is less complex and more efficient, so it uses less energy

b) Animals with a one-way digestive system can typically eat more varied food than others

c) One-way gut systems are not very susceptible to poisons

d) All of the above



Chitinous mouthparts: arthropods• Chitinous paired mouthparts in arthropods

– specialisation in diet

• In insects, modification of the basic pattern of mouthparts allows a range of diets, including liquid feeders– nectar– plant sap– fruit– blood– tears


Jaws and teeth: vertebrates• Teeth covered with hard enamel• Fish

– teeth and jaws specialised for different diets needle-like teeth in predators flattened teeth in herbivores

– specialist feeders molluscivores polyp predators

• Teeth-bearing bones in upper and lower jaws can be moved– kinesis


Jaws and teeth: vertebrates (cont.)• Reptiles

– undifferentiated peg-like teeth– no lateral movement in jaw for chewing– snakes can disarticulate lower jaw and move elements

independently

• Birds– consume easily-digestible food– teeth lost to reduce weight for flight– mechanical processing by muscular gizzard

Fig. 25.15: Bird digestive system



Mammals• Teeth differentiated

– specialised for different functions

• Incisors grasp and hold• Canines stab and grip• Premolars shear• Molars grind


Mammals (cont.)• Teeth differentiated

– specialised for different diets

• Herbivores: crushing and grinding teeth for tough plant fibres

• Carnivores: tearing and shearing teeth for animal flesh

• Insectivores: crushing and puncturing teeth for invertebrate exoskeletons

Fig. 25.16: Tasmanian devil


Fig. 25.17: Eastern grey kangaroo



Filter feeding• Animals extract small organisms or other particles

by filtering large volumes of water• Examples

– invertebrates sponges, bivalves, tunicates

– vertebrates whale sharks, fish, flamingos, baleen whales

Fig. 25.19a: Baleen whale



Digesting cellulose• Structural materials in cell walls are difficult to

digest– structural carbohydrates inaccessible to most herbivores

• Cellulose broken down by enzyme cellulase– few animals produce cellulase– many have colonies of symbiotic bacteria and protists in

gut these produce cellulase microbial fermentation


Microbial fermentation• Symbiotic bacteria and protists

– hydrolyse cellulose into glucose– use glucose– produce short-chain fatty acids as wastes

acetic acid propionic acid butyric acid

– also ferment proteins

• Host – uses fatty acids as energy source– digests microbes for essential amino acids


Site of microbial fermentation• Foregut

– food held in anterior part of stomach– foregut fermenters

example: kangaroos

– ruminant foregut fermenters example: sheep

• Hindgut– food held in caecum and colon

example: koala


Fig. 25.20a: Foregut fermentation


Fig. 25.20b: Foregut fermentation


Ruminants• Ruminants regurgitate contents of anterior

stomach (rumen, reticulum) and chew it again– cannot pass through to omasum unless particles are

small enough

• Food retained for prolonged period– extends time for fermentation

• High fibre/low quality foods must be chewed for longer than low fibre/high quality food– limits amount of food that can pass through gut per unit of

time


Fig. 25.23b: Hindgut fermentation


Hindgut fermentation• Sugars and proteins in cell contents hydrolysed by

herbivore’s digestive enzymes• Undigested cell walls pass through to hindgut

– site of microbial fermentation

• Microbes not digested (as they are in foregut fermenters)– pass out in faeces, so source of amino acids is lost

• Microbial protein recovered by caecotrophy (coprophagy)

Summary• Animals are heterotrophic and must obtain organic

compounds from other organisms• All animals need energy, nitrogen-containing

compounds, fats, vitamins, minerals and water• Plant tissues are rich in carbohydrates, but

generally poor sources of protein. The reverse is true for animal tissues

• Digestion is necessary for food to be absorbed• Animal evolution has resulted in a diverse range of

digestive systems specialised to utilise very different foods


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