20-1 copyright 2005 mcgraw-hill australia pty ltd ppts t/a biology: an australian focus 3e by knox,...

20-1Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint

Chapter 20: Animal and human nutrition


Nutrients

• 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. 20.2: Composition of some foods


Metabolic rate

• 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. 20.5: Mass-specific metabolic rate


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


Enzymes

• 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 enzyme secretion

• 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


Intra- 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


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. 20.12: Gastrovascular cavity of Hydra


One-way digestive tract

• 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


Hard mouthparts

• 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


Vertebrate teeth• 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

(cont.)


Vertebrate teeth (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


Mammals

• Teeth differentiated– specialised for different functions

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

(cont.)


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


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


Digesting plants

• 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. 20.24a: Foregut fermentation


Fig. 20.24b: 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. 20.27b: 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 lost

• Microbial protein recovered by caecotrophy (coprophagy)

20-1 copyright 2005 mcgraw-hill australia pty ltd ppts t/a biology: an australian focus 3e by knox,...

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