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Chapter 20: Animal and human
nutrition
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-1
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-2
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
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-3
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-4
Fig. 20.2: Composition of some foods
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-5
Metabolic rate
•
Nutrient requirements depend on
– age
– reproductive state
– metabolic rate
•
Metabolic rate varies with
– level of activity
– body mass
– environmental conditions
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-6
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-7
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-8
Fig. 20.5: Mass-specific metabolic rate
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-9
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-10
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-11
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-12
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-13
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-14
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-15
Fig. 20.12: Gastrovascular cavity of Hydra
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-16
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-17
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-18
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.)
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-19
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
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20-20
Mammals
•
Teeth differentiated
– specialised for different functions
•
Incisors grasp and hold
• Canines stab and grip
• Premolars shear
• Molars grind
(cont.)
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-21
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-22
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-23
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-24
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-25
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-26
Fig. 20.24a: Foregut fermentation
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-27
Fig. 20.24b: Foregut fermentation
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-28
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
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-29
Fig. 20.27b: Hindgut fermentation
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-30
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)
Copyright  2005 McGraw-Hill Australia Pty Ltd
PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
20-31