Transcript 25-8 Metabolic rate and body mass

Chapter 25: Animal and human
nutrition
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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
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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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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
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Fig. 25.2: Composition of some foods
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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
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Basal metabolic rate
• Endotherms
– metabolic rate in inactive animal in thermoneutral
environment (within thermal comfort zone)
• Ectotherms
– metabolic rate in inactive animal is temperaturedependent
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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
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25-8
Fig. 25.4: Nutritional quality and body
mass
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25-9
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
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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
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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
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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
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25-13
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
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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
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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
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25-16
Fig. 25.8: Amoeba feeding
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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
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Fig. 25.10: Gastrovascular cavity of
Hydra
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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
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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
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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
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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
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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
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Fig. 25.15: Bird digestive system
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Mammals
• Teeth differentiated
– specialised for different functions
•
•
•
•
Incisors grasp and hold
Canines stab and grip
Premolars shear
Molars grind
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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
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Fig. 25.16: Tasmanian devil
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Fig. 25.17: Eastern grey kangaroo
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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
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Fig. 25.19a: Baleen whale
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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
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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
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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
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Fig. 25.20a: Foregut fermentation
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Fig. 25.20b: Foregut fermentation
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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
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Fig. 25.23b: Hindgut fermentation
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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)
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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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