Nutrition
• Autotroph – an organism that produces
complex organic compounds from simple
inorganic molecules, using energy from
light or inorganic chemical reactions
– The producers in a food web
• Heterotroph – an organism that obtains
energy by breaking down organic
molecules; cannot derive energy from
photosynthesis or inorganic chemicals
– The consumers in a food web
Nutrition
• Autotrophs
– Plants
– Some Protists
– Some Bacteria
– Nearly all Archaea
• Heterotrophs
– Animals
– Fungi
– Most Protists
– Most Bacteria
Plant Nutrition
• Plants, like animals, require nutrients
• Plants acquire nutrients through
photosynthesis and from the soil
• Soil – the highly weathered outer layer of
the Earth’s crust
– A mixture of sand, rocks, clay, silt, minerals
an microorganisms
– The Earth’s crust include ~92 elements
• Most in the form of inorganic compounds called
minerals
Plant Nutrition
• Soil is composed of minerals, organic
matter, water, air, and organisms
• Soil is full of microorganisms that break
down and recycle organic debris
• Most roots of plants are found within the
topsoil
– Topsoil – a mixture of minerals, living
organisms and humus (partly decayed
organic matter)
Plant Nutrition
Plant Nutrition
• Only minerals that are dissolved in water
are available for uptake by roots
• Approximately one half of the soil volume
is occupied by spaces known as pores,
which may be filled with air or water
• Water held in small pores is readily
available to plants
Plant Nutrition
Plant Nutrition
• If topsoil is lost, the water-holding
capability and nutrient content of the soil
are adversely affected
• >50 billion tons of topsoil are lost from
fields in the US every year!
• The “Dust Bowl” of the 1930s was a
dramatic example of what can happen
when the vegetative cover of soil is
disrupted
The “Dust Bowl”
• Southwestern Great Plains of the U.S. in
the 1930’s
• Poor farming practices combined with
several years of drought enhanced wind
erosion  dust storms
Plant Nutrition
• Acidic (low pH) and saline (“salty”) soils
are challenging habitats for plants
• The pH of a soil affects the release of
minerals from weathering rock; at low pH,
toxic elements may “leech” from rocks
• Most plants grow best at a neutral pH (~7)
• Saline soils are caused by excess
accumulation of salts (Na+, Cl-)
• Excess salt makes it more difficult for plant
to absorb soil moisture
Plant Nutrition
• Plants require 9 macronutrients and 7
micronutrients
– Macronutrients – used by plant in large
quantities
– Micronutrients – used by plant in trace
amounts
– Carbon, oxygen, hydrogen, nitrogen
(essential for amino acids), potassium,
calcium, magnesium (the center of the
chlorophyll molecule), phosphorus, and sulfur
Plant Nutrition
• Plants require ammonia (NH3) or nitrate
(NO3-) to build amino acids
• Most of the nitrogen in the atmosphere is
in the form of Nitrogen gas, N2
• Plants lack the ability to convert N2 to
ammonia, but some bacteria have this
capacity
• Symbiotic relationships between some
plants and these bacteria have evolved
Plant Nutrition
• Nitrogen fixation is very energetically
expensive
• Rhizohium bacteria require oxygen and
carbohydrates to support their energetic
demands
• Nitrogen-fixing bacteria live in close
association with the plant
– with roots
– Housed in plant tissues (nodules)
Plant Nutrition
• Mycorrhizae aid a large
portion of terrestrial plants
• ~90% of vascular plants
have symbiotic
relationships with
mycorrhizal fungi
• Mycorrhizae enhance
phosphorus transfer to
plant, as well as many
micronutrients
http://ecology.botany.ufl.edu/ecologyf02/Art/CH08/JPG/figure%2008-06.jpg
Plant Nutrition
• Some plants are able to obtain nitrogen
directly from other organisms, as animals
do
• These carnivorous plants grow in acidic
soils, such as bogs, that lack organic
nitrogen
• By capturing and digesting small animals
directly, such plants obtain adequate
nitrogen and are able to grow in otherwise
unfavorable conditions
Plant Nutrition
• Carnivorous plants have
modified leaves adapted
for luring and trapping
prey
• Prey is digested with
enzymes secreted from
specialized glands
Carnivorous Plants
• Pitcher plants (common in northeast bogs)
– have pitcher-shaped leaves with cavity
filled with digestive fluid
Carnivorous Plants
• Venus flytrap – (grows in bogs in North
and South Carolina) – has 3 sensitive
hairs on each side of leaf that, when
touched, trigger the two halves of the leaf
to snap together
– Once the prey is enfolded within a leaf,
secreted enzymes from leaf surfaces digest
the prey
Venus flytrap
Carnivorous Plants
• Sundews – secrete sticky mucilage, which
traps small animals, and digestive
enzymes
Plant Nutrition
• Parasitic plants exploit resources of other
plants
– Photosynthetic
– Non-photosynthetic
• 3,000 species
• Adaptations include structures that tap into
the vascular tissue of the host plant so that
nutrients can be siphoned into the
parasitic plant
Parasitic Plants
• Mistletoe – grow attached
to and within the branches
of a tree or shrub
• Photosynthetic, uses the
host mainly for water and
mineral nutrients
• Spread by birds; sprout
from bird feces deposited
on the trunk of trees
http://www.flickr.com/photos/jim-ar/2117900952/
Parasitic Plants
• Indian pipe
– Lacks chlorophyll
– Hooks into host trees
through the fungal
hyphae of the host’s
mycorrhizae
– The conspicuous
portion (above-ground)
of the plant consists of
flowering stems
Parasitic Plants
• Epiphytes – an organism that grows upon,
or attaches to a living plant
• Most commonly refers to higher plants, but
can also include bacteria, fungi, lichens,
mosses, and ferns
• “Air plants” – do not root in the soil
• Obtain moisture from the air or from
dampness (rain and cloud moisture) on
the surface of their hosts
Epiphytes
http://www.flickr.com/photos/pierre_pouliquin/74397619/
Animal Nutrition
The human digestive system
is a marvel of nutritional
storage and acquisition!
Animal Nutrition
• Heterotrophs are divided into 3 groups
based on their food sources
• Herbivores are animals that eat plants
exclusively
• Carnivores are animals that eat other
animals
• Omnivores are animals that eat both
plants and other animals
Animal Nutrition
• Single-celled organisms as well as
sponges digest their food intracellularly
• Other multicellular animals digest their
food extracellularly, within a digestive
cavity
– In Cnidarians and Flatworms, the digestive
cavity called a gastrovascular cavity, has
only one opening that serves as both mouth
and anus
– No specialization; every cell is exposed to all
stages of digestion
Animal Nutrition
• Specialization occurs when the digestive
tract has a separate mouth and anus
• The most primitive digestive tract is seen
in the phylum Nematoda
– A simple tubular gut lined by an epithelial
membrane
• All more complex animals have a digestive
tract specialized in different regions for
ingestion, storage, fragmentation,
digestion, and absorption of food
Animal Nutrition
• The tubular gastrointestinal tract of
vertebrates has 4 layers
– Mucosa – innermost layer, epithelium that
lines the lumen, or interior of the tract
– Submucosa – made of connective tissue
– Muscularis – consists of a double layer of
smooth muscles
– Serosa – epithelial layer, covers the external
surface of the tract
Animal Nutrition
• Ingested food may be stored or first
subjected to physical fragmentation
• Chemical digestion occurs next, which
breaks the food down into subunit
molecules
• Food particles then pass through the gut’s
epithelial lining into the blood (absorption)
• Wastes are excreted from the anus
• Mouth and pharynx
• Esophagus – a
muscular tube that
delivers food to
stomach – site of
preliminary digestion
• Small intestine –
digestive enzymes
continues the digestive
process; products of
digestion are absorbed
across the wall of the
small intestine into the
bloodstream
• Any food product that
remains in small
intestine is emptied
into the large
intestine, where some
of the remaining
water and minerals
are absorbed
• From the large
intestine, wastes
enter the cloaca (nonmammals) or rectum
Animal Nutrition
• Accessory digestive organs
– Liver – largest organ in body; produces bile
which emulsifies fat
– Gallbladder – stores and concentrates the bile
– Pancreas – produces pancreatic juice which
contains digestive enzymes
– Bile and pancreatic juice are secreted into the
small intestine
Animal Nutrition
• Liver – chemically modifies substances
absorbed from the digestive tract before
they reach the rest of the body
– Removes toxins and carcinogens, converting
them to less toxic forms
– Regulates levels of steroid hormones (makes
them more water soluble)
– Produces most proteins found in blood
plasma
Animal Nutrition
• In general, carnivores have shorter
intestines for their size than herbivores
• Herbivores ingest a large amount of plant
cellulose, which resists digestion; these
animals have a long, convoluted small
intestine
Animal Nutrition
• In the mouth, food is physically broken
down by teeth (mastication)
– Similar in function to the gizzard of birds and
worms
• Salivary glands excrete saliva
– Antibacterial agents, mucin production
– Breaks down starch into glucose
– Controlled by the nervous system; tasting,
smelling, or even thinking about food
stimulates salivation
Animal Nutrition
• Vertebrate teeth are adapted to their food
source
• Carnivorous teeth are pointed that lack flat
grinding surfaces
• Herbivores have large, flat teeth suited for
grinding cellulose cell walls of plant tissues
• Humans (omnivores) have carnivore-like
teeth in the front and herbivore-like teeth
in the back
Animal Nutrition
• Swallowing is initiated by voluntary action,
but is continued under involuntary control
• When food is ready to be swallowed, the
tongue moves it to the back of the mouth
• In mammals, the soft palate elevates,
pushing against the back of the wall of the
pharynx
• Elevation of the soft palate seals off the
nasal cavity
• Pressure against the pharynx triggers the
swallowing reflex
Bolus (food)
The Uvula
• The uvula is the
projection from the
posterior edge of the
middle of the soft palate
• Not to be confused with
the epiglottis
• Plays a key role in the
articulation of sound
• Initiates the gag reflex
• Can contribute to
snoring
Animal Nutrition
• The esophagus actively moves a
processed lump of food (bolus) through
muscular action
• Swallowing stimulates successive, unidirectional waves of contraction that move
food along the esophagus into the
stomach
– peristalsis
The Stomach
• The stomach is a sac-like portion of tract
• Has convoluted surface, allowing
expansion
• Stores food (functions as crop of other
animals)
• Contains an extra layer of smooth muscles
for churning food and mixing it with
gastric juice – an acidic secretion of the
tubular gastric glands of the mucosa
The Stomach
• Parietal cells of stomach secrete
hydochloric acid (HCl)
• Chief cells secrete pepsinogen (inactive),
which becomes pepsin (active) at low pH
(~2)
• 2 liters of HCl and other secretions is
produced by human stomach every day!
• The low pH of the stomach helps denature
proteins
The Stomach
• Acidity of stomach also kills most bacteria
ingested with food
• Overproduction of gastric acid can lead to
ulcers, a hole through the wall of the
stomach
• The mixture of partially-digested food and
gastric juice is called chyme; chyme
leaves the stomach and enters the small
intestine
The Stomach
Small Intestine
• Site of terminal digestion of carbohydrates,
lipids, and proteins
• Site of absorption of products of digestion
(amino acids, glucose, fatty acids, etc)
• Efficient digestion takes time, and so only
small amounts of chyme may be
introduced into the small intestine at any
one time
Small intestine
• Longest part of the digestive tract
– Up to 6 meters in humans
• Consists of duodenum, jejunum, and ileum
– Duodenum – first 25 cm; site of most digestion,
receives enzymes from the pancreas and bile
from the liver and gallbladder
– Jejunum and ileum – site of absorption
• Very large surface area (3200 ft2) – folds,
villi and microvilli
– Similar to function of mycorrhizae
Small intestine
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Pancreatic islet
(of Langerhans)
 cell
From liver
 cell
Common Pancreas
bile duct
Gallbladder
Pancreatic
duct
Duodenum
Large intestine
• The large intestine concentrates and
stores wastes
• Much shorter than the small intestine, but
larger diameter
• Small intestine empties directly into the
large intestine at a junction where 2
vestigal structures remain
– The cecum and appendix
Large intestine
• No digestion occurs
• Absorption of water, remaining electrolytes
and vitamin K (products of bacterial
metabolism)
• Many bacteria live and reproduce within
the large intestine; excess bacteria are
incorporated into the feces
• Feces are moved along by peristalsis and
exit the body through the anus
Variations in Vertebrate Digestive
Systems
• Animals lack the enzymes necessary to
digest cellulose, the structural component
of the primary cell wall of green plants
• However, the digestive tracts of some
animals contain bacteria and protists that
convert the otherwise undigestable
cellulose into substances that the host can
absorb
Variations in Vertebrate Digestive
Systems
• Ruminants have a four-chambered
stomach (“foregut fermenters”)
– Rumen – has cellulose-degrading microbes
which convert cellulose into simpler
compounds; contents regurgitated (“cud”) and
re-chewed
– Reticulum
– Omasum
– Abomasum – the true stomach, contents mix
with gastric juices
Variations in Vertebrate Digestive
Systems
• Non-ruminant herbivores, such as horses,
deer and rabbits, digest cellulose in the
cecum (“hindgut fermenters”)
• Cecum – site of microbial digestion of
cellulose
• Regurgitation of contents is not possible
(cecum is located behind the stomach)
• Instead, rodents and lagomorphs (rabbits
and hares) eat their feces (coprophagy)
Variations in Vertebrate Digestive
Systems
• The second passage of food through
coprophagy allows the animal to absorb
the nutrients produced by the organisms in
its cecum
• Coprophagic animals cannot remain
healthy if they are prevented from eating
their feces!
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nonruminant Herbivore
Ruminant Herbivore
Simple stomach, large cecum
Four-chambered stomach with large rumen;
long small and large intestine
Esophagus
Stomach
Small
intestine
Esophagus
Reticulum
Rumen
Abomasum
Omasum
Cecum
Small
intestine
Large
intestine
Anus
Cecum
Spiral
loop
Large
intestine
Anus
Insectivore
Carnivore
Short intestine, no cecum
Short intestine and
colon, small cecum
Esophagus
Small
intestine
Stomach
Esophagus
Stomach
Small
intestine
Large
intestine
Anus
Anus
Cecum
Large
intestine
Animal Nutrition
• The activities of the gastrointestinal tract
are coordinated by the nervous system
and the endocrine system
• The nervous system stimulates salivary
and gastric secretions in response to sight,
smell, and consumption of food
• When food arrives in the stomach,
proteins in the food stimulate the secretion
of gastrin, which triggers the release of
HCl and pepsinogen from the gastric
glands
Animal Nutrition
• After a carbohydrate-rich meal, the liver
and skeletal muscles remove excess
glucose from the blood and store it as
glycogen
• During fasting or exercise (low levels of
glucose), an increased secretion of
glucagon by the pancreas promotes the
breakdown of glycogen and release
glucose (glycogenolysis)
Animal Nutrition
• Type 1 diabetes – insulin-dependent
diabetes, common in children
– Too much glucose, little or no insulin
(mutation, no insulin made or non-functional),
glucose excreted in urine
• Type 2 diabetes – insulin-independent
diabetes, adult onset
– Normal or elevated levels of insulin, but cells
no longer respond to the insulin
– Insulin is the only hormone that decreases
glucose in the body