Heterotrophs Obtaining Nutrients

Patterns in Nature
Topic 12: Heterotrophs Obtaining Nutrients
Part of the Patterns in Nature Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
DOT Point
 Describe the role of teeth in increasing the surface area of
complex foods for exposure to digestive chemicals
Heterotrophs Obtaining Nutrients
Heterotrophs are living things that must feed on others because
they cannot provide their own energy supply by photosynthesis.
Obtaining nutrients and energy from food involves several
1. Ingestion: the intake of complex food (eating)
2. Digestion: the breakdown of food into soluable molecules
that can easily be absorbed
3. Absorption: Basic units of food absorbed into the
4. Assimilation: turning the ‘food’ into tissue
5. Egestion: elimination of wastes
We’ll look at Ingestion and Digestion today
Teeth and Surface Area
Most vertebrates have jaws and teeth that enable them to obtain
and process foods. In this section we will mainly be referring
to mammals.
Teeth and Surface Area
The digestion of foods involves two stages:
1. Mechanical or physical breakdown, where food is
chewed and large chunks are physically broken down into
smaller pieces.
2. Chemical breakdown, where digestive enzymes act on
the food to chemically break down the large complex
molecules into simpler, smaller molecules.
Teeth and Surface Area
Digestive enzymes function more efficiently if the food to
which they are exposed has a large surface area to volume ratio.
Large chunks of food are broken down by the teeth which
exposes a greater surface area on which the chemicals can act.
The volume of food is the same, but the overall surface area to volume
ratio is increased.
Teeth of mammals
There are four main teeth types present in mammals, each with
specific functions:
1. Incisors (front teeth): used to grasp, hold and bite food
2. Canines (‘eye’ teeth or ‘fangs’): used for stabbing and
gripping prey and for tearing flesh.
3. Premolars (cheek teeth): used for chewing and for
cutting flesh and cracking hard body parts such as bones
and shells.
4. Molars (back teeth): used for grinding and chewing
Teeth of mammals
Omnivores (animals that eat both plants and animals) have all
four types of teeth. The teeth of herbivores and carnivores
differ in their structural detail to best cope with its specialised
Teeth of mammals
Herbivores: are heterotrophs that consume plant material.
They have front teeth adapted for tearing off vegetation and
back teeth adapted to chewing an abrasive, high fibre diet.
Teeth of mammals
The incisors are used to bite off vegetation. The molars are
broad crushing teeth with relatively large surface areas. The
molars are specially equipped with ridges to help break open
the cellulose cell walls of plants.
In herbivores an enormous amount of chewing is needed.
Teeth of mammals
Canine teeth are absent in herbivore jaws, leaving a gap called
the diastema, which assists manipulation of food onto the
molars, keeping chewed and un-chewed food separate.
Teeth of mammals
Have powerful jaws and well
developed canine teeth,
conical in shape and
specialised for holding and
killing prey and tearing meat
from the bone.
Teeth of mammals
Meat is torn off in chunks, and many carnivores have molars
with deep cusps to briefly chew the meat, increasing the surface
area before swallowing it.
Some carnivores such as cats have carnassial cheek teeth, adapted for
slicing and shearing meat and they have lost their molars.
Teeth of mammals
Some carnivores such as insectivores have teeth adapted to
piercing and penetrating the tough cuticle of their prey. They
puncture and crush the exoskeleton with their premolars and
then use these teeth to shear the inner tissues.
DOT Point
 Explain the relationship between the length and overall
complexity of digestive systems of a vertebrate herbivore and
a vertebrate carnivore with respect to:
 The chemical composition of their diet
 The functions of the structures involved
Plant material high in fibre and starch provides the main energy
source in the diet of herbivores. This includes sugars, proteins
and oils.
Cellulose and other cell wall thickenings are difficult to digest and they
create a barrier around the cell contents which are capable of being
Digestive Tract:
Herbivores have adaptations of their digestive tract that enables
them to deal with this diet. Most large herbivores rely on
microbes in their gut to digest cellulose.
Digestive Tract:
To allow for the slow process
of microbial fermentation,
the gut of these herbivores is
complex and very long
relative to their body size.
An increase in the length
provides space to hold large
quantities of food and time for
microbes to break down the food
so it can be absorbed.
Digestive Tract:
Small herbivores often eat
plant tissue that has much
less cell wall material and is
energy rich. The gut of
these organisms are usually
simple and short, in
comparison to that of
grazers and browsers.
The plant tissue in their diet is
easier to digest and high in
Carnivores eat animal matter which is made up of cells, which
the content of, is more accessible (no cell wall) and are
therefore easier to digest.
Animal matter is high in protein, low in fibre and usually has a higher
energy content than that of plants.
So even though the food of carnivores may be more difficult to
obtain, it has higher nutritional value and can be consumed in
lesser quantities.
There is a small amount of fat and very little carbohydrates associated
with their diet.
Digestive Tract:
The gut is relatively
short and
unspecialised, as fat
and protein is
relatively easy to
Very little undigested
material is egested, due to
the low fibre content of
their diet.
Adaptations for feeding are thought to be one of the main
forces behind the evolutionary process. If an adaptation makes
it easier for an organism to obtain food it is to their advantage
because competition is reduced.
Microbial fermentation is a good example
Students to complete:
-DOT Point 3.7 and 3.8 (Prelim Dot Point Text pg 40)
**Reminder to hand out Table 3.2 The Digestive System of
Humans (Bio in Focus Text pg152)

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