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Biology
Preliminary Course
Stage 6
Patterns in nature
Part 6: Obtaining materials in animals
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Contents
Introduction................................................................................ 2
Obtaining nutrients in animals ................................................... 4
Increased surface area in animals ......................................................4
Digestion in grazing herbivores ...........................................................6
Digestion in carnivores ........................................................................8
Nectar feeders....................................................................................10
Suggested answers ................................................................. 13
Exercises–Part 6 ..................................................................... 15
Part 6: Obtaining materials in animals
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Introduction
Animals have specialised cells, tissues and organs to obtain the nutrition
they require and carry out their body processes. Some of these will be
investigated in this part.
In this part you will be given opportunities to learn to:
•
describe the role of teeth in increasing the surface area of complex
foods for exposure to digestive chemicals
•
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.
In this part you will be given opportunities to:
•
perform a first–hand investigation to demonstrate the relationship
between surface area and rate of reaction
•
identify data sources, gather, process, analyse and present
information from secondary sources and use available evidence to
compare the digestive systems of mammals, including a grazing
herbivore, carnivore and a predominantly nectar feeder.
Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. The most up-to-date version can be found on the Board’s website
at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html.
This version November 2002.
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To complete the practical activities in this part you will require the
following equipment. Alternative exercises have been included.
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mortar and pestle or a suitable grinding tool and vessel
petri dish or small plate
Bunsen burner or hotplate
3 test tubes or similar
sand
small quantity of liver from a butcher
•
hydrogen peroxide (this can be purchased at a pharmacist)
Part 6: Obtaining materials in animals
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Obtaining nutrients in animals
You have seen that plants have structures such as root hairs that increase
surface area for absorption. Animals have increased surface area for the
absorption of nutrients, as well.
Food and water are taken in through the mouth and pass through the
alimentary canal. The nutrients are digested and absorbed along the way.
The physical breakdown in the mouth by the teeth increases the surface
area for chemical digestion in the stomach and the small intestine.
The lining of the intestines is made of folded membranes called villi that
increase the surface area for the absorption of nutrients.
Increased surface area in animals
The following activity will help you demonstrate how increased surface
area assists the digestive process in the body. If you grind up a substance
you produce a much larger surface area for any reaction to occur.
This is what happens in your mouth when you chew on your food.
You increase the surface area for enzymes to work on the food.
In this experiment you will compare the rate of reaction of a whole piece
of liver and one that has been ground up. The whole piece of liver will
have a smaller SA:V than the equal size piece of ground liver.
Hydrogen peroxide is broken down by an enzyme found in the liver.
This produces oxygen which can be seen as bubbles in the container.
Materials required:
4
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mortar and pestle or a suitable grinding tool and vessel
•
petri dish or small plate
•
3 test tubes or similar
•
Bunsen burner or hotplate
•
sand
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small quantity of liver from a butcher
•
hydrogen peroxide (this can be purchased at a chemist)
Procedure
1
Divide the liver into two equal quantities.
2
Place a small quantity of clean sand into a test tube or onto a dish or
plate.
3
Take one piece of liver and grind it together with the sand and place
into test tube or onto dish.
4
Place one piece (whole) into a test tube or onto dish.
5
Add an equal volume of hydrogen peroxide to each of the four test
tubes and observe carefully.
Observations
1
Describe what is seen in each of the test tubes by completing the
table below.
2
A control is used in an experiment to ensure that a fair test is being
carried out. Which test tube is the control in this experiment?
_____________________________________________________
Results
Sample
Description of reaction
Amount of gas produced
sand only
fresh liver ground with
sand
whole piece of liver
Conclusion
What can you say about surface area and rate of reaction from this
experiment?
_________________________________________________________
_________________________________________________________
Part 6: Obtaining materials in animals
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Digestion in grazing herbivores
Digestion begins in the mouth. The shape of the teeth give a clue to the
type of food eaten by an animal. Herbivores have large grinding molars
that crush the food to increase the surface area for digestion.
incisors
molars
Herbivore teeth.
Herbivores have diets high in complex carbohydrates. These complex
carbohydrates such as cellulose and lignin require a complex digestive
system.
The ruminant digestive system. Can you identify the components?
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Grazing herbivores use micro–organisms contained within their digestive
systems to break down complex carbohydrates such as cellulose.
The process of cellulose digestion is called fermentation. This may occur
before or after the stomach.
Many farm animals like sheep, cattle, goats and camels are foregut
fermenters. The have complex digestive systems with three or four
stomach compartments to deal with their diet. The largest of these
stomach compartments is called the rumen, so they are called
ruminant animals.
Cattle, for example, have a stomach that is made of four compartments
called the rumen, reticulum, omasum and abomasum. It is the special
ruminant bacteria that are located in the rumen that carry out the majority
of the fibre digestion.
oesophagus
reticulum
omasum
rumen
abomasum
duodenum
small
intestine
caecum
large
intestine
Organs of the ruminant digestive system.
Ruminant animals require water, carbohydrates, proteins, fats, vitamins
and minerals in their diet.
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Animals use carbohydrates to provide energy. All animals can make
use of sugars and starches in food, but only ruminants such as sheep
and cattle can make full use of the complex carbohydrate, cellulose.
The great benefit of the ruminant digestive system is that it can
decompose cellulose through the activity of micro–organisms in
the rumen.
Proteins are the basic structural material of many parts of an animal and
its products. In the rumen the protein that an animal eats is altered.
The protein requirements of grazing animals are mostly supplied from
the pasture they graze. However, ruminants are able to make their own
proteins through the action of micro–organisms.
Cell contents also contain minerals. These are chemical substances
needed by all animals for proper growth and development.
Most ruminant animals live in sunlight and have access to green feed,
so they usually do not suffer from a shortage of vitamins. Ruminant
animals have an inbuilt supply of the B group vitamins, which are
synthesised by micro–organisms in the rumen.
The other main group of grazing herbivores are the hindgut fermenters.
Examples of this group are horses, rabbits and possums. They carry out
cellulose digestion in an organ after the stomach called the caecum.
In rabbits the caecum has the capacity ten times the stomach and it fills
most of the abdomen.
Digestion in carnivores
Carnivore teeth are adapted to catching and holding prey and then
ripping it to pieces. They have large canines. Examples of carnivores
are dogs, cats and the Tasmanian devil.
incisors
canines
molars
Carnivore teeth.
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The digestive systems of carnivores are the simplest among mammals.
The large intestine of carnivores is relatively shorter than herbivores.
The food source for carnivores is animal cells eg. muscle cells. These do
not have a cell wall and so they can be digested rapidly. Muscle cells in
meat are high in protein so carnivores do not need to eat large amounts of
food to gain the same amount of nutrients that a herbivore requires.
Muscle cells are also higher in energy content and take less energy to
digest than the food of herbivores.
The differences in food eaten are reflected in the different structures in
the digestive systems of herbivores and carnivores. Herbivores have to
take in a large amount of food that requires complex digestion.
They have large specialised digestive systems. Carnivores take in a
smaller amount of high energy food and have smaller and less complex
digestive systems.
stomach
small intestine
dog
(Canis familiaris)
10 cm
(for a 80 cm
length dog)
rectum
colon
Digestive system of a dog.
1
What type of teeth is used for eating meat? Can you suggest a reason
for their special shape?
_____________________________________________________
_____________________________________________________
2
What type of teeth is used by animals that eat only plants? Can you
suggest why they have a different shape to that of the meat eaters?
_____________________________________________________
_____________________________________________________
3
What type of teeth do humans have? How does this reflect the type
of food eaten?
_____________________________________________________
_____________________________________________________
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4
Carnivores do not possess a four chambered stomach. They do not
have a use for fibre digestion, as they consume only meat.
Carnivorous animals have only one stomach chamber.
How many stomach chambers do humans have? Can you suggest a
reason for this?
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
Nectar feeders
The length and structure of the intestines will vary according to the diet
of the organism. The more complex the substances that enter the
intestines the longer they are. Organisms such as nectar feeders that eat
simple carbohydrates will have a shorter digestive tract overall compared
to that of the animals that eat complex carbohydrates such as the
herbivores and carnivores. This is due to the fact that their primary food
source is simple sugars which are easily digested or broken down.
stomach
honey possum
(Tarsipes rostratus)
small intestine
1 cm
rectum
colon
The honey possum – an example of a nectar feeder.
Comparison of different digestive systems
You have seen from the previous information that the digestive systems
of different species have different structures that reflect their food source.
Each has structural differences that allow the animal to obtain the
appropriate nutrients. The table on the next page summarises this
information.
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Feature
Herbivore
Carnivore
Nectar feeder
major chemical
composition of
diet
complex
carbohydrates
including
cellulose
proteins, fats
simple sugars,
protein
teeth
large grinding
molars to crush
food
sharp canines
and molars for
catching and
holding prey
few teeth
time in mouth
chewed for a long
period of time
rapidly swallowed
rapidly swallowed
time spent eating
most of the day
short feeding
period
Honey possums
can drink up to
20% of their body
mass in minutes
stomach
foregut
fermenters
(ruminants eg.
cattle) have a four
chambered
stomach for break
down of cellulose
small, one
chambered
stomach
two chambered
stomach, one
may be for nectar
storage
intestines
hindgut
fermenters have
an enlarged
caecum for break
down of cellulose
short and
unspecialised
large and small
intestines
indistinguishable,
no caecum
You will need to gather, process and analyse information from secondary
sources to carry out the following task.
Suggested places to look for information include Internet, journal articles,
and text–books. There is also some information above. Make sure your
source is reliable by checking it against other sources. A table such as the
one above is a good way of presenting information.
You need to identify your data source and present information to compare
the digestive systems of mammals, including a grazing herbivore, carnivore
and a nectar feeder There are some good starting points on the LMP website.
http://www.lmpc.edu.au/science
Complete Exercise 6.1.
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Suggested answers
Digestion in grazing herbivores
1
Canines and incisors for cutting and tearing the meat, molars for chewing.
2
Incisors for cutting and molars for chewing or grinding.
3
Humans have an omnivorous diet and so have incisors for cutting,
canines for tearing and molars for chewing.
4
Humans have one stomach. They do not eat significantly high
proportions of fibre compared to herbivores and do not have the
ruminant bacteria for this purpose.
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Exercises – Part 6
Exercise 6.1
Name: _________________________________
Exercise 6.1: Obtaining nutrients in animals
a)
Describe the role of teeth in increasing the surface area of food for
the exposure to digestive enzymes.
_____________________________________________________
_____________________________________________________
_____________________________________________________
b) Prepare a table to summarise the differences between the digestive
tract of vertebrate herbivores, carnivores and nectar feeders.
Organise your answers into the columns shown in the table below.
Type of
vertebrate
Chemical
composition of
diet
Structures of the
digestive system
Function of
structure
herbivore
carnivore
nectar feeder
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