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Biology
Preliminary Course
Stage 6
Patterns in nature
Part 7: Transporting materials in animals
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Introduction ................................................................................2
Transport systems in animals ....................................................3
Respiratory system...............................................................................3
Circulatory system................................................................................3
Excretory system..................................................................................4
Circulatory systems....................................................................5
Gas exchange in animals...........................................................8
Insects...................................................................................................8
Fish .....................................................................................................10
Frogs ...................................................................................................11
Mammals ............................................................................................12
Investigative technology...........................................................16
Exercises–Part 7......................................................................19
Part 7: Transporting materials in animals
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Introduction
In plants and animals transport systems and gaseous exchange move chemicals through the
internal environment as well as the external environment.
In the previous parts you have identified the nutrients required by living things and how they
are obtained form the surroundings. In this part you will be looking at how these nutrients are
transported around animals.
In this part you will be given opportunities to learn to:
•
compare the roles of the respiratory, circulatory and excretory systems
•
identify and compare the gas exchange surfaces in an insect, a frog, a fish and a mammal
•
explain the relationship between the requirements of cells and transport system in
multicellular organisms
•
compare open and closed circulatory systems using one vertebrate and one invertebrate as
examples
In this part you will be given opportunities to:
•
use available evidence to discuss, using examples, the role of technologies, such as the
use of radioisotopes in tracing the path of elements through living plants and animals.
Extract 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/syllabus2000_lista.html
This version November 2002.
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Patterns in nature
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Transport systems in
animals
In animals there are three systems that move materials around the body and between the body
and the surrounding environment.
These systems are:
•
respiratory system
•
circulatory system
•
excretory system.
Respiratory system
The respiratory system is responsible for the movement of gases throughout the body.
Oxygen is required for every cell in the body and carbon dioxide must be removed from every
cell in the body.
The respiratory system performs this function. Organs that are part of the respiratory system
of animals are lungs, gills and spiracles in insects.
Circulatory system
The circulatory system transports food, oxygen and wastes throughout the body. Every cell
has requirements for nutrients and must get rid of poisonous waste materials. This is the role
of the circulatory system. Organs of circulatory systems are heart, veins, arteries, capillaries
and the haemocoel in insects. Circulatory systems may be open or closed.
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Excretory system
All animals need to excrete wastes produced from metabolic processes in their cells. A
build–up of wastes can produce unwanted effects and many substances such as urea can
become toxic in excess qualities. Wastes substances that have to be remove include water,
carbon dioxide and nitrogenous compounds. Organs of excretion include kidneys, lungs, skin
and malpighian tubules in insects.
Comparison of the systems
All three systems have different tasks but they share common features and common roles.
The circulatory system has a role in the other two systems because the blood vessels move
materials to the organs of respiration and excretion. Organs of the respiratory system such as
the lungs have a function in excretion of carbon dioxide. All three systems work together to
transport nutrients and waste products from where they enter the body to where they leave
the body.
The table below summarises this information.
Respiratory system
Circulatory system
Excretory system
Organs
Lungs, gills, skin,
spiracles
Heart, blood vessels,
lymph, haemocoel
Kidneys, lungs, skin,
malpighian tubules
Function
Movement of gases
through the body
Transport nutrients and
waste products around the
body
Rid the body of
waste materials,
water balance
Complete Exercise 7.1.
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Circulatory systems
All multicellular plants and animals require a transport mechanism to move nutrients, gases
and wastes to and from cells. These materials need to be moved around an organism’s body
efficiently. This to ensure that all cells obtain the appropriate materials to maintain function
and any products and wastes are removed.
Both plants and animals have methods of transporting materials within the body. However,
the transport of materials occurs in different ways. In this section you will focus on transport
in animals.
The circulatory system transports oxygen, food material and wastes to and from cells. The
movement of the blood through an organism depends on the action of a heart.
All vertebrates and some invertebrates such as earthworms have a closed circulatory system.
This means that blood is transported around an organism within muscular tubes or blood
vessels.
The diagram following shows the movement of blood through the human circulatory system.
Invertebrates such as arthropods have an open circulatory system.
A pool of blood is circulated by the action of a heart, there are no specialised vessels for
transporting blood.
An insect’s blood is in direct contact with its body cells–blood is not contained in blood
vessels as such. The internal space of an insect’s body can be considered as a single blood
vessel called the haemocoel.
This name comes from Greek words: haima (blood) and koilia (hollow). An insect’s
circulation system is in fact not entirely ‘open’ as they have pumping vessels to promote the
flow of blood.
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anterior
vena cava
capillaries
in arms and
head
capillaries
in lungs
capillaries
in lungs
posterior
vena cava
pulmonary
artery
right
atrium
pulmonary
vein
left
atrium
right
ventricle
left
ventricle
hepatic
portal vein
hepatic
artery
capillaries
in liver
mesenteric
vein
capillaries in
stomach and
small intestine
renal
vein
mesenteric
artery
capillaries
in kidneys
renal
artery
capillaries in
legs and
abdominal organs
oxygenated blood
de-oxygenated blood
Human circulatory system – a closed system.
accesory pump
haemocoel
pumping vessel
brain
gut
Insect circulatory system – partially open system.
A closed circulatory system ensures that there is one pathway ensuring tissues are supplied
with blood. It relies on a central heart to pump the blood around within the specialised blood
vessels. These require large amounts of energy. All vertebrates have a closed circulatory
system.
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Open circulatory systems do not require the large amounts of energy required by closed
circulatory systems. They suit smaller animals that do not make rapid
movements.
Patterns
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Complete Exercise 7.2.
Part 7: Transporting materials in animals
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Gas exchange in animals
All animal cells respire. Animal cells respire aerobically (most of the time). They use
oxygen gas in the process and release carbon dioxide gas as a waste product. Animal cells do
not photosynthesise.
In this section you will investigate and compare gas exchange surfaces of an insect, a fish, a
frog and a mammal. The gas exchange tissues and organs of major groups of multicellular
animals are often different.
In this section you will examine those differences.
Insects
Insects do not have lungs or gills. Insects exchange gases with the atmosphere using trachea,
tracheoles and spiracles.
longitudinal
trachea
spiracle
tracheoles
Structures used in gas exchange in an insect.
Insects carry out gas exchange through a series of internal tubes (trachea) that connect to the
outside through holes (spiracles) located at various points on the insect body.
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The trachea branch into smaller and smaller tubes (tracheoles). Tracheoles are very tiny
(about one micron in diameter). The branching into many tiny tubes has two advantages for
the insect.
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•
Because the tracheoles are extensively branched throughout the insect, most cells are
close to specialist gas exchange surfaces.
•
The branching and the small size of the tracheoles greatly increases the surface area to
volume ratio of the gas exchange surfaces.
Fluid collects in the ends of the tracheoles and it is into this fluid that gases dissolve before
diffusing into the surrounding cells.
The tracheoles are close to body cells. When waste gases eg. carbon dioxide concentrations
are higher in the cell than the neighbouring trachea, then the waste gases diffuse out of the
cell. When oxygen levels are higher in the trachea than the surrounding cells oxygen will
diffuse into the cells.
The spiracles connect the trachea to the atmosphere surrounding the insect. When the insect
uses its muscles the trachea are compressed and this causes gases to be pushed out of the
spiracles. When the muscles relax the trachea are not compressed and gases flow back into
the trachea.
Spiracles are able to close to help reduce water loss. Because the internal parts of the body
are very humid it is possible for water be removed as a vapour from the body.
Spiracles also have fine hair–like structures to prevent dust entering the system. If dust were
to enter, the tracheoles could become blocked and this would reduce the efficiency of the gas
exchange surfaces.
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Fish
Most fish use gills for gas exchange. Gills are external structures–they hang outside the main
body cavity and often have a protective cover over them. Gills have a large surface area
because they are thin and highly folded.
Gas exchange in fish
Water enters a fish’s mouth and passes over the gills. When most fish are stationary they gulp
water to maintain the flow over the gills.
This also explains why so many fish (sharks included) swim with their mouth open–this
allows the water to pass into the mouth and over the gills without the need to gulp water.
Gases are exchanged between the surrounding water and the fish on the gill surface. The
gases enter the circulatory system where they are transported to cells throughout the body.
The main blood vessels entering the gills branch into tiny tubes called capillaries.
The capillaries are very close to the gill surface. It is the colour of the blood in the capillaries
that makes gills appear red. Capillaries being tiny and numerous make the surface area to
volume ratio for diffusion of gases very high in the gills.
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Frogs
Frogs have two methods of gas exchange: gas exchange via the lungs and gas exchange via
the skin. The diagram below shows the structures involved.
lungs
diffusion in moist skin
Frogs exchange gases through their lungs and moist skin.
Gas exchange via the lungs
Lungs are internal organs involved in gas exchange. The gas exchange surfaces of terrestrial
organisms are usually internal to prevent desiccation (drying out). You will have noticed that
the gas exchange surfaces of insects (also terrestrial) are internal too.
Frogs ventilate their lungs by positive pressure breathing. This means that they force air into
the lungs. This method of breathing is very different to the negative pressure breathing seen
in mammals. You will look at negative pressure breathing later.
Unlike human nostrils, which stay open all the time, frogs are able to open and close their
nares (nostrils). To breathe, a frog
•
closes its mouth and opens its nares
•
lowers the floor of the mouth causing air to be ‘sucked’ into the mouth cavity
•
closes the nares (nostrils)
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raises the floor of the mouth.
This forces the air in the mouth into the lungs.
Lung structure of a frog
The internal structure of a frog lung is not too dissimilar to a human lung. Air enters the
lungs and then moves through a series of branching tubes. The tubes become smaller and
smaller as they branch (this is becoming a familiar theme for gas exchange). The finest tubes
are in close association with capillaries (small blood vessels). Gases diffuse into and out of
the blood at these sites.
Like the fish, the circulatory system delivers gases to the cells.
The circulatory system also receives the waste gases from cells and delivers them to the lungs.
You will
takeinaanimals
much closer look at the structure of lungs in the next section. 11
Part 7: Transporting
materials
Gas exchange via the skin
The skin of a frog is thin and kept moist by the habitats in which the frog lives. The skin is
permeable to water (unlike human skin).
Frogs dehydrate rapidly if they are not kept in a moist environment.
This is why you find frogs in moist locations.
Gases from the atmosphere dissolve into the moisture on the skin.
From there the gases can diffuse into the capillaries beneath the skin. The skin does not
exchange sufficient gases for all of a frog’s needs. However, the gas exchange is important
and allows the frog to remain submerged for longer than if it had to depend on lungs alone.
While submerged, gaseous exchange occurs on the frog’s skin.
Mammals
Mammalian lungs are internal. This helps to reduce the loss of water and heat through these
structures that have a high surface area to volume ratio.
To get air into the lungs the mammal lowers the air pressure in the lungs. When the air
pressure in the lungs is lower than the surrounding atmosphere, air enters via the nose.
To remove air from the lungs, mammals increase the pressure of the air in the lungs. When
air pressure in the lungs is higher than the surrounding atmosphere air moves out of the lungs.
The structure of the human respiratory system is shown on the diagram on the following page.
nose
nasal cavity
trachea wall
magnified
epiglottis
cilia
to the stomach
trachea
bronchus
bronchiole
rib
right lung
showing
lobes
left lung
dissected to
show
internal
diaphragm
from pulmonary
artery
cluster of
alveoli
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air
to pulmonary
vein
capillaries
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Structures involved in the exchange of gases in humans.
Air enters the body through the nostrils. The nasal cavity warms the air, filters it and removes
dust. The air then moves into the throat region or pharynx (pronounced farrinks). It enters
the largest air tube–the trachea (pronounced track–ee–ah) through the opening called the
glottis.
The epiglottis is a flap of tissue that closes over the glottis and stops food going down the
wrong way when we swallow.
The trachea branches into two bronchi (pronounced bron–key).
Each bronchus (singular) branches into smaller air passages called bronchioles
(bron–key–oles) and these end in very thin–walled alveoli (pronounced al–vee–oh–lie),
singular alveolus. Blood capillaries are wrapped closely around the alveoli.
It has been estimated that the total surface area of the alveoli of an adult male is about one
third the area of a tennis court. A large surface area obviously allows for a greater quantity of
gases to be exchanged.
The thinness of the walls of the alveoli allows for rapid diffusion of oxygen into the blood and
carbon dioxide out of the blood. The moisture in the alveoli walls allows gases to dissolve.
blood from body
(low in oxygen, high in carbon dioxide)
blood capillary
wall of alveolus
air inhaled
air exhaled
carbon dioxide
oxygen
blood cell
blood to rest of body
(high in oxygen,
low in carbon dioxide)
Movement of material in an alveolus.
Composition of inhaled and exhaled air is shown in the table below.
Gases
Percentage in inhaled air
(%)
Percentage in exhaled air
(%)
oxygen
21
16
0.04
4
about 80
about 80
varies according to the
humidity of the air
more than in inhaled air
carbon dioxide
nitrogen
water vapour
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Air passages
Rings of cartilage keep the trachea and bronchi open and prevent them closing when the air
pressure inside the body falls. The lining cells of the air passages have numerous cilia
(sill–ee–ah). These are minute hair–like projections that sweep to and fro.
Mucus is secreted by special gland cells, also present in the lining or epithelial
(ep–e–theel–e–al) cells. Dust particles and bacteria in the air are trapped by the mucus film.
The movements of the cilia sweep them away in the mucus to the larynx and the mucus is
swallowed or coughed up.
The nose hairs and mucus also trap dust and foreign particles.
Around the lungs is a membrane, the pleural (ploo–ral) membrane, which covers the outside
of the lungs and the inside of the chest cavity.
It contains a fluid that lubricates the surface so that there is no friction between the tissues
during breathing movements.
The mechanism of breathing
In mammals, breathing refers to the movements of the chest that result in air entering and
leaving the lungs.
The movement of air in and out of our chest is bought about by changes in the pressure of the
air in the chest cavity. This pressure varies because the volume of the chest cavity varies.
The chest cavity is airtight and enclosed by ribs with intercostal (inter–cos–tal) muscle
between them.
At the base of the chest cavity is the diaphragm (die–ah–fram).
The diaphragm is the muscular sheet separating the chest (also called thorax) and abdomen.
At rest, the diaphragm is curved upwards. The intercostal muscles relax at the same time and
the ribs move downwards and inwards.
These collapsing movements reduce the size of the chest cavity, increase the pressure of the
air in the lungs and thus force it out.
During inhalation, the diaphragm contracts and flattens, being more taunt or tight in this state.
At the same time, the intercostal muscles contract and move the rib cage up and outwards.
This increases the volume of the chest cavity and reduces the pressure of the air in it. Air thus
moves into the lungs. You can check these movements by placing your fingers over your rib
cage as you inhale and exhale.
Complete Exercise 7.3.
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Investigative technology
Much of what is known about the structure and function of living things has been directly
associated with the improvements in technology available.
New technology is increasing the range of investigative methods in research laboratories,
industry, environmental management and in the medical profession. The use of radioisotopes
have improved productivity and gained information that cannot be obtained in any other way.
Radioisotopes produce radioactive emissions that can be easily detected. This property makes
radioisotopes very useful as tracers.
Radioactive materials can be tracked through a process, system or organism. Examples of use
include mapping pathways of nutrients and toxins through ecosystems, absorption of nutrients
by plants and tracing metabolic pathways. Increasingly medical diagnosis is making use of
tracers for organ and tissue function.
Many chemical elements have isotopes. (Isotopes have the same number of protons but a
different number of neutrons in the nucleus of an atom.) Some isotopes are unstable and emit
alpha or beta particles and sometimes gamma radiation.
Tracers can be used to follow movement of substances in large amounts or at molecular or
even atomic levels. The observations are made by measuring the radioactivity or by
measuring the relative abundance of the stable isotopes. The instruments used for detecting
the tracers pathway include electroscopes, scintillation counters, the Geiger–Müller counter
and the mass spectrometer.
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Radioactive tracers
Radiation is used in nuclear medicine to diagnose the functioning of organs such as the liver
and kidneys. Radioactive tracers are used which emit gamma rays for very short periods of
time. Radioactive materials are introduced into the body orally, by injected or they are
inhaled.
An image of the organ showing the location of the radioisotope is used in diagnosis. An
unusual pattern indicates a malfunction in the organ. Bone and other tissue can be seen much
more clearly using these imaging techniques than by x–rays.
Blood flow to the brain, liver and kidney function and bone growth can be diagnosed using
radioisotopes as tracers. The amount of radioisotope given to patient is a very small dose,
only enough to obtain an image for diagnosis.
Technetium–99 is a very common isotope used in medicine.
It has a half–life of six hours. Technetium–99 emits low energy gamma rays so the patient
receives only a very low radiation dose.
Geiger counters
A Geiger counter is a machine that measures radioactivity.
In the experiment on the following page radioactive carbon was taken in by the leaves
through the process of photosynthesis. The Geiger counter was used to measure the amount
of radioactive carbon in the leaves and in the fruit. The next day the readings showed that the
radioactive carbon had moved from the leaf to the fruit.
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Day 1
sugar with radioactive carbon on scraped leaf
Geiger counter
HIGH
tomato fruit
Geiger counter
LOW
Day 2
sugar with radioactive carbon on scraped leaf
Geiger counter
LOW
tomato fruit
Geiger counter
HIGH
Gather information from secondary sources on the use of radioisotopes in
tracing the path of elements through living plants and animals.
You will need to carry out a search of secondary information sources such as
contacting research institutions such as ANSTO, CSIRO or the Internet.
Conventional sources such as libraries will have many references you can
use and may be a good place to start.
Process the information by answering the questions in Exercise 7.4.
Part 7: Transporting materials in animals
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Exercises - Part 7
Exercises 7.1 to 7.4
Name: _________________________________
Exercise 7.1: Transport systems in animals
Compare the roles of the excretory, respiratory and circulatory systems in the body. systems
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Exercise 7.2: Circulatory systems
a)
What is the role of the circulatory system in humans?
_____________________________________________________
_____________________________________________________
b) What is the difference between open and closed circulatory systems? Give examples.
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Patterns in nature
c)
Which system is more efficient – open or closed circulatory system? Give reasons.
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Exercise 7.3: Comparison of gas exchange
Identify and compare the gas exchange surfaces in an insect, a frog a fish and a mammal by
filling in the table below.
Organism
Name of gas
exchange structures
insect
frog
Surface Area/Volume
ratio
Gas exchange
structures
internal/external
high
skin
low
lungs
high
external
fish
mammal
internal
Exercise 7.4: Radioactive tracers
Discuss the role of radioisotopes as tracers in medicine. What are the issues? Provide points
for and against the use of radioactive materials in medicine.
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Patterns in nature