PRACTICAL 4: RESPIRATION SYSTEM OF FISH, INSECT AND MAMMAL

Objectives:

1) To train students to dissect fish, insect and small mammal

2) To train students how to use dissecting instruments

3) To increase student’s skill in displaying, drawing and labelling respiratory

organs.

4) To enable students to examine the structures of the main organs involved in

respiration (lung, trachea, diaphragm, rib cage and intercostals muscle).

5) To increase student understanding of the process of gas exchange in

animals.

Introduction:

Respiration is a vital living process carried out by all living organisms.

Respiration can be divided into two stages that are external respiration and internal

respiration. External respiration is a mechanical process that maintains a continuous

exchange of gases between the respiratory surfaces of an organism and its

environment. For most organisms, the exchange of gases occurs through a

specialised structure called the respiratory structure. Internal respiration is the

biochemical process in which energy is made available to all living cells. This

process involves the oxidation of organic molecules to release the chemical energy

stored within molecules. There are two types of cellular respiration that are aerobic

respiration and anaerobic respiration.

Hypothesis: Various types of animals have different types of respiratory system.

Literature reviews:

Respiration is the process by which living things break down some kinds of

food chemicals in their bodies and use them as a source of energy. To do so this,

most living things need a supply of oxygen and a means of removing the waste

carbon dioxide. The process of gas exchange, by which oxygen is made to enter the

body and carbon dioxide to leave it, is called breathing. Larger animals have special

organs to make this process very rapid and efficient: examples are the lungs of

humans and other mammals and the gills of fish. Respiration, of which breathing is a

necessary part, is a complex chemical breakdown process in which energy from food

(chemical-potential energy) is made available for all life-processes, including the

movement of muscle and the building up of new and replacement tissues.

Respiration is sometimes said to be rather like a process of burning, with food

as the fuel. This is fundamentally misleading. Burning is a high-temperature process

in which fuel and oxygen are combined chemically very rapidly, so that the burning

material and the environment are strongly heated. In contrast to this, respiration is

low-temperature process in which food is broken down and energy transferred in a

series of controlled steps, so there is much less heating and the energy can be

transferred in ways which the body can use.

This extract I’ve taken from Understanding Primary Science book written by Martin

Wenham.

Materials and apparatus:

Rats/guinea pig/ white mice, cockroaches, bony fish, dissecting board, dissecting

microscope, hand lens, transparent plastic ruler, and thread.

Procedure:

Dissection of the fish respiratory system

1. The shape of the fish is observed: streamlined, neck less, paired fins and

flexible tail

2. The advantage of having such shapes is found out.

3. Fish bodies are covered with scales. The function of the scales is found out.

4. Bony fishes have a movable operculum or gill-cover protecting the gills.

Number of pairs of gill is found out.

5. The gills are mounted on bony structures called gill arch. Each complete gill

consists of a bony gill arch supporting two rows of delicate gill filaments. The

gill filaments are examined under the dissection microscope, they are labelled

and drawn. The blood vessels are found out in the gill filaments.

6. Gaseous exchange takes place in the gill filaments. The characteristic of the

gill filament are described so that an efficient gaseous exchange can happen.

The function of the gill filament is explained.

Dissection of the cockroach respiratory system

External anatomy

1. The cockroach is killed using chloroform in the killing jar.

2. The cockroach is taken and the segmented body parts are identified.

3. The head, thorax and abdomen are drawn and labelled. The number of

segments that make up the head, thorax and abdomen is counted.

4. The exoskeleton is made up of the hard and waxy chitin layer. The legs

attached to are found out.

5. The wings are opened up. The different between the two pairs of wings and

their function are found out.

6. The spiracle at each side of the segment is observed. The number of

spiracles found on the thorax and abdomen is counted. Is there any spiracle

on the thorax?

Internal anatomy

1. The legs and wings of the cockroach is cut

2. From the dorsal posterior to the anterior part, the cockroach is cut gently.

3. The inner part is opened up and it has been observed under the dissection

microscope. Air will flow through the spiracles, trachea and end up in very

fine tubules called tracheoles.

4. Some tissues are got and it is mounted on a slide. A drop of water is put and

the cover slip is lowered gently.

5. The tissues are examined under microscope. The respiratory tract is drawn

and labelled (trachea and tracheoles).

Dissection of the mammalian respiratory system

1. The rat is pinned to the dissecting board with the ventral surface uppermost.

2. A mid-ventral incision is made through the skin and is cut forward as far as

lower jaw and the backwards to the anus.

3. The skin is holding with forceps, the connective tissues are cut away between

the skin and the body wall as far as possible around the animals, body and

the skin is pinned back.

4. The ventral and lateral thoracic walls is cut away to expose the thoracic

cavity.

5. The thymus gland is removed.

6. The muscle and tissues of the neck is cut away to expose the trachea and

larynx.

7. The larynx is cut above. The connective tissues attached to the trachea is cut

off.

8. The heart, lungs, trachea, esophagus and larynx is removed together.

9. The esophagus is separated carefully from the heart. The larynx, trachea and

lungs are pinned to the board.

10.A large labelled drawing of the structures that I have taken out is made.

Results:

Drawing and labelling

Magnification of drawing

Observation:

Rats (Mammal)

Rats that have been putting chloroform

A rat that faint for a while due to chloroform effect

A rat that has been dissected

The thin fat layer surrounded the organs have been removed.

Respiratory system of rat

Focusing on the posterior part (the head) of the rat

Coackroach (Insect)

Antennae

Right forewing

Femur

Tibia

A cockroach that has been putting chloroform on it

The structure of a cockroach from in front point of view

Tarsus

Left forewing

Left handwing Right handwing

Stylus

Back leg

Hind legFore leg

Prothorex

Cercus

The structure of a cockroach from its back point of view

The dissection of a cockroach

Mesothorex

Metethorex

Part of Hindgut

(colon)

Tracheol

Trachea

The Respiratory System of Cockroach

Fish

A fish that is laid down, ready to be dissected

A fish that has been dissected at it respiratory system part

The location of the gill

Gill filament

Structure of a gill

A fish gill

Opening the operculum part of the fish to detect the gill

The fish detailed structured

A gill structure under microscope observation

The gill filament structure under microscope observation

Discussion:

1. The respiratory system of insects is made up of many branching tubes. The

tubes start at openings called spiracles found on the surface of the cockroach.

Air enters the cockroach’s body through the spiracles. The spiracles are found

in each of the cockroach’s segments. The larger tubes are called trachea.

Trachea is found close to the cockroach’s dorsal vessel or heart. The trachea

branch into smaller tubes called tracheoles. The tracheoles surround all of the

insect’s organs and tissues. Air passes into the trachea and moves on into the

tracheoles and finally into the body tissues. The oxygen in the air diffuses, or

spreads into the cells that form the tissues. Carbon dioxide leaves the cells

and diffuses back through the tracheal system consisting of the tracheoles

and the trachea and leaves the insect’s body through the spiracles.

2. The structural adaptation of tracheoles for gaseous exchange is as follows:

The gill filament structure under microscope observation

The tracheoles branch intricately throughout the body of an insect and

penetrate into the body tissues

This means the tracheoles are close to each body cell and can channel

oxygen directly to the cells in different parts of the body.

The larger number of tracheoles provides a large surface area for the

diffusion of gases.

The tips of the tracheoles have thin permeable walls and contain fluid

in which the respiratory gases can dissolve.

Air enters the trachea through the spiracles and travels through teh

tracheoles to the fluid-filled tips.

Oxygen in the fluid diffuses directly from the tracheoles into the cells,

and carbon dioxide diffuses out from the cells into the tracheoles.

3. The breathing mechanism of insects goes as follows:

Insects inhale and exhale through the rhythmic contraction and

expansion of their abdominal muscles.

The body movements and the contractions of abdominal muscles

speed up the rate of diffusion of gases from the trachea into the body

cells.

When an insect inhales, the abdominal muscles relax and the spiracles

open.

Air pressure inside the trachea decreases and air is drawn in.

When the insect exhales, the abdominal muscles contract.

The increased air pressure forces air out through the spiracles.

This is because the tracheal tubes of insects carry oxygen from the air

directly to body cells, the circulatory system is not involved in

transporting oxygen and carbon dioxide.

4. Gills are specialised respiratory structures for gaseous exchange in water.

Bony fish have four pairs of gills: four on the right and four on the left. The gills

are supported by a gill arch and protected by the operculum. Each gill has two

rows of thin filaments arranged in a V shaped. These filaments consist of

numerous thin-walled lamellae.

5. The structural adaptation of gills for gaseous exchange:

The large surface area of the filaments and lamellae increases the

efficiency of gaseous exchange in fish.

The membrane of the gill filaments is thin to allow the absorption of

respiratory gases into the blood capillaries.

The filaments are also supplied with blood capillaries for an efficient

exchange and transport of respiratory gases.

The gill filaments which are constantly surrounded by water enable

respiratory gases to dissolve in them.

The efficiency of the gaseous exchange is further enhanced by the

countercurrent exchange mechanism at the respiratory surface.

The countercurrent flow maximises the oxygen transfer because as

water flows over the gills in one direction, the blood flows in the

opposite direction through the blood capillaries in the lamellae.

This means that as deoxygenated blood enters the blood capillaries, it

encounters water with higher oxygen content.

So, the concentration gradient in the blood enters the blood capillaries

allows the diffusion of oxygen into the blood to take place.

The efficiency of fish gills is further increased by ventilation, that is, the

increase in the flow of water over the respiratory surface.

Fish ventilate by swimming and by opening and closing operculum.

This draws freshwater into their mouth which then passes over the

gills.

6. The rat’s body is divided into a head, thorax, and abdomen. The thorax and

abdomen are separated internally by the diaphragm, a large muscle. There

are four limbs (which terminate in digits with claws), and a long tail. The eyes,

ears, vibrissae (whiskers), and external nares (nostrils), all of which give the

rat sensory information.

7. The respiratory system of rat consists of two lungs and the passages by which

their internal cavities are connected to the exterior. Starting anteriorly, these

cavities include the nasal cavities, which are separated from one another by

the nasal septum and from the buccal cavity by the palate. The pharynx is

divided into the naso-pharynx above the palate, and the oro-pharynx behind

the buccal cavity. The edge of the soft palate acts as a valve to prevent food

from passing into the naso-pharynx and then into the nasal cavities during

swallowing. The opening from the pharynx into the larynx, or voice box, is

called the glottis. As mentioned previously, the glottis is closed over, during

swallowing of food, with a gate-like epiglottis, to prevent the passage of food

into the larynx and lower respiratory passages.

8. The external features and their functions for respiratory system of a rat are as

follows:

Diaphragm- This is a muscular sheet that separates cavities and its

action is to draws air into the lungs.

Ear, Whisker, Nostril, Eyes – The sensory organs

Tail – For balance

Claws – For defense, eating, grasping and climbing

9. The organ that are involved in the mechanism of respiratory system are as

follows:

Mouth and Nostril – Intake for air

Larynx – produce sound for communication

Trachea – Tube to bring air into lungs

Bronchus – Branches into lungs

Lung – Exchange oxygen form air into blood an expel carbon dioxide

waste

Diaphragm  - Muscle that helps fill lung with air

10.Here is the mechanism of respiratory system for rat. When air enters the rat’s

respiratory system through its nostrils or mouth, it will goes into the throat and

then into the trachea, a hollow tube supported by cartilaginous rings that

should be visible in the thoracic cavity. The trachea branches into two

bronchi, which divide further into smaller branches and sacs that make up the

lungs. The two lungs are on either side of the heart. In preserved animals,

they appear small and dense, but are much larger and sponge-like when they

are filled with air in the living animal.

11.Precaution that should be taken:

Dissecting tools will be used to open the body cavity of the rat and

observe the structures. Keep in mind that dissecting does not mean "to

cut up". In fact, it means "to expose to view". Careful dissecting

techniques will be needed to observe all the structures and their

connections to other structures. You will not need to use a scalpel.

Contrary to popular belief, a scalpel is not the best tool for dissection.

Scissors serve better because the point of the scissors can be pointed

upwards to prevent damaging organs underneath.

Always raise structures to be cut with your forceps before cutting, so

that you can see exactly what is underneath and where the incision

should be made. Never cut more than is absolutely necessary to

expose a part.

Questions:

1. a) How many pairs of ribs does this animal have?

10 pairs of ribs for rat

b) How does the rib cage function during gas exchange in this animal

During gas exchange in this animal, the rib cage is pulled upwards and

outwards when inhalation. For exhalation, the rib cage is pulled downwards and

inwards.

2. a) Describe the appearance and characteristic of a diaphragm

A diaphragm is a dome-shaped sheet of muscles that lies across the bottom of

the chest cavity. It is also separates the thorax from the abdomen. It

characteristic is elastic.

b) What is the importance of this characteristic of the diaphragm in relation to its

function during gas exchange?

The diaphragm’s function is to pump the carbon dioxide out of the lungs and

pull the oxygen into the lungs.

3. Describe the appearance of the left and right lungs. Squeeze the lungs and

note its texture. Place it in hot water. The air within the lung expands causing it

to float.

Right lung is bigger in size and left lung is smaller in size. The lungs contain

millions of air sacs called alveoli. The large number of alveoli provides a large

surface area for gaseous exchange. The inner surface of each alveolus is lined

with a layer of moist epithelial cells which enable oxygen and carbon dioxide to

dissolve in it and diffusion to take place. The entire outer surface of each

alveolus is covered by a dense network of blood capillaries provide a large

surface area to volume ratio for the rapid diffusion and transport of respiratory

gases. The wall of an alveolus is very thin. It is only one-cell thick. This allows

the diffusion of gases across membranes to take place easily.

When the lung is placed in a hot water, the air within the lungs expands

causing it float. Actually, the air is come from alveolus that is situated inside the

lung. Alveolus is air sacs, so if it is placed in a hot water, it will expand because

the air in the alveolus increases its volume due to the higher temperature.

4. Measure the length of the trachea (from the larynx to the point where it

branches into bronchus).

The length of the trachea (from the larynx to the point where it branches into

bronchus) is 1 cm.

Conclusion:

The differences in the respiratory system between rat (mammal), cockroach (insect)

and fish are as follows:

a) The respiratory organ for rat involves lungs and it is like human respiratory

system.

b) The respiratory organ for cockroach involves tracheae and it respiratory

system is tracheal system.

c) The respiratory organ for fish involves gills and it respiratory system is gills

system.

Hence, various types of animals have different types of respiratory system. The

hypothesis is accepted.

Reference:

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Wenham, M. (2005). Understanding Primary Science (ideas, concepts &

explanations) . London: Paul Chapman Publishing.