ventilation in fish and insects

how many pairs of gills do most bony fish have

5 pairs

gill structure components

• gill arch

• gill filaments (primary lamellae)

• gill plate (secondary lamellae)

operculum

bony flap that covers the gills

how many rows of primary lamellae does each gill have

2 rows attached to a gill arch

secondary lamellae

folded surface of primary lamellae to increase surface area

ventilation in bony fish process

1. mouth opens (operculum closed)

2. buccal cavity floor is lowered

3. increases the volume and decreases the pressure of the buccal cavity below outside

4. water rushes into the buccal cavity down a pressure gradient

5. mouth closes which raises the floor of the buccal cavity

6. volume decreases and pressure increases inside the buccal cavity higher that opercular cavity

7. increased pressure forces open operculum

8. water is forced over the gills and out of the operculum

countercurrent flow process

1. blood flows along the gill arch and out along the filaments to the secondary lamellae

2. the blood flows in the opposite direction to the water flow across the gills

3. this helps the fish absorb as much oxygen as possible as there is always a concentration gradient

what is countercurrent flow

when the blood flows along the lamellae in the opposite direction to the water flowing over the gills to maintain a concentration gradient of oxygen

why is countercurrent flow efficient

• water and blood concentration gradient of oxygen is maintained over the whole lamellae

• so oxygen can diffuse down the concentration gradient from the water to the blood

why is countercurrent flow more efficient than concurrent flow

in concurrent flow the concentration of oxygen in the blood and in the water will eventually equalise so there would be no concentration gradient and no oxygen exchange would take place

in countercurrent flow the concentration of oxygen in the water is always higher than in the blood so as much oxygen as possible diffuses into the blood

how to dissect fish gills

1. wear apron and gloves

2. place fish on dissection tray

3. push back operculum and use scissors to remove gills

4. cut each gill arch trough the bone at the top and bottom

5. draw and annotate it along with a scale bar

how do fish ensure a large surface area for gas exchange

primary and secondary lamellae

how do insects ensure a large surface area for gas exhange

tracheoles and tracheal fluid

how do fish ensure a steep concentration gradient for gas exchange

countercurrent flow

how do insects ensure a steep concentration gradient for gas exchange

• cells are always respiring so always producing co2

• some insects can ‘pump’ air in and out of their bodies to replace air saturated with co2

how do fish ensure a short diffusion distance for gas exchange

• very thin lamellae

• blood in close contact with water

• walls of capillaries are 1 cell thick

how do insects ensure a short diffusion distance for gas exchange

• tracheoles walls are very thin

tracheal system features

• cuticle (exoskeleton)

• spiracle

• trachea

• tracheole

cuticle (exoskeleton) of an insect

provides protection and structure

spiracle strucure

tiny holes in an insects body with that can open and close to prevent water loss and have sensory hairs

spiracle function

where gases enter and where water can evaporate from an insect

trachea of an insect structure

network of internal tubes with o rings of chitin to prevent collapsing

trachea of an insect function

air filled pipes in an insect for gas exchange

tracheole structure

fine respiratory tube of the trachea of an insect with thin permeable walls

tracheole function

extend throughout the whole insect and go directly into respiring cells to provide o2

similarities between an insect and mammals respiratory system

• have trachea

• have structures with thin permeable walls

differences between an insect and mammals respiratory system

• mammals have lungs and insects dont

• insect trachea has o chitin but mammal trachea has c cartilage

• insect trachea splits into tracheoles but mammal trachea splits into bronchi

what affects rate of ventilation in large insects

• rhythmic abdominal movements

• wing movements when larger insects are flying

• flexible trachea wall

how do insects limit water loss

• spiracles have a small surface area to volume ratio

• spiracles cal open and close

• waterproof exoskeleton contains lipid layer

• water can only evaporate through spiracles

how does the flexible trachea wall affect ventilation in large insects

• can ventilate the tracheal system by expanding and acting as air sacs which can be squeezed by the action on the flight muscles

how can movements of the wings affect ventilation in large insects

• alter the volume of the thorax

• if thorax volume decreases air pressure increases and air is pushed out

• opposite if volume increases

how can rhythmic abdominal movements affect ventilation in large insects

• locusts

• as the abdomen expands the spiracles at the front end of their body open and air enters

• as the abdomen reduces in volume the spiracles at the rear end of the body cavity open and air leaves

what are the examples of large insects

• locusts

• crickets

how the tracheal system works in insects

1. oxygen travels down the concentration gradient to the cells

2. carbon dioxide moves down its own concentration gradient to the spiracles

3. the trachea branches off into tracheoles

4. tracheoles contain tracheal fluid which oxygen dissolves in

5. oxygen diffuses from tracheal fluid into body cells

6. carbon dioxide diffuses in the opposite direction

7. the body cavity is filled with haemolymph

tracheal fluid

• increases surface area and the rate of diffusion of oxygen from the tracheoles to the cells of an insect

haemolymph

• transports nutrients and waste around the insect body

• not contained within vessels

• doesnt transport o2 or co2

• transports sugars and proteins (hormones)

how to dissect an insect

1. grasshoppers or cockroaches

2. fix insect to dissecting board with dissecting pins through legs

3. cut and remove piece of the exoskeleton from along the length of its abdomen to examine the tracheae

4. fill the abdomen with saline solution with a syringe

5. network of very think grey tubes are the tracheae

6. can examine under a light microscope with a wet mount slide