RESPIRATORY STRUCTURE AND

BREATHING MECHANISM

IN FISH & FROG

Fish

Aquatic animals such as fish have specialised respiratory structure called gills for breathing

A fish have 4 pairs of gills which are covered by the operculum

Each gill consists of a small rod of bone called gill arch

Each gill arch consists of double row of gill filaments.

Gill of filaments

The surface of gill filaments has many plate-like projections called lamella to increase surface area

The gill lamella are richly supplied with a network of blood capillaries for gaseous exchange

The gill filaments are adapted for gaseous exchange are as follows:

1. Many plate-like projections ( lamella) ~increase the surface area for gaseous exchange

2. Thin epithelial walls of the gill filaments ~allows oxygen to diffuse easily into the blood capillaries

3. A network of blood capillaries ~increase the rate of gaseous exchange by diffusion

The breathing mechanism in fish involves the movement of the operculum and the floor of the mouth to create the flow of water into the mouth cavity and through the gill slits

Flow of water into the mouth ( inhalation)

~ Mouth open ~Floor of mouth is lowered ~ Volume of pharynx cavity

increases ~ pressure in the mouth cavity

decrease ~outside pressure higher then

presses the operculum to close ~water enter the mouth

Flow of water through the gills ( exhalation)

~ mouth closes ~ floor of the mouth is raised ~volume of pharynx cavity

decreases ~pressure in the mouth cavity

increase ~operculum opens ~water flows through the gills ~ gaseous exchange occur ~water flows out through the

operculum

Dissolved oxygen diffuse through the gill epithelium into the blood capillaries at the gill filaments

Carbon dioxide diffuses from the blood capillaries into the surrounding water

The direction of the water flow over the gill lamella is opposite to the flow of the blood in order to maximize the rate of diffusion from water into the blood capillaries.

QUIZ

Give & explain 3 adaptation of gill filaments for gaseous exchange.

Answer: gill filaments have,

1. Many plate-like projections ( lamella) ~increase the surface area for gaseous exchange

2. Thin epithelial walls of the gill filaments ~allows oxygen to diffuse easily into the blood capillaries

3. A network of blood capillaries ~increase the rate of gaseous exchange by diffusion

QUIZ

Give & explain 3 adaptation of gill filaments for gaseous exchange.

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Frog

Amphibians such as frogs breathe through skin, mouth and lungs

In the water, the frog’s skin functions as the respiratory surface for gaseous exchange

Adaptations of skin for gaseous exchange:

1. Its thin skin allow gases to diffuse easily

2. Its moist skin dissolve gaseous and allow the exchange of gases to occur readily

3. Supplied with many blood capillaries to increase the rate of diffusion & transportation of oxygen & carbon dioxide

Adaptations of mouth for gaseous exchange:

1. The floor of the mouth cavity always move up & down to enable the air to enter into the mouth through the nostrils

2. Thin lining of the mouth cavity with many blood capillaries increase the rate of diffusion of oxygen & carbon dioxide in the mouth

The frog breathes through its lungs when it is active

The lungs of the frog consist of a pair of air sacs in the thoracic cavity

Adaptations of lungs for gaseous exchange:

1. The inner walls of the lung are folded to increase the surface area & hence, increase the rate of diffusion of gases

2. Thin walls of the lungs allow the gases to diffuse readily

3. A layer of moisture on the walls of the lungs enable the oxygen to dissolve in it before diffusing across the wall

4. A network of blood capillaries on the walls of the lungs to increase rate of diffusion & transportation of oxygen & carbon dioxide

Inhalation:

~floor of the mouth lowers ~volume inside mouth increases ~pressure inside decrease ~air enters through nostrils into the mouth ~nostril closes ~floor of the mouth is raised up ~pressure increases ~ glottis opens ~air passes into the lungs ~gaseous exchange occurs

exhalation

~nostril opens ~ air flows out of the mouth ~lungs bulge upwards ~glottis opens ~lung shrink due to its elasticity ~air flows out