UNIT

2The nutrition function

Natural Science 2. Secondary Education

RESPIRATION IN DIFFERENT ANIMALS

UNIT

2What is diffusion?

• Diffusion is the transfer of gases between the external environment and the circulating liquid, through tissues that are thin enough to allow these gases to pass.

• When the circulating liquid reaches the respiratory organs, it is carbon dioxide-rich and oxygen-poor. When air reaches the respiratory organs, on the other hand, it is oxygen-rich and carbon dioxide-poor.

• This is when diffusion occurs: oxygen will move from the area of high concentration to the area of low concentration (from the air to the circulating liquid), and carbon dioxide will do the same (it will move from the circulating liquid to the air).

Diffusion in living things

Air with O2

Air with CO2

Blood with O2

Blood with CO2 O2

CO2

Exchange tissue

Natural Science 2. Secondary Education

UNIT

2What is diffusion?

• Diffusion can occur:

Diffusion in living things

• Through the body surface. This occurs in sponges, polyps, worms and some amphibians.

• Through gills: This occurs in molluscs, crustaceans, fish and some amphibians.

• Through tracheae: In insects.

• Through lungs: In amphibians, reptiles, birds and mammals.

Natural Science 2. Secondary Education

UNIT

2

RESPIRATIONIN WATER

THROUGH THE BODY SURFACE

THROUGHGILLS

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How some animals take oxygen from the water

is carried out

Natural Science 2. Secondary Education

UNIT

2• This is seen in animals that live underwater or in very wet environments, like the soil.

• Sponges, cnidarians (polyps and jellyfish), worms and some amphibians absorb air in this way.

Respiration through the body surface

The animal absorb O2 through its surface

The animal eliminates CO2 through its surface

O2 O2CO2 CO2

Respiration through the body surface in an annelid.

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Wetenvironment

Bodysurface

How some animals take oxygen from the water

Natural Science 2. Secondary Education

UNIT

2• Gills are very thin sheets or filaments full of capillaries.

• When water passes through the gills, carbon dioxide from the circulating liquid inside the organism is exchanged for oxygen from the water.

• Gills are the respiratory organs of aquatic molluscs, crustaceans, fish and some amphibians.

Respiration through gills

Blood with O2 Blood with CO2

Water

Water with O2

Water with CO2 Respiration through

gills in a fish.

O2

CO2

How some animals take oxygen from the water

Go back to the Start menuNatural Science 2. Secondary Education

UNIT

2

RESPIRATIONIN AIR

THROUGHTRACHEAE

THROUGHLUNGS

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How some animals take oxygen from the air

is carried out

Natural Science 2. Secondary Education

UNIT

2• This type of respiration occurs in almost all insects.

• Tracheae are very thin tubes that branch out to provide the animal’s tissues with oxygen.

• They lead out of the body through pores called spiracles.

Respiration through tracheae

CO2

O2

Spiracle

TracheaThe insect’s tissues

Exoskeleton

Respiration through tracheae in an insect.

How some animals take oxygen from the air

Go back to the Start menuNatural Science 2. Secondary Education

UNIT

2• This type of respiration occurs in amphibians, reptiles, birds and mammals.

• Lungs are made up of millions of tiny tubes or cavities called alveoli, which are full of capillaries. This is where oxygen passes into the blood.

• Lungs are connected to the external environment by the rest of the respiratory tract (airways).

Respiration through lungs

Blood with O2

Blood with CO2

O2

CO2

Respiration through lungs in a mammal.

Lungs

Airways

How some animals take oxygen from the air

Go back to the Start menuNatural Science 2. Secondary Education