Gas Exchange

What are the tiny holes on the surface of an insect’s body called?

Spiracles

What do spiracles allow the movement of?

They allow air to flow in and out of the insect

What is the name of the tubes that spiracles are connected to?

Trachea

What do trachea branch into?

Tracheoles

What do the tracheoles extend into?

Insect’s muscle tissue

What is the name of the liquid found at the end of each tracheole?

Tracheal fluid

What are the trachea and tracheoles supported by?

Spirals of chitin

What is the role of the spirals of chitin supporting the trachea and tracheoles?

Prevent the tubes from collapsing when the insect moves

What are four differences between the trachea found in humans and the trachea found in insects?

• Human tracheae are larger in diameter and length

• Humans only have one trachea, insects have many

• Human tracheae branch into bronchi, insect tracheae branch into tracheoles

• Human tracheae are supported by cartilage, insect tracheae are supported by chitin

What must oxygen do before it diffuses from the tracheoles into the muscle tissues?

Dissolves from the air into the tracheal fluid

How is the insect gas exchange system adapted to have a large surface area?

Large number of tracheoles

In which two ways is the insect gas exchange system adapted to give a short diffusion pathway?

• The tracheoles extend into the muscle tissue

• Tracheole walls are one cell thick

Why does absorbing tracheal fluid into surrounding muscle tissue increase the rate of diffusion?

Diffusion takes place faster in gases than in liquids

What are insects able to do if their demand for oxygen increases?

Tracheal fluid can be absorbed into surrounding muscle tissue

Why are insects at risk of more water loss than other animals?

They have a high surface area to volume ratio

In which two ways are insects adapted to reduce water loss?

• They have a waterproof outer layer on their exoskeleton

• Their spiracles can be closed

Which organ does gas exchange take place in for fish?

The gills

What is the name of the ‘backbone’ that each gill has?

The gill arch

What is the name of the thin and hair-like structures extending out from the gill arch?

Gill filaments

What is the name of the plate-like structures making up the surface of the gill filaments?

Lamellae

What does each gill lamella contain?

A network of capillaries

What does each gill arch have running down its centre?

A blood vessel- this branches off to provide each gill filament with blood

Which organs does the water travel through in fish?

Water goes in through the fish’s mouth and is pushed out over the gills

What must be established in order for gas exchange to take place?

A concentration gradient

What is the relative concentration of oxygen in the fish’s blood?

Low

What is the relative concentration of oxygen in the water running between the lamellae?

High

At the lamellae, oxygen diffuses down a concentration gradient in which direction?

From the water into the fish’s blood

At the lamellae, carbon dioxide diffuses down a concentration gradient in which direction?

From the fish’s blood into the water

Why is there a relatively high concentration of carbon dioxide in the fish’s blood?

Due to respiration

What are the three ways in which the gills are adapted for efficient gas exchange?

• Short diffusion pathway

• Large surface area

• Counter-current flow

What are the two ways in which the gills are adapted to have a short diffusion pathway?

• Each gill lamella has a network of capillaries, which brings blood very close to the surface

• The surface of each gill lamella is made up of a single layer of flattened cells

What are the two ways in which gills are adapted to have a large surface area?

• Large number of gill filaments

• Large number of lamellae

What is the relationship between a fish’s gill surface area to body mass ratio and the concentration of oxygen in its environment?

As oxygen concentration increases, gill surface area to body mass ratio decreases

What does counter-current flow refer to?

Water and blood flowing in opposite directions in the lamellae

Why is counter-current flow useful for efficient gas exchange?

Maintains a steep concentration gradient of oxygen (and carbon dioxide) between the blood and water along the length of the lamella

What are the 3 essential features alveoli have to maximise rate of diffusion?

• Short diffusion path

• Large surface area

• Steep concentration gradient of O₂ and CO₂ between alveoli and capillaries

How do alveoli maintain a large surface area?

There are large numbers of them

How do alveoli maintain a short diffusion path?

Alveolar epithelium and capillary endothelium are both one cell thick

How is a steep concentration gradient of O₂ and CO₂ between the alveoli and capillaries maintained?

Constant ventilation and a good blood supply

What is the main site of gas exchange in the lungs of mammals?

The alveolar epithelium

What are alveoli?

Tiny air sacs in mammalian lungs

What is the human gas exchange system composed of?

Trachea, lungs, bronchi, bronchioles, alveoli

What does ventilation do?

Moves air continuously into and out of the lungs

What is the thorax composed of?

Internal intercostal muscle, external intercostal muscle, diaphragm, ribcage

What happens during inhalation?

Diaphragm contracts

External intercostal muscles contract

Volume in the thorax increases

Pressure in the thorax decreases

Air is forced into the lungs down a pressure gradient

What happens during exhalation?

Diaphragm relaxes

Internal intercostal muscles contract

Volume in the thorax decreases

Pressure in the thorax increases

Air is forced out of the lungs down a pressure gradient