Chapter 7: Exchange Surfaces And Breathing

Question 1

What is the need for specialised exchange surfaces?

Answer 1

The larger the organism, the higher the metabolic activity and the lower the SA:V so large organisms cannot rely on diffusion alone

Question 2

What are the features of an efficient gas exchange system?

Answer 2

Increased Surface Area

• overcomes limitations of the small SA:V
• root hair cells, villi

Thin layers

• decreases diffusion distances
• alveoli

Steep concentration gradient

• constant delivery and removal of substances
• maintained by good blood supply, ventilation
• alveoli, gills

Question 3

Nasal Cavity

Answer 3

Function:
- provided the airways required to inspire and expire

Structure:
- moist surface to increase humidity of the incoming air to decrease evaporation
- hairy lining that secretes mucus
- large surface area and good blood supply which warms the incoming air
-

Question 4

Trachea

Answer 4

Function:

• main airway
• helps trap dust and pathogens from incoming air

Structure:

• surrounded by smooth muscle
• incomplete cartilage rings that keep the trachea open, prevents it from collapsing, allows smooth movement of food down the oesophagus
• ciliates epithelium has cilia which beats the mucus produced by the goblet cells

Question 5

Bronchus

Answer 5

Function:
- airway for each lung

Structure:

• similar to the trachea but smaller
• complete rings of cartilage

Question 6

Bronchioles

Answer 6

Function:

• smaller airways in the lungs
• some gas exchange can take place

Structure:

• no cartilage rings
• walls of smooth muscles that control the amount of air reaching the lungs through contractions and dilations
• layer on squamous epithelium and some blood vessels to allow some gas exchange

Question 7

Alveoli

Answer 7

Function:
- they are the main gas exchange surfaces

Structure:

• tony air sacs - 200-300 micrometers in diameter
• one epithelial cell thick for shorter diffusion distances
• elastic fibres for elastic recoil
• surrounded by a network of capillaries for a steep concentration gradient
• good ventilation
• lung surfactant - a phospholipid that keeps alveoli inflated and stops the formation of surface tension as surface tension causes alveoli to collapse