MODULE 3 SPECIFICATION NOTES

Module 3: exchange and transport

3.1-exchange and transport

3.1.1- exchange surfaces

a)   the need for specialised exchange surfaces

Organisms need to absorb certain substances, (e.g. oxygen, glucose, proteins, fats, water and minerals) from the surrounding environment and remove waste products (carbon dioxide, oxygen and other wastes).

Single celled organisms have a large surface-area-to-volume ratio so they can exchange the necessary gases, nutrients and wastes.

Multicellular organisms not only need more supplies as they have more cells, but they also have a smaller

Surface-area-to-volume ratio, meaning that the outer surface is not large enough to enable gases and nutrients to enter the body fast enough to keep all of the cells alive.

Nutrients and gases also have to travel a larger distance to the centre of the organism.

So, larger organisms need a large area to exchange more substances, so often they combine this with a transport system to move substances around the body.

b)   the features of an efficient exchange surface

Large surface area to provide more space for molecules to pass through

Thin barrier to reduce the diffusion distance

Fresh supply of molecules on one side to maintain the diffusion gradient

Carbon dioxide is brought in the blood to the lungs. The concentration is higher in the blood than in the alveoli, so it diffuses across.

Breathing fills the lungs with air, so there is more oxygen in the alveolus than in the blood

Removal of required molecules on the other side to maintain the steep diffusion gradient

Blood carries oxygen away from the lungs

Breathing removes Carbon Dioxide from the lungs

c)   the structures and functions of the components of the mammalian gaseous exchange system

The trachea and bronchi have a similar structure, but the bronchi are narrower than the trachea

Thick walls made of several layers of tissue

Much of the wall consists of cartilage

Regular C-rings in the trachea

Less regular in the bronchi

On the inside surface of the cartilage is a layer of glandular tissue, connective tissue, elastic fibres, smooth muscle and blood vessels

The inner layer is an epithelium layer than has two types of cells. Most of the cells are ciliated epithelium, and there are goblet cells amongst them

Bronchioles

Much narrower than the bronchi

Larger bronchioles have some cartilage, but the smaller ones don’t.

The wall is made mostly of smooth muscle and elastic fibres

Alveoli

Wall is one cell thick

100-300μm diameter

Good blood supply

Cartilage,

Structure.

Holds the trachea and bronchi open

Prevents collapse when the air pressure is low during inhalation

Cilia,

Move in a synchronised pattern to waft mucus up the airway to the back of the throat. Once there, the mucus is swallowed and the acidity of the stomach will kill any bacteria

Goblet cells,

Secrete mucus.

Traps tiny particles from the air

Reduces risk of infection

Smooth muscle

Can contract to restrict airway

Prevents harmful substances from reaching the alveoli

Elastic fibres

Reverses the effect of the smooth muscle

When…