[organising animals] breathing and gas exchange

[ AQA GCSE Biology Student Book, page 60-61 ] [ BBC Bitesize 'Organisation ⇢ Animal Organisation - Gaseous Exchange Systems' page 3-5 ]

Gas Exchange

The process by which oxygen and carbon dioxide move between the bloodstream and the lungs.

Diffusion

The movement of molecules from an area of higher concentration to an area of lower concentration.

Breathing

Movement of air into and out of the lungs

Respiratory System

Organ system which replaces oxygen and removes carbon dioxide from the blood

Lungs are made up of...

…elastic tissue so tissue so that they can expand when you breathe in

1st Stage of Gas Exchange

Air enters your body through your mouth and nose.

2nd Stage of Gas Exchange

Air moves down the trachea

3rd Stage of Gas Exchange

Air moves down each bronchus and moves through each bronchiole

4th Stage of Gas Exchange

Air moves into the alveoli where it diffuses through a cell wall, into the bloodstream

Composition of (inhaled) Air

• Nitrogen 78%

• Oxygen 21%

• Other Gases 1%

Composition of (exhaled) air

• Nitrogen 78%

• Oxygen 16%

• Carbon Dioxide 5.04%

• Other 0.96%

The amount of oxygen your body needs determines…

…how fast you need to breathe

Diaphragm

Strong sheet of muscle at the bottom of the chest cavity that helps with breathing.

Ribs

Bones which surround the lungs to form the ribcage and protect the lungs

Pleural Membranes

Thin, moist membranes surrounding the lungs that make an airtight seal.

Intercostal Muscles

Sets of muscles between the ribs which raise and lower the rib cage.

Thorax

The ribs and upper backbone, and the organs found in the chest, also known as the pleural or chest cavity.

Trachea

The tube that leads from the mouth towards the lungs.

Bronchi

The plural of 'bronchus'. The bronchi are the two major air tubes in the lungs.

Bronchioles

The many small, branching tubes into which the bronchi subdivide.

Alveoli

Tiny air sacs in the lungs, where gas is exchanged during breathing.

Stage 1 of Breathing in

The intercostal muscles contract, causing the ribs to move upwards and outwards. The diaphragm contracts, pulling downwards. (increased volume of thorax)

Stage 2 of Breathing in

Volume of thorax increases so pressure inside the lungs decreases leading to air being drawn into the lungs.

Stage 1 of Breathing out

The intercostal muscles relax, causing the ribs to move downwards and outwards. The diaphragm relaxes and moves up (decreased volume of thorax)

Stage 2 of Breathing out

Volume of thorax decreases so pressure inside the lungs increases and air leaves the lungs.

Villi

Finger-like projections in the small intestine that provide a large surface area for the absorption of food.

Concentration Gradient

The difference in the concentration of a chemical across a membrane. The moving blood and ventilated surfaces mean that a steep concentration gradient can be maintained. This increases effective exchange.

As multicellular organisms increase in size, they face two problems:

- their surface area does not increase as fast as the volume -> Insufficient surface area to meet their needs; body systems that add additional absorbing area to exchange surfaces
- their volume increases -> Diffusion is not quick enough to move substances to where they're needed in the organism's body; A transport system

Exchange of gases in fish is very efficient because of:

- the large surface area of the gills
- the large surface area of the blood capillaries in each gill filament
- the short distance required for diffusion - the outer layer of the gill filaments and the capillary walls are just one cell thick
- the efficient ventilation of the gills with water - there is a counter current flow of water and blood

The ventilation of the lungs and the blood flow through the surrounding capillaries mean...

...gases are being removed continually, and steep concentration gradients are set up and maintained for gases to diffuse.