Exchanging gases

Key understanding:To discuss features of effective surfaces of gaseous exchange and the mechanisms for gas exchange in animals

Cellular Respiration

• What do we know?

• What are the inputs?

• What are the outputs?

C6H12O6 + 6O2 6CO2 + 6H2O + (36-38ATP)

• Carbon dioxide forms acid in solution so it must be removed

• Oxygen needed in cellular respiration

• Some animals and plants can exchange gases direct from cell→environment

• Others need a system

Mechanism for gas exchange in mammals

Respiartion

• http://www.youtube.com/watch?v=HiT621PrrO0

Gas exchange

• Always takes place by diffusion across a moist plasma membrane (extracellular fluid)

• Oxygen and carbon dioxide are uncharged (non-polar) molecules so diffuse across membranes

• The rate of diffusion depends on: size and maintenance of concentration gradient, and properties of the membrane

Amounttransferred

= Permeability x surface area x concentration gradient

Distance of diffusion

Fick’s formula

•Emphysema reduces the surface area of lungs•Pneumonia increases distance of diffusion•Anaemia reduces concentration gradient

The following illnesses can effect gas exchange because they affect one of the factors listed in formula

Features of an efficient gas exchange surface:

• Large surface area

• Thin barrier and made of material that allows gas to pass through it easily

• Adequate supply of gas being transferred

• Efficient removal of substance after transfer

Gills • Water flows in one direction: through the

mouth and pharynx, past the gills and out under the operculum

• Countercurrent flow: blood flows in opposite direction to the water so blood can extract up to 90% of the oxygen in the water (mammals can only extract 25%!)

Lungs

• Air breathed in and passes into pharynx.

• From here it passes into the airways- the trachea, paired bronchi and branching bronchioles.

• Terminal air sacs called alveoli.

• This is the site of gas exchange .

Features for efficient gas exchange

• Trachea and bronchi lined with ciliated cells which produce mucus - traps dust and bacteria and transports them back to the pharynx, where they are swallowed

• Alveoli provide large surface area for gas exchange

• Alveoli richly supplied with blood capillaries• Diffusion barrier very thin

Respiratory pigments

• Increase the efficiency of gas transport in animals.• Consist of proteins complexed with iron and copper• Haemoglobin is the most widely distributed pigment

found in all vertebrates and many invertebrates.• Oxygen-carrying molecules• Increasing the oxygen-carrying capacity of blood

reduces amount of energy needed to pump blood

Haemoglobin • Mammalian respiratory pigment

• Increases oxygen-carrying capacity 100 fold

• In red blood cells

• Contains iron

• 4 oxygen molecules can combine with 1 haemoglobin molecule

Hb + 4O2 → Hb(O2)4

Hb + 4O2 ← Hb(O2)4

In lungshigh O2

In tissuelow O2

•When haemoglobin combines with oxygen it is called Oxyhaemoglobin

•Muscles contain type of haemoglobin called Myoglobin. These carry a reserve store of oxygen.

What about the carbon dioxide?

• 7% dissolved in blood plasma• 23% combines with haemoglobin molecules

forming carbaminohaemoglobin• 70% converted to hydrogen carbonate ions in

red blood cells and transported to plasma

Resources

• Chapter 8 of Heinemann text • Complete p145 -147 of Biozone. Use the

answer book for the questions.

• p148 Biozone – Respiratory pigments