B3.1 Gas exchange

Gas exchange

The diffusion of oxygen and CO2 in opposite directions

Outline the need for gas exchange in living organisms.

Gas exchange allows organisms to obtain the gases required for cellular processes such as aerobic respiration and photosynthesis, and remove waste gases produced in metabolic reactions.

How does gas exchange occur?

diffusion: net movement of particles from an area of higher concentration to an area of lower concentration

Properties of gas exchange surfaces (PHLCC)

Permeability

Having a moist surface

Large surface area

Composed of a thin tissue layer

Concentration gradient

Permeability as a property

the exchange surface must have pores or openings that allow gases to be exchanged across its surface

Moist Surface as a property

this helps to dissolve gases before they diffuse across the exchange surface

Large surface area as a property

there is more membrane surface available for gases to diffuse across

Thin tissue layer as a property

there is a short distance across which gases need to move

Concentration gradient as a property

for diffusion to occur there has to be a difference in concentration of the gas between two areas. The gas will move from an area of higher concentration to an area of lower concentration.

Explain how concentration gradients are maintained at exchange surfaces in animals.

Adapted gas exchange surfaces, such as:

- Ventilation of air

- Continuous blood flow

- A dense network of blood vessels

Ventilation of air as an adaptation

Maintains and supplies the oxygen concentration to the lungs. Helps maintain a constant supply of oxygen into the lungs and removal of CO2 from the lungs

Continuous blood flow as an adaptation

ensures that, as soon as substances move into the blood, they are transported away by the continuous blood flow, ensuring a low concentration of that substance in the blood supply.

Also it continuously exchanges gas in the blood from CO2 to oxygen.

A dense network of blood vessels as an adaptation

there is much opportunity for substances to be exchanged between the surface and the blood.

More blood vessels= higher concentration gradient.

Adaptations of mammalian lungs for gas exchange.

- Alveolar fluid/surfactant

- A highly branched network of bronchioles

- Extensive capillary beds

- Many alveoli (high surface area)

Surfactant as a mammalian adaptation

This is found on the surface of aveoli and it helps keep the surface moist

Branched network of bronchioles as a mammalian adaptation

Each bronchiole branches into many alveoli, creating millions of alveoli. These alveoli maximize the SA:V ratio (meaning there is more surface area available for substances but a shorter diffusion distance)

Extensive capillary beds as a mammalian adaptation

Around the alveoli are many capillaries. This means that there is a very short distance for substances to diffuse from the alveoli into the blood (or vice versa)

Many alveoli as a mammalian adaptation

Many alveoli create a larger surface area

4 ways an exchange surface can maximize the rate of diffusion

- High SA:V (millions of alveoli)

- Permeable/moist surface (surfactants)

- Maintainance of concentration gradients (extensive capillary networks, continuous blood flow, ventilation)

- Short diffusion distance (thin capillaries and alveoli)

Direction of gas exchange from aveoli to the blood

- Oxygen (O₂) diffuses from the air in the alveoli (high O₂ concentration) into the blood (low O₂ concentration).

- Carbon dioxide (CO₂) diffuses from the blood (high CO₂ concentration) into the alveoli (low CO₂ concentration) to be exhaled.

Direction of gas exchange from the blood into body tissues

- Oxygen (O₂) diffuses from the blood (high O₂ concentration) into body cells (low O₂ concentration) for cellular respiration.

- Carbon dioxide (CO₂) diffuses from the cells (high CO₂ concentration) into the blood (low CO₂ concentration) to be transported back to the lungs.