3.2 Gas exchange

How are single-called organisms adapted for gas exchange?

Thin, flat body and large surface area to volume ratio. Short diffusion distance to all parts of the cell

How are tracheoles adapted for gas exchange?

Thin walls so short diffusion distance to cells

High numbers of highly branched tracheoles so large surface area

Explain the structural features of insects that allow efficient gas exchange and limit water loss

Thick waxy cuticle → increases diffusion distance so less water loss

Spiracles can open to allow gas exchange and can close to reduce water loss

Hairs around spiracles → trap moist air, reducing water potential gradient so less water loss

Explain how gills of fish are adapted for gas exchange

Gills made of many filaments covered with many lamellae, increasing surface area for diffusion

Thin lamellae wall/epithelium so short diffusion distance between water/blood

Lamellae have a large number of capillaries → remove O2 and bring CO2 quickly so maintain concentration gradient

Explain the counter-current system in fish

Blood and oxygen flow in opposite directions through lamellae so oxygen concentration is always higher in the water than nearby blood. So maintains a concentration gradient of O2 between water and blood for diffusion across whole length of lamellae

Explain how the leaves of dicotyledonous plants are adapted for gas exchange

Many stomata → large surface area for gas exchange and limit

Spongy mesophyll contains air spaces → large surface area for gases to diffuse through

Thin → short diffusion pathway

Explain the structural features of xerophytic plants that allow efficient gas exchange while limiting water loss

Thicker waxy cuticle → increases diffusion distance so less evaporation

Sunken stomata/ curled leaves/ hairs → trap water vapour and protect stomata from wind so reduced water potential gradient between leaf and air so less evaporation

Spines/needles → reduces surface area to volume ratio

What is a xerophyte?

A plant adapted to live in very dry conditions

Explain how the alveolar epithelium is adapted for gas exchange

1 cell thick → Short diffusion pathway

Folded → large surface area

Permeable → allows diffusion of O2/ CO2

Close to large network of capillaries → maintains concentration gradient

How does gas exchange occur in the lungs?

Oxygen diffuses from alveolar air space into blood down its concentration gradient. Across alveolar epithelium then across capillary endothelium

Explain how humans breathe in (inspiration)

Diaphragm muscles contract and flatten

External intercostal muscles contract, internal intercostal muscles relax (antagonistic)

Ribcage pulled up and out, increasing volume and decreasing pressure in thoracaic cavity

Air moves into lungs down pressure gradient

Explain how humans breathe out (expiration)

Diaphragm muscles relax and move upwards

External intercostal muscles relax and internal intercostal muscles contract

Ribcage moves in and down, decreasing volume and increasing pressure in thoracic cavity

Air moves out of the lungs down a pressure gradient

Why might people with lung disease experience fatigue?

Cells receive less oxygen → rate of aerobic respiration reduced → less ATP made