3.3.2 Gas exchange

Name the features of gross structure of the human gas exchange system

1. trachea

2. bronchi

3. broncioles

4. alveoli

Describe the essential features of the alveolar epithelium as a surface for gas exchange

• single layer of flattened cells so short diffusion distance

• moist so gases can dissolve for diffusion

• permeable which allows diffusion of oxygen and carbon dioxide

• folded which increases surface area so faster rate of diffusion

Describe how gas exchange occurs in the lungs (oxygen)

1. oxygen diffuses down its concentration gradient from the alveolar air space into the blood

2. across alveolar epithelium

3. across capillary endothelium

How is the concentration gradient for gas exchange maintained in humans?

• ventilation in the lungs

• continuous flow of blood from capillaries

Describe inspiration in humans

1. external intercostal muscles contract and ribcage pulled up

2. diaphragm contracts and pulled down

3. volume of thorax increases and pressure decreases (below atmospheric pressure)

4. air moves down pressure gradient into the lungs

Describe expiration in humans

1. internal intercostal muscles contract ribcage pulled down

2. diaphragm relaxes and moves up

3. volume of thorax decreases and pressure increases (above atmospheric pressure)

4. air moves out of lungs down pressure gradient

Name 3 features of the tracheal system of an insect

1. spiracles

2. tracheae

3. tracheoles

What is the role of spiracles in gas exchange?

allows diffusion of oxygen

What is the role of tracheae in gas exchange in insects?

.

What is the role of tracheoles?

(branch from tracheae) to directly deliver oxygen to cells and tissues

Explain 2 adaptations of tracheoles for efficient gas exchange in insects

1. tracheole wall is one cell thin so short diffusion distance

2. highly branched so short diffusion distance and large surface area for diffusion

Explain how abdominal pumping increases the efficiency of gas exchange in insects

• changes pressure in body causing air to move

• maintains concentration gradient of oxygen for diffusion

Describe gas exchange via diffusion in insects

• oxygen moves down its concentration gradient from the atmosphere into tracheoles

• carbon dioxide moves down its concentration gradient from tracheoles into atmosphere

Describe anaerobic respiration in insects

• when insects are in flight, lactate produced

• lowers water potential of fluid in tracheoles

• water moves back into cells via osmosis

• air fills tracheoles which increases rate of diffusion (faster diffusion through air)

Describe adaptations in insects to prevent water loss

• exoskeleton is impermeable

• spiracles can open for gas exchange and close to minimise water loss (via evaporation)

• hairs around spiracles reduce water loss

Explain how gills in fish are adapted for gas exchange

• made up of many filaments with many lamellae so large surface area for diffusion

• thin lamellae so short diffusion distance

• lamellae have large number of capillaries to maintain concentration gradient

Explain how the counter-current principle allows efficient oxygen uptake in thr fish gas exchange system

1. blood and water flow in opposite directions

2. oxygen concentration always higher in water (than blood)

3. concentration gradient of oxygen maintained

4. diffusion across length of lamella

What is the advantage of counter current flow?

ensures equilibrium is not reached

Describe and explain adaptations of leaves which maximise gas exchange

• many stomata for diffusion of gases

• spongy mesophyll contains air spaces

• thin leaves so short diffusion distance

• large leaf surface area:volume ratio to increase rate of diffusion

Explain features of xerophytic plants which allow efficient gas exchange while limiting water loss

• thick waxy cuticle increases diffusion distance so less evaporation

• sunken stomata, curled leaves, hairs to trap moisture