gas exchange

Question 1

Diffusion in insects

Answer 1

air moves through the spiracles and then enters the tracheae. The gas is then exchanged directly to cells. Oxygen diffuses down conc. gradient to respiring cell

Carbon dioxide diffuses down conc. gradient from respiring cells

Adaptations: lots of thin, branching tracheoles → short diffusion pathway and SA(:V) →
rapid diffusion

Question 2

adaptation of insects

Answer 2

To maximise efficient gas exchange and limit water loss the insects have:
-Thick waxy cuticle=Increases diffusion distance → less evaporation
-Spiracles can open and close=Open to allow oxygen in, close when water loss is too much

Question 3

Diffusion inside fishes (counter current flow)

Answer 3

Blood and water flow over the lamellae in opposite directions. There is Always a higher concentration of oxygen in water than the blood it is near Hence, a concentration gradient of oxygen between the water and blood is maintained along the whole length of lamellae (/gill plate) → equilibrium
not met. Maximising diffusion of oxygen

Question 4

Adaptation of fishes

Answer 4

Each gill is made of lots of gill filaments (thin plates) which are covered in many lamellae → gill filaments provide a large surface area, lamellae increase surface area even more

Vast network of capillaries on lamellae → remove oxygen to maintain a
concentration gradient

Thin/flattened epithelium → shorter diffusion pathway between water and
blood

Question 5

Gas exchange in humans

Answer 5

Oxygen diffuses from alveoli

Down its concentration gradient

Across the alveolar epithelium

Across the capillary endothelium

Into the blood (in haemoglobin)

Question 6

How does ventilation ensure efficient gas exchange

Answer 6

Ventilation maintains a oxygen concentration gradient

Brings in air containing higher concentration of oxygen

Removes air with lower concentration of oxygen

Question 7

How is the alveolar epithelium adapted to maximise diffusion rates

Answer 7

Squamous epithelium = thin/one cell thick=Short diffusion pathway → fast diffusion

Large surface area to volume ratio=Fast diffusion

Good blood supply from network of capillaries=
Maintains concentration gradient

Elastic tissue allows it to recoil after expansion.

Question 8

Importance of diffusion

Answer 8

Each organism is adapted to maximise diffusion rates. Fick’s law states that rate of diffusion is directly proportional to SA and concentration difference over the diffusion distance. All these organisms have some sort of special adaptation to increase diff. e.g. counter current flow ensures that oxygen concentration is maintained.

For humans diffusion is extremely important as we need to quickly diffuse oxygen into our bodies for metabolic processes such as respiration. Oxygen is needed by mitochondria for oxidative phosphorylation to produce ATP in order to release energy. e.g. actively transport sodium ions so that they can move glucose and amino acids into the small intestine to get absorbed into the blood stream