Gas Exchange

Question 1

Two major adaptions of gas exchange

Answer 1

1. Large SA
2. Thin - short diffusion distance

Maintains a steep conc gradient of gases across exchange surfaces

Question 2

How do singe called organisms exchange gases across their body surfaces

Answer 2

• absorb and release gases by diffusion through outer surfaces
• large SA, thin surface and short diffusion pathway - no need for gas exchange system

Question 3

How do fish use counter current system for gas exchange

Answer 3

Lower conc of o2 in the water than in the air

1. Water, containing o2, enters the fish through the mouth and passes out through the gills
2. Each gill has thin plates called gill filaments, big SA for gas exchange of gases
3. Gill filaments are covered in lots of tiny structures called lamellea, increase the SA even more
4. Lamella have lots of blood capillaries and thin surface layer of cells to speed up diffusion
5. Blood flows through the lamella in one direction and water flows over in the opposite direction. Called counter current. Maintains a large conc gradient between water and the blood. The conc of o2 in water is always higher than in the blood. As much o2 as possibles diffuses from the water into the blood.

Question 4

Gas exchange in humans - how are the lungs specialised for gas exchange

Answer 4

1. As you breathe in, air enters the trachea
2. The trachea splits into 2 bronchi and one bronchus leading into lung
3. Each bronchus branches off into smaller tubes called bronchioles
4. End in small sacs called alveoli
5. Rub cage and intercostal muscles and diaphragm all work together to move air in and out

Question 5

Process of inspiration

Answer 5

1. External I and diaphragm muscles contract
2. Causes ribcage to move upwards and outwards - diagram flatters - increases the vol of the thoracic cavity
3. As the vol increases in thoracic cavity, the lung pressure decreases
4. Air always flows from an area of high to low pressure - air flows down trachea into the lungs
5. Active process requires energy

Question 6

Expiration

Answer 6

1. External intercostals and diaphragm muscles relax - internal intercostals contract, pull the ribcage further down and in. (Antagonistic)
2. Ribcage moves downwards and inwards - diagram becomes curved
3. Vol of the thoracic cavity decreases - air pressure increases
4. Air forced down the pressure gradient and out the lungs
5. Passive process - doesn’t require energy

Question 7

Gas exchange in the alveoli

Answer 7

1. O2 diffuses out the alveoli, across the alveolar epithelium and the capillary endothelium into Hb in the blood
2. Co2 diffuses into the alveoli from the blood, breathed out

Question 8

How is the alveoli adapted for gas exchange

Answer 8

1. Thin exchange surface - the alveolar epithelium is one cell thick. Short diffusion pathway
2. Large SA - the large number of alveoli - large SA for gas exchange