3.2 Gas Exchange

Question 1

Describe the process of inhalation in humans

Answer 1

• Diaphragm contracts and flattens
• External intercostal muscles contract, and internal intercostal muscles relax
• Ribcage pulled up and out
• So volume of thorax increases
• So pressure in thorax decreases
• Pressure in thorax lower than atmospheric, so air moves into lungs down the pressure gradient

Question 1

What are the three most key important features of an efficient gas exchange system

Answer 1

• Large surface area
• Short diffusion distance / pathway
• Concentration gradient maintained

Question 2

Describe the process of exhalation in humans

Answer 2

• Diaphragm relaxes and domes
• External intercostal muscles relax, and internal intercostal muscles contract
• Ribcage pulled in and down
• So volume in thorax decreases
• So pressure in thorax increases
• As pressure in thorax is greater than in atmosphere, air moves down pressure gradient out of lungs

Question 3

Pulmonary ventialation rate equation

Answer 3

PVR = tidal volume x breathing rate

Question 4

Tidal volume equation

Answer 4

PVR / breathing rate

Question 5

Breating rate equation

Answer 5

PVR / tidal volume

Question 6

Points to assess if data is reliable

Answer 6

• Large sample size
• Individuals chosen at random
• Individuals healthy
• Equal number of males and females / same sex
• Repeat readings

Question 7

Points to challenge assumptions made with data

Answer 7

• Influence of other factors
• Further studies required
• How great is the difference / data

Question 8

Explain how the human gas exhange system is specialised - for large surface area

Answer 8

Large number of alveoli

Question 9

Explain how the human gas exhange system is specialised - for short diffusion distance/pathway

Answer 9

• Alveoli epithelium cell is one flattened cell thick
• Capillary walls are one flattened cell thick

Question 10

Explain how the human gas exhange system is specialised - for maintaining high concentration gradient

Answer 10

• Constant flow of blood through capillary network
• Ventilation in lungs replenishes air

Question 11

How are single celled organisims speciallised for gas exchange

Answer 11

• Cells are flattened and long, so large surface area and reduced diffusion distance/pathway
• Oxygen quickly used in respiration so maintains a high concentration gradient

Question 12

Explain how the fish gas exhange system is specialised - for large surface area

Answer 12

• Large number of gill fillaments and lamellae

Question 13

Explain how the fish gas exhange system is specialised - for short diffusion distance/pathway

Answer 13

• Lamellae are thin
• Many capillaries in the lamellae

Question 14

Explain how the fish gas exhange system is specialised - for concentration gradient maintained

Answer 14

Counter-current mechanism

Question 15

Explain the counter-current mechanism

Answer 15

• Blood and water flow in opposite directions
• Blood always passes water with higher oxygen concentration
• Oxygen diffusion gradient maintained across entire length of gill
• So diffusion occurs across entire length of gill

Question 16

Explain how the insect gas exhange system is specialised - for large surface area

Answer 16

Tracheoles are highly branched

Question 17

Explain how the insect gas exhange system is specialised - for short diffusion distance/pathway

Answer 17

• Tracheoles are highly branched
• Tracheole walls are thin and permeable to oxygen
• Many spiraces

Question 18

Describe the movement of oxygen in insect gas exhange systems

Answer 18

Spiracles open to allow oxygen to move by diffusion down diffusion gradient which then lead to trachea to traceoles to cells

Question 19

Describe adaptations to insect gas exchange system when anaerobically respiring

Answer 19

Water moves out of tracheoles, reducing diffusion distance of oxygen in water

Question 20

Describe abdominal pumping

Answer 20

• Only occurs when CO2 concentration very high
• Pumping raises pressure in body
• So carbon dioxide moves out down pressure gradient into atmosphere

Question 21

How is the insect gas exhange system adapted to prevent water loss

Answer 21

• Chitin exoskeleton is impermeable
• Spiracles close during inactivity
• Spiracle surrounded by hairs which traps a layer of air saturated with water, decreasing concentation gradient

Question 22

How are plants specialised to maximise gas exchange

Answer 22

• Large surface area of leaves, so greater number of stomata
• Many stomata, so short diffusion distance to/from spongy mesophyll cells
• Thin leaves, so short diffusion distance to/from spongy mesophyll cells
• Carbon dioxide quickly used in photosythesis to maintain high concentration gradient

Question 23

How are plants specialised to reduce water loss

Answer 23

• Thicker waxy cuticle to increase diffusion distance of water, and so reduce evaportation of water
• Atomata in pits
• Stomata surrounded by hairs
• Leaves are rolled
• All trap water and decrease the water potential gradient
• Leaves are spines so reduces the SA:V ratio