(U2) T&EM - Gaseous Exchange

Question 1

What factors affect gas exchange at respiratory surfaces? (4)

Answer 1

• SA - large = higher rate
• moist surface for permeability - allow gases to dissolve = higher rate
• diffusion gradients for oxygen and carbon dioxide - steeper = higher rate
• short diffusion pathway e.g. through squamous endothelium of capillaries = higher rate

Question 2

State the equation for Fick’s Law

Answer 2

Diffusion rate ∝

[(SA of membrane) x (concentration difference across membrane)]
———————————————————————————
thickness of membrane

Question 3

Which 2 processes require gas exchange in plants?

Answer 3

• respiration
• photosynthesis

Question 4

At what times of the day does:

• photosynthesis occur at a greater rate
• respiration occur at a greater rate
• both at the same time

Answer 4

1. Photosynthesis > respiration: dawn to dusk, peak at midday
2. Photosynthesis < respiration: dusk to dawn (nighttime)
3. Photosynthesis = respiration: dusk and dawn (compensation point)

• Respiration virtually stays at the same rate, photosynthesis changes with light intensity
• respiration absorbs O₂ and releases CO₂, photosynthesis does the inverse

Question 5

What are the adaptations of a leaf for gas exchange? (4)

Answer 5

1. Thinness of leaf:

• overall SA/V ratio is high
• short diffusion distance

2. Spongy mesophyll are moist and rounded:

• large SA in contact with air spaces
• permeable and allow gases to dissolve through membrane

3. Intercellular air spaces:

• ensure a steep diffusion gradient for CO₂ and O₂

4. Stomata closed at night, open during day:

• mainly for limiting transpirational water loss
• open when guard cells are turgid, closed when they aren’t
• also facilitates CO₂ uptake

Question 6

What is the gas exchange surface in mammals?

What size relatively speaking is the mammalian SA/V ratio to prokaryotes?

Answer 6

• Squamous epithelial cells of alveoli
• Small SA/V ratio (generally; due to impermeable body covering)

Question 7

What are the adaptations of a mammal for gas exchange? (10)

Answer 7

1. Thin squamous epithelial cells of alveoli:

• short diffusion distance

2. Alveoli surrounded by dense network of capillaries:

• increased SA for diffusion

3. Thin, single layer of squamous endothelial cells in capillaries:

• short diffusion distance

4. Capillaries tight against alveolar wall:

• short diffusion distance

5. Red blood cells in contact with endothelial wall:

• decreased diffusion distance

6. Millions of alveoli:

• large SA for diffusion

7. Degree of proliferation of capillaries around alveoli:

• continuous layer of blood around each alveolus
• maintains diffusion gradient of gases

8. Mass flow of gases through ventilation:

• steep diffusion gradient

9. Surfactant produced in alveoli:

• reduces surface tension of moisture
• prevents collapse

10. Macrophages and other white blood cells:

• protect against infection which can adversely impact gas exchange processes

Question 8

Outline the pathway for breathing (6/7)

Answer 8

• buccal / nasal cavity
• trachea
• bronchi
• bronchioles
• alveolar ducts
• alveoli

Question 9

Outline the process of inspiration (6)

Answer 9

• external intercostal muscles contract
• ribs move up and out
• diaphragm contracts and moves down
• volume of thorax increases
• pressure decreases
• lung pressure < atm, air enters lungs

Question 10

Outline the process of expiration (6)

Answer 10

• internal intercostal muscles contract
• ribs move down and in
• diaphragm relaxes and becomes domed
• volume of thorax decreases
• pressure increases
• lung pressure > atm, air leaves lungs

Question 11

What is the general cause of:

• lung cancer
• emphysema
• bronchitis

Answer 11

• lung cancer: carcinogens in tar
• emphysema: damage by tar
• bronchitis: damage by tar

Question 12

What is lung cancer?

What complications can it cause?

Answer 12

• uncontrolled cell division in lungs, forming a tumour
• tumour can block airways, or can spread around the body if it enters the blood

Question 13

Outline how emphysema occurs & its complications (5)

Answer 13

• tar damages squamous epithelial cells of alveoli, walls break down
• SA of the lungs is reduced; less diffusion of gases
• elastin breaks down, reducing recoiling ability of alveoli in expiration
• air can’t be naturally expelled; layer of residual air prevents fresh air reaching alveoli
• resulting in a lack of oxygen

Question 14

Outline how bronchitis occurs & its complications (4)

Answer 14

• bronchial tubes swell and become narrower (after damage by heat/tar)
• narrowing and increased mucus reduces airflow
• tar paralyses cilia, so mucus and pathogens can’t be removed
• risk of infection increases