Gas Exchange

Question 1

Describe the relationship between size + surface area:volume ratio of organisms?

Answer 1

The larger the size of the organism, the smaller the surface area:volume ratio

Question 2

What is Fick’s Law?

Answer 2

SA x Conc. Gradient
/////////////////////////////
Diffusion Distance

Question 3

What are the most effective properties for gas exchange? (3)

Answer 3

• Large SA
• Thin
• Large conc. gradient (permeable - allowing gases to pass through)

Question 4

How do insects limit water loss? (2)

Answer 4

• Waterproof covering
• Small SA:Volume ratio

Question 5

Explain the movement of oxygen into the gas exchange system of an insect when it is at rest? (4)

Answer 5

• Oxygen used in (aerobic) respiration;
• (so) oxygen (concentration) gradient (established) - accept description of gradient
• (so) oxygen diffuses in

Question 6

Why does diffusion happen in the gas exchange system of insects?

Answer 6

Oxygen diffusion:
- Tissues respire using oxygen, which reduces conc. of O2
- Moves from tracheae to tissue down conc. gradient

Carbon dioxide:
- Respiration produces CO2, increasing conc. at the tissue
- From tissues to tracheae down conc. gradient

Question 7

At flight, insects may partially repair anaerobically which leads to what?

What does this cause?

Answer 7

Lactic acid build up

Lowers water potential of the muscles as water passes from tracheoles into muscles via osmosis

Question 8

Explain 2 ways in which the structure of fish gills is adapted for efficient gas exchange?

Answer 8

• Many filaments so there’s a large surface area
• Lamellae are thin for a short diffusion distance

Question 9

Diagram of fish gills? (2)

Answer 9

Question 10

A fish uses its gills to absorb O2 from water. Explain how the gills of a fish are adapted for efficient gas exchange? (6)

Answer 10

• Large SA provided by many filaments, which increases diffusion
• Thin epithelium of lamellae for short diffusion distance
• Water + blood flow in opposite directions so conc. gradient is maintained
• Water is always next to the blood with lower conc. of oxygen
• Circulation replaces blood saturated with oxygen
• Ventilation replaces water

Question 11

Explain how the counter current mechanism in fish gills ensures maximum amount of oxygen passes into the blood flowing through the gills? (3)

Answer 11

• Water + blood flow in opposite directions
• Blood always passes water with a higher O2 conc.
• Oxygen conc. gradient is maintained across its full length of the gill filaments

Question 12

Structure of a leaf? (7)

Answer 12

Question 13

Adaptations of a leaf for gaseous exchange? (3)

Answer 13

• Flat - Larger SA:Volume ratio
• Many stomata - Pores allow air to move in + out
• Air spaces - short diffusion distance

Question 14

Explain the gaseous exchange of oxygen within a leaf? (3)

Answer 14

• Mesophyll cells produce O2 through photosynthesis
• O2 diffuses into air spaces
• This increases conc. of oxygen in air spaces, causing O2 to diffuse outside of leaf via stomata

Question 15

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside a leaf? (3)

Answer 15

• Diffuses through air spaces
• Down conc. gradient
• Via stomata, opened by guard cells

Question 16

What are xerophytic plants?

Answer 16

Plants that prevent water loss due to living in dry environments

Question 17

How are xerophytic plants adapted to reduce water loss? (6)

Answer 17

• Reduced number of stomata - Less SA for water loss
• Stomata in pits - Reduced conc. gradient
• Hairs to trap water vapour - Reduced conc. gradient
• Rolled leaves - Reduced conc. gradient
• Leaves reduced to spines - Less SA
• Thick waxy cuticles - Increased diffusion distance

Question 18

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs? (4)

Answer 18

• O2 passes through trachea, bronchus, bronchioles then alveoli
• Down a pressure gradient
• O2 diffuses across squamous epithelial
• Down concentration gradient
• Across capillary endothelium

Question 19

Describe the gross structure of the human gas exchange system + how we breathe in + out? (6)

Answer 19

1. Named structures – trachea, bronchi, bronchioles, alveoli;
2. Above structures named in correct order
3. Breathing in – diaphragm contracts and external intercostal muscles contract;
4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);
5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);

Question 20

Describe the pathway taken by an oxygen molecule from an alveolus to the blood?

Answer 20

Diffuses across alveolar epithelium and endothelium of capillary into blood

Question 21

Explain how one feature of an alveolus allows efficient gas exchange to occur?

Answer 21

One cell think so short diffusion distance

Question 22

Structure of lungs? (7)

Answer 22

Question 23

Equation for pulmonary ventilation?

Answer 23

Tidal Volume x Breathing Rate

Question 24

Binding of 1 molecule of oxygen to haemoglobin makes it easier for the second oxygen molecule to bind. Explain why? (2)

Answer 24

• When 1 O2 molecules binds it alters the quaternary/tertiary structure of haemoglobin
• It exposes a second binding site