gas exchange & lungs

Question 1

how does oxygen move through the insect ?

Answer 1

1. oxygen diffuses in through the spiracles
2. spiracle closes
3. oxygen moves through the trachea into the tracheoles
4. oxygen delivered directly to the respiring tissues

Question 2

explainthreeways in which an insect’s tracheal system is adapted for efficient gas exchange

Answer 2

1. tracheoles have thin wallssoshort diffusion distance to cells
   2.highly branched / large number of tracheolessoshort diffusion distance to cells
2. highly branched / large number of tracheolessolarge surface area (for gas exchange)
   4.tracheae provide tubes full of airsofast diffusion (into insect tissues)
   5.fluid in the end of the tracheoles that moves out (into tissues) during exercisesofaster diffusion through the air to the gas exchange surface
   OR
   fluid in the end of the tracheoles that moves out (into tissues) during exercisesolarger surface area (for gas exchange)
3. body can be moved (by muscles) to move airsomaintains diffusion / concentration gradient for oxygen / carbon dioxide

Question 3

describe and explain the advantage of the counter-current principle in gas exchange across a fish gill

Answer 3

1. water and blood flow in opposite directions
2. maintains diffusion/concentration gradient of oxygen OR oxygen concentration always higher (in water)
3. (diffusion) along length of lamellae/filament/gill/capillary

Question 4

a fish uses its gills to absorb oxygen from water
explain how the gills of a fish are adapted for efficient gas exchange

Answer 4

1 large surface area provided by many lamellae over many gill filaments
2 increases diffusion/makes diffusion efficient
3 thin epithelium/distance between water and blood
4 water and blood flow in opposite directions/countercurrent
5 (point 4) maintains concentration gradient (along gill)/equilibrium not reached
6 as water always next to blood with lower concentration of oxygen
7 circulation replaces blood saturated with oxygen
8 ventilation replaces water (as oxygen removed)

Question 5

describe the gross structure of the human gas exchange system and how we breathe in and out

Answer 5

1. named structures – trachea, bronchi, bronchioles, alveoli
2. above structures named in correct order OR above structures labelled in correct positions on a diagram
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 6

describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf (4)

Answer 6

1. (carbon dioxide enters) via stomata
2. (stomata opened by) guard cells
3. diffuses through air spaces
4. down diffusion gradient

Question 7

explain why plants grown in soil with very little water grow only slowly

Answer 7

1. stomata close
2. less carbon dioxide (uptake) for less photosynthesis/glucose production

Question 8

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

Answer 8

1. Many filaments SO large surface area
2. Thin lamellae FOR short diffusion pathway

Question 9

Explain the movement of oxygen into the gas exchange system of an insect when it is at rest (3)

Answer 9

1. Oxygen used in (aerobic) respiration
2. Oxygen concentration gradient established
3. Oxygen diffuses in; 2 and 3.

Question 10

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.
Details of breathing are not required (4)

Answer 10

1. Pass through trachea, into bronchi, into bronchioles
2. Down pressure gradient
3. Down diffusion gradient
4. Across alveolar epithelium
5. Across capillary endothelium

Question 11

Describe the pathway taken by an oxygen molecule from an alveolus to the blood (2)

Answer 11

1. Across alveolar epithelium
2. Across endothelium of capillary

Question 12

Explain how one feature of an alveolus allows efficient gas exchange to occur (2)

Answer 12

1.One cell thick
2. So short diffusion distance

Question 13

Explain why death of alveolar epithelium cells reduces gas exchange in human lungs (2)

Answer 13

1. Reduced surface area
2. Increased distance for diffusion

Question 14

Describe inhalation (5)

Answer 14

1. External intercostal muscles contract pulling rib cage up and out
2. Diaphragm contracts and pulls down
3. Thoracic cavity volume increases
4. Pressure in lungs lower than atmospheric pressure
5. Air moves into lungs down a pressure gradient

Question 15

Describe exhalation (5)

Answer 15

1. External intercostal muscles relax
2. Diaphragm relaxed and moves up
3. Thoracic volume decreases
4. Pressure in lungs greater than atmospheric pressure
5. Air moves out of lungs down a pressure gradient

Question 16

Describe the pathway of oxygen from the atmosphere to the blood (6)

Answer 16

1. Pass through trachea
2. Enter bronchi, leading to bronchioles
3. Enter alveoli
4. Squamous epithelial cell
5. Capillary endothelial membrane
6. Red blood cell membrane