gas exchange

Question 1

Describe and explain the movement of oxygen in an insect.

Answer 1

Spiracles open
Oxygen diffuses in through spiracles.
Spiracles close
Oxygen diffuses through the trachea into the tracheoles.
Delivered directly to respiring tissues.

Question 2

Describe and explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.

Answer 2

Tracheoles have thin walls so short diffusion distance to cells.

2. Highly branches so large surface area for gaseous exchange.
3. Fluid in the end of the tracheoles moves out into tissues during exercise so faster diffusion through the air to the gas exchange surface.

Question 3

Describe and explain the counter-current principle in gas exchange across a fish gill.

Answer 3

1.  Water and blood (NOT OXYGEN) flow in opposite directions
2.  Maintains concentration gradient of oxygen
3.  along entire length of lamellae/filament/gill/capillary
4. Oxygen concentration always higher in water than blood

Question 4

Describe and explain three ways in which a fish’s gills system is adapted for efficient gas exchange.

Answer 4

1. Many gill filaments and lamellae so large surface area.
2. Thin epithelium of lamellae has short diffusion distance.
3. Water and blood flow in opposite directions so that a concentration gradient is maintained along entire length of lamella

Question 5

Describe and explain the movement of carbon dioxide into leaves.

Answer 5

Mesophyll cells photosynthesise reducing concentration of CO2

CO2 diffuses from air spaces into the cells.

Creating concentration gradient of CO2,lower concentration in air spaces.

Guard cells open stomata in light conditions

CO2 diffuses through stomata down concentration gradient. .

Question 6

suggest and explainhowthe features of a xerophytic plant help prevent water loss.

Answer 6

Rolled leavesso‘trap’ water vapour and water potential gradient decreased ->less transpiration

Spines/needlessoreduces surface area to volume ratio ->less evaporation

Hairsso‘trap’ water vapour decreasing water potential/concentration Gradient

Sunken Stomata in pits so‘trap’ water vapour decreasing water potential/concentration gradient.

Thicker cuticle soincreases diffusion distance.
Waxy layer soreduces evaporation/transpiration.
Fewer stomata so less surface area for transpiration

Question 7

Describe how you could use an eyepiece graticule to determine the mean diameter of stomata

Answer 7

Measure using eye piece graticule
Calibrate eyepiece graticule against stage micrometre
Take a large number of repeat measurements to calculate mean

Question 8

Describe and explain the features of the lungs that allow for efficient gaseous exchange.

Answer 8

Rich blood supply to maintain a large concentration gradient
many alveoli gives a large surface area
one cell thick so short diffusion pathway

Question 9

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.

Answer 9

1. Oxygen moves through the trachea, bronchi, bronchioles to the alveoli down a pressure gradient.

Oxygen then moves by diffusion:
-Across the alveolar epithelium
-Across the capillary endothelium
Then binds with haemoglobin in a red blood cell.

Question 10

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

Answer 10

1.trachea -> bronchi -> bronchioles -> alveoli
2.Breathing in – diaphragm contractsandexternalintercostal muscles contract
3.causes volume increase and pressure decrease in thoracic cavity so air moves in down a pressure gradient.
4.Breathing out - Diaphragm relaxes,external intercostal muscles relax and elastic tissue recoils.
5.Causes volume decrease and pressure increase in thoracic cavity so air moves out down a pressure gradient.

Question 11

ficks law

Answer 11

diffusion = surface area x difference in concentration / diffusion path