3.3.2 Gas exchange

Question 1

Gas exchange

-across the body surface of a single-celled organism

Answer 1

-absorb and release gasses by diffusion through their outer surface

Question 2

Gas exchange
Adaptations of gas exchange surfaces
-across the body surface of a single-celled organism

Answer 2

-large surface area/ thin surface for a short diffusion pathway

Question 3

Rate of diffusion

Equation

Answer 3

(surface area x difference in concentration) / diffusion distance

Question 4

What type of gas exchange system do insects have?

Answer 4

Tracheal system

Question 5

Tracheal system

Structure

Answer 5

• internal network of tubes called trachea

- spiricles → trachea → tracheoles → respiring tissues

Question 6

Tracheal system
Process of gas exchange
3 ways gases move in and out of the tracheal system

Answer 6

1. Along a diffusion gradient (aerobic respiration)
2. Mass transport
3. End of tracheoles are filled with water(anaerobic respiration)

Question 7

Tracheal system

Process of gas exchange

Answer 7

• air enters through spiracles on the surface
  -oxygen travels through trachea
  └down the concentration gradient
  └towards cell-trachea branch off into smaller tracheoles
  └they have thin permeable walls
  └O2 diffuses directly into respiring cells
  -CO2 moves down its own concentration gradient
  └towards spiricles
  └to be released into the atmosphere
  -abdominal movements are used to move air in and out of spiracles

Question 8

Tracheal system
Process of gas exchange
During exercise

Answer 8

-withdrawal of fluid in tracheole tips during exercise
-anaerobic respiration occurs
└lactic acid/lactate accumulates in respiring muscle cells
└=soluble in water so reduces water potential in respiring muscle cells
-osmosis of water from tracheoles into muscle cells
└increasing SA of treacheae

Question 9

Tracheal system
Process of gas exchange
Along a diffusion gradient

Answer 9

-during respiration
└concentration of oxygen lowers towards end of tracheoles
└so oxygen moves in and carbon dioxide moves out

Question 10

Tracheal system
Process of gas exchange
mass transport

Answer 10

-contraction of muscles in insects can squeeze the trachea

└=enables mass movements of air, in and out

Question 11

Gas exchange
Adaptations of gas exchange surfaces
-in the tracheal system of an insect

Answer 11

-tracheal system
-chitin rings support trachea system
└prevent them from collapsing
-many tracheoles
└increases surface area
-tracheoles have small diameter
└increases surface area to volume ratio
-hard waxy cuticle
└prevents water loss
-spiracles have valves
└to control levels of carbon dioxide (open if too high)
-withdrawal of fluid in tracheole tips during exercise further reduces diffusion distance (final diffusion distance pathway is in a gas rather than liquid phase, and therefore diffusion is more rapid)

Question 12

Trachea

Answer 12

-are supported by strengthened chitin rings
└prevent them from collapsing
-divides into smaller tracheoles

Question 13

Tracheoles

Answer 13

• thin permeable walls

- large surface area

Question 14

Spiracles

Answer 14

-tiny pores where gases enter and leave the trachea
-spiracles may be opened and closed by a valve
└when spiracles are open, water vapour can evaporate from this insect

Question 15

Limitations of this gas exchange system

Answer 15

-relies mostly on diffusion to exchange gases between the environment and cells
-need a short diffusion pathway
└=limits the size that insects can attain.