E&T: Gas Exchange in Insects

Question 1

What two things do most gas exchange surfaces have in common?

Answer 1

• Large surface area
• Thin - often just one layer of epithelial cells - providing a short difusion pathway across surface.

Question 2

How do single-celled organisms absorb and release gases?

Answer 2

Diffusion through their outer surface.

Question 3

In single-celled organisms, why is there no need for a gas exchange system?

Answer 3

• Have a relatively large surface area, thin surface and short diffusion pathway.
  
  • Means oxygen can take part in biochemical reactions as soon as it diffuses into the cell.

Question 4

How do insects exchange gases?

Answer 4

Through an evolved internal network of tubes called tracheae.

Question 5

What are the tracheae supported by?

Answer 5

Strengthened rings of cartilage.

Question 6

What do the tracheae divide into in insects?

Answer 6

Tracheoles

Question 7

Tracheae.

Answer 7

Microscopic air-filled pipes.

Question 8

Tracheoles.

Answer 8

Smaller, dead end divisions of the tracheae.

Question 9

What do tracheoles extend through?

Answer 9

All the body tissues of the insect.

Question 10

Spiracles.

Answer 10

Pores on the surface of the insect.

Question 11

Microscopic air-filled pipes.

Answer 11

Tracheae.

Question 12

Smaller, dead end divisions of the tracheae.

Answer 12

Tracheoles.

Question 13

Pores on the surface of the insect.

Answer 13

Spiracles.

Question 14

How do respiratory gases move in and out of the tracheal system?

Answer 14

• Along a diffusion gradient.
• Mass transport.
• Osmosis.

Question 15

Describe how respiratory gases move in and out of the tracheal system by moving along a diffusion gradient:

Answer 15

• Cells respire, oxygen is used up and the concentration gradient at the end of the tracheaeoles falls.
• Creates diffusion gradient.
• Gaseous oxygen diffuses from atmosphere along tracheae and tracheoles to cell.
• Carbon dioxide is produced during respiration.
• Creates diffusion gradient in other direction.

Question 16

Describe how respiratory gases move in and out of the tracheal system by mass transport:

Answer 16

• Contraction of muscles in insects can squeeze the trachea, enabling mass movement or air in an out.
• Speeds up exchange of gases.

Question 17

Describe how respiratory gases move in and out of the tracheal system by osmosis:

Answer 17

• Ends of tracheoles are filled with water.
• Major activity - muscle cells around tracheoles respire anaerobically.
• Produces lactate - insoluble and lowers water potential of muscles.
• Water moves into cells from tracheoles by osmosis.
• Water in ends of tracheoles decreases in volume and so more air is drawn in.
• So final diffusion pathway is in a gas, not a liquid and is more rapid.

Question 18

What is an issue with respiratory gases being moved in and out of tracheoles via osmosis?

Answer 18

Leads to greater water evaporation/water loss.

Question 19

How are spiracles opened and closed?

Answer 19

By a valve.

Question 20

When the spiracles are open …

What does this mean?

Answer 20

… water can evaporate from the insect.

Means most of the time spiracles are shut to prevent water loss, and opened periodically for gas exchange.

Question 21

What is a limitation of the tracheal system?

Answer 21

• Relies on diffusion - so diffusion pathway must be short.
• Limits the size insects can attain.

Question 22

What system do fish use for gas exchange?

Answer 22

Counter-current system

Question 23

Why do fish need adaptions to get enough air?

Answer 23

Lower concentration of oxygen in water than in air

Question 24

Describe gas exchange in fish:

Answer 24

• Oxygenated water enters fish through mouth and passes through gills.
• Gill filaments are covered in lamellae.
• Blood flows through lamellae in one direction and water flows over in the opposite.
• Maintains concentration gradient between water and blood.
• Concentration of O2 always higher in water than in blood, so as much O2 diffuses into blood.

Question 25

What is each gill made of?

Answer 25

Thin plates called gill filaments which give a big surface area.

Question 26

What are gill filaments covered with?

How are these adapted?

Answer 26

Tiny structures called lamellae which increase SA even more.

These also have lots of blood capillaries and a thin surface layer of cells to speed up diffusion

Question 27

Where do dicotyledonous plants exchange gases?

Question 28

Why is fish gas exchange knwon as a counter current system?

How does this aid gas exchange?

Answer 28

Blood flows through lamellae in one direction and water flows over in the opposite direction.

Maintains large concentration gradient between water and blood.

Question 29

Describe how stomata open

Answer 29

Become turgid and open

Question 30

Describe how stomata close

Answer 30

Become flaccid and close

Question 31

What also needs to be considered with gas exchange?

Answer 31

Water loss

Question 32

How are insects adapted to control water loss?

Answer 32

• Close spiracles using muscles.
• Waterproof, waxy cuticle all over their body and tiny hairs around spiracles - reduce evaporation

Question 33

How do plants reduce water loss?

Answer 33

• Stomata controlled by guard cells.
• Water enters guard cells - turgid - opens stomatal pore.
• If dehydrated, guard cells lose water - flaccid - closes stomatal pore.

Question 34

Xerophytes

Answer 34

Plants specifically adapted for life in warm, dry or windy habitats where water loss is a problem.

Question 35

Give examples of xerophyte adaptions:

Answer 35

• Stomata sunk in pits - traps moisture, reduces concentration gradient and thus diffusion.
• Hairs on epidermis - again traps moisture.
• Curled leaves with stomata inside - protects from wind which increases diffusion and evaporation.
• Reduced number of stomata - less water can leave
• Waxy, waterproof cuticles - reduce evaporation.