6.2 gas exchange in single celled organisms and insects

Question 1

How do single-celled organisms exchange gases?

Answer 1

they have a large surface area to volume ratio so gases can be transferred by diffusion across their surface.

Question 2

What are tracheae?

Answer 2

An internal network of tubes for gas exchange in insects supported by strengthened rings to prevent them from collapsing, they divide into tracheoles.

Question 3

What are tracheoles?

Answer 3

Dead end tubes extending from tracheae, extending through the body tissues of the insect.

Question 4

How do tracheae and trachioles aid gas exchange?

Answer 4

they create a small diffusion pathway from the tracheole to any cell, meaning oxygen is brought directly to respiring tissues.

Question 5

What are the three ways in which gases move in and out of the tracheal system.

Answer 5

• Along a diffusion gradient
• mass transport
• the ends of the trachioles fill with water

Question 6

Describe how gases move along a diffusion gradient.

Answer 6

• In respiration, oxygen is used up so its concentration to the end of the tracheoles falls.
• this creates a diffusion gradient causing oxygen to diffuse down the tracheae and trachioles.
• carbon dioxide is produced by cells during respiration
• this creates a concentration gradient in the opposite direction, so carbon dioxide diffuses along the trachioles and tracheae into the atmosphere.

Question 7

Describe how gases move by mass transport.

Answer 7

• the contraction of muscles squeezes air in and out

Question 8

Describe how gases move by the ends of the trachioles filling with water.

Answer 8

• during major activity muscle cells around the tracheoles respire anaerobically
• this produces soluble lactate which lowers the water potential of the muscle cells, causing water to move in by osmosis from the trachioles
• the water decreases in volume so draws air in, meaning the diffusion pathway is in gas rather than liquid.

Question 9

How do gases enter the tracheal system?

Answer 9

through the spiracles- tiny pores

Question 10

When do spiracles open and close and what limitations does this have?

Answer 10

They open periodically in order to allow gas exchange. however when they are open water can be lost through evaporation, so they keep them closed for much of the time.

Question 11

What are the limitations of gas exchange in insects?

Answer 11

• the diffusion pathway has to remain short to be effective so the length of the diffusion pathway limits the size that insects can attain
• Water loss from the spiracles.