Gas Exchange in Single-Celled Organisms and Insects

Question 1

What do single celled organisms have?

Answer 1

A large surface area to volume ratio

Question 2

How do single celled organisms absorb oxygen?

Answer 2

By diffusion across their body surface

Question 3

For a single celled organism to absorb oxygen, what must it cross?

Answer 3

A cell-surface membrane

Question 4

If a living cell is surrounded by a cell wall, is their an additional barrier to the diffusion of gases?

Answer 4

No

Question 5

What have insects evolved that allows for gas exchange?

Answer 5

An internal network of trachea §

Question 6

What are trachea supported by to prevent them from collapsing?

Answer 6

Strengthening rings

Question 7

What do the trachea divide into?

Answer 7

Dead-end tubes called tracheoles

Question 8

Where do the tracheoles extend through?

Answer 8

All the body tissues of the insect

Question 9

What do the tracheoles allow?

Answer 9

Atmospheric air to be brought directly to the respiring tissues

Question 10

What do tracheoles give?

Answer 10

Short diffusion pathways from a tracheole to any body cell

Question 11

What are the three ways respiratory gases move in and out of the tracheal system?

Answer 11

• Along a diffusion gradient
• Mass transport
• The ends of the tracheoles are filled with water

Question 12

How do respiratory gases move in and out of the tracheal system along a diffusion gradient?

Answer 12

• As the cells respire oxygen is used up so its concentration falls towards the ends of the tracheoles which creates a diffusion gradient that causes gaseous oxygen to diffuse from the atmosphere along the trachea and tracheoles to the cells.
• As carbon dioxide is produced by respiring cells a diffusion gradient is formed causing gaseous carbon dioxide to diffuse along tracheoles and trachea from cells to the atmosphere
• diffusion in air is quicker than in water so gases are exchanged quickly

Question 13

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

Answer 13

Insects muscles contract and squeeze the trachea enabling mass movements of air in and out, speeding up the exchange of respiratory gases

Question 14

How do respiratory gases move in and out of the tracheal system with the ends of the tracheoles being filled with water?

Answer 14

During periods of major activity, the muscle cells

Question 15

What are the pores called that gases enter and leave the tracheal system through?

Answer 15

Spiracles

Question 16

How are the spiracles opened and closed?

Answer 16

By valves

Question 17

What happens when the spirals are opened?

Answer 17

Water vapour can evaporate from the insect

Question 18

How do insects keep their spiracles in order to prevent water loss?

Answer 18

Closed

Question 19

What happen to spiracles to allow gas exchange?

Answer 19

They are periodically opened

Question 20

What are the limitations of the tracheal system?

Answer 20

It relies mostly on diffusion to exchange gases between the environment and the cells and for diffusion to be effective diffusion pathways need to be small therefore limiting the size the insect can grow to.