4.3 Gas exchange

Question 1

What is the sa:v ratio for small and large organisms?

Answer 1

small - large SA:V
large - small SA:V

Question 2

What factors affect the rate of diffusion?

Answer 2

• surface area
• concentration gradient
• diffusion distance

Question 3

How are mammals adapted for gas exchange?

Answer 3

• large SA, small SA:V
• moist surface
• thin layers - minimize diffusion distance
• rich blood supply - maintain steep concentration gradient
• permeable surfaces - free passage of respiratory gases

Question 4

How is the alveoli adapted for gas exchange?

Answer 4

• large SA
• short diffusion distance - 1 cell thick
• steep concentration gradient - continuous flow of blood

Question 5

What happens during inhalation?

Answer 5

its an active process:

1. muscles around diaphragm contract - lowered + flattened
2. intercoastal muscles contract - ribcage raised up and out
3. thorax volume increases

Question 6

What happens during normal exhalation?

Answer 6

• passive process
• external muscles relax
• ribs fall under gravity
• thorax volume decreases

Question 7

What happens during forced exhalation?

Answer 7

• intercostal muscles contract
• ribcage pulled down and in

Question 8

How are lungs protected from pathogens being breathed in?

Answer 8

• airways lined with mucus to trap tiny particles
• mucus is runny so it moves to the back of your throat where you swallow it and your stomach HCl and digestive enzymes digest the pathogens.

Question 9

How are insects adapted for gas exchange?

Answer 9

• spiracles - found along thorax and abdomen of most insects and are the entry and exit site for respiratory gases
• sphincters - open and close spiracles to prevent water loss
• tracheae - largest tubs in insect respiratory system, they carry air directly into the body for gas exchange.
  they are supported by by rings of chitin to prevent collapse
• tracheoles - smaller branches dividing off tracheae to provide large SA

Question 10

How are fish adapted for gas exchange?

Answer 10

• gills - made of filaments covered with filaments to provide a high SA
• lamellae - folds that cover the filaments. water passes over them due to pressure from floor to mouth. providing a high SA
• overlapping gill filaments - increasing resistance to the flow of water, slowing it down, so there is more time for gas exchange to occur
• countercurrent exchange system - water and blood flow in opposite directions to maintain a steep concentration gradient

Question 11

How are plant leaves adapted for gas exchange?

Answer 11

• spongey mesophyll layer provides large SA
• waxy cuticle is impermeable to gas - preventing water loss
• lenticels - are loosely packed cells that are site of gas exchange in woody stems. they allow gases to enter and leave

Question 12

What is the role of the stomata?

Answer 12

specialized pores found mainly in the epidermis on underside of leaf through which gases diffuse in and out the cell

Question 13

What are the role of guard cells?

Answer 13

limit water loss and control rate of gas exchange
- they open and close stomatal pores