Exchange and Transport

Question 1

what are the reasons for gas exchange?

Answer 1

• because multicellular organisms have a small SA:V ratio, cells in the centre of the organism would not receive any materials if multicellular organisms survived on diffusion alone as they have too big of a diffusion distance.
• multicellular organisms have a high metabolic rate so gas exchange systems are needed

Question 2

what are the features of efficient gas exchange?

Answer 2

• large surface area to maximise rate of diffusion
• good blood supply (to maintain a steep concentration gradient)
• thin cells (short diffusion distance)
• ventilation (maintains the diffusion gradient)
• moist surfaces (allows gases to dissolve and diffuse more easily and stops walls of alveoli from sticking together

Question 3

what are examples of good exchange surfaces?

Answer 3

alveoli, villi, root hair cell