7.1- Specialised Exchange Surfaces

Question 1

Why can diffusion alone supply the needs of single celled organisms?

Answer 1

• the metabolic activity is relatively low, so oxygen demands and co2 production are low.
• sa:v ratio is large

Question 2

Why is diffusion not enough for larger organisms?

Answer 2

They have high metabolic activity.

• oxygen demands are high and lots of co2 is produced.
• diffusion is in effective as distance between cells is too far.
• the bigger the organism the smaller the sa:v ratio so gases can’t be exchanged fast enough to survive.

Question 3

What are the features of effective exchange surfaces?

Answer 3

1. Increased surface area- provides space needed for exchange and overcomes limitation of sa:v ratio in larger organisms.
2. Thin layers- distances for diffusion are short, so process is faster.
3. Good blood supply- maintains a steep concentration gradient by ensuring substances are continuously delivered to and removed from the exchange surface.
4. ventilation- also helps maintain steep concentration gradient, making process more efficient.