Chapter 7.1

Question 1

What is an amoeba?

Answer 1

A single celled organism

Question 2

Why do single celled organisms don’t need specialized exchange surfaces?

Answer 2

This is because all oxygen needs by the organism and all the waste CO2 produced - can be exchanged with the external environment by diffusion of through the cell surface. (as the distance is very small)

diffusion alone can supply the needs of the cell
{ - this is because SA to volume ratio in the organism is large

-metabolic demands is very low so oxygen demands and carbon dioxide production is very low of the cell}

Question 3

Why can diffusion alone be enough to supply the needs of a single celled surface?

Answer 3

• this is because SA to volume ratio in the organism is large
• metabolic demands is very low so oxygen demands and carbon dioxide production is very low of the cell

Question 4

Give the 2 reasons why large organism needs effective exchange surfaces t?

Answer 4

• This is because as the organisms increase in size, they get made up of millions and billion number of cells….. Furthermore the more amount of energy needed for movement. As a result the oxygen demand in the muscles will increase and the production of carbon dioxide increases. As an organism increases in size, the distance between cells where the oxygen is needed and the supply of oxygen is too far for effective diffusion to take place.
• The bigger the organism the smaller the SA:V ratio, so gases can’t exchanged fast enough in large enough amounts for the organism to survive.

Question 5

How are exchange surfaces adapted for job?

Answer 5

They have Increased surface area - which provides exchange surfaces area for exchange and helps overcome limitations to SA:V

They have thin layers - which means the distance that substance has to travel is short making the process fast and efficient.

They have good supply - allows for a steeper concentration gradient as a result it means faster diffusion…….. Also good blood supply ensures that substances are constantly delivered to and remove from the exchange surface which maintains steep concentration gradient for diffusion

Ventilation to maintain diffusion gradient - helps maintain concentration gradient and makes the process more efficient.