exchange surface basics

Question 1

state the three reasons that large or multicellular organisms require a specialised exchange surface

Answer 1

• high metabolic rate
• small SA:V
• large size

Question 2

explain why large or multicellular organisms require a specialised exchange surface

Answer 2

they have a large size but small SA:V and have a high metabolic rate. therefore, the distance that substances need to travel is too far to keep up with the metabolic rate. so diffusion alone is not efficient.

Question 3

explain three characteristics of specialised exchange surfaces in animals

Answer 3

• increased SA: eg root hair to overcome limited SA:V
• thin layers: eg alveoli to decrease diffusion distance
• good blood supply: eg gills to create a steep concentration gradient which increases rate of diffusion and ensures constant exchange

Question 4

give examples of substances that need to be exchanged across a surface

Answer 4

• oxygen and glucose for metabolic reactions
• carbon dioxide and urea excretion
• water
• fats
• minerals

Question 5

how is SA:V calculated?

Answer 5

-surface area: 2 (length x height)
2 (length x width)
2 (height x width) : total cm squared

-volume: length x width x height cm cubed

Divide SA by volume = sa:v

Question 6

why do single cellular organisms not need a specialised exchange surface?

Answer 6

-in single-cellular organisms substances can diffuse directly into the cell across the cell surface membrane because of the small diffusion pathway so it’s efficient enough