Exchange surfaces

Question 1

Why do cells use diffusion
Include examples

Answer 1

take in substances they take in and get rid of waste products.
Example: oxygen, co2 transferred between cells and environment during gas exchange

Question 2

What is urea

Answer 2

( waste product produced by breakdown of proteins )
diffuses from cells into blood plasma for removal from body by kidneys

Question 3

How easy is it for an organism to exchange substances with its environment depend on organisms

Answer 3

SA : V

Question 4

Calculation on SA:V on page 20

Answer 4

AQA

Question 5

In single celled organisms ..

Answer 5

gases and dissolved substances can diffuse directly into the cell across the cell membrane.

Because they have large SA compared to volume so enough substances can be exchanged across membrane to supply volume of the cell.

Question 6

In multi cellular organisms ..

Answer 6

they have smaller SA compared to volume so not enough substances can diffuse from their outside surface to supply their entire volume. This means they need some sort of gas exchange for efficient diffusion.

Exchange surface structures have to allow enough of this necessary substances to pass through.

Question 7

How are exchange surfaces adapted to maximise effectiveness ?

Answer 7

• thin membrane so substances have short distance to diffuse
• Large SA so lot’s of substances can diffuse at once.
• Exchange surfaces in animals have lots of blood vessels, to get stuff into and out of the blood quickly
• Gas Exchange in animals often ventilated - air moves in and out