B1 Exchange Surfaces (page 20) Flashcards
Cells can use diffusion to take in substances they need and get rid of waste products, give example?
Oxygen and carbon dioxide are transferred between cells and the envirnment during gas exchange.
what is Urea in humans?
a waste product produced from the breakdown of proteins). It diffuses from cells into the blood plasma for removal from the body by the kidneys.
How easy is it for an oranism to exchange substances with its environment depends on what?
it depends on the organism’s surface area to volume ratio (SA : V).
What do a ratio show?
A ratio shows how big one value is compared to another. The larger an organism is, the smaller its surface area is compared to its volume. You can show this by calculating surface area to volume ratios.
How do you calculate the following surface area to volume ratio:
A hippo can be represented by a 2cm x 4cm x 4cm block.
A mouse can be represented by 1cm x 1 cm x 1 cm block
Calculate the surface area to volume ratio?
The area of a surface is found by the equation:
LENGTH X WIDTH
So the hippo’s total surgace area is:
(4 x 4) x 2
(top and botom surfaces of block see pic page 20)
+ (4 x 2) x 4 (four sides of the block
= 64cm².
The volume of a block is found by the equation: LENGTH X WIDTH X HEIGHT
So the hippos olume is 4 x 4 x 2 = 32cm³
The surface area to volume ratio of the hippo can be written as 64 : 32
To simplify the ratio, divide both sides of the ratio by the volume.
So the surface area to volume ratio of the hippo is 2 : 1
A mouse can be represented by a 1cm x 1cm x 1cm block
Its surface area is (1 x 1) x 6 = 6cm²
Its volume is 1 x 1 x 1 = 1cm³
So the surface area to volume ratio of the mouse is 6 : 1
(The cube mouse’s surface area is six times its volume, but the cube hippo’s surface area is only twice its volume. So the mouse has a larger surface area compared to its volume.
In Single-celled organisms, why can gasses and dissolved substance diffuse directly into (or out of) the cell across the cell membrane?
Its because they have a large surface area compared to their volume, so enough substances can be exchanged across the membrane to suply the volume of the cell.
Multicellular Organisms have a smaller surface area compared to their volume - Not enough substances can diffuse from their outside surface to supply their entire volume, Explain why?
This means they need some sort of exchange surface for efficient diffusion (see page 21-22 for some examples) The exchange surface structures have to allow enough of the necessar substances to pass through.
Why are Exchange Surfaces Adapted to maximise effectiveness?
They have a thin membrane, so substances only have a short distance to diffuse.
They have a large surface area so lots of substance 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 surfaces in animals (e.g. alveoli) are often ventilated too - air moves in and out.
A bacterial cell can be represented by a 2 um x um x 1 um block, calculate the cell’s surface area to volume ratio? (3 marks)
Surface area:
(2 x 2) x 2 = 8
(2 x 1) x 4 = 8
8 + 8 = 16 um² (1 mark)
Volume:
2 x 2 x 1 = 4um³ (1 mark)
So the surface area to volume ratio is 16 : 4,
or 4 : 1 (1 mark)
