Surface area to volume ratio

Question 1

What happens to the Surface Area : Volume ratio as organisms get larger?

Answer 1

• Decreases
• This is as larger organisms have less surface area compared to their volume.

Question 2

How do you calculate the surface area of a cube?

Answer 2

• Calculate the area of a single face, then multiply by 6 (as cubes have 6 faces)

Question 3

How do you calculate the volume of a cube?

Answer 3

• Length x Width x Height

Question 4

What can bacteria rely on to get everything they need?

Answer 4

• As bacteria have a high surface area : volume ratio, it can rely on diffusion across their surface to exchange everything they need.

Question 5

What can’t humans rely on to get everything they need?
What do they have to solve this?

Answer 5

• As humans have a low surface area to volume ratio, we can’t rely on diffusion for our needs.
• Instead we have specialised exchange surfaces e.g: lungs, instenstines.

Question 6

What do specialised exchange surfaces do?

Answer 6

• Increase our surface area to volume ratio:
• This is as they give an extra surface on the insides of our body.

Question 7

Examples of specialised exchange surfaces:

Answer 7

• In the lungs, there are millions of alveoli which gives a huge surface area, allowing oxygen to be absorbed and carbon dioxide can be gotten rid of.
• In the intestines, there is villi which provides a massive surface area for the absorption of nutrients.

Question 8

What is diffusion difference? What does this mean?

Answer 8

• As organisms get larger, the distance that molecules would have to diffuse to get from the OUTSIDE of their body to the INSIDE of their body INCREASES massively
• This means that diffusion will be a lot slower for larger organisms, so they cannot purely rely on diffusion to get all the stuff they need into their cells.

Question 9

What do larger organisms have as they can’t purely rely on diffusion to get the stuff they need into their cells?
Give an example:

Answer 9

• Transport systems
• E.g: Circulatory system - transports molecules from the exchanged surfaces, where they enter the body, then around the body to whichever cells needs them.
• This means that the molecules then only need to diffuse a short distance into the cells