ocr biology maths question help

image-e04fb416-3065-4c23-9cf6-d5f77ef553c8973725678-compressed.jpg.jpeg

This is what I tried:

half of diameter is 4.55cm
r= 45.5mm
convert to Um is 45500

4/3 ×pi × (45500)^3
= 3.95×10^14

But the answer is

Screenshot_20180517-152654-compressed.png.jpeg

Screenshot_20180517-152654-compressed.png.jpeg

where am I going wrong??

Reply 1

macpatgh-Sheldon

Hi,

You have worked out the volume of the cell as it appears to the eye in the given pic. Your answer has no units so it is meaningless in any case!

The diagram given gives a representation of the scale with the length that is equal to 4 microns.

So, instead of using 9.1 cm as the diameter of the Kupffer cell, you need to multiply the 9.1cm by whatever ratio the 4 um represents (you seem to have measured this as 1 cm) to work out the actual diameter of the cell = x um

So radius = x/2 um

Volume = 4/3 X pi X r^3

Substitute the values and you should get the correct answer.

NB: If you look a your answer, it is obviously wrong as no cell is as large as a hockey ball !!!!! :colondollar:

(if your answer is in um^3)

(edited 5 years ago)

Reply 2

MikaelYacob

You did not get your answer wrong! There was an error in the mark scheme and surprisingly no one spotted it yet; well, as far as I know! The answer in the marking is for a scale line of 2cm which is wrong as the correct scale line is measured at 1cm! Sadly a lot of students lost a few marks on this unfairly! No unit conversion is needed and just put micrometers cubed at the end! SOLVED! 👍