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# Biology Help - Fish/gills/respiration/maths watch

1. Does anybody know how to answer this?😊

Volume of water absorbed by the gills from each dm3 of water / cm3 = 7

Mass of fish /kg = 0.4

Oxygen required by fish / cm3 kg-7 hour-1 = 90

Calculate the volume of water that would have to pass over the gills each hour to supply the oxygen required by the fish. Show your working.
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2. 1. The volume of O2 per dm3 of water is 7cm3
2. The O2 required per hour is 90cm3
3. If one dm3 of water passed over the gills per hour, this would mean the fish gets 7cm3 of O2 per hour
4. I found it easiest to get down to 1cm3 of O2 per hour and work from there.
5. 7cm3 of O2/7 = 1cm3 of O2. In order to work out the volume of water you'd need to get this amount you need to do the same thing:
6. 1dm3 of water/7 = 0.143dm3 of water
7. The fish needs 90 cm3 of O2. To get this, you need to multiply the 1cm3 from part 5 by 90. Again, you need to do the same thing with the water.
8. 0.143dm3 of water x 90 = 12.86dm3 of water.

Therefore, you need 12.86 dm3 of water per hour.

Hope this makes sense (and that it's right).
3. Thanks so much this is a massive help😊x
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