calculations in biology

• finding the difference

  bigger number - smaller number
• times greater


  bigger number ÷ smaller number
• average

  add up all the numbers and divide by the number of numbers
• average change

  change in quantity ÷ change in time
• find a percentage

  divide the number in the question by 100 multiply this by the percentage in the question
• change a number to a percentage

  divide the small number by the big number x 100
• percentage change


  DOOTH - difference over original times 100

  find the difference between the numbers ÷ the original number x 100
• ratio


  write the numbers down in the order given in the question, try to simplify the 2 numbers as much as possible
• the independent variable is what you change

  the dependent variable is what you measure

  the constant variable is what you keep the same
• in an experiment you should only change 1 thing everything else should stay the same to make the experiment valid
• repete for reliability

  to increase the reliability of an experiment repeat it
• controls are used to compare results, the are used to show that it is what you are investigating that has produced the results

  the are often done with water
• describing trends

  as the (𝑥 axis value) increases/ decrease the (y axis value) increase/ decrease until it reaches (point on 𝑥 axis ) where it increases/ decreases
• conclusions

  conclusions should always answer the aim, you should use the word of your aim in your answer
• evaluating results

  results are given as a percentage when the starting values are different