Practice with the use of numbers is a crucial biological skill. These interesting questions will allow you to practise these skills whilst developing awareness of orders of magnitude in scientific contexts.
Possible approach
There are several parts to this question. The individual pieces could be used as starters or filler activities for students who finish classwork early. Enthusiastic students might work through them in their own time. Since there is no absolutely 'correct' answer to many of these questions, they might productively be used for discussion: students create their own answers and then explain them to
the rest of the class. Does the class agree? Disagree? Is there an obvious best 'collective' answer?
Key questions
What assumptions will you need to make in this question?
How accurate do you think you answer is?
What order of magnitude checks could you make to test that your answer is sensible?
Possible extension
Can students make up similar questions? Can they put any upper or lower bounds on the numbers?