A student wants to estimate the number of snails living in a garden.
On day 1, she collects 40 snails. She puts a small dot of non-toxic paint on the bottom of each shell. She releases the snails where she found them.
On day 2, she collects 50 snails. 8 of these snails have a paint dot.
The student uses this equation:
population size=number caught on day 1×number caught on day 2number of marked snails caught on day 2\text{population size} = \dfrac{\text{number caught on day 1} \times \text{number caught on day 2}}{\text{number of marked snails caught on day 2}}population size=number of marked snails caught on day 2number caught on day 1×number caught on day 2
Calculate the estimated population size of snails in the garden.
The student uses non-toxic paint and puts the dot on the bottom of the shell.
Explain why.
The student waits one day before she collects the second sample.
Suggest why.
Give one reason why the estimate may not be accurate.
109 exam-style questions on OCR GCSE Biology 6.1 Monitoring and maintaining the environment, covering 6.1.1 Field investigation of distribution and abundance, 6.1.2 Human interactions and biodiversity, 6.1.3 Maintaining biodiversity, and 6.1.4 Environmental change and distribution of organisms. Each one has a worked solution and a mark scheme showing where the marks go.