Question

How many significant figures does this number contain?

.007 a0

Answer 1

All zeros before a non-zero digit are considered non-significant. So .007 or \(7*10^{-3}\) only contain one significant digit. In terms of biology and science you can think about significant digits as the accuracy of your measurement.
To take your example:
.0070 is more accurate than .007, as .0070 contains 2 significant digits while .007 only contains one. So if we talk in terms of uncertainty 0.007 would be the number where out uncertainty lies (the measurement with the lowest number of significant figures determines where our uncertainty in our calculations lies)