Term 1 review: reactions, electricity and heredity
Answers are for parents and teachers.
1
Balance: Al + O₂ → Al₂O₃.
4Al + 3O₂ → 2Al₂O₃.
2
A 6 V battery is connected to 3 Ω and 3 Ω in series. Find the current and the power of the whole circuit.
R = 6 Ω, I = 6 ÷ 6 = 1 A, P = 6 × 1 = 6 W.
3
Tt × Tt gives 48 offspring. About how many are tt?
1/4 × 48 = 12.
4
Explain in two sentences the difference between natural and artificial selection.
In natural selection the environment decides which individuals survive and reproduce more; in artificial selection people choose the parents.
5
Draw a timeline of 4 eons and say one reason why ages are called “good estimates”.
Hadean, Archean, Proterozoic, Phanerozoic; measurements have small errors.