Surface area to volume ratios, Punnett-square probabilities, expected numbers, doubling bacteria, BMI and correlation.
What you will learn
- Calculate a surface area to volume ratio
- Turn a cross into a probability or expected number
- Tell correlation from cause
Ratios and chances
- Surface area to volume: a 2 cm cube has 24 cm² and 8 cm³, ratio 24 ÷ 8 = 3. Smaller objects have bigger ratios.
- A Punnett square has four equally likely boxes: Aa × Aa gives aa in 1 of 4, so 25%.
- From a ratio 3 : 1 and 400 offspring, expect 300 : 100.
- Bacteria double every division: after n divisions there are 2ⁿ times as many.
A positive correlation means that as one variable increases, so does the other; a negative correlation means that as one increases, the other decreases.
A correlation in data does not prove that one thing causes the other.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Ratios and chances
9 practice questions, marked as you go; about 20 minutes in all.
Key terms
Positive correlation, Negative correlation
In this unit: Required practicals and maths skills
The skills behind every biology practical: units and magnification, means and percentages, rates and graphs, sampling, ratios and planning.