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Biology
Grade 11-12
AP Biology Reference Sheet Cheat Sheet
A printable reference covering AP Biology statistics, population models, Hardy-Weinberg equations, water potential, and energy concepts for grades 11-12.
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This AP Biology reference sheet brings together the equations and concepts students use most often when solving data-based biology problems. It supports quick review for labs, free-response questions, and multiple-choice practice. Students need it because AP Biology often tests whether they can choose the correct model, substitute values correctly, and explain biological meaning from a calculation.
Key Facts
- Mean is calculated as x-bar = sum of all values / n, where n is the number of data points.
- Standard deviation measures spread around the mean and is commonly used to compare variation among biological samples.
- Chi-square is calculated as X2 = sum of (observed - expected)^2 / expected, and a larger value means a larger difference between observed and expected results.
- Hardy-Weinberg allele frequencies follow p + q = 1, and genotype frequencies follow p^2 + 2pq + q^2 = 1.
- Population growth can be modeled as dN/dt = rN for exponential growth, where N is population size and r is the per capita growth rate.
- Logistic growth can be modeled as dN/dt = rN((K - N) / K), where K is carrying capacity.
- Water potential is calculated as psi = psi_s + psi_p, where psi_s is solute potential and psi_p is pressure potential.
- Free energy change is calculated as delta G = delta H - T delta S, and a negative delta G indicates an energetically favorable process.
Vocabulary
- Chi-square test
- A statistical test used to compare observed data with expected data and decide whether differences are likely due to chance.
- Hardy-Weinberg equilibrium
- A model describing a population in which allele and genotype frequencies stay constant across generations when no evolutionary forces act.
- Carrying capacity
- The maximum population size an environment can support with its available resources.
- Water potential
- A measure of the tendency of water to move from one area to another, usually from higher potential to lower potential.
- Free energy
- The usable energy in a system that can do work during a biological or chemical process.
- Allele frequency
- The proportion of a specific allele among all alleles for a gene in a population.
Common Mistakes to Avoid
- Using genotype frequency as allele frequency is wrong because p and q represent alleles, not whole genotypes.
- Forgetting to square the difference in a chi-square calculation is wrong because X2 requires (observed - expected)^2 for each category.
- Treating standard deviation as standard error is wrong because standard deviation describes variation in data, while standard error estimates uncertainty in the sample mean.
- Ignoring units in water potential problems is wrong because pressure potential and solute potential must use the same units before they are added.
- Assuming exponential growth continues forever is wrong because real populations often face limited resources and may shift toward logistic growth.
Practice Questions
- 1 In a population at Hardy-Weinberg equilibrium, the frequency of the recessive phenotype is 0.16. Find q, p, and the heterozygote frequency 2pq.
- 2 A chi-square test has observed counts of 42 and 58, while expected counts are 50 and 50. Calculate X2.
- 3 A population has N = 500 and r = 0.04. Using exponential growth, calculate dN/dt = rN.
- 4 Explain why a population that is not evolving must meet multiple Hardy-Weinberg conditions, including random mating and no natural selection.