AP Biology Unit 1: Chemistry of Life

Scientific Method

a step-by-step process used by scientists to investigate questions, gather evidence, and draw conclusions based on experiments and observations

Hypothesis

a testable explanation for an observation

• explains the relationship between variables and what the researcher expects to happen to one variable if another changes

Hypothesis Tests

statistical test procedures to test hypotheses about a population based on a sample

Null Hypothesis

hypothesis that there is no effect or no difference between two groups of data

• observations are due to chance

Alternative Hypothesis

hypothesis that there is a relationship/effect/difference between the two groups of data

• observations are due to a nonrandom cause

Why do we need a null hypothesis for testing?

provides a baseline, which we can use to compare our sample results to

How many trials are needed at least for each control and experimental group?

3

Control

used for comparison to the experimental group

• helps validate statistical analysis and increase confidence in conclusions drawn from the experimental results

Negative Control

group NOT exposed to any treatment OR exposed to a treatment known to have NO effect

• ensures there is NO effect when there should be NO effect

Positive Control

group not exposed to IV but is exposed to a treatment known to HAVE an expected effect

• ensures the experimental setup can produce a known effect

• provides a reference point for what a known effect looks like

Experimental Group

receives the experimental treatment (IV) being tested to observe its impact on the outcome (DV)

Independent Variable

the one factor that is changed between all groups; what is being manipulated

• graphed on x-axis

Dependent Variable

factor that is measured and affected by the IV

• graphed on the y-axis

Constant

factors kept consistent for all groups to ensure only the IV affects the outcome

• aka controlled variables

Statistics

methods used to collect, process, or interpret quantitative data

• In biology, helps us understand important information by:

  • summarizes our observations

  • makes predictions based on a summary

• helps scientists:

  • avoid jumping to conclusions

  • be cautious about generalizations

Descriptive Statistics

methods used to summarize or describe observations/samples

• measures of central tendency (mean, median, mode)

• measures of variability (range, standard deviation, variance, skewness, quartiles)

Inferential Statistics

using observations to make estimates or predictions; generalizing from a sample to a wider population

• SEM, confidence intervals

• hypothesis tests (Chi-square, ANOVA, t-test)

Sample

a small, random group selected from a population

• used to make inferences about a population

Population

all members of a group being studiedd

What is the shape of a normal distribution?

symmetric, unimodal

What is the shape of a uniform distribution?

symmetric, all outcomes equally likely

What is the shape of a bimodal distribution?

symmetric, two modes

What is the shape of a positive skewed distribution?

right skewed, unimodal

What is the shape of a negative distribution?

left skewed, unimodal

We can describe the data distribution by its _____, its ______, and its __________.

shape, center, variability (spread)

What distribution do most biological examples follow?

normal distribution

Central Tendencies

the center can be described by the mean, median, and mode

Mean

the average of the data set

• sensitive/most affected by outliers

• most preferred in approximately normal distributions

Median

the middle number in a range of data points

• preferred measure of central tendency in skewed distributions

Mode

value that appears most often

• used in categorical data (i.e. surveys)

• used when looking for most common outcome

The ______ ____ serves as an ________ for the population mean.

sample mean, estimate

Variability

the degree to which data are spread out in a data set

• helps give a more complete summary of a distribution

• can be measured using range, standard deviation, and IQR

Standard Deviation

the average amount by which all the values deviate from the mean; measures the spread of data

• used in approximately normal distributions

What does a low (small) standard deviation mean?

data is closer to the mean; less spread out

What does a high (large) standard deviation mean?

data is farther from the mean; more spread out

Interquartile Range (IQR)

measures the spread of the middle 50% of data

• used in non-normal distributions (e.g. skewed)

How do you find IQR?

Q₃ - Q₁

Confidence Interval

a range of values in which we are 95% confident the true population mean will fall within

Standard Error of the Mean (SEM)

used to assess how accurately the sample mean estimates the population mean

What does it mean if the error bars overlap?

there is not a statistically significant difference between the means; observed changes are due to chance

Chi-sqaure

a form of statistical analysis used to compare the actual counts/frequencies (observed) with the expected counts/frequencies

• determines if the expected data is a “good fit” for the observed data

• determines if deviations are random or due to other circumstances

• analyzes categorical data

• tests the null hypothesis

Matter

anything that has mass and takes up space

• rocks, metals, oils, gases, organisms, etc.

Element

a substance that cannot be broken down into other substances by chemical reactions

Compound

a substance consisting of two or more different elements combined in a fixed ratio

• H₂O

• NaCl

Essential Elements

CHOPN

• Carbon, Hydrogen, Oxygen, Phosphorous, Nitrogen

• essential for survival and reproduction

Trace Elements

required by an organism in very small quantities

Atomic Number

number of protons

Atomic Mass

number of protons + neutrons averaged over all isotopes

Group

elements in the same vertical column; same number of valence electrons

Period

elements in the same horizontal row; same total number of electron shells

Elements want to be ______.

stable

How do elements become stable?

forming chemical bonds with other elements

Octet Rule

elements will gain, lose, or share electrons to complete their valence shell and become stable (like noble gases)

Valence Shell

outermost layer of electrons in an atom

Chemical Bonds

an attraction between two atoms, resulting from the sharing or transferring of valence electrons

Electronegativity

the measure of an atom’s ability to attract electrons to itself

• on periodic table:

  • increases left to right

  • decreases going down

Covalent Bonds

when two or more atoms share elections

• usually between two nonmetals

What do covalent bonds form? (hint: there’s two)

molecules and compounds

What are the two types of covalent bonds?

nonpolar covalent and polar covalent

Nonpolar Covalent

electrons are shared equally between two atoms

• example: O₂

Polar Covalent

electrons are not shared equally between two atoms

• example: H₂O

• results in partial charges

Ionic Bonds

the attraction between oppositely charged atoms (ions)

• usually between metals and nonmetals

  • metal transfers electron to nonmetal

What do ionic bonds form? (hint: there’s two)

ionic compounds, salts

• NaCl

• LiF

When do ionic bonds occur?

when there is a transfer of electrons from one atom to another atom forming ions

Cation

positively charged ion

Anion

negatively charged ion

Hydrogen Bonds

the partially positive hydrogen atom in one polar covalent molecule will be attracted to an electronegative atom in another polar covalent molecule

• type of polar covalent bond

Intermolecular Bond

bond that forms between molecules

Why do hydrogen bonds occur?

electrons are not being shared equally between atoms, resulting in hydrogen having a partial positive charge and the electronegative atom to have a partial negative charge

• example: hydrogen bonds between water molecules

What type of bond are hydrogen bonds?

polar covalent

Polarity

polar covalent bonds created by unequal sharing of electrons between oxygen and hydrogen within the molecule of water

Cohesion

attraction of molecules for other molecules of the same kind

• example: H₂O to H₂O

  • held together by hydrogen bonds

What does cohesion allow for?

transport of water and nutrients against gravity in plants

What is cohesion responsible for?

surface tension

Surface Tension

surface H₂O molecules experience greater inward pull because there are no molecules above them to balance the forces

Adhesion

the attraction to other molecules that are polar or have charge

• example: H₂O to other molecules

Why does adhesion occur?

the polarity of H₂O

What does adhesion allow in plants?

allows water to cling to the cell walls to resist the downward pull of gravity

Capillary Action

the upward movement of water due to the forces of cohesion, adhesion, and surface tension

When does cohesion occur?

when adhesion is greater than cohesion

What is capillary action important for?

the transport of water and nutrients in plants

High Specific Heat

H₂O resists changes in temperature

How does water have a high specific heat?

hydrogen bonds

What is the importance of water’s high specific heat?

• moderates air temperature

  • large bodies of water can absorb heat in the daytime and release heat at night

• stabilizes ocean temperature

  • benefits marine life

• organisms can resist changes in their own internal temperature

High Heat of Vaporization

water requires a large amount of energy to evaporate due to strong hydrogen bonds

Evaporative Cooling

as water molecules evaporate, the surface they evaporate from gets cooler

• example: sweating

Why is evaporative cooling important?

• moderates Earth’s climate

• stabilizes temperatures in lakes or bonds

• prevents terrestrial organisms from overheating

  • example: sweating

• prevents leaves from becoming too warm in the sun

Density

as water solidifies it expands and becomes less dense

Solvent

dissolving agent in a solution

Solution

homogeneous mixture of 2+ substances

Solute

substance that is dissolved

Why does water expand as it solidifies?

hydrogen bonds

pH

a measure of how basic or acidic (alkaline) a solution is

Acid

substance that releases hydrogen ions (H+) when dissolved in water

Base

a substance that accepts H+ or releases hydroxide ions (OH-)

What can water dissociate into?

hydrogen (H+) and hydroxide ions (OH-)

Buffer

a solution that resists changes in pH when an acid or base is added

What do buffers help maintain?

pH stability

Organic Chemistry

the study of compounds with covalently bonded carbon

Organic Compounds

compounds that contain carbon and hydrogen