ap bio unit 1 quiz

Polarity

A molecule has an uneven distribution of electrical charge, with slightly positive and slightly negative regions. Water is polar because oxygen is more electronegative than hydrogen. Example: water molecules attract each other because of their opposite partial charges.

Cohesion

The attraction between molecules of the same substance. In water, hydrogen bonding causes water molecules to stick to one another. Example: water molecules hold together as water moves up a plant's xylem.

Adhesion

The attraction between molecules of different substances. Example: water molecules stick to the walls of a plant's xylem vessels.

Surface tension

The resistance of a liquid's surface to being broken or stretched, caused by cohesion between molecules. Example: small insects such as water striders can walk on the surface of water.

High specific heat

Water requires a large amount of energy to increase its temperature because hydrogen bonds absorb energy. Example: oceans moderate coastal temperatures.

High heat of vaporization

A large amount of energy is required to change water from a liquid to a gas because hydrogen bonds must be broken. Example: sweating cools the body as water evaporates from the skin.

Ice is less dense than liquid water

When water freezes, hydrogen bonds form a crystal structure that spaces molecules farther apart. Example: ice floats on lakes, insulating the liquid water underneath.

Water is an excellent solvent

Because water is polar, it can dissolve many ionic and polar substances. Example: table salt (NaCl) dissolves in water.

Water has a high heat of fusion

A relatively large amount of energy is required to change water from a solid to a liquid because hydrogen bonds must be disrupted. Example: ice requires significant heat energy to melt.

Solute

The substance that is dissolved in a solution. Example: salt is the solute in saltwater.

Solvent

The substance that does the dissolving in a solution. Example: water is the solvent in saltwater.

Solution

A homogeneous mixture in which one or more solutes are dissolved in a solvent. Example: saltwater is a solution.

Covalent bonds

Chemical bonds formed when atoms share electrons. They can be polar or nonpolar. Example: the bonds between hydrogen and oxygen in H₂O are covalent.

Ionic bonds

Attractions between oppositely charged ions that form after electrons are transferred from one atom to another. Example: NaCl forms when sodium transfers an electron to chlorine.

Hydrogen bonds

Weak attractions between a partially positive hydrogen atom and an electronegative atom, usually oxygen or nitrogen, in another molecule or within a molecule. Example: hydrogen bonds form between neighboring water molecules.

Polarity — Example

Water (H₂O) is polar because oxygen has a partial negative charge while the hydrogen atoms have partial positive charges.

Cohesion — Example

Water droplets stick together because water molecules form hydrogen bonds with one another.

Adhesion — Example

Water sticks to the walls of a glass or the xylem of a plant.

Surface tension — Example

A water strider can remain on the surface of water because of water's strong surface tension.

High specific heat — Example

Large bodies of water heat and cool slowly, helping stabilize surrounding temperatures.

High heat of vaporization — Example

Evaporation of sweat removes heat from the body and cools it.

Ice is less dense than liquid water — Example

Ice floats, allowing aquatic organisms to survive in liquid water underneath.

Excellent solvent — Example

Water dissolves ionic compounds such as NaCl, allowing ions to participate in biological reactions.

Independent Variable

The variable that the researcher deliberately changes or manipulates. It is plotted on the x-axis.

Dependent Variable

The variable that is measured or observed in response to changes in the independent variable. It is plotted on the y-axis.

X-axis

The horizontal axis of a graph. It normally displays the independent variable.

Y-axis

The vertical axis of a graph. It normally displays the dependent variable.

Constants

Conditions that are kept the same for all experimental groups so they do not influence the results. Example: keeping temperature constant in all groups.

Control Group

The group used as a baseline for comparison in an experiment. It may not receive the experimental treatment.

Positive Control

A control group that receives a treatment known to produce a predictable positive result. It demonstrates that the experimental system is capable of producing the expected response.

Negative Control

A control group that does not receive the experimental treatment and is expected to produce no response. It helps show that the experimental treatment caused the observed effect.

Experimental Group

The group that receives the experimental treatment or condition being tested.

Central Tendency

A statistic used to describe the center or typical value of a dataset. The three main measures are mean, median, and mode.

Mean

The arithmetic average of a dataset, calculated by adding all values and dividing by the number of values.

Median

The middle value of an ordered dataset. If there are two middle values, the median is their average.

Mode

The value that occurs most frequently in a dataset. A dataset can have more than one mode or no mode.

Skewness

The degree to which a dataset is asymmetrical. Skewness can cause the mean to be pulled toward the long tail of the distribution.

Right-Skewed Distribution

A distribution with a long tail toward larger values. The mean is typically greater than the median because unusually high values pull the mean upward.

Left-Skewed Distribution

A distribution with a long tail toward smaller values. The mean is typically less than the median because unusually low values pull the mean downward.

L

The median is generally preferred because it is less affected by extreme values and skewness than the mean.

Range

A measure of variability calculated by subtracting the minimum value from the maximum value. Range is strongly affected by outliers.

Interquartile Range (IQR)

A measure of variability representing the spread of the middle 50% of the data. It is calculated as Q3 − Q1 and is relatively resistant to outliers.

Variance

A measure of variability that describes the average squared distance of data values from the mean. Larger variance means greater spread.

Standard Deviation (SD)

A measure of how spread out individual data values are from the mean. A small SD means values are clustered near the mean

Standard Error of the Mean (SEM)

A measure of how precisely a sample mean estimates the population mean. SEM generally decreases as sample size increases.

Why Researchers Use SEM

Researchers use SEM to estimate the uncertainty or precision of a sample mean as an estimate of the population mean. Smaller SEM indicates a more precise estimate.

SD vs. SEM

Standard deviation describes variability among individual observations, while standard error of the mean describes the precision of the sample mean as an estimate of the population mean.

M

Increasing sample size generally decreases SEM, making the sample mean a more precise estimate of the population mean.

Variability

The amount of spread or dispersion in a dataset. Common measures include range, interquartile range, variance, standard deviation, and standard error of the mean.

Range vs. IQR

Range measures the entire spread from minimum to maximum, while IQR measures the spread of the middle 50% of the data. IQR is less affected by outliers.

Variance vs. Standard Deviation

Variance measures average squared deviations from the mean, while standard deviation is the square root of variance and is expressed in the same units as the original data.

Why Use a Control?

Controls provide a baseline for comparison and help researchers determine whether changes in the dependent variable are caused by the independent variable rather than another factor.

Null Hypothesis (H₀)

A statement that there is no statistically significant effect, relationship, or difference caused by the independent variable.

Alternative Hypothesis (Hₐ)

A statement that there is a statistically significant effect, relationship, or difference between variables.

Support vs. Prove

Experimental data can support or refute a hypothesis, but scientific experiments generally do not prove a hypothesis with absolute certainty.

Scientific Method 6 Steps

make observation, ask a testable question, form a hypothesis, design and conduct an experiment, collect and analyze data, and draw a conclusion