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 form an observation; explains relationship between variables and what the researcher expects to happen to one variable if the other 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 the 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 use a null?

provides a baseline, which we can use our sample results to; use data to reject null hypothesis and support the alternative

Control Group

used for comparison to the experimental group; helps to validate statistical analysis and increase confidence in conclusions drawn from the experimental results

Negative vs Positive Control

Negative: group not exposed to any treatment OR exposed to a treatment known to have no effect

Positive: group not exposed to the IV but IS exposed to a treatment known to have an expected effect

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 groups; what is being manipulated; graphed on the 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; helps us understand important info by summarizing our observations and making predictions based on the summary. also helps scientists to avoid jumping to conclusions and be cautious about generalizations

Descriptive Statistics

methods used to summarize or describe observations/samples; measure of central tendency and variability

Inferential Statistics

using observations to make estimates or predictions; generalizing from a sample to a wider population (Standard Error of the Mean, Confidence Intervals); Hypothesis Tests (Chi Square)

Sample

a small, random group selected from the population

Population

all members of the group being studied

Negative (left) Skewed

Positive (right) Skewed

Normal Distribution

theoretical distribution of values for a population; shape is described using the mean and standard deviation

Central Tendencies

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

mean

the average of a data set

median

the middle number in a range of data points

mode

the value that appears most often

the preferred measure of central tendency for skewed vs normal distibutions

normal: mean

skewed: median, because it is not as affected by the outliers and gives a better “middle”

Variability

the degree to which data is spread out in a data set; gives us a more complete summary of a distribution

Variability can be measured using

range, standard deviation, and IQR

Standard Deviation

the average amount by which all the values deviate form the mean (measure the spread of data); used for approx. normal distributions

Low standard deviation

data is closer to the mean

High standard deviation

data is farther from the mean

IQR

(interquartile range) measures the spread of the middle 50% of a data set: TO FIND THE IQR: Q3-Q1, used for non-normal (skewed) distributions

Confidence Intervals

a range of values in which we are 95% confident the true population mean will fall within; built using sample mean and the Standard Error of the Mean— upper limit= Mean + 2x SEM, lower limit= Mean - 2x SEM

Standard Error of the Mean (SEM)

used to assess how accurately the sample mean estimates the population mean; uses standard deviation to estimate the variation in the population

if the error bars do not overlap,

the researches reject the null hypothesis, and the alternative hypothesis is supported; the is a STATISTICALLY SIGNIFICANT difference due to a nonrandom cause

Chi Square

a form of statistical analysis used to compare actual counts/ frequencies (observed) with the expected counts/ frequencies; helps determine whether the expected data provides a “good fit” to the observed data obtained

What are the 6 general steps of the scientific method

1. Make an Observation

2. Ask a question

3. Form a hypothesis

4. conduct an experiment

5. collect data

6. form a conclusion

How are hypotheses formulated?

by turning a research question into an educated guess

What is the difference between null and alternative hypotheses? Do you always need both?

a null hypothesis states that there is no effect or no difference while an alternative hypothesis states that there is a statistically significant different. It is good to have both

How do researchers determine their dependent and independent variables? How are they often graphed (what is on the y-axis and what is on the x-axis)?

Researchers determine dependent and independent variable by looking at what is being manipulated and what is being affected and measured. The independent variable is graphed on the X-axis, and the dependent variable is graphed on the Y axis

Are constants the same as controls? Why or Why not?

No, constants are not the same as controls. Constants are variables kept consistent for all groups to ensure that only the IV affects the outcome, while controls are groups used for comparison to the experimental group.

When should a positive control be used? When should a negative control be used?

A negative control is used to gives a baseline and ensure that there is no effect where there should be no effect, and a positive control is used as a reference point for what a known effect looks like.

Describe Central tendencies. Identify when each type of central tendency should be used.

the center can be described by the mean, median, and mode. skewed distributions- median, normal distributions- mean

What is used to measure variability?

Variability is measure using range, standard deviation, and IQR

Is data more reliable with low or high standard deviation? Why?

low standard deviation because the values are more stable, predictable, consistent, and reliable

Why do researchers use SEM?

they use it to assess how accurately the sample mean estimates the population mean

If the standard error bars overlap, is the difference between the means statistically significant? Why or Why not?

No, if the standard bars overlap the difference between the means is not statistically significant because it suggests that the observations are due to chance

Matter

anything that has mass and takes up space

Element

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

Compound

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

atomic number

number of protons

atomic mass

number of protons plus neutrons averaged over all isotopes

Octet Rule

elements will gain, lose, or share electrons to complete their valence electron shell and become stable

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

Covalent Bonds

when two or more atoms share electrons; two types: polar covalent and nonpolar covalent

Nonpolar Covalent

e- are shared equally between atoms

Polar Covalent

electrons are not shared equally between two atoms

Ionic Bonds

the attraction between oppositely charged atoms (ions); occurs when there is a transfer of electrons from one atom to another

Hydrogen Bonds

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

Intermolecular bond

bond that forms between molecules

Polarity

polar covalent bonds created by an unequal sharing of electrons between O and H within the water molecule

Cohesion

attraction of molecules for other molecules of the same kind— hydrogen bonds hold them together and increase cohesive forces; NATURE: allows for transport of water and nutrients against gravity in plants and helps with surface tension

Adhesion

the attraction to other molecules that are polar or have charge — due to polarity; NATURE: capillary action

Capillary Action

the upward movement of water due to the forces of cohesion, adhesion, and surface tension— occurs when adhesion is greater than cohesion; NATURE: important for teh transport of water and nutrients in plants

High Specific Heat

H20 resists changes in temperature bc hydrogen bonds absorb energy (to be broken) and heat is released when they form; NATURE: moderates air temp (bodies of water absorb heat and day and release at night), stabilizes ocean temp, + organisms can resist changes in their own internal temp

High Heat of Vaporization

water requires a large amount of energy to evaporate due to strong hydrogen bonds— Evaporative Cooling: as water molecule evaporate, the surface they evaporate form gets cooler; NATURE: Moderates Earth’s climate, stabilizes temp in lakes and ponds, prevent terrestrial organisms form overheating + prevents leaves from becoming too warm in sun

Low Density of Ice

as water solidifies, it expands and becomes less dense— due to hydrogen bonds: when cooled, water mol. move too slowly to break the bonds; NATURE: allows marine life to survive under floating ice sheets

Solvent vs Solution vs Solute

Solution: homogenous mix of 2+ substances

Solvent: dissolving agent in a solution

Solute: substance that is dissolved

Water as a solvent

“like dissolves like”— water will form hydrogen bonds with with the sugar/ protein containing O or H to dissolve it.

Ionic Compounds: partially neg. O in water interacts with a pos. atom, partially pos. H will interact with a negative atom—- dissociates ions

pH

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

Acid

a substance that releases H+ ions when dissolved in water

Base

a substance that accepts H+ ions OR releases hydroxide ions OH-

Buffer

a solution that resists changes in pH when an acid or base is added; NATURE: helps maintain pH stability

Identify the elements that make up nearly all of living matter

Carbon, Nitrogen, Oxygen, Hydrogen, Phosphorus

Differentiate between a solute, solvent, and solution

A solution is a homogenous mix of two or more substances, the solute is what is being dissolved, and a solvent is the dissolving agent.

How are hydrogen bonds different form other types of bonds?

Hydrogen bonds are between molecules (intermolecular), while covalent bonds are within a molecule (intramolecular)

how does electronegativity affect the interactions between water molecules

Electronegativity causes an uneven distribution of charge across the water molecule. This means that the oxygen is partially negative while the hydrogens are partially positive, which allows for hydrogen bonds.

If O and H had the electronegativity, what would that do the properties of water?

then the water molecule wouldn’t be polar. This would diminish most of water’s properties since they are only possible because of waters polarity

Organic Chemistry

the study of cpds with covalently bonded carbon

Organic Compounds

compounds that contain carbon and hydrogen

What forms the skeletons of many molecules

carbon chains; can differ in length, branching, double bond position, and presence of rings

hydrocarbons

organic molecules consisting of only carbon and hydrogen

functional groups

chemical groups attached to the carbon skeleton that participate in chemical reactions

Macromolecules

large molecules made of smaller subunits

what makes carbon such a versatile element?

its ability to form four covalent bons

how do functional groups affect the structure and behavior of organic molecules

functional groups affect the way that a molecule is shaped and participate in chemical reactions. function group can also be polar or nonpolar— directly affecting the chemical reactivity and behavior of the molecule

what is the difference between hydrocarbons and other organic molecules?

hydrocarbons contain ONLY carbon and hydrogen, but organic molecules can contain other elements

dehydration reaction

covalently bonds two monomers with loss of H2O

hydrolysis

breaks the covalent bonds in a polymer by adding H2O

polymers

chain-like macromolecules made of similar or identical repeating units that are covalently bonded together

monomers

the repeating units that make up polymers

differentiate between and hydrolysis and a dehydration reaction

dehydration reactions create covalent bonds with the loss of H2O while hydrolysis breaks covalent bonds with the addition of H2O

carbohydrates

includes sugars and polymers of sugars; contains a carbonyl group and many hydroxyl groups (C, H, O in a 1:2:1)

monosaccharides

simple sugars. they are molecular formulas with multiples of the unit CH2O. most common is glucose— used as nutrients, fuel for cells, and in cellular respiration. can serve as building blocks for amino acids or as monomers for di and polysaccharides

disaccharides

two monosaccharides joined together by covalent bonds; most common is sucrose from glucose and fructose

polysaccharides

polymer with many sugars joined via dehydration reaction

starch

storage polysaccharide; plants store STARCH (polymer of glucose monomers): allows plants to store excess glucose

Glycogen

Animals store GLYCOGEN (polymer of glucose): stored in liver and muscle cells

Cellulose

structural polysaccharides: (plants) tough substance that forms plant cell walls

Chitin

structural polysaccharides: (animals) forms exoskeletons of arthropods