Bio R and A final

accuracy

true value

precision

how close your measurements are to eachother

mass

a measure of the amount of matter an object has

weight

a measure of how strongly an object is pulled by the planets gravity

Weight is an accuracte indicator of

mass on Earth

Top loading

weights .01g

Analytical balance

weights to .0001g

why does an analytical balance have a wind screen

bc pan is so sensivtive

Microbalance

weighs to .000001g (=10^-6 g= 1 microg) or even less

round to

second to last digit

be sure surface of balance is

level (bubble must be cenetered)

1mL=

1cc

1mL of H20 weighs

1g

1L of H20 weighs

weighs 1kg

serological pipettes

many graduations, can measure many values

adjustable pipettors

smaller measurements

beakers and erlenmyer flasks

good for mixing solutions

neither accurate or precise for measuring volumes

Graduated cylinders

good precision and accuracy

not ideal shape for mizing

volumetric flasks

excellent accuracy and precision

shape is ideal for swirling

can only be used to measure one volume

water can cling to

glass, dispensing slightly less than originally poured in

TC

to contain

TD

to deliver

when an instrument marked TC is filled, it ______

when emptied, it will_____

contains that volume

deliver less than that volume, due to clinging

TD instruments actually contain ____ but they deliver ___

slightly more than the marked volume

the specified amount

cant use TD for liquids

with different viscosity than water bc a greater amount might cling

can use TC for

liquids other than water

Use TD if you are

using water and care most about the volume that comes out

Use Tc if you care

most about how much is inside

pipettes labeled

TD

Importance of water in biological research

important component of many solutions

water quality, composition, and pH can affect experimental outcomes

Tap water

variable chemistry and purity depending on region and local treatment of municipal water

Lab grade water

from reverse osmosis or distillation

for rinsing glassware, prep of some growth media

reagent grade water

from filtration, deionization, and carbon absorption

used when highest water purity required

solution

a mixture in which molecules are dispersed into a liquid

solvent

does the dissolving

majority of a solution

water or alc

solute

dissolved

minority of a solution

often a solid before mixing

Units of concentration

amounts of solute per volume of solution

1 part per million

1 mg/L

parts per hundred

%

weight per volume

mg/L or microg/L

molarity unit

mol/L

concentration as %

% by volume/volume

mL per hundred m: of solution

Molarity

moles of solute per L of solution

the mass of 1 mole of a compound is the

molecular weight/formula weight of that compound

to prepare a solution of a given molarity, need

volume and concetration desired

MW/FW of solute

A 1M solution is the

MW or FW of a substance in 1 L of solution

Normality

molarity of equivalents produced by a compound in solution

for many chemicals the molarity and normality are

the same

differences occur when molecules have >1 exchangeable proton

To make very dilute solutions

make a concentrated stock solution and then dilute from stock

Dilution from 1 concentration to another formula

C1V1=C2V2

c1=initial concentration

v1= initial vol

c2= desired concentration

v2- desired final volume

add water to

acid not acid to water

prevents splashing and over-heating

full strength is not

necessarily 100%

types of two group comparisons

independent samples

related samples

independent samples

each observation in sample 1 has no special relationship ito an observation in sample 2

related samples/matched pairs

each individual is measured twice

carefully matched pairs of individuals are measured

Independent samples parametric

independent samples t test

Independent samples nonparametric

Mann-Whiteney Test (Wilcoxon rank sum test)

related pairs parametric

paired t test

related pairs parametric nonparametric

wilcoxon signed ranks test

assumptions of independet samples t test

the two samples are unbiased samples from the population of interest

the measured variable is continuous and normally distributed

two normal groups with equal variances

two normal groups with unequal variance

we will use _____ to test for equality of variances

Bartlett’s test

null and alternative for Bartlett’s test

Ho: variances of the 2 groups are equal

Ha: variance are uneqal

if p<a, we conclude that the two varinces are unequal

Welch’s test uses fewer

df, so its lest powerfull that bartletts

the null hypothesis states that

there are no differences between the two pop means

null and alternative for two tailed test

Ho: mu_a=mu_b

Ha: mu_a does not equal mu_b

equation for test statistic

mua-mub is usually 0

Mann whitney test

tests whether medians of 2 pops differ

null and alternative for mann whitney test

Ho: median a=median b

Ha: median a does not equal median 2

assumptions of mann whitney test

2 population distribution have the same shape

have unbiased samples drawn from two pops

in mann whitney, data from the 2 samples are

first combined and then ranked

lowest value is ranked 1

tied scores are assigned avg of 2 ranks

the outcome of mann whitney depends on

the sum of ranks in eahc group

more variable delta, higher

SE

Paired t test assumptions

each individual is measured twice or that matched pairs of individuals are measured

Paired t test 2 tailed null and alternative

Ho: mu_d=O

Ha: mu_d does not equal O

mu_d is pop mean difference

Paired t test 1 tailed null and alternative

Ho: mu_dO

Ha: mu_d d< O

tesitng Ho in a pair t test

test stat (t cal, SE, n)

compare tcalc to t critical (from t table) using df

tcalc

mean/SE

SE

SD/sq rt(N)

Wilcoxon signed ranks test

nonparametric test for paired measurements

used when the differences can be ranked with respect to eachother

why use wilcoxon ranks test

data are continuous or discrete, but not normally distributed

OR we have ordinal scale ranks

Ho for 2 tailed test wilcoxon ranks test

sum of positive ranks in a pop of differences=the sum of negative ranks in a pop of differences

ANOVA

analysis of variance

tests whether the means of three or more groups differ significantly from eachother

the problem with multiple pairwise comparisons

the probability of committing a type 1 error increase for each comparison tested in the following way: 1-(1-x)^x (where x is the number of pairwise comparisons)

ANOVA allows for

multiple pairwise comparisons without an inflated change of type 1 error

variance equation

Single Factor ANOVA

completely randomized design with fixed effects

Single Factor ANOVA assumptions

same as for an independet t test

ANOVA partions the overal variance into

2 parts:

• variance due to differences between groups (Effect of the treatment imposed)

• variance due to uncontrolled differences among subjects within groups

Single factor ANOva hypothesis

Ho: mean1=mean2=mean3=…

Ha: at least 1 pair of means are not equal

No one tailed

ANOVA

unequal variance

Welches test

other sources of variation of mice

body mass, length, age, genetic variation

The F distribution/fcalc

used in ANOVA

F= treatment (between groups) variance/error (within groups) variance

a large Fcalc suggest that

treatment effect compared to random error

a small Fcalc suggests that treatment effects

are no greater that the random variation in a pop

if treatment has no effect, expect Fcalc to be

close to 1

if treatment has large effect expect Fcalc

to be »1

How to test Ho for ANOVA

compare Fcalc to Fcritical (value from F table)

If Fcalc>Fcritical, then reject Ho