Experimental Design Notes Essay Sample

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Hypothesis: an explanation of an observation, written as a statement and testable. Can be based on previous knowledge


a characteristic or property capable of taking on a range of values and with the potential taffect things

Independent variables: variable set before starting the investigation

Dependent variables: variable that is measured during the investigation

Control variables: factor kept the same in the investigation

Parts of Experimental Method

Aim- purpose of the experiment



Method: physical steps required ttest hypothesis and predictions

Things tconsider

Materials needed


Sample size and replication of experiment

Experimental Design


Aim and hypothesis

Hypothesis and predictions are testable with resources available

Assumptions and variables

Awareness of assumptions that you are making in experiment

All variables are identified

Independent variable range has been set

Layout of experiment considered

Data Collection

Units for all variables have been identified

Amount of data tbe collected has been identified

Consideration of how data will be analyzed

Method for systematically recording results

Repeat or Trials: investigation that is carried out again at a different time

Ensures experiment is reproducible and data is consistent

Treatments: well defined conditions applied tthe sample

Specific and predetermined


subset of a whole used testimate the values that might have been obtained if every individual was measured


What is it going tlook like? -> data table or graph

Things tconsider: How are you going tarrange your data?

Data presentation: Table: allows one torganize data in a way that shows relationships

Graph: Visual image is easier tsee

Statistical Analysis

Why use it?

Science requires observations and collections of measurable data

Ex. Investigation question is what is the height of bean plants growing in the shade?

How many bean plants tstudy?

Can’t study thousands of bean plants b/c time, money and land, labor

Need ttake a sample of bean plants trepresent the population of all bean plants

Need tget a representative sample


helps sample small portions of habitats, communities, biological populations tdraw conclusions about the larger population

Measures differences of the relationships between the sets of data

Compare small populations of bean plants in sunlight vs. shade

Depends on sample size, mathematically form conclusion with a level of confidence

In science, level of confidence is usually around 95%, can never be 100

Statistics- can be describe conditions in countries around the word

Data can heighten our awareness of global issues

Ex. Poverty level of the world

At least of 80 percent of the world live off of 10 used

Descriptive Stats

numerical summaries of data

Mean: average of data points

Range: measure of the spread of data. Finds the difference between largest and smallest value

Standard Deviation: measure of how a data set is spread out around the mean

Error bars: graphical representation of the variability of data

Can be used tshow range of data or standard deviation

In normal distribution 68 percent of all values lie within in + or – 1 of SD of the mean and 95 if values lie within in plus or minus 2 of SD of the mean

Plotting the number would likely result in a bell curve

Most data won’t have perfect distribution

Flat bell curve: data is spread out widely from the mean

Tall and narrow bell curve: data is close tthe mean

SD tells how tightly data points are clustered around the mean

Data close together: small SD

Data far apart: Larger SD

Tells how many extremes are in the data

More extremes = larger SD

Few extremes = small SD

Scientific Method

2 forms- Biologist use 2 main types of scientific inquiry

Discovery science

Hypothesis based science

Discovery Science

Describes natural structures and processes

Observation and analysis of data

Conclusions through inductive reasoning using observation

Ex. Jane Goodall and chimpanzee behavior

Hypothesis Based

Potential answer ta well framed question

Educated guess based on experiment and data available from previous experiments and discovery science

Theory: a hypothesis that is supported by an overwhelming amount of data and results

Attempts texplain nature

Underlines most scientific research

Allow scientists tmodify their conclusions as new inform become available

5 steps


Ask questions

Form hypothesis

Make predictions

Test the prediction using additional observations or by conducting experiments

2 ways ttest hypo.

Controlled experiments


All factors other than the one hyptbe causing the effect can be kept constant

Comparative method

Stats 2

Reliability of the Mean

Variance is other measure of dispersion

1 method calculate standard error

Standard Error

Allows for calculation of the 95 percent confidence interval

CI used tindicate relativity of an estimate

Degrees of freedom = n-1

Calculated 955 of it can be plotted as error bars on a graph

Smaller CI more reliable the data staminate

Determines if there’s a significant difference between sets of data


Only valid for certain situations

2 group tests

Only have 2 samples tcompare


Normal and not skewed distribution

SD for both samples is similar

Null hypothesis- the hypothesis of ndifference or neffect

Probability that chance alone could make a difference have an effect

5% = difference is due tchance 5% of the time

Degree of freedom = sum of total number of sample sizes of both groups


Calculate degree of freedom

V1 + V2 -1 = DF

Look at t values and match degree of freedom now with t value column

Values lie between 1 and 5 percent

Reject null hypothesis when P is 5 or less



1st century Ad glass as invented, Roman observed it and tested

Experimented with different designs

Thick in the middle and thin outwards

Discovered that holding lens over an object made it larger

Magnifying glass

1590, 2 Dutch spectacle makers, Zaccharias and Hans Janssen put more then one lens together and looked through saw object larger

More novelty than function

Anthony Van Leeuwenhoek

Simple hand held microscope

Made better lenses by grinding small glass balls intthin lenses magnification = 270x

Using it, saw bacteria, yeast, blood cells

17th century, compound microscope 1+ lens invented tenhance resolution and magnification

Robert found basic unit of life- cells

2 functions

Enlarge image, can be seen with naked eye or camera

Contrast details stand out

Light Microscopy

Intact cells low magi. Limits of relation are 200 nanometers

Classic light microscope method – bright field

Uses pure white light

2 series of lenses- objective and ocular lens

Total magi of a compound microscope is the product of magi of ocular and objective lens

Increase contrast

Cells absorb little visible light

Little contrast available

Staining is used tincrease contrast

Phase Contrast Microscopy

Made tsee improved contrast differences in between and surrounding medium

Can see cell without staining

Based on principle that cells slow speed of light passing through specimen

Result is difference of phase between the cell and its surroundings

Difference is amplified by a special ring in the objective lens of the microscope

Leads tdark image on light background


Light micrwhere light reaches specimen form the side only the specimen looks light

Better contrast than bright field and phase contrast microscopes

Fluorescence microscope

Uses electrons timage cells and cell structures

2 types

TEM transmission electron microscope

SEM scanning electron microscope


Uses electromagnets tact as lenses

Works as a vacuum and filled of cameras sthat a micrographs can be taken

Typically used texamine inside of a cell

Resolving power is greater than light micro

Must use thin section because of electron beams don’t penetrate very well resolving power – .2 nanometers?


Used tlook at external features

Surface image only

Coat specimen with thin film of heavy metal like gold

Electron beam then directed intthe specimen and scans back and forth across it

Electron moved by the metal are collected tproduced an image

Wide range of magnification 15x-100,000x

Parts of microscope

Specimen control

Stage where specimen rests

Clips used thold the specimen still

Micromanipulator device that allows you t move the specimen in controlled small increments along the x and y axis

Illuminating sheds light on the specimen

Lamp light source

Condenser lens that aligns and focuses form the lamp ontthe specimen

Diaphragm apertures alters the amount of light that reaches the condenser used tenhance contrast of lens


Objective lens gathers light from the specimen

Ocular transmits and magnifies image from the objective lens tyou eyes


Coarse focus know used tbring object the focal plane of the object lens

Fine focus know used tmake fine adjustments tfocus the image

Seed Germination

Seed dormancy

In seeds, development and activity may be suspended

Dormant seeds don’t divide, expand or differentiate

Seed dormancy must be broken for the embrytbegin developing


Beginning of growth

Growth in a seed calls it a seedling

Process where the seed begins tgrow

Seed Germination Dependency

Internal and external





Start of Germination

Begins with water- called imbibitions

Seed takes up water, undergoes metabolic changes

Activates bichemical process resulting in protein synthesis

Oxygen = seed metabolism and energy production

Seeds that are waterlogged or buried todeeply in soil won’t get enough oxygen needed

Steps of Germination

Seed gets water, seed coat bursts

Chemical energy provides the energy needed for the embrytenlarge and push out of the seed coat

Tip of root comes out first and anchors plant and lets plan absorb minerals and water form soil

Plant Vocab

Cotyledon: embryonic leaf inside the seed

Monocotyledon: one of twmajor groups of plants has only 1 cotyledon ex onions corn lilies

Diacotyledon: other major group of plants, 2 cotyledons, beans, castor oil plant

Monocot Germination

Primary root pierces seed coat and grows downward

Primary leaf grows up and is protected by the coleptile, hallow cylindrical structure

When the seedling is above round the coleptile stops growing

Dicot Germination

As embrygrows seeds out shoot called a radical

Radical becomes primary root and grows

Hypocotyls then emerges and lifts grouping tip

With light, hypocotyls straightens and cotyledons spread apart texpose the primary leaves

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