Edexcel Biology Unit 1 Notes The notes are a compilation of my notes, teacher's provided notes and notes from "Merchant Taylors’ School Notes".
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Unit 6: Practical biology and investigative skills WBI06 Time: 1 hour 30 minutes Total marks: 0 !umber o" #uestions: 3
$U%&TI'! 1: Based on one o" the (ore Practicals) •
There are are 8 Core Practicals Practicals at A2 and these includes:
Unit 4: core practicals 1. Describe Describe how to study study the ecology ecology o a habitat e.g. e.g. Does the abundance o a particular species !ary with a change o a particular biotic actor or abiotic actor" Does the pattern o !egetation change as you #o!e ro# one point to another" 2. Describe Describe how to in!estigate in!estigate the e$ect o te#peratu te#perature re on the de!elop#ent o organis#s. %.g. &eedling growth or hatching success rate o brine shri#ps eggs. '. PC( )Poly#e )Poly#erase rase Chain (eactio (eaction* n* 4. D+A D+A P(,P(,-/ /+0 +0 . n!estigating n!estigating the the strength strength o antibiotics antibiotics •
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Unit : Core practicals . Describe Describe how to in!estigate in!estigate rate o respiration respiration practically practically using si#ple respiro#eters respiro#eters 3. n!estigate n!estigate the e$ect o eerci eercise se on tidal !olu#e and breathing breathing using spiro#eters 8. n!estigate n!estigate habituat habituation ion to a sti#ulus sti#ulus e.g. using using snails
+ote: A& core practicals #ay also be included e.g. 5ay 2616 paper had beetroot eperi#ent
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&tudents #ay be re7uired to suggest a suitable hy*othesis or null hy*othesis "or investigations) A hy*othesis is a testable scientic prediction. Thin9 o the# as 7uestions to be answered in an in!estigation. The null hy*othesis is the re!erse o the hypothesis. t or#s the basis o statistical tests and is either reected or accepted in these tests +ull hypothesis always begins with; or ?now the practical procedures o each core practical ndependent and dependent !ariable Controlled !ariables %rrors: dentiy syste#atic and rando# errors Ano#alous results (eliability ssues @alidity ssues
$uestion + This second 7uestion is a data based #uestion) •
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&tudents #ay be re7uired to suggest a suitable hypothesisnull hypothesis )read re!ision guide page 88* The student should be able to tabulate data ) page 83* Calculate #eans Present the data in suitable graphical or# )page 83* Apply a statistical test ) notes below B page 88* The student should be able to eplain the #eaning o any calculated test statistic in ter#s o signi,cance limits. - signi,cance level which is also written as *. 0)0#eans that there are chances in 166 that the result obtained in an in!estigation could occur e!en i there was no di$erence between two data sets All biological in!estigations are based on - signi,cance levels or /- con,dence level
Ty*es o" statistical tests
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ou are not epected to 9now the or#ulae or ne details o each test but you should concentrate on selecting the correct ty*e o test and de#onstrate your understanding o ho to inter*ret the results There are three #ain statistical tests 1. 2. '. 4.
&tudentEs T test 5annF Ghitney U test &pear#anEs (an9 Correlation test ChiFs7uared test
1) &tudents T test This is used to #easure the amount o" overla* beteen to data sets. t tests whether there is signicance di$erence in means between two data sets e.g. the di$erence between the #ean lengths o lea!es in a shaded site and a sun eposed site. The calculated t value is co#pared against the critical value at signicance le!el or the nu#ber o degrees o reedo# )d..*. d)" . na2nb+ where n is the nu#ber o sa#ples the calculated t value is larger than the critical value4 e re5ect the null hy*othesis and accept the alternate hypothesis that there is a signicant di$erence between the #eans o the two data sets.
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%am*le 1 A t test was applied to test whether there is a signicance di$erence between #ean o red blood cells o athletes be"ore and a"ter training in a highland.
A+&G%(
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%am*le +
Answer
+) 7ann Whitney U test The 5ann Ghitney U test whether there is a signi,cance di8erence between medians o two data sets. %.g. The density o blue bells at two sites o a roc9y show. Then a or#ula is used to calculate U !alues i.e. U1 and U2 The smallest U value is co#pared against the critical !alues which are gi!en in a table at signicance. the s#allest U !alue is less than or e#ual to the critical value e re5ect the null hy*othesis ; and accept the alternate
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hypothesis that there is a signicant di$erence between the #edian o two data sets.
3) &*earman rank correlation test 9r s This test is used to loo9 or correlations between two !ariables i.e. the independent and dependent !ariables in an in!estigation. n a correlation; a change in one !ariableactor is reHected in change o another actor i.e. when one increases the other actor increases or decreases. %.g. whether there is correlation between increasing the te#perature and enIy#e acti!ity. There is a or#ula used to calculate rs !alue which is then co#pared against critical !alue at signicance le!el. The or#ula is always gi!en and a table o critical !alues is also gi!en in a table. the rsvalue is greater than or e#ual to the critical value "or the number o" sam*les4 then e re5ect the null hy*othesis; and accept the hypothesis that states that there is a signicant correlation between two !ariables.
%am*le:
Answer
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;) (%? T%&T 9@A - t is used to test or goodness o t; that is; ho the observed and e*ected values com*are i.e. one #ust ha!e epected !alues so that during the in!estigation the obser!ed !alues are co#pared with epected !alues. - The re7uire#ents or the JK test are: The chiFs7uared !alue L which is always gi!en Degree o reedo# )nF1* Condence le!el M N Critical !alue which is obtained ro# the table using signicance le!el )* and degree o reedo# )D-*. • • • •
I" the @A value is more than or e#ual to critical value4 re5ect the null hy*othesis and vice versa)
6BI0: Practical Biology and Investigative &kills $uestion 3: Planning $uestion) This Ouestion re7uires the student to describe issues relating to *lanning o" scienti,c investigations. The candidates are re7uired to gi!e answers under the ollowing headings )a* F= consideration o" sam*ling techni#ues to be em*loyed in the investigation i" it is a ,eld investigation. FThere are only two types o sa#pling 1. (ando# sa#pling using 7uadrats 2. &yste#atic sa#pling using line transects.
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The student is also re7uired to consider sa"ety or ethical issues o" the *ro*osed method) The #ost *otential sa"ety haCards o the in!estigation are described and the ste*s to minimiCe them are also identi,ed) F Consider use o labFcoats or protection against paintsdyesbiting insectsscratches ro# bushes; etc. F Consider use o goggles or eye protection F Consider use o glo!es to protect ro# sharp cutting obects holding toic or haIardous substances F Use gu#boots in slippery and wet areas F Use sterile apparatus in #icrobial eperi#ents and nutrient agar solutions
!'T%: All ani#al eperi#ents raise ethical issues F This 7uestion re7uires the student to suggest and describe the *reliminary ork to be underta9en. This is li9e a trial in!estigation or a pilot study #eant to ensure the proposed #ethod wor9s. itEs a laboratory in!estigation the #ethod should be tried out and i it is a eld wor9 the site should be !isited and the proposed sa#pling techni7ue tried out. This is done : F to deter#ine the independent !ariable F to deter#ine the dependent !ariable F identiy !ariables to be controlled i.e. 9ept constant F deter#ine the ti#e scales %am*les
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)b* This part o the 7uestion re7uires the student to gi!e a detailed #ethod and eplanations o how i#portant !ariables are to be controlled. F A clear state#ent o the de*endent variable is gi!en i.e. eactly what is to be #easured. F A clear state#ent o the inde*endent variable is stated F The range o the independent !ariables is suggested. F A clear consideration o the time o!er which the in!estigation is to be carried out. F &uitable details o ho the measurements are ta9en or how data is collected. F At least to variables that can a$ect the in!estigation are identied. F A description o how the abo!e to variables are controlled) F The in!estigation #ust be re*eated or reliability. F The total #ar9 or the 7uestion is 16 which includes 2 #ar9s or &P0 )&pelling and 0ra##ar* )c* This part o the 7uestion re7uires the student to gi!e a clear eplanation o how the data are to be recorded4 *resented and analyCed in order to draw conclusions. F The student is epected to draw a table o" results which #atches the proposed #ethod. F The tables should ha!e clear headings and units. F The means should be calculated ro# the repeated data. F A suitable graph; a line or a bar graph; should be drawn with correctly labeled aes. F The student should #a9e reerence to a suitable statistical test e.g. a ttest or a 7annWhitney or signicant di$erence; a &pear#anEs (an9 test or correlations; or (hi test goodness o t. )e* This 7uestion re7uires the student to gi!e limitations or #ethod o in!estigation used.
/i#itations are genuine diculties or actors that the in!estigator cannot be able to control. %am*les: F you are co#paring two areas in ecology; itEs dicult to #atch the conditions on both sites. F t is dicult to control en!iron#ental conditions
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F Qudging the gender o insects is dicult. F tEs dicult to control #o!e#ent o ani#als. F Controlling tness or health le!els o organis#s. F eperi#ent is done in the laboratory itEs dicult to #atch the natural conditions in the natural wild conditions F Dicult to control genetic !ariations within organis#s. F Dicult to control all !ariables a$ecting a particular dependent !ariable.
