CIE+A+Level+Resources

[] **CIE BIOLOGY FORUM**

[|Bio Worksheets]

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Meiosis [|Meiosis]

[|Meiosis]

**Any questions about the Practical Examinations should be directed to CIE.**

Please contact CIE by e-mail: International@cie.org.uk by phone: +44 1223 553554  begin_of_the_skype_highlighting   +44 1223 553554  end_of_the_skype_highlighting by fax: +44 1223 553558

stating the Centre number, the nature of the query and the syllabus number.

Plan diagrams do not show cells. They just show the arrangement of the tissues as you would see them at low power with the microscope. Even if you can see individual cells at that magnification they are too small to draw accurately.

**Confusion in Incomplete dominance & codominance** Can you give me the exact definition of incomplete dominance and codominance as expected by the examiners. Definition - two or more allele both equally expressed in the heterozygous condition Yes, in Syllabus - 2012 Biology 0610 in page no. 56, in Appendix A, 6.2.5 Genetics (g) " The term incomplete dominance should be discontinued and in the particular case where alleles are equally dominant it should be called codominance. Thus codominance should be used where the influence of both alleles is shown in the phenotype, e.g. the AB blood group in humans."

Incomplete dominance is when inheritance of one allele for a specific trait is not completely dominant over the other allele. It results in combined phenotype. Ex. Pink and white flower are crossed and it results in pink flower.

Co-dominance is also similar, when inheritance of one allele for a specific trait is not completely dominant over the other allele but both the traits are expressed together. Ex. Red and White hair cattle is crossed it results in roan coat so for example in a question: where when a red flower was crossed with a white flower, if the resulting flowers were pink can this be called coodominace or incomplete dominance, which one should the students write. will both coodminance and incomplete dominance be accepted? In this case the students could write either and they would be credited.

I have asked everyone and we agree that in questions you will see the term codominance - and that applies to the ABO and pink flower examples. However, if the candidates are asked to name the condition and they call it incomplete dominance they will be credited with a mark.

In teaching I would just use the term codominance and not use incomplete dominance at all.

**Think** Statement 1. Two electrons from reduced NAD help passing 6 proton from matrix to inter membrane space Statement 2. When three proton passed through ATPase will produce 1 ATP. By this way 6 proton will produce 2 ATP. But why book state that 3 or 2½ ATP will produce from energy given by one reduced NAD?

**Practicals** The con. of protease in papaya and pineapple extracts are too low, that's why they dont work. You need to concentrate them by using a greater volume.

1 ml protein + 5-10 ml juice.

Moreover, use green pawpaw which contains better protease.

Still if it doesn't work then use meat tenderiser from the supermarket. It also contains papain.

1. What is the difference between reliability, accuracy, validity and improvement as set in practical paper questions.

reliability

How close are the repeat results (replicates); if close, then the results are reliable; if not, then they are not reliable. A good thing to remember is all the r's. Reliability is assessed by taking replicates. Is the procedure repeatable so it always gives results that are close together? If the procedure is carried out by someone else how reproducible are the results? If they get the same results then the results are reliable.

accuracy

How close to the true value are the results? You cannot always be sure of this with many biology practicals unlike chemistry or physics. Very reliable results are not necessarily accurate.

validity

Refers to the confidence that you can have in your conclusions. If you have a valid investigation then you have measured what you thought you set out to measure; for example, the effect of changing the independent variable leads to changes in the dependent variable that you have measured. If asked to comment on the validity of an investigation then you should consider the following: • the limitations in the procedure • any uncontrolled variables • the effects of errors (systematic and random) on the results • the reliability (repeatability) of the results • the precision of the data collected • the accuracy of the results

improvement

If you have made some criticisms of the procedure or identified limitations in the results, then what changes would you make to the procedure (including data collection) that would improve the reliability and accuracy of the results and therefore improve the validity.

I should add precision which can mean the number of decimal places or significant figures to which results are expressed. Weighing to the nearest 0.1 g is more precise than weighing to the nearest 1 g.

Does that help?

You might like to download this document - recently published in the UK to address these terms.

[|Relibility & validity in pr]

Could anybody explain the difference between smooth line graph, smooth curve, trend line and line of best fit?

First some quotes from the booklet Biological Nomenclature published in the UK by the Society of Biology (formerly the Institute of Biology).

'The line used to show the relationship may be either straight or curved. In maths the term curve is used to describe the line, whether it is straight or curved.'

'A smooth line can be drawn to represent the relationship [between variables] when there are sufficient data points to be confident in the relationship or because, from theory, there is good reason to believe that the intermediate values (values between the data points from the investigation) fall on the line.'

'When there is insufficient data to be able to confidently interpolate the relationship, by convention, straight lines joining the points should be drawn, thus indicating uncertainty about the intermediate values.'

'A 'line of best fit' should take account of the uncertainty in the data points as well as the reasoning above.'

So. Plot the points. If you are confident that a relationship exists between the variables so you can draw a 'line of best fit' you either draw that line as a straight line (e.g. effect of increasing enzyme concentration on rate of reaction with substrate always in excess) or (what we would call) a smooth curve (e.g. effect of light intensity on the rate of photosynthesis).

A trend line is similar to a 'line of best fit' and may be drawn by eye or may be determined by using statistical methods such as linear regression. It may be a straight line or a curved line.

I am sure we all use these terms interchangeably. I think they all mean the same thing. They do not apply to graphs where you 'join the dots'.