VCE Biology Exam Discussion and Solutions

[ATARNOTES321]

For question 11d about the 'control measures', do you think they will accept having separate trials as controls (instead of writing about controlled variables)? I wrote that those trials could be used as a standard of comparison against the actual test experiment to show how the results are affected by the variable (by showing what would happen if it were kept constant in the control test)...
Hopefully this makes sense!
Thanks in advance

[HubHub]

Hi everyone,
For the experimental method section, why do you think they included that table showing the CO2 and O2 concentrations as well as temperature of the chamber without the cockroach? I used this table as the basis for my 11d) response, in the sense that the temperature and concentrations fluctuated in the chamber, thus, this may sway the reliability and validity of results for during the actual experiment, small changes (not due to the cockroaches respiration) in the chambers concentrations and temperature may impact results, however seemingly minute. Do you think this is why that table was included?

[MLGityaJ^A]

Hey guys, for Question 11.c. in the suggested solutions for the Biology Exam that were published here, it was said that Matthew measured the O2, CO2 concentration and temperature for four minutes to record more data and reduce the effect of random errors. However, wouldn't it be because he wanted to find out what point the values being recorded stopped changing? In the last three entries of Matthew's recordings, the values stayed the same. In addition, if Matthew wanted more precise values, wouldn't he simply take recording repeated times rather than just waiting for a period of time? My answer was that Matthew took four minutes to record so that he could obtain more ACCURATE values, rather than precise ones, by waiting long enough for the recordings taken every minute to stop changing, allowing for the true amount of O2, CO2 and level of temperature present in the container to be recorded.

Hubhub, i think the table was just provided for question 11.c., not sure whether you could talk about it in 11.d. though

Mod edit: Posts merged. Please edit existing post instead of posting again.

[vox nihili]

Hey guys, for Question 11.c. in the suggested solutions for the Biology Exam that were published here, it was said that Matthew measured the O2, CO2 concentration and temperature for four minutes to record more data and reduce the effect of random errors. However, wouldn't it be because he wanted to find out what point the values being recorded stopped changing? In the last three entries of Matthew's recordings, the values stayed the same. In addition, if Matthew wanted more precise values, wouldn't he simply take recording repeated times rather than just waiting for a period of time? My answer was that Matthew took four minutes to record so that he could obtain more ACCURATE values, rather than precise ones, by waiting long enough for the recordings taken every minute to stop changing, allowing for the true amount of O2, CO2 and level of temperature present in the container to be recorded.

Hubhub, i think the table was just provided for question 11.c., not sure whether you could talk about it in 11.d. though

Mod edit: Posts merged. Please edit existing post instead of posting again.

The sample solutions say nothing about precision. Reducing the effect of random error does make the results more accurate. Error means that the results are inherently inaccurate; therefore, by removing error we increase accuracy. The sample solutions perhaps should have mentioned accuracy directly.

Hi everyone,
For the experimental method section, why do you think they included that table showing the CO2 and O2 concentrations as well as temperature of the chamber without the cockroach? I used this table as the basis for my 11d) response, in the sense that the temperature and concentrations fluctuated in the chamber, thus, this may sway the reliability and validity of results for during the actual experiment, small changes (not due to the cockroaches respiration) in the chambers concentrations and temperature may impact results, however seemingly minute. Do you think this is why that table was included?

Hmmm I think the table just gives you a sense of how long it takes the chamber to heat up and actually shows you that at 30°C the CO2 and O2 are actually pretty constant. The table makes you feel more confident that the results he is taking are quite precise.
I'm not sure that the mild variability in the results would really have any bearing on the reliability and validity of the results.

[MLGityaJ^A]

The sample solutions say nothing about precision. Reducing the effect of random error does make the results more accurate. Error means that the results are inherently inaccurate; therefore, by removing error we increase accuracy. The sample solutions perhaps should have mentioned accuracy directly.

I'm pretty sure random errors don't make the results less accurate. When random errors occur, they result in a high amount of variation within the results. This means that random errors affect precision rather than accuracy. The one kind of errors that can affect accuracy are systematic errors, where the equipment being used consistently gives values deviate away from the true value. Not all errors affect accuracy. The effect of random errors can be lessened by repeating measurements to obtain a more precise average, but this is not what question 11.c. is talking about.

[vox nihili]

I'm pretty sure random errors don't make the results less accurate. When random errors occur, they result in a high amount of variation within the results. This means that random errors affect precision rather than accuracy. The one kind of errors that can affect accuracy are systematic errors, where the equipment being used consistently gives values deviate away from the true value. Not all errors affect accuracy. The effect of random errors can be lessened by repeating measurements to obtain a more precise average, but this is not what question 11.c. is talking about.

You're right about that. The reason for that is that random errors tend to underestimate or overestimate results with the same magnitude. Systematic errors skew towards overestimating or underestimating. As such, if you take lots and lots of measurements, if you're only contending with random error you should get a result that reflects the true result; however, if you have a systematic error it won't, no matter how many measurements you take.


I don't like the way I've worded my answer to 11c. On reading your answer again, I think that you would get marks for it. It's not 100% correct, but I'm not sure VCAA will be that pedantic. For instance, if you compared 10s to 1 min, you could actually say exactly the same thing you said, despite the fact that there is actually quite a degree of change left in the system. The reality is that we do not know that at 10min we'd be getting the same results as four minutes, we're just more confident because we measured for longer.
I think the point of the four minutes is to increase one's confidence that the measurements they have obtained are a good estimate of the  "true" result. That's because by taking more measurements you reduce the standard error (i.e. the degree to which the results vary based on random error alone).

[Zaljc]

 I JUST REALISED THAT I READ THE CHOLESTROL QUESTION WRONG ?!??! I READ WHAT HAPPENS WHEN THERE IS LOW CHOLESTROL INSTEAD OF LOVISTA OR WHATEVER IT WAS

It’s funny how during the exams, you read things incorrectly. But bye guys, I’m gonna go contemplate my life

[Calebark]

I JUST REALISED THAT I READ THE CHOLESTROL QUESTION WRONG ?!??! I READ WHAT HAPPENS WHEN THERE IS LOW CHOLESTROL INSTEAD OF LOVISTA OR WHATEVER IT WAS

It’s funny how during the exams, you read things incorrectly. But bye guys, I’m gonna go contemplate my life

I completed Biology last year. Once the AN discussion/solutions came out, I realised that I misread a lot on information. I was barely expecting to crack a 30 raw, but I managed a 39 raw. You can surprise yourself -- don't lose hope

[ATARNOTES321]

For question 11d about the 'control measures', do you think they will accept having separate trials as controls (instead of writing about controlled variables)? I wrote that those trials could be used as a standard of comparison against the actual test experiment to show how the results are affected by the variable (by showing what would happen if it were kept constant in the control test)...
Hopefully this makes sense!
Thanks in advance

If somebody could please let me know their opinion on this I would really appreciate it! Thanks

[vox nihili]

If somebody could please let me know their opinion on this I would really appreciate it! Thanks

Sorry, missed this one. Describe the separate trials to me. Not entirely sure what you mean. Simply having separate trials is not enough to be a control.

[ATARNOTES321]

Sorry, missed this one. Describe the separate trials to me. Not entirely sure what you mean. Simply having separate trials is not enough to be a control.

Sorry, I meant using a completely different group as a control, for example doing a seperate experiment where the temperature remained constant. Then another experiment where another variable was kept constant...I wrote that these different control groups could be compared to the regular test. Does that makes a bit more sense ?
Thanks for your reply!

[vox nihili]

Sorry, I meant using a completely different group as a control, for example doing a seperate experiment where the temperature remained constant. Then another experiment where another variable was kept constant...I wrote that these different control groups could be compared to the regular test. Does that makes a bit more sense ?
Thanks for your reply!

It's probably a bit of overkill, but that control is fine. Another potential control would be no cockroach.