CIE A-level Biology Paper 3 Tips

There's a lot of things we need to know when sitting for Biology paper 3. It may be difficult or easy depends on how much tips you know about it.

1. Dilution

There are 2 types of dilutions: simple dilution and serial dilution
Use the formula m1v1 = m2v2 to calculate

If it is simple dilution, you need to know the total volume of solution, volume of ____ solution and also volume of distilled water. 
Volume of ____solution can be found by using the formula m1v1 = m2v2  while volume of distilled water is found by : total volume of solution - volume of _____ 


For serial dilution, remember to draw arrows and labelled the arrows with correct volume and concenration. 

2. Table

First column must be independent variable and subsequents columns are dependent variables. 
Remember UNITS!

Common mistake when recording the data :
-NO decimal places for time taken. Eg. for second, write 1 but not 1.0.
-NEVER write no colour change. 
-ALWAYS write both the initial and final colour change.
-Compare the darkness of the colour of solution. Eg. you can use word like slightly darker/ paler OR ____ is paler than ____ but darker than ____.


*Be careful if the questions ask you to replicate the experiment, that's mean you need to have another column of data and another column for the average data.

3. Risks and Hazards

Risk: low/ medium/ high

Hazard: the item name 

4.Set up control

-Solutions
replace _____solution with (same volume) of distilled water.

-Enzyme
replace enzyme with (same volume) of distilled water 

5. Standardized variables

Standardize means kept constant / controlled, which means, you need to set up a controlled variable.

-Volume of solutions
Use a syringe to standardize the volumes at ___ml for each test

-Temperature
Use thermostatically controlled water bath to standardize the temperature at __

-Mixing solutions
Use mechanical stirrer

-Size of sample
Use vernier calipers to standardize the length at ___mm for each test

6. Estimate unknown value

If the value lies between 2 data, do not give a random value between the 2 data values. Always write betweem ___ and ___.

7. Systematic and random errors.

Systematic error is caused by flawed in measuring instruments and also other apparatus. 
It affects all results in the same way and true value is hard to obtained. 
Ways to improve : use the same instrument for a ll samples so that the error is consistent.

Random error is caused by human error or unpredictable change in the experiment. 
It does not affect results in the same way. It affects the general trend (anomalous result)
Ways to improve : take more readings and calculate the mean 

8. Significant sources of error & Suggesting improvements

Errors that affect all samples equally cannot be taken into account. Eg, syringe used, solutions degrading. Human reaction time and contamination also not allowed. 

Cutting samples
-Size of samples are different.
~Use vernier caliper to measure the length of samples before cutting 

Stirring 
-Mixing of solutions are different
~Use a mechanical stirrer

Incubation periods
-Time of samples soaked in the incubating solutions are different
~Staggered the starting time

Colour changes
-Difficult to judge the end point
~Use a colorimeter to judge the end point colour

9. Reliability & Accuracy

To improve reliability:
-Make more replicates and calculate the mean
-Standardize variables

To improve accuracy :
-Use more intermediate of (independent variable), such as ___________________
-Standardize variables
-Plot a graph and read off the anomalous value

10. Modifying experiment 

Set up (independent variable) at (at least 5 readings) + how the independent variable conditions set up

Eg.
Set up the temperature for ______ at 25°C, 30°C, 35°C, 40°C and 45°C by using a thermostatically controlled water bath. 

11. Calculating errors

(1/2 x smallest division on instrument) / total  x 100%

12. Plotting graph

-Label both x- and y-axis with suitable UNITS
-Use scales like factor of 2, 5 and 10. You don't have to start with 0
-Plot must be smaller than the little box of the graph paper.
-Smooth line

Be careful of bar charts and histogram. DO NOT shade them!
Bar chart do not touch each other while histogram do touch each others. 

13. Drawing 

Plan diagram :
-NO ruler
-DO NOT shade the drawing
-DO NOT draw any celss
-draw bigger than the diagram given
-read the questions properly and watch out for annotation

High power diagram : 
-Draw cell wall as double line
-only draw what you see

14. Calculation

-Always in mm
-Show full calculation steps! 
-convert to μm first for calculation before convert back to mm for final answer
-Magnification must be whole number
-Ratios must be whole number and lowest denominator

15. Comparison/ Differences
Draw a table with 3 columns : features and 2 heading of the samples

For comparison, show both similarities and differences.
For differences, show only differences.

Compare only visible features.
-shape
-distribution of structures
-presence and absence of structures
-size
-number