Biology paper 6 tips

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This paper needs to analyze the relationships between variables and readings. The questions (topics) required from paper 6 are:

  1. Taking reading from instruments and apparatus (measuring cylinder,
    stopwatch, burette, gas syringe).
  2. Measuring length by ruler (take care of required unit cm or mm)
  3. Calculate the    magnification and the unit times ( X )
  4. Draw a suitable graph and must include the following:
  5. Appropriate scale.
  6. Axes labeled and their units.
  7.  Plot all points by pencil then pen to be clear

a) Types of graph

– Line graph: when say ‘passing through points’ or ‘suitable graph’ or ‘when there is time as variable’. It can be straight (best fit line) or smooth curve.

– Bar charts: when to compare

– Pie charts: when he draws a pie charts and figure is given

7.  Take readings from graph (Line graphs) by extending line or curve.

8.  Explain results: ethers directly or inversely proportion and some details from graph to support your answer.

9.  To label some parts (palisade, xylem, etc. )

10. Purpose of experiment: As control experiment to compare results

11. Applying some formulas given to you

12. Complete headings of a table ( g, cm , s, etc.)

13. Counting and making tally tables

14. Calculate percentage increase or decrease

15. Safety precautions (fume cupboard, heat in hot water path, wear gloves and googles)

16. Giving surface area by counting and completing squares

17. Experimental accuracy improvements:Using electronic balance instead of spatula

  • Use larger number of sample
  • Using lid and polystyrene cup in heating experiment – Using data logger instead of timer and stopwatch
  • To be fair and keep factors same and constant
  • Use burette instead of measuring cylinder
  • Common one: to repeat and take average (mean)
  • Same apparatus and instruments
  • Control temp and PH.

18. Classification of innervates (name of group, feature)

19. Adaptations of animals (ex: camouflage)

20. pH measured by universal indicator and pH meter

21. Hydrogen carbonates indicator and its color.
22. Round results always 2 or 3 significant figures

23. Giving ratios in simplest form.

24. Rate is always: volume of gas/time taken.

25. Some observations to be recorded.

26. Leaving experiment after heating:

  • To avoid the effect of the previous one
  • To provide time to adapt temperature

27. In temperature-enzyme experiment:

Steps to follow are:

  • Same volume and concentrations of same reagents
  • Same of volume of same enzyme
  • Same apparatus used
  • Same time intervals
  • Control pH
  • Apply different temperatures.
  • Note readings and results
  • Plot them and compare
  • Repeat and take average.

28. Steps to follow in pH-enzyme experiment:

  • Same volume and concentrations of same reagents.
  • Same of volume of same enzyme
  • Same apparatus used.
  • Same time intervals
  • Control temperature
  • Apply different pH
  • Note readings and results.
  • Plot them and compare
  • Repeat and take average

29. In germination experiments where pH is a variable:

  • Use same seeds due to age and species
  • Use same number of seeds
  • Same of volume of same enzyme
  • Use same apparatus
  • Keep time intervals the same
  • Control temperature
  • Conduct experiments over different pHs
  • Note readings and results
  • Plot them and compare
  • Repeat and take average

30. Experiments where rate needs to be calculated:

  • Add 2~3 cm3 of culture to test tube
  • Shake it
  • Connect test tube to gas syringe
  • Note gas volume
  • Control temperature
  • Record time taken by stopwatch
  • Plot them and compare
  • Repeat and take average of results

31. Variables to be constant in experiments involving cooling:

  • Room temperature
  • Time interval
  • Temperature
  • Volume of water

32. To determine number of stomata:

  • View the leaf under microscope at high magnification
  • Count the number of stomata
  • Determine the area of stomata
  • Calculate area of stomata (using a grid)

33. Determining the rate of uptake of water by plants (transpiration rate)

Conditions to keep constant

  • Plant species
  • Number of plants
  • Volume of water
  • Time interval
  • Apparatus
  • Light intensity

Method

  • Control pH and temp.
  • Note readings
  • plot and compare
  • Repeats and take average

34. Making brief comparisons (comprising of number, size, color, presence of some special parts, shape, surface area)

35. Drawing certain parts of plant/ animal:

  • Use a sharp HB pencil.
  • Draw a clear and similar shape.
  • Avoiding shading
  • Make accurate labels (at least 2)
  • Draw according to the magnification asked in the paper.

36. Make biological tests: Scientists often need to know whether or not a particular type of molecules is present in a solution. There are number of simple chemical tests that can be carried out on biological solutions.

a) A special test for lipids.

An important feature of fats and oils is that they are insoluble in water. This means that you cannot make an aqueous solution of a fat or oil on which to carry out a biochemical test. However, the fact that lipids are insoluble forms the basils of a physical test. This is known as the emulsion test: How to?

  • 2 cm3 of ethanol are added to the unknown solution, and the mixture is gently shaken.
  • the mixture is poured into a test tube containing an equal volume of distilled water.
  • If a lipid is present, a milky-white emulsion is formed.

b. Testing for vitamin C using DCPIP. Vitamin C takes the color out of a blue dye called  DCPIP.

  • The number of drops of vitamin C solution needed to make this happen depends on how concentrated the vitamin C solution is.
  • So, if few drops: strong vitamin C solution.
  • If many drops: weak vitamin C solution.

c. A control is needed to make sure that results are valid:

-To show that the test is working properly a solution that is known to the substance is tested (for example, the biuret reagent is used with a solution known to contain protein). This should give a result.

-To show that the test solutions are not contaminated, each test should be carried out on a sample of water. This should give a negative result.

Examples:

  • To test for Protein, a few drops of Biuret reagent are added to 2 cm3 of the unknown solution (to be tested for containing protein) and the mixture is gently shaken. A MASSIVE/PURPPLE color is a positive result (protein is present)
  • To test for starch, a few drops of iodine solution are added to 2 cm3 of the unknown solution (to be tested for containing starch) and the mixture is gently shaken. A DEEP BLUE-BLACK color is a positive result (starch is present).
  • To test for glucose (a reducing sugar), 2 cm3 of Benedict’s reagent are added to 2 cmof the unknown solution and the mixture is heated in a boiling water bath for 2-3 minutes. An ORANGE/BRICK-RED color is a positive result. (glucose is present)

When making comparison between different solutions – for example, to compare the glucose content of different wine samples – it is important to carry out all tests under the same conditions. For example, a series of Benedict’s tests should be performed:

  • on equal volume of unknown solutions.
  • using equal volumes of Benedict’s solution.
  • with all mixtures heated to the same temperature.
  • for the same length of time.

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