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National 5 Biology Experimental design, presentation and interpretation skills

Learn about the importance of experimental design and presentation skills in biology. Discover how to conduct a control experiment, ensure reliability, draw valid conclusions, and present results effectively. Improve your understanding of variables, data presentation, and calculations.

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National 5 Biology Experimental design, presentation and interpretation skills

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  1. National 5 BiologyExperimental design, presentation and interpretation skills

  2. Experiments Every experiment needs: • A controlexperiment. • To be reliable. • To be designed so that it is possible to draw valid conclusions from a valid experimental design. • Well presented results and conclusions. • Correct calculations You can move to each section by clicking on the link You can return here by clicking the symbol

  3. The Control Experiment A control experiment allows you to be certain that the variable that you are investigating is the variable that is causing the effect. What do you do? • You do the experiment again. • You leave out the variable that you are investigating.

  4. A ControlExperiment - examples: • A scientist wants to know the effect of heat on the enzyme pepsin. • Pepsin will turn a cloudy solution of protein clear as it digests the insoluble protein into soluble peptides • Test tubes of pepsin and protein are placed in water baths at 10, 20, 30, 40 and 50ºC • The time taken to clear is recorded Do a second experiment with boiled (destroyed) enzyme What is needed for a control experiment? ? *click*

  5. A ControlExperiment - examples: Investigating the production of heat from germinating peas Do a second experiment with boiled (killed) peas ? *click* Investigating the effect of acid rain on the growth of seedlings Do a second experiment using distilled water instead of the acid ? *click*

  6. Reliability A reliable experiment is an experiment that you can be sure will give you an repeatable result every time you do it. To ensure that you have not, by chance, got a result from one of the extreme ends of the normal range of variability. What do you do? Replicate (repeat) the experiment several times and get an average of the results.

  7. Valid Conclusions and Valid Experimental Design A valid experimental design is an experiment where you control all the variables apart from the one you are investigating. If the design is valid then you are able to draw valid conclusions.

  8. Good Words and Bad Words Some descriptive words linked to variables are not acceptable Mass Volume AmountQuantity Length Width Height Volume Size Temperature Warmth, coldness, heat, cold Acidity, alkalinity pH

  9. For example (1): In an experiment to test the effect of temperature on enzyme activity you must control: • pH • The concentration of the enzyme • The concentration of the substrate(s) • The volume of the liquid • The shapes of the containers

  10. For example (2): In an experiment to test the effect of light on rate of photosynthesis you would need to control: • pH • The temperature • The concentration of Carbon dioxide • The volume of the watering liquid • The shapes of the containers

  11. Results Temperature (°C) 10 20 30 40 50 Bubbles (number/s) 1 5 7 5 0 Results can be presented as a table, as a graph or both. To draw a table. • Lines are drawn with a ruler and surround the table. • There must be headings for each row or column including SIunits where appropriate. • There are no units in the body of the table.

  12. SI units Do not use any other units or abbreviations

  13. y Experiments - Presentation outcome variable For every experiment you need: to know the input variable. x input variable • The variable youchange. • This goes along the x-axis. • This is the top row or first column in a table. The outcome variable. • The variable youmeasure. • This goes along the y-axis. • This is the bottom row or last column in a table.

  14. A Bar Chart – separate bars 8 7 6 Bubbles (number/s) 5 4 3 2 1 0 10 20 30 40 50 Temperature (°C) • Draw the axes • Mark in the labels • Mark the x scale • Mark the y scale • Draw the bars • If you have time shade in the bars

  15. 8 7 6 Bubbles (number/s) 5 4 3 2 1 0 10 20 30 40 50 Temperature (°C) A Histogram – joined bars • Draw the axes • Mark in the labels • Mark the x scale • Mark the y scale • Draw the bars • If you have time shade in the bars

  16. A Line graph 8 7 6 Bubbles (number/s) 5 4 3 2 1 0 0 10 20 30 40 50 Temperature (°C) • Draw the axes • Mark in the labels • Mark the x scale • Mark the y scale • Draw the points • Join the points with straight lines

  17. A Pie Chart Temperature (°C) 10 20 30 40 50 Total 24 1. Find the total 2. Calculate the fractions 3. Draw a circle 4. Mark off the segments 5. Make a key

  18. Averages To find the average number of bubbles … 1. Find the total number of bubbles 1. Find the total = 30 4 + 8 + 14 + 4 + 0 2. Divide the total by the number of items There are 5 items in the table 30  5 = 6 3. Don’t forget units in your answer Average = 6 bubbles/s Try this example … Click here for answer

  19. Percentages To find the percentage of bubbles at 20ºC … 1. Find the total number of bubbles 1. Find the total 4 + 8 + 14 + 4 + 2 = 32 2. Divide the number of bubbles at 20ºC by the total number 8  32 = 0.25 this is the decimal fraction 3. Multiply the decimal fraction by 100 to get the percentage 0.25 x 100 = 25% 25% of the bubbles are produced at 20ºC What percentage of bubbles are produced at 30ºC?

  20. Ratios To find the simple whole number ratio of bubbles at 10 degrees compared to bubbles at 20 degrees … 1. Write down the ratio of the numbers 10ºC : 20ºC 4 bubbles : 8 bubbles 2. Find a number that will divide into both numbers to give a whole number – in this case 2 4 bubbles  2 : 8 bubbles  2 = 2 bubbles : 4 bubbles 3. Repeat step 2 until you cannot divide again without getting a fraction 2 bubbles  2 : 4 bubbles  2 = 1 bubble : 2 bubbles

  21. Ratios To find the simple whole number ratio of bubbles at 20 degrees compared to bubbles at 30 degrees … 1. Write down the ratio of the numbers 20ºC : 30ºC 8 bubbles : 14 bubbles 2. Find a number that will divide into both numbers to give a whole number – in this case 2 8 bubbles  2 : 14 bubbles  2 = 4 bubbles : 7 bubbles 3. You cannot divide any more without getting a fraction so … the simple whole number ratio is: 4 : 7

  22. Percentage Increase • To work out a percentage increase you can use the following formula: • Example: End value – Start Value X 100 Start Value 75 – 50 X 100 50 25 1 = X 100 = X 100 = 50% 50 2

  23. Percentage Decrease • To work out a percentage increase you can use the following formula: • Example: Start value – End Value X 100 Start Value 50 – 25 X 100 50 25 1 = X 100 = X 100 = 50% 50 2

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