Osmosis in PotatoesIB Biology

Topic 2Internal Assessment

Now your turn!!

• Lesson 1:-pre-lab-carrying out a standardised practical using handouts I will give you-familiarising yourself with working in a lab and thinking about how you could adapt the experiment for an Internal Assessment

• Lesson 2:-Using your Design Lab Training Sheet you will work in teams to design a practical investigating an aspect of osmosis.

• Lesson 3: -You will carry out the practical and collect data as a team.

• Lesson 4 + 5:-I will show you how to process your data with statistics!-specifically using Excel to calculate means, standard deviations and draw graphs

• Lesson 6:-I will guide you on how to write a conclusion and evaluation

• Lesson 7:-Your practical will be handed in-written up individually and in the correct format-self assessment should be complete as well

Pre-lab3 cm

3 cm

Writing A Statement of the Problem for the Experiment

It should state: “The Effect of the Independent Variable on the Dependent Variable”.

A good statement of the problem for “Rate of photosynthesis” would be

The effect of light intensity on the rate of photosynthesis

What should it state?

More about our variables:

The independent variable is the variable that is purposely changed. It is the manipulated variable.

The dependent variable changes in response to the independent variable. It is the responding variable.

What is the “photosynthesis” independent variable?Light intensity measured in LuxWhat is the dependent variable?

Volume of O2 produced per minute

Title for the photosynthesis experiment

The effect of light intensity on the rate of photosynthesis of

Elodea

Another Look at Our HypothesisINDEPENDENT VARIABLE

If the light intensity increases,

DEPENDENT VARIABLE

then the rate of photosynthesis will increase.

To make this IB worthy you MUST:

a)Include a sketch graph of your predicted results

b) Give SCIENTIFIC reasoning as to why you predict this

Controls in an ExperimentFactors that are kept the same and not

allowed to changeWhat should be kept constant in the experiment?

CONSTANTS

Type of plant

C02 concentration

Time the experiment runs for

Time intervals at which the DV is measured

Wattage of light bulb

Colour of bulb

Temperature of experiment

Time of day

Values of the Independent VariableHow many different values of the

independent variable should we test?

Enough to clearly illustrate a trend in the data –always use the 5x5 rule for

continuous data

e.g. 10cm, 20cm, 30cm, 40cm, 50cm

Repeated TrialsHow many repeated trials are needed in the experiment

At least 5, then calculate n mean value for each level of the independent variable

(this will also give enough data to calculate standard deviation)

Drawing of Experiment

Now complete your Design Lab sheet as a team!

Carrying out your practical…

Qualitative Observations (must have these or zero for DCP1!!)

•It seemed as it the rate of oxygen production started slowly at first but then speeded up

• The bubbles of oxygen were all different sizes

Quantitative: Sample Data TableTitle: The effect of changing light intensity on the rate of

photosynthesis in ElodeaDistance of light

source

(±1cm)

Mean Vol of 02 produced in 5 min (±0.01ml)

Vol of 02 produced in 5 min (±0.01ml)

TRIALS

1 2 310

20

30

40

50

3.00 5.00 4.00 4.00

4.00 5.00 6. 00 5.00

6. 00 7.00 5.00 6.00

7.00 8.00 6. 00 7.00

9.00 7. 00 8. 00 8.00

Data Processing for Internal Assessment AND Topic 1

Data Processing• You need to:

1. Calculate percentage change for EACH trial of EACH molarity of solution –(why % change and not just change in mass?)

2. Calculate the mean percentage change for EACH molarity of solution –(why % change and not just change in mass?)

3. Calculate the error for EACH mean

4. Plot a graph comparing percentage changes

Two classes took a recent quiz.

There were 10 students in each class

Each class had an average score of 81.5

Since the averages are the same, can we assume that the students in both classes all did pretty much the same on the exam?

The answer is… No.

The average (mean) does not tell us anything about the distribution or variation in the grades.

Here are scatter diagrams of the grades in each class:

Mean

So, we need to come up with some way of

measuring not just the average, but also the

spread of the distribution of our data.

Why not just give an average and the range of

data (the highest and lowest values) to describe

the distribution of the data?

Well, for example, lets say from a set of data, the average is 17.95 and the range is 23.

But what if the data looked like this:

Here is the average

And here is the range

But really, most of the numbers are in this area, and are not evenly distributed throughout the range.

The Standard Deviation is a number that measures

how far away each number in a set of data is from

their mean.

If the Standard Deviation is large, it means the numbers are spread

out from their mean.

If the Standard Deviation is small, it means the numbers are

close to their mean.small,

large,

Here are the scores on the biology quiz for Team A:

72768080818384858589

Average: 81.5

The Standard Deviation measures how far away each number in a set of data is from their mean.

For example, start with the lowest score, 72. How far away is 72 from the mean of 81.5?

72 - 81.5 = - 9.5

- 9.5

- 9.5

Or, start with the lowest score, 89. How far away is 89 from the mean of 81.5?

89 - 81.5 = 7.5

7.5

Now, lets compare the two classes again

Team A Team B

Average on the Quiz

Standard Deviation

81.5 81.5

4.88 15.91

Now...how do you do it the easy way?

Concluding and Evaluating

•ConclusionThis is the section where you draw conclusions about the experiment as it relates to your aim and hypothesis. Calculated results should be compared to values from the literature (i.e. accepted values from professional laboratories) where possible.

This section should include: • Conclusion based on your Aim or Hypothesis. (using appropriate

language)• States the quantitative or qualitative relationship• Correctly interprets the graph of the data• Includes relevant calculated values to support conclusion• Includes some elaboration based on the science being learned

Discussion of errors and limitations to the experiment

• Must comment on the “quality” of the results, do they make sense?• Identifies anomalous results where appropriate (use your SDs to help you do

this!)• Prioritizes errors and suggests where they came from.

• Utilizes the ideas of “systematic” and “random” errors in the discussion• Indicate what effect the error(s) would have on the results• Human errors should not be the main source of errors!

• Suggestions for improvements• Identifies weaknesses in the experiment and suggests realistic suggestions for

improvement• Improvements should help to improve the errors previously identified

How to write an effective conclusion

Also known as putting it all together

What is a conclusion?

• A conclusion is a summary of the experiment.

• It is putting the hypothesis together with the data and coming up with a conclusion or ending thought.

• It is a written answer to the original question.

So where to start…

• Every conclusion begins with a topic sentence.

• In a conclusion, the topic sentence is the restatement of the problem/question.

Can your group state a hypothesis for the research question below?

• The effect of different temperatures on the activity of an enzyme?

Can you write a conclusion for the data below?

0 10 20 30 40 50 60 70 80 900

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Rate of reaction of an enzyme at different temperatures

Temperature (±0.1°C)

Rate

of r

eacti

on

Keep your group’s conclusion close to hand

• We will now go through step by step of the format and information that should have been included….

Our conclusion outline

1. Restate the Problem

This experiment was investigating the affect of different temperatures on enzyme activity.

Our conclusion outline

1. Restate the problem2. Restate your hypothesis

(It was predicted that…)

It was predicted that as the temperature increased from 0°C, the rate of enzyme reaction will increased up until the optimum temperature for this enzyme.

This is the temperature at which the enzyme will be working with maximum efficiency. After this point the rate of reaction will begin to decrease as the enzyme denatures.

So was your hypothesis right, wrong or indifferent?

3. Accept or reject your hypothesisDoes the data support the hypothesis?

If it does-we accept the hypothesisIf it doesn’t-we reject the hypothesis

My processed data supports my hypothesis

Now provide evidence

4. Provide actual data in sentence form that backs up your previous statement.

• What type of relationship was there, if any?– How did the independent variable effect the

dependent variable?• Were there any trends? • changes; (increases, decreases in data)• patterns (repeated data that is similar)

Our conclusion outlineAs the temperature increased from 0°C to 25°C, the rate of reaction also increased until at 25°C where the rate of reaction reached it’s maximum of 1.5 units.

After this temperature the rate of reaction dropped to 0.5 units at 45°C. As the temperature was increased to 65°C the rate of reaction fell to 0 units and stayed at 0 units at 85°C as well.

Next5. Justify your data with scientific theory

As the temperature increases the molecules have greater kinetic energy. This increases the number of collisions thereby increasing the rate of reaction.

As the temperature continues increasing the rate of reaction decreases after the optimum temperature.

This is because the enzyme, which is a protein molecule denatures. The specific 3D structure of the active site is irreversibly changed so it can no longer form an enzyme-substrate complex.

Our conclusion outline

1. Restate the problem2. Restate your hypothesis

(It was predicted that…)3. Accept or reject your hypothesis4. Provide actual data in sentence form that

backs up your previous statement.5. Justify your data with scientific theory

Yeah! We’re almost there….

6. Concluding sentence

• This sentence should– Begin with a transition word

• To sum up• In conclusion• Therefore, it can be said that

– Rephrase the original question or problem– Explain the importance of carrying out the

experiment

Our conclusion outline

In conclusion, it can be stated that different temperatures do have an affect on enzyme activity.

Therefore, it is possible to deduce the optimum conditions for an enzyme to ensure maximum efficiency of this particular enzyme.

6 points to scientific success!

1. Restate the problem2. Restate your hypothesis 3. Accept or reject your hypothesis4. Provide actual data in sentence form that

backs up your previous statement.5. Justify your data with scientific theory6. Concluding sentence that justifies the

experiment

Conclusion

This experiment was investigating the affect of different temperatures on enzyme activity.

It was predicted that as the temperature increased from 0°C, the rate of enzyme reaction will increased up until the optimum temperature for this enzyme. This is the temperature at which the enzyme will be working with maximum efficiency. After this point the rate of reaction will begin to decrease as the enzyme denatures.

My processed data supports my hypothesis. As the temperature increased from 0°C to 25°C, the rate of reaction also increased until at 25°C where the rate of reaction reached it’s maximum of 1.5 units. After this temperature the rate of reaction dropped to 0.5 units at 45°C. As the temperature was increased to 65°C the rate of reaction fell to 0 units and stayed at 0 units at 85°C as well.

As the temperature increases the molecules have greater kinetic energy. This increases the number of collisions thereby increasing the rate of reaction. As the temperature continues increasing the rate of reaction decreases after the optimum temperature. This is because the enzyme, which is a protein molecule denatures. The specific 3D structure of the active site is irreversibly changed so it can no longer form an enzyme-substrate complex.

In conclusion, it can be stated that different temperatures do have an affect on enzyme activity. Therefore, it is possible to deduce the optimum conditions for an enzyme to ensure maximum efficiency of this particular enzyme.

EvaluationTo evaluate your science experiments simply answer the following questions:

• How could you have improved the way you did your practical?

• What improvements would you make to your method if you did it again? Why?

• Did the data you collected give you enough information? Why? • What could you do to improve the reliability of your data?

Evaluations : What to include... Examples...

1) Write down how well you think the experiment went and why.

2) "The experiment went quite well but my human error contributed to unreliable results. This is because….".

3) Point out any odd results that you had

• "Looking at the graph/standard deviations anomalous results can be identified. These are….”

4) Explain why IN DETAIL, you may have some odd results / what problems you had with the experiment.

• Include MINIMUM THREE and it MUST refer back to the method

• "One of the reasons that these large standard deviations/anomalous results were obtained could be due to not getting the bung into the test tube quick enough, which meant that some of the gas would have escaped."

5) Explain how you could improve the experiment if you had to do it again IN DETAIL. Suggest AT LEAST THREE things. Include a diagram and explain why.

• "The experiment could be repeated using a data logger to measure the pH, because it was hard to tell if the solution was pH 6 or 7".

6) Explain what further experiments you could do in the future, if you had the time.

• "If this investigation could be extended, the effect of temperature on the rate of reaction would compliment the data obtained in this experiment.. This could be done by…"