Practical Work & How Science Works (AO3) Flashcards by Tytus Murphy

RP7 Chromatography

Explain why the student marked the origin using a pencil rather than using ink.

(With pencil) origin/line in same position
OR
(With ink) origin/line in different position
OR
(With pencil) origin/line still visible;

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RP7 Chromatography

Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin (2 marks).

Level of solvent below origin/line;
Remove/stop before (solvent) reaches top/end;

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RP7 Chromatography

The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves.

(Absorb) different/more wavelengths (of light) for photosynthesis;

Accept light-dependent reaction / photophosphorylation /photoionisation for photosynthesis.

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RP7 Chromatography

Factors which determine the distance travelled by the pigments during chromatography

Solubility in the running solvent

Size of the pigment

Smaller mass + increased solubility = closer to solvent front

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RP7 Chromatography

Describe how to separate the photosynthetic pigments by chromatography? (4 marks)

1. Draw line/origin on (chromatography) paper
(using ruler and pencil);

2. (Use pipette/tubing/dropper to) add
chlorophyll/solution to origin/line;

3. Add solvent below line/origin;

4. Remove/stop (from glassware) before solvent
reaches end (of chromatography paper)
OR
Mark (position) where solvent reaches/front;

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RP7 Chromatography

TRUE or FALSE:

The Rf value is specific to a photosynthetic pigment

TRUE

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RP7 Chromatography

TRUE or FALSE:

Changing the running solvent will NOT affect the calculated Rf value

FALSE

Rf values depend on the running solvent used

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RP7 Chromatography

Why calculate the Rf value?

Allows comparisons ;

Determines which pigments are present in a photosynthesising organism;

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RP7 Chromatography

Why is the Rf value always between 0-1?

Rf = distance moved by pigment / distance moved by solvent front ;

As solvent front distance is always larger than the pigment distance, Rf value must be below 1.

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RP7 Chromatography

Pigment E has a low …………

Solubility
(in the running solvent used)

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RP7 Chromatography

Pigment E has a large …………

Mass / size

(therefore does not move far from the origin)

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How Science Works

Correlation does not mean _____________

causation

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How Science Works

Draw out a linear relationship

Look for a straight line / constant gradient

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How Science Works

Linear or non-linear:

Non linear

No straight line and the gradient changes

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How Science Works

Linear or non-linear:

There is a proportional Y increase as X increases

Linear

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How Science Works

When to use a t test?

When comparing the differences between two means (e.g. control vs. treatment group)

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How Science Works

Name of statistical test used to assess the strength of relationship between two continuous variables.

Correlation coefficient

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How Science Works

A t-test produced a p value of 0.02.

What can you conclude?

Significant difference between means;

LESS than 5% probability the DIFFERENCE is due to chance

OR 2% probability the DIFFERENCE is due to chance

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How Science Works

A t-test produced a p value > 0.07

What can you conclude?

NO Significant difference between means;

MORE than 5% probability the DIFFERENCE is due to chance

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How Science Works

A t-test produced a p value = 0.001.

What can you conclude?

HIGHLY Significant difference between means;

LESS than 5% probability the DIFFERENCE is due to chance

OR 0.01% probability the DIFFERENCE is due to chance

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How Science Works

Explain why a log scale is used to record the number of cells.

Large range/difference/increase in numbers;

How Science Works (AO3)

Why should a sample be large?

To ensure it is representative;

To calculate a mean so results are more reliable;

Identify anomolus results;

How Science Works (AO3)

Why should sampling be random?

To reduce bias

This also make the results / experiment more reliable

How science works (AO3)

Suggest why the scientist made repeat measurements.

Increases reliability (of results)

Anomalous results can be identified;

# **How science works (AO3)** Give two reasons why it was important that the student counted the number of stomata in several parts of each piece of leaf tissue.

**1.** Distribution may not be uniform OR So it is a representative sample; **2.** To obtain a (reliable) mean;

# **RP8 Dehydrogenase** Artificial electron acceptor examples

DCPIP Methylene blue

# **RP8 Dehydrogenase** In RP8, what is the source of the electrons?

Plant tissue e.g. spinach, which contains chlorophyll

# **RP8 Dehydrogenase** ________________ enzymes are required for the reduction of NADP to NADPH

Dehydrogenase

# **RP8 Dehydrogenase** DCPIP solution is blue when oxidised and colourless when ___________

reduced

# **RP8 Dehydrogenase** Tube 1 contained 1 cm^3 of solution without chloroplasts and 9 cm^3 of DCPIP solution in light. Why was this tube set up?

1. To show light does not affect DCPIP; 2. To show chloroplasts are required (are the source of electrons to reduce DCPIP);

# **RP8 Dehydrogenase** A tube contained 1 cm^3 of chloroplast suspension and 9 cm3 of DCPIP solution in light. After 30 minutes DCPIP turned from blue to colourless. Explain why (2 marks).

**1.** Reduction of DCPIP by electrons; **2.** (From) chlorophyll / light dependent reaction;

# **RP8 Dehydrogenase** Explain how chemicals which inhibit the decolourisation of DCPIP could slow the growth of weeds (*3 marks*)

1. **Less** / no ATP produced; 2. **Less** / no reduced NADP produced; 3. **Less** / no GP reduced to triose phosphate;

# **RP8 Dehydrogenase** The solution that the student used to produce the chloroplast suspension had the same water potential as the chloroplasts. Explain why it was important that these water potentials were the same (*2 marks*).

**1.** Osmosis does not occur; **2.** Chloroplast / organelle does not burst / lyse / shrivel / shrink;

# **RP9 Respiration in Yeast**

Concentration/mass of yeast Concentration/mass of glucose/sugar (solution/s) Concentration of oxygen (in solution) Volume of yeast Volume of glucose/sugar (solution/s) pH (of glucose/sugar solution/s) Species/type of yeast Size/diameter/volume of test tubes

# **RP9 Respiration in Yeast**

(So the) oxygen is used/absorbed/respired;

# **RP9 Respiration in Yeast** Figure 2 shows a typical population growth curve for yeast under laboratory conditions. Many yeast cells die during the death phase. Suggest one reason why.

Decrease/no glucose/substrate OR Increase in ethanol/carbon dioxide/acidity;

# **How Science Works** Conclusion with a correlation coefficient of r = **+**0.72

Strong positive correlation; (between named variables) e.g. as x increases, there is an increase in y.

# **How Science Works** Conclusion with a correlation coefficient of r = **-**0.22

(weak) negative correlation; (between named variables) e.g. as x increases, there is a decrease in y.

# **How Science Works** Conclusion with a correlation coefficient of r = **-**0.01

no correlation (between named variables)

# **How Science Works** A correlation coefficient produced a p value > 0.2. What can you conclude?

**NO Significant correlation** **MORE** than 5% probability the **CORRELATION** is due to chance

# **How Science Works** A correlation coefficient produced a p value < 0.045. What can you conclude?

**Significant correlation** **LESS** than 5% probability the **CORRELATION** is due to chance

# **How Science Works** A correlation coefficient produced a p value < 0.001. What can you conclude?

**Highly significant correlation** **LESS** than 5% probability the **CORRELATION** is due to chance OR **LESS** than 0.1% probability the **CORRELATION** is due to chance

# **How science works (AO3)** Correlation does not mean _____________

causation

# **How science works (AO3)** Researchers carried a correlation coefficient to assess the relationship between the concentration of carbon monoxide and the number of asthma attacks. They found **R** = 0.50, with **P** <0.0001 Explain the meaning of the result of their calculations.

**1.** Positive correlation (R = 0.50) - as carbon monoxide increases, the number of asthma attacks increases; **2.** P value of <0.0001 shows a highly significant correlation; **3.** Less than a 5% probability this correlation is due to chance;

# **How Science Works (Maths)** Describe how to determine the median

Put the values for the dependent variable into rank/order (i.e. smallest to largest) **and** then identify the middle value

# **Inheritance (AO1)** Which statistical test could the scientist use to determine whether his observed results were significantly different from the expected results? Give the reason for your choice of statistical test.

1. Chi squared test; 2. Categorical data.

# **Inheritance (Maths)** What do the compontents of the chi squared equation represent?

# **Inheritance (Maths)**

# **Inheritance (Maths)** When using the chi squared test, how do you calculate the degrees of freedom?

n - 1 Where 'n' represents the number of categories / groups / phenotypes

# **Inheritance (Maths)** There are 3 possible phenotypes with expected and observed results. Use this information to determine the critical value from the table below.

2 degrees of freedom; Critical value = 5.99 *(when P = 0.05)*

# **Inheritance (AO3)** Following a genetic cross involving 4 possible phenotypes, researchers obtained a chi squared value of 2.32. Use the table below to state what you can conclude from this data.

The chi squared value is **SMALLER** than the critical value of 7.82 *(when P = 0.05)*; There is **NO SIGNIFICANT DIFFERENCE** *(between the observed and expected values)* There is **more** than a 5% probability **the differences** are due to chance.

# **Inheritance (AO3)** Following a genetic cross involving 2 possible phenotypes, researchers obtained a chi squared value of 4.07. Use the table below to state what you can conclude from this data.

The chi squared value is **LARGER** than the critical value of 3.84 *(when P = 0.05)*; There is a **SIGNIFICANT DIFFERENCE** *(between the observed and expected values)*; There is **less** than a 5% probability **the differences** are due to chance;