A level to GCSE transition

When is a measurement valid?

When it measures what it is supposed to be measuring.

When is a result accurate?

When it is close to the true value.

What are precise results?

When repeat measurements are consistent and agree closely with each other.

What is repeatability?

How precise repeated measurements are when they are taken by the same person, using the same equipment, under the same conditions.

What is reproducibility?

How precise repeated measurements are when they are taken by different people, using different equipment.

What is the uncertainty of a measurement?

The interval within which the true value is expected to lie.

Define measurement error.

The difference between a measured value and the true value.

What type of error is caused by results varying around the true value in an unpredictable way?

Random error.

What is a systematic error?

A consistent difference between the measured values and true values.

What does zero error mean?

A measuring instrument gives a false reading when the true value should be zero.

Which variable is changed or selected by the investigator?

The independent variable.

What is a dependent variable?

A variable that is measured every time the independent variable is changed.

Define a fair test.

A test in which only the independent variable is allowed to affect the dependent variable.

What are control variables?

Variables that should be kept constant to avoid them affecting the dependent variable.

What are monomers?

Smaller units from which larger molecules are made.

What are polymers?

Molecules made from a large number of monomers joined together.

What is a condensation reaction?

A reaction that joins two molecules together to form a chemical bond whilst eliminating a molecule of water.

What is a hydrolysis reaction?

A reaction that breaks a chemical bond between two molecules and involves the use of a water molecule.

What is a monosaccharide?

A monomer from which larger carbohydrates are made.

How is a glycosidic bond formed?

A condensation reaction between two monosaccharides.

Name the three main examples of polysaccharides.

Glycogen, starch and cellulose.

Describe Benedict's test for reducing sugars.

Gently heat a solution of a food sample with an equal volume of Benedict's solution for five minutes. The solution turns orange/brown if reducing sugar is present.

Name the two main groups of lipids (fats and oils).

Phospholipids and triglycerides.

Give four roles of lipids.

Source of energy, waterproofing, insulation and protection.

What is an ester bond?

A bond formed by a condensation reaction between glycerol and a fatty acid.

Describe the emulsion test for lipids.

Mix the sample with ethanol in a clean test tube and shake. Add water and shake again. A cloudy white colour indicates that lipid is present.

What are the monomers that make up proteins?

Amino acids.

What is the general structure of an amino acid?

A central carbon atom bonded to an amino group (NH₂), a carboxyl group (COOH), a hydrogen atom and an R group.

How is a peptide bond formed?

A condensation reaction between two amino acids.

What is a polypeptide?

Many amino acids joined together.

Describe the Biuret test for proteins.

Mix the sample with sodium hydroxide solution at room temperature, add very dilute copper(II) sulfate solution and mix gently. A purple colour indicates that peptide bonds are present.

How does an enzyme affect a reaction?

It lowers the activation energy.

Give five factors which can affect enzyme action.

Temperature, pH, enzyme concentration, substrate concentration and inhibitor concentration.

What is a competitive inhibitor?

A molecule with a similar shape to the substrate, allowing it to occupy the active site of the enzyme.

What is a non-competitive inhibitor?

A molecule that changes the shape of the enzyme by binding somewhere other than the active site.

What multiplication factor does the prefix giga (G) represent?

10⁹

What multiplication factor does the prefix mega (M) represent?

10⁶

What multiplication factor does the prefix kilo (k) represent?

10³

What multiplication factor does the prefix centi (c) represent?

10⁻²

What multiplication factor does the prefix milli (m) represent?

10⁻³

What multiplication factor does the prefix micro (μ) represent?

10⁻⁶

What multiplication factor does the prefix nano (n) represent?

10⁻⁹