AS Biology Practical Tips and Skills

What are the two words you should avoid?

amount and how much

What quantitive measurements should you use instead of amount and how much?

concentration, mass, number etc

What is the goal of paper chromatography?

seperate and analyse a mixture, usually used for colour

What is the stationary phase of paper chromatography?

filter paper

What is the mobile phase / equant of paper chromatography?

solvent

What the goal of electrophoresis?

seperate RNA, DNA or protein molecules based on their size and electrical charge

How does electrophoresis work?

electrical current used to move molecules through a gel or other matrix

What is electrophoresis often used for?

haemoglobin levels, diagnosing anaemia, sickle cell

What is a control?

experiment set up without the independent variable to compare with other results

What is a control variable?

factors to keep the same to improve validity

What is a photometer?

measures brightness of light through electromagnetic radiation

What is a colorimeter?

measures intensity of colour, used to identify colour differences

What is a potometer?

used to measure rate of water uptake of a leafy shoot

What are three ways to improve reliability of an experiment?

repeats of measurements to calculate mean and identify and ignore anomalies, large sample size

What are two ways to improve validity of an experiment?

keep (named) control variables the same, standardise procedures (example)

What are two ways to increase accuracy of an experiment?

smaller intervals and example, equipment with higher resolutions e.g ruler with smaller intervals

What can food tests be used for?

detecting biological molecules present in a sample, but not how much

What does Benedicts solution test for?

reducing sugars (monosaccharides)

What is the formula for Benedicts reagent?

CuSO4

Chemically, how does the Benedicts test work?

blue Cu2+ ions reduce to form a brick red Cu2O

How can a non-reducing sugar be identified?

Must undergo acid hydrolysis to break them down into monosaccharides. Acid hydrolysis is adding dilute hydrochloric acid then neutralising with sodium hydrogen carbonate solution.

What else does the Benedicts test require?

water bath

What is the benedicts test colour change?

blue to brick red

What test tests for lipids?

emulsion test

How is an emulsion test carried out?

shake sample with ethanol until dissolved, add water, if lipids present colour change from clear to milky white emulsion

Why does an emulsion test work?

lipids are insoluble in water

What is the test for proteins?

biurets

What is biuret made out of?

sodium hydroxide and copper sulfate

What is a positive colour change for biuret test?

blue to purple

What is the test for starch?

iodine

What is the colour change for an iodine test?

orange to blue black

What is the test for Vitamin C?

DCPIP

What is the colour change for DCPIP

blue to colourless

What is catalase?

an enzyme

What does catalase do?

protects bacteria/organisms from hydrogen peroxide by converting it to water and oxygen

What is the chemical formula for the catalase reaction with hydrogen peroxide?

2H2O2 → catalase → 2H2O and O2

What will happen if catalase is very active due to an abundance of 2H2O2?

lots of oxygen produced, so bubbles

What is the positive result of a test for catalase activity?

bubbles of oxygen

Why can an experiment to find catalase action not be carried out with blood ?

blood has catalase action

What does ethanol do to catalase?

ethanol disables the ability of catalase to react with hydrogen peroxide

What does a higher ethanol concentration result in for catalase?

increases denaturation

What is the conclusion for this experiment?

as ethanol concentration increases, the number of oxygen bubbles produced decreases, indicating a lower rate of catalase activity so a lower rate of hydrogen peroxide being broken down