Osmosis & Food Tests

Test yourself

Investigating Osmosis

This experiment shows the effect of water concentration on osmosis.

Measure change in mass

Cut discs of raw potato and measure their mass.
Put discs in different concentrations of sugar or salt solution.
After 30 minutes, measure the mass of each disc again.

Calculate percentage change in mass

Subtract the final mass from the initial mass of each disc.
Divide this number by the initial mass and then multiply by 100 to give a percentage change in mass.
The concentration in which the potato's mass changed the least is closest to the water concentration of the potato (because the least water has moved into or out of the potato by osmosis).

Testing for Carbohydrates, Lipids and Proteins

Reagents can be used to test for the presence of various food substances. The first step is to grind up the food and add distilled water to dissolve some of the food. You can then test for the food substances:

Starch

To test for starch, add iodine solution.
It will turn blue-black if starch is present.

Sugar

To test for sugar, add Benedict’s reagent and heat for about two minutes.
It will turn any of green, yellow or red if sugar is present.
The colour depends on the concentration.

Proteins

To test for proteins, add Biuret solution.
It will turn mauve or purple if proteins are present.

Lipids

To test for lipids, add Sudan III.
If lipids are present, a red-stained oil layer will float on the water surface.

1Biology

1.1Practicals

1.1.1Microscope & Bacteria

1.1.2Bacteria

1.1.3Osmosis Tests

1.1.4Osmosis & Food Tests

1.1.5Enzymes

1.1.6Enzymes 2

1.1.7Photosynthesis & Plant Responses

1.1.8Photosynthesis Experiments

1.1.9Reaction Time

1.1.10Quadrats

1.1.11Decay

2Chemistry

2.1Practicals

2.1.1Salts

2.1.2Neutralisation

2.1.3Titration

2.1.4Electrolysis

2.1.5Electrolysis 2

2.1.6Rate of Reaction

2.1.7Rate of Reaction 2

2.1.8Chromatography

2.1.9Identifying Gases

2.1.10Identifying Gases 2

2.1.11Identifying Ions

2.1.12Carbonates, Halides & Sulfates

2.1.13Flame Emission Spectroscopy

2.1.14Water Purification

2.1.15Water Purification 2

3Physics

3.1Practicals

3.1.1Specific Heat Capacity

3.1.2Thermal Capacity & Insulation

3.1.3Latent Heat

3.1.4Resistance & Current

3.1.5Resistance & Current 2

3.1.6Density

3.1.7Density 2

3.1.8Force & Extension - Springs

3.1.9Waves - Ripple Tank

3.1.10Light

3.1.11Light Reflection & Refraction

3.1.12Radiation

3.1.13Radiation 2

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