Decay

The Rate of Decay of Biological Material

Biological material in the form of waste products or dead organisms decays as a result of the activity of decomposers. Decomposers are organisms such as worms (which eat the decaying matter) or microorganisms (which use enzymes to break down the organic matter). The rate of the decay process depends on:

Temperature

High temperature is usually best.

Moisture availability

High moisture availability is usually best.

Oxygen availability

High oxygen availability is usually best.

Practical - Temperature and Milk Decay

Investigate the effect of temperature on the rate of decay of fresh milk by measuring pH change.

Outline

The effect of temperature on the rate of decay can be observed using milk.
As milk takes a long time to decay, lipase and sodium carbonate are added to speed up the decay.
As milk decays, its pH reduces. This can be observed with an indicator called Cresol red.

Method

Use a water bath to heat all of the components to a given temperature.
Mix the milk, sodium carbonate and Cresol red. The resulting solution should be purple.
Add lipase to the solution and start timing.
When the solution turns yellow, stop timing.
Repeat using different temperatures.

Independent and dependent variable

The independent variable is the temperature.
The dependent variable is the time taken for the solution to turn yellow.

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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