[ecology] decomposition

[ https://www.bbc.co.uk/bitesize/guides/zy7gw6f/revision/1 ]

Decomposition

The process of breaking down material to release nutrients back into the soil.

Decay

When plants wither and die.

Decomposers

Organisms which break down dead plant and animal matter by secreting enzymes into the environment.

Rate of Decay

The speed at which dead matter is broken down by decomposers; can be estimated by measuring changes in pH, (for example in milk), change in mass (decaying fruit) or change in temperature (grass cuttings).

Factors Affecting the Rate of Decay:

• temperature

• presence of water

• presence of oxygen

Temperature

• colder temperatures → decomposing organisms will be less active; rate of decomposition remains low

• moderately warm temperatures → decomposers become more active and rate of decay increases

• higher temperatures → decomposers will be killed and decomposition will stop

Water

• no water = no decomposition as decomposers cannot survive

• many decomposers secrete enzymes onto decaying matter and then absorb any dissolved molecules; without water, these reactions cannot occur

Oxygen

• no oxygen = no decomposition as decomposers cannot survive

• many decomposers need to respire aerobically to enable them to grow and multiply

Compost

Decayed organic matter which can be used as a plant fertiliser as decomposers break them down to recycle minerals, increase aeration, and improve water retention.

Manure

Animal dung (solid waste) used as fertiliser.

Anaerobic Decay

Occurs when bacteria and fungi break down dead matter without oxygen. This can happen water logged soil, lakes, marshes, and when people overwater their houseplants and flood the roots.

Biogas

A type of biofuel (methane) derived from anaerobic decay or decomposition.

Biogas Generators

Large vessels where animal waste or specially grown crops, like maize, are anaerobically digested.

Milk Decaying

• pH of 6.5

• when milk decays, bacteria produce an enzyme that breaks lactose down and produces lactic acid

• lactic acid has an acidic pH, so when milk decays, it becomes more acidic

• lipids in milk will be broken down into fatty acids

pH Indicators:

• cresol red indicator

• phenolphthalein indicator

An alkali, like sodium carbonate, needs to be added to ensure that there is a colour change.

Cresol Red Indicator

• yellow in acidic conditions

• purple in alkali conditions

Phenolphthalein Indicator

• pink in alkaline conditions

• colourless below pH 8.3

Required Practical 10

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

Step 1 of Required Practical 10

Place 20 cm³ of fresh milk into three beakers.

Step 2 of Required Practical 10

Decide the three temperatures you will investigate. Write these onto the sides of the beakers. They may be 5, 20 and 35°C.

Step 3 of Required Practical 10

Use universal indicator paper or solution to determine the pH of the milk in the three beakers.

Step 4 of Required Practical 10

Cover each beaker in cling film and incubate at the appropriate temperature.

Step 5 of Required Practical 10

Use universal indicator paper or solution to determine the pH of the milk in the three beakers after 24, 48 and 72 hours.

Rate of Change Equation

rate of change = change in value / change in time