3.22 Decay

Question 1

Describe the process of decomposition

Answer 1

Decomposition, often called “rotting”, is the process by which dead organic matter is broken down into simpler organic or inorganic substances, such as carbon dioxide, water, simple sugars, and minerals.

Question 2

What are detritus feeders (detritivores)?

Answer 2

Small animals like worms and woodlice that feed on dead organic matter.

Question 3

What are decomposers?

Answer 3

Microorganisms, such as bacteria or fungi

Question 4

Which 3 environmental factors affect the rate of decomposition?

Answer 4

• Oxygen availability
• Temperature
• Water content

Question 5

How does oxygen availability affect the rate of decomposition?

Answer 5

Many decomposers need oxygen for aerobic respiration so the rate of decomposition increases where there is plenty of oxygen available. When there are low oxygen levels, the rate of decomposition is slower. When there are low oxygen levels, the rate of decomposition is slower. Some decomposers can respire anaerobically but this transfers less energy, so these decomposers work more slowly.

Question 6

How does temperature affect the rate of decomposition?

Answer 6

Most decomposers work best in warm conditions - the rate of decomposition is highest at around 50 degrees. This is because decomposers contain enzymes, which digest the dead/waste material. The rate of enzyme-controlled reactions varies with temperature - at lower temperatures the rate of reaction is slower and above certain temperatures the enzymes become denatured and the reaction stops.

Question 7

How does water content affect the rate of decomposition?

Answer 7

Decomposers need water to survive, so the rate of decomposition increases in moist conditions. However, waterlogged soils don’t contain much oxygen as water fills the air gaps within the soil, so there will be less oxygn(which many decomposers need to respire) so the rate decreases if there is too much water.

Question 8

How do decomposers in landfill sites contribute to global warming?

Answer 8

• Greenhouse gases such as methane and carbon dioxide naturally trap energy in the atmosphere - this helps to keep the Earth warm. But increasing levels of greenhouse gases are causing the global temperature to rise. This is global warming.
• Landfill sites tend to be low in oxygen - this means there are lots of decomposers respiring anaerobically.
• Anaerobic respiration by decomposers produces methane, which has a much greater greenhouse effect than the carbon dioxide produced during aerobic decomposition. So landfill sites contribute more to global warming than natural decomposition in ecosystems.