B17 Organising an ecosystem

Question 1

What is a producer?

Answer 1

Plants that begin food chains by making energy from carbon dioxide and water.

Question 2

What is a food chain?

Answer 2

A sequence (usually shown as a diagram) of feeding relationships between organisms, showing which organisms eat what and the movement of energy through trophic levels.

Question 3

What are the levels of consumers?

Answer 3

All animals above the producer are called consumers. The first is the
primary consumer
, the next is the secondary consumer. Animals that hunt and kill others are called predators, and those that are hunted and killed are called
prey. The top animal in the feeding relationship is called the apex predator.

Question 4

What are decomposers?

Answer 4

Decomposers
are bacteria and fungi, which break down dead organisms in a process called decomposition or rotting. They do this by releasing
enzymes onto the dead matter and afterwards, consume the broken down substances. They form a vital role in the recycling of matter. When organisms die and
decompose plants absorb the broken down nutrients through their roots.

Question 5

What are the stages of the carbon cycle?

Answer 5

Stage1: Carbon enters the atmosphere as carbon dioxide from respiration and combustion.
Stage 2:
Carbon dioxide is absorbed by producers to make carbohydrates in photosynthesis.
Stage 3:
Animals feed on plants, passing the carbon compounds along the food chain. Most carbon they consume is exhaled as carbon dioxide during respiration. The animals and plants eventually die.
Stage 4:
Dead organisms are eaten by decomposers and carbon in their bodies is returned to the atmosphere as carbon dioxide. In some conditions decomposition is blocked. The plant and animal material may then be available as fossil fuel in the future for combustion.

Question 6

What is the rate of decay?

Answer 6

The rate of
decay
is the speed at which dead matter is broken down by
decomposers
. The rate can be estimated by measuring changes in pH, (for example in milk), change in mass (decaying fruit and vegetables) or change in temperature (grass cuttings). Rates of decay are affected by a number of key factors.

Question 7

What key factors affect rate of decay?

Answer 7

Temperature
At colder temperatures decomposing organisms will be less active, thus the rate of decomposition remains low. This is why we keep food in a fridge. As the temperature increases, decomposers become more active and the rate increases. At extremely high temperatures decomposers will be killed and decomposition will stop.

Water
With little or no water there is less decomposition because decomposers cannot survive. As the volume of available water increases, the rate of decomposition also increases. Many decomposers secrete enzymes onto decaying matter and then absorb any dissolved molecules. Without water these reactions cannot occur.

Oxygen
Similar to water, decomposers need oxygen to survive and without it there is little or no decomposition. Oxygen is needed for many decomposers to respire, to enable them to grow and multiply. This is why we often seal food in bags or cling film before putting it in the fridge. As the volume of available oxygen increases, the rate of decomposition also increases. Some decomposers can survive without oxygen. We use these in biogas generators.

Question 8

How is compost useful?

Answer 8

Gardeners and farmers improve the quality of their soil by adding
compost
or
manure
. Compost is made from dead plants and manure is the waste from animals. Once spread on the soil, compost and manure are broken down into minerals by decomposing bacteria and fungi, as well as by other organisms, such as worms. Adding compost or manure helps recycle minerals so that they are absorbed by new plants and used in growth. Compost and manure also improve the quality of soil by increasing aeration and water retention.

Farmers can also use inorganic fertilisers on soil to overcome specific mineral deficiencies, although this does not require the involvement of decomposers.

One key element which is recycled is nitrogen. This element is needed by plants to make proteins in order to grow and repair themselves. Plants cannot absorb nitrogen gas, and need it to be provided as nitrate ions. These nitrate ions are produced as a result of a long series of reactions by decomposers breaking down proteins and urea in the soil. The nutrients and minerals are then passed along the
food chain
as the organisms are consumed by others.