nutrient cycles Flashcards
Why do nutrients need to be constantly recycled?
There is no external supply entering the system.
What are detritivores?
These are organisms that feed on detritus (dead/decaying matter).
What happens when dead/decaying matter pass through the internal digestive systems of detritivores?
It is digested into smaller fragments. These smaller fragments have an increased surface area and are the passed out in the faeces. These faeces can then be further digested by the decomposers.
Examples of detritvores?
Earthworms, woodlice, - feed on dead leaves, wood etc.
What are decomposers (saprotrophs)?
Feed on DOM, including the faeces released by the detritivores.
What do decomposers do when digesting food?
They digest their food externally (extracellular digestion), by releasing enzymes onto the DOM. These enzymes break down large organic molecules into smaller ones, which the decomposer then absorbs to use for energy and growth. Through their actions, they release mineral ions and inorganic compounds/ elements back into the environment. These can then be re-used.
Examples of decomposers?
Various species of fungi and bacteria living in the soil.
What is the carbon cycle?
- Carbon is found in all organic molecules.
- It enters food chains via producers, carrying out photosythesis to convert inorganic carbon into organic molecules. the plant can use this to make all the organic molecules it needs.
- The plant may then be eaten by an animal, passing the organic carbon- containing molecules up the food chain.
- Carbon is constantly being returned to the atmosphere, in the form of CO2 by the process of respiration (this can be re-used in photosynthesis).
- When an organism dies, or sheds material (e.g. fur, feathers) they are decomposed. —–The decomposers use the organic molecules in this DOM for their own growth and also for the process of respiration - so release CO2 back to the atomsphere.
What happens if DOM do not decompose?
- Sometimes, DOM does not decompose, because the conditions are not right. An example would be peat bogs ( acidic conditions where decomposers cannot survive).
- If DOM does not decay, it can sometimes end up forming fossil fuels. Burning of these returns CO2 back to the atmosphere.
Trees and peat bogs can act as “carbon sinks”. What does this mean?
-Trees use CO2 to make sugars/organic molecules (photosynthesis), some which are used for growth.
Much of the carbon in these molecules is “locked up” until the tree dies/decomposes.
-Peat bogs are acidic and anaerobic, so decomposers cannot survive there. Any DOM remains as it is, the CO2 is not released by decomposer respiration.
Any activity that aerates the soil (helps to increase O2 conc in the soil) will promote the activity of decomposers (aerobic), which will respire at a faster rate, so DOM will be broken down faster, and carbon recycled faster. Examples of activities that promote this?
Ploughing, digging the soil, good drainage.
Why are atmospheric CO2 levels higher at night than during the daytime?
At night, there is no photosynthesis occurring, so plants are not removing CO2 from the atmosphere, as they do in the daytime, but they are still respiring - releasing CO2.
Why are atmospheric CO2 levels higher on a day in winter compared to a summer day?
The rate of photosynthesis is much lower in the winter than the summer (lower light intensities, lower temperatures), so less CO2 is used up in plants.
How have global atmospheric carbon dioxide levels increased significantly, over the past 200 years?
