Recycling within ecosystems 23.3 Flashcards
What is decomposition?
A chemical process in which a compound in dead matter that cannot be used directly is broken down into smaller molecules which can be used and returned to the environment. Organic compounds are turned into inorganic ones.
What are decomposers?
Decomposers are organisms like bacteria and fungi that feed on dead organisms and break them down from organic compounds into nutrients which can then be used by producers to grow.
What are saprotrophs?
Saprotrophs are organisms that get their energy from eating dead or waste organic material.
How do decomposers work?
They perform external digestion by releasing enzymes onto dead organisms and break down their complex organic molecules into simple soluble molecules. They then absorb these and release the inorganic compounds back into the environment.
How do detritivores work?
Detritivores speed up the decay process by breaking down the decaying matter into smaller pieces so that the surface area is bigger for decomposers to work on.
Give some examples of detritivores
Woodlice and worms
Why is nitrogen a key element?
Nitrogen is used in making amino acids so therefore proteins. It is used by both plants and animals. Animals get their nitrogen from eating food, but plants have to absorb it from their environment.
Can plants absorb nitrogen?
Plants cannot absorb N2 as it is a gas in the air, however, when nitrogen is combined with oxygen or hydrogen, it can be absorbed by plants. This relies on bacteria
What compound containing nitrogen can soil absorb?
Ammonia (NH3)
What is nitrogen fixation?
Nitrogen fixation is when N2 gas is combined with hydrogen to make ammonia NH3
Name the bacteria that are used in nitrogen fixation and how they do it
Azotobacter and Rhizobium are nitrogen-fixing bacteria and they contain an enzyme called nitrogenase which combines N2 with hydrogen to make ammonia
Where does azotobacter live?
It’s free-living in the soil
Where does rhizobium live?
Inside root nodules of legumes such as peas and beans
What is the relationship between rhizobium and the plants in which they live?
They have a symbiotic relationship which means they both benefit as the legume gets amino acids from rhizobium during nitrogen-fixing and rhizobium gets carbohydrates produced by the plant which it uses as an energy source
What is the process of nitrification?
This is when ammonium compounds in the soil are converted to nitrogen-containing compounds that can be used by the plant.
What bacteria is used in nitrification?
Nitrifying bacteria is used called Nitrosomonas and Nitrobacter
What kind of reaction and conditions are needed for nitrification?
It’s an oxidation reaction which means oxygen is added and it has to occur in aerated soil
List the 2 steps for nitrification
- Nitrosomonas oxidise the ammonium compounds into nitrites (NO2-)
- Nitrobacter oxidises nitrites into nitrates (NO3-)
Why are nitrate ions formed
Nitrates are very soluble so this is the way they can enter the plant
What happens if there’s no oxygen in the soil?
If the soil isn’t aerated and is waterlogged denitrification will take place
What is denitrification?
Its when nitrates in the soil are converted back into nitrogen gas by denitrifying bacteria. The bacteria use the nitrates as a source of energy for respiration and they release hydrogen gas.
What is ammonification?
This is when decomposers convert nitrogen-containing molecules e.g. faeces or dead organisms into ammonium compounds.
What is the most important chemical element in the environment?
Carbon
How do organisms get their carbon and what is it used for?
They get carbon from CO2 in the atmosphere and it is used for carbohydrates and proteins etc…
How do producers take in carbon?
They photosynthesise so need to take in CO2
How do producers release carbon when alive?
They respire and release CO2
How do consumers take in carbon?
They eat producers or other consumers that have eaten producers
How do consumers release carbon when alive?
They breathe it out as it is a product of respiration
How do decomposers take in carbon?
They take in carbon compounds from decomposing producers and consumers who have been broken down into carbon compounds
How do decomposers release carbon?
Through decomposition, they release carbon as CO2 as they respire. If the dead matter is accumulated in areas with no decomposers, the carbon compounds become trapped and turned into fossils
How is carbon released from the dead matter if no decomposers are present?
They become fossils and these are now called fossil fuels which release CO2 into the atmosphere when combusted.
At what time of day are CO2 levels the highest and why?
The CO2 levels are highest at night because, during the day, plants photosynthesize so remove the CO2 but they don’t photosynthesize at night. All organisms respire and release CO2 constantly throughout the day which means it builds up at night.
What time of year are CO2 levels highest?
CO2 levels are the highest in winter as there aren’t as many plants photosynthesising as in the summer.
Why have atmospheric CO2 levels increased globally?
- combusting too many fossil fuels means that plants can’t take in as much CO2 as the combustion is releasing so there is too much CO2 in the atmosphere
- deforestation also removes more photosynthesising biomass from the earth so not as much CO2 can be removed.
Why is increased CO2 really harmful to the environment?
Increased levels of CO2 trap thermal energy in the atmosphere which means the earth heats up, this is why it’s called a greenhouse gas. The amount of carbon dissolved in water is affected by the water’s temperature. The higher the temperature the less carbon is dissolved so it doesn’t dissolve in the sea and more of it is in the atmosphere so becomes even more harmful.
How have scientists gained information about CO2 levels in the past
They took samples from deep within a glacier. When the Antarctic glaciers were formed, air bubbles were trapped within the ice so scientists can use this to see the composition of the atmosphere at the time.
