Recycling within ecosystems 23.3

Question 1

What is decomposition?

Answer 1

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.

Question 2

What are decomposers?

Answer 2

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.

Question 3

What are saprotrophs?

Answer 3

Saprotrophs are organisms that get their energy from eating dead or waste organic material.

Question 4

How do decomposers work?

Answer 4

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.

Question 5

How do detritivores work?

Answer 5

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.

Question 6

Give some examples of detritivores

Answer 6

Woodlice and worms

Question 7

Why is nitrogen a key element?

Answer 7

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.

Question 8

Can plants absorb nitrogen?

Answer 8

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

Question 9

What compound containing nitrogen can soil absorb?

Answer 9

Ammonia (NH3)

Question 10

What is nitrogen fixation?

Answer 10

Nitrogen fixation is when N2 gas is combined with hydrogen to make ammonia NH3

Question 11

Name the bacteria that are used in nitrogen fixation and how they do it

Answer 11

Azotobacter and Rhizobium are nitrogen-fixing bacteria and they contain an enzyme called nitrogenase which combines N2 with hydrogen to make ammonia

Question 12

Where does azotobacter live?

Answer 12

It’s free-living in the soil

Question 13

Where does rhizobium live?

Answer 13

Inside root nodules of legumes such as peas and beans

Question 14

What is the relationship between rhizobium and the plants in which they live?

Answer 14

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

Question 15

What is the process of nitrification?

Answer 15

This is when ammonium compounds in the soil are converted to nitrogen-containing compounds that can be used by the plant.

Question 16

What bacteria is used in nitrification?

Answer 16

Nitrifying bacteria is used called Nitrosomonas and Nitrobacter

Question 17

What kind of reaction and conditions are needed for nitrification?

Answer 17

It’s an oxidation reaction which means oxygen is added and it has to occur in aerated soil

Question 18

List the 2 steps for nitrification

Answer 18

• Nitrosomonas oxidise the ammonium compounds into nitrites (NO2-)
• Nitrobacter oxidises nitrites into nitrates (NO3-)

Question 19

Why are nitrate ions formed

Answer 19

Nitrates are very soluble so this is the way they can enter the plant

Question 20

What happens if there’s no oxygen in the soil?

Answer 20

If the soil isn’t aerated and is waterlogged denitrification will take place

Question 21

What is denitrification?

Answer 21

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.

Question 22

What is ammonification?

Answer 22

This is when decomposers convert nitrogen-containing molecules e.g. faeces or dead organisms into ammonium compounds.

Question 23

What is the most important chemical element in the environment?

Answer 23

Carbon

Question 24

How do organisms get their carbon and what is it used for?

Answer 24

They get carbon from CO2 in the atmosphere and it is used for carbohydrates and proteins etc…

Question 25

How do producers take in carbon?

Answer 25

They photosynthesise so need to take in CO2

Question 26

How do producers release carbon when alive?

Answer 26

They respire and release CO2

Question 27

How do consumers take in carbon?

Answer 27

They eat producers or other consumers that have eaten producers

Question 28

How do consumers release carbon when alive?

Answer 28

They breathe it out as it is a product of respiration

Question 29

How do decomposers take in carbon?

Answer 29

They take in carbon compounds from decomposing producers and consumers who have been broken down into carbon compounds

Question 30

How do decomposers release carbon?

Answer 30

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

Question 31

How is carbon released from the dead matter if no decomposers are present?

Answer 31

They become fossils and these are now called fossil fuels which release CO2 into the atmosphere when combusted.

Question 32

At what time of day are CO2 levels the highest and why?

Answer 32

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.

Question 33

What time of year are CO2 levels highest?

Answer 33

CO2 levels are the highest in winter as there aren’t as many plants photosynthesising as in the summer.

Question 34

Why have atmospheric CO2 levels increased globally?

Answer 34

• 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.

Question 35

Why is increased CO2 really harmful to the environment?

Answer 35

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.

Question 36

How have scientists gained information about CO2 levels in the past

Answer 36

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.