4.3 Cycles within ecosystems

Question 1

carbon cycle

Answer 1

the cycle where carbon moves between organisms and the environment, namely in the form of carbon dioxide and involving:
respiration
photosynthesis
fossilisation
combustion

Question 2

decomposers in the nitrogen cycle

Answer 2

organisms that release enzymes that catalyse the breakdown of dead plant and animal material
releasing nitrogen containing compounds such as ammonia into the soil

Question 3

Combustion

Answer 3

when fossil fuels are burnt
- releases carbon dioxide into the atmosphere

Question 4

nitrogen fixation

Answer 4

nitrogen-fixing bacteria in the soil and roots of legume plants absorb nitrogen and reduce it to make ammonia

Question 5

Nitrification

Answer 5

the ammonia is converted to nitrites and nitrates by nitrifying bacteria

Question 6

What happens to nitrates after being absorbed by plant roots?

Answer 6

they are combined with carbohydrates (from photosynthesis)
to form amino acids which are then made into proteins, and nucleotides which are joined to make DNA and RNA

Question 7

What happens when animals eat plants?

Answer 7

they digest the proteins and DNA, absorbing the small soluble molecules (amino acids ad nucleotides)
these are then used by the animal to synthesise new proteins and DNA (assimilation)

Question 8

What happens when a plant or animal dies?

Answer 8

its tissues are decomposed by bacteria and fungi (saprotrophic nutrition)

Question 9

What happens to the molecules containing nitrogen such as proteins?

Answer 9

broken down by the bacteria and fungi and ammonia is released into the soil

Question 10

deritrification

Answer 10

some nitrates are converted into N2 by denitrifying bacteria

Question 11

denitrifying bacteria

Answer 11

bacteria that convert nitrates in the soil into nitrogen gas
occurs when conditions are anaerobic and can be prevented by ploughing the soil –> ensures there is enough oxygen to prevent the growth of these organisms

Question 12

nitrifying bacteria

Answer 12

aerobic organisms that convert ammonia to nitrites and then nitrates which can be absorbed by plants using active transport

Question 13

nitrogen cycle

Answer 13

the cycle through which nitrogen moves between living organisms and the environment

Question 14

nitrogen fixing bacteria

Answer 14

bacteria that convert nitrogen gas into nitrogen containing compounds that plants can use
- can be free living in the soil or found in root nodules of leguminous plants