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Subjects · Leaving Cert Agricultural Science

Leaving Cert Agricultural Science: Soil biology & nutrient cycles

How often Soil biology & nutrient cycles comes up on the Agricultural Science papers, every year it was asked, and questions to try.

HL Asked on 5 of the last 5 Higher Level papers, most recently in 2025. banker

OL Asked on 4 of the last 5 Ordinary Level papers, most recently in 2025. most years

Soil biology & nutrient cycles, Higher Level(6 marks)

Quick ones on Soil biology & nutrient cycles.

(a)Which bacterium converts ammonium to nitrite in the soil?
  1. Nitrobacter
  2. Nitrosomonas
  3. Rhizobium
(b)Which process returns nitrogen gas to the air from waterlogged soils?
  1. Nitrogen fixation
  2. Nitrification
  3. Denitrification
(c)Where does Rhizobium live on a clover plant?
  1. In nodules on the roots
  2. In the flower heads
  3. In the leaf stomata
Show the answers

(a) Nitrosomonas

(b) Denitrification

(c) In nodules on the roots

Your turn: Higher Level questions on Soil biology & nutrient cycles.

Higher Level

Asked on 5 of the last 5 Higher Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025Q7, Q8
2024Q4, Q10, Q17
2023Q16c
2022Q1a, Q11a, Q11b, Q16, Q17
2021Q6b, Q13b

Links open the State Examinations Commission’s paper for that year.

More Soil biology & nutrient cycles questions

Soil biology & nutrient cycles, 2 marks

Which is a benefit of earthworms to soil?

  1. They fix nitrogen from the air in the soil
  2. They make the soil strongly acidic as they feed
  3. Their burrows improve drainage and aeration
Show the answer

Their burrows improve drainage and aeration

Burrows act as channels for air, water and roots, and worms pull litter down and mix it, speeding decomposition. Their casts are rich in available nutrients.

Soil biology & nutrient cycles, 2 marks

In the carbon cycle, which process releases CO2 from dead plant material?

  1. Nitrogen fixation
  2. Decomposition by microbes
  3. Photosynthesis by green plants
Show the answer

Decomposition by microbes

Bacteria and fungi break down dead matter and respire, releasing CO2. Photosynthesis does the opposite, taking CO2 from the air into plant sugars.

Soil biology & nutrient cycles, 2 marks

What is nitrification?

  1. Conversion of ammonium to nitrate by bacteria
  2. Conversion of nitrate to nitrogen gas
  3. Fixing nitrogen gas into ammonia
Show the answer

Conversion of ammonium to nitrate by bacteria

Nitrification is a two-step process: Nitrosomonas turns ammonium into nitrite and Nitrobacter turns nitrite into nitrate, which plants absorb.

Ordinary Level

Asked on 4 of the last 5 Ordinary Level papers, most recently in 2025. most years

Every paper, year by year

YearWhere it came up
2025Q17
2024Q9a, Q16
2023Q11
2022Q8
2021Not asked

Links open the State Examinations Commission’s paper for that year.

More Soil biology & nutrient cycles questions

Soil biology & nutrient cycles, 2 marks

Which bacteria in clover root nodules fix nitrogen from the air?

  1. Nitrobacter
  2. Lactobacillus
  3. Rhizobium
Show the answer

Rhizobium

Rhizobium in clover nodules turns nitrogen gas into a form plants can use. The plant gives it sugars in return, a symbiosis.

Soil biology & nutrient cycles, 3 marks

Which bacteria convert nitrite into nitrate in the soil?

  1. Rhizobium
  2. Nitrobacter
  3. Nitrosomonas
Show the answer

Nitrobacter

Nitrification has two steps: Nitrosomonas turns ammonium into nitrite, then Nitrobacter turns nitrite into nitrate, which plants absorb.

Soil biology & nutrient cycles, 2 marks

How do earthworms improve the soil?

  1. They make channels for air and drainage
  2. They fix nitrogen from the air in the soil
  3. They make the soil more acidic as they feed
Show the answer

They make channels for air and drainage

Burrows let air and water in, and worms pull dead leaves down and mix humus through the soil. Their casts help form a stable crumb structure.

Other Agricultural Science topics

All of Leaving Cert Agricultural Science