EN: Nutrient Cycles

Question 1

Natural ecosystem

Answer 1

An ecosystem that hasn’t been changed by human activity and whose nutrients are recycled through the food webs.

Question 2

Extracellular digestion

Answer 2

When saprobionts secrete enzymes and digest their food externally, then absorb the nutrients they need.

Question 3

Saprobiotic nutrition

Answer 3

Obtaining nutrients from dead organic matter using extracellular digestion.

Question 4

An ecosystem that hasn’t been changed by human activity and whose nutrients are recycled through the food webs.

Answer 4

Natural ecosystem

Question 5

When saprobionts secrete enzymes and digest their food externally, then absorb the nutrients they need.

Answer 5

Extracellular digestion

Question 6

Obtaining nutrients from dead organic matter using extracellular digestion.

Answer 6

Saprobiotic nutrition

Question 7

Mycorrhizae

Answer 7

When some fungi form symbiotic relationships with roots of plants.

Question 8

What are fungi made of?

How does this help them connect to plant roots?

Answer 8

Long, thin strands called hyphae - connect to plant roots.

Question 9

How are fungi beneficial to plants?

Answer 9

The hyphae connect to the plant’s roots.

This greatly increases the surface area of the root system - helps it to absorb ions from the soil that are usually scarce.

Also increases the uptake of water by the plant.

Question 10

Why are plants beneficial to fungi?

Answer 10

They obtain organic compounds from the plant, eg glucose.

Question 11

Why do plants and animals need nitrogen?

Answer 11

To make proteins and nucleic acids.

Question 12

Can plants and animals use nitrogen in gaseous form?

Answer 12

No - they need bacteria to convert it into nitrogen-containing compounds first.

Question 13

What are the 4 stages of the nitrogen cycle?

Answer 13

1. Nitrogen fixation
2. Ammonification
3. Nitrification
4. Denitrification

Question 14

What do all stages of the nitrogen cycle have in common?

Answer 14

They all involve saprobiontic microorganisms.

Question 15

What is converted in nitrogen fixation?

Answer 15

Nitrogen gas is converted into the nitrogen-containing compounds.

Ammonia –> ammonium ions.

Question 16

How can nitrogen fixation be carried out?

Answer 16

Industrially or naturally when lightning passes through the atmosphere.

Question 17

What are the two main types of microorganisms that carry out nitrogen fixation?

Answer 17

• Free-living nitrogen-fixing bacteria
• Mutualistic nitrogen-fixing bacteria

Question 18

Describe the role of free-living bacteria in nitrogen-fixation:

Answer 18

• Reduce gaseous nitrogen to ammonia.
• This is used to manufacture amino acids.
• Nitrogen-rich compounds are released from them when they die and decay

Question 19

Describe the role of mutualistic bacteria in nitrogen-fixation:

Answer 19

• Live in nodules on the roots of plants like peas and beans.
• Obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria.

Question 20

Briefly describe ammonification:

Answer 20

Nitrogen compounds in dead organisms are turned into ammonia by saprobionts, which goes on to form ammonium ions.

Nitrogen returns to the non-living part of the ecosystem.

Question 21

What is nitrification performed by?

What is needed for these to perform this?

Answer 21

Nitrifying bacteria called Nitrosomonas and Nitrobacter

Requires oxygen to carry out these conversions and so they require a soil that has many air spaces.

Question 22

What are the two stages of nitrification?

Answer 22

1. Oxidation of ammonium ions to nitrite ions (NO₂^-)
2. Oxidation of nitrite ions to nitrate ions (NO₃^-)

Question 23

What is denitrification?

Answer 23

When nitrates in the soil are converted into nitrogen gas by denitrifying bacteria - they use nitrogen in the soil to carry out respiration and produce nitrogen gas.