6 - ICH - Recycling nutrients in Ecosystems

Question 1

Name the 2 cycles that are involved in recyling nutrients within ecosystems

Answer 1

Carbon cycle

Nitrogen cycle

Question 2

Why do nitrogen and carbon have to be constantly recycled?

Answer 2

There’s a finite supply in the ecosystem. It’s never created nor destroyed - simply recycled

Question 3

Explain the importace of decomposers and detrivores in the recyling of matter in ecosystems

Answer 3

• They hydrolyse macromolecules → smaller molecules meaning that molecules can be reused
• Without them there would be NO recyling of organic matter

Question 4

Name the 4 main stages that can be used to summarise the nitrogen cycle

Answer 4

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

Question 5

What is ammonification

Answer 5

Production of NH₃ from N containing compounds from plants and animals by decomposers.

This includes death and also from nitrogenous excretory compounds (urine + faeces)

Question 6

What is nitrification

Answer 6

The use of nitrifying bacteria to convert NH₄⁺ ions → nitrites/ NO₂^- → nitrites/ NO₃^- which can be taken upp by plants through assimilation

Question 7

What type of organism are decomposers mainly?

Answer 7

Fungi and bacteria

Question 8

2 types of nitrifying bacteria and what they do

Answer 8

Nitrosomonas - NH₄⁺ → NO₂^-

Nitrobacter - NO₂^- → NO3^-

Question 9

Why is the relationship between nitrogen fixing bacteria by living organisms and the plants a mutualistic relationship?

Answer 9

Rhizobium = N fixing bacteria in root nodules of leguminous plants

Azotobacter = Free living N fixing bacteria in the soil

Plant provides them with carbohydrates and they provide plant with nitrogen compounds. Both partners benefit from the relationship so it’s called mutualism

Question 10

2 ways in which nitrogen fixation can happen via non-living processes

Answer 10

Lighting

Haber process

Question 11

What does denitrifying bacteria do? Example

Answer 11

Converts NO₃^- → N₂ in atmosphere

e.g. Pseudomonas denitrificans

Question 12

What can happen if large amounts of nutrients e.g. nitrates and phosphates are added to bodies of fresh water?

Answer 12

Eutrophication

Question 13

Events of how Eutrophication occurs and it’s affect on fish + other organisms (4)

Answer 13

1. Increase in nitrates from fertilisers or sewage
2. Increased growth of algae and water plants
   
   • Algae don’t live for very long so large numbers die very quickly
3. Bacteria are decomposers
   
   • Large no’ of dead algae means there’s a rapid increase in the no’ of bacteria. Bacterial respiration lowers oxygen conc in the water
4. Fish + other organisms die because of low oxygen conc

Question 14

For eutrophication how does excess nitrates get washed into the lakes + rivers in the first palce? (2)

Answer 14

• N containing ions are very soluble and can be leached or washed out of the soil to accumulate in lakes + rivers.
• Breakdown of sewage + waste from cattle and pigs also result in the addition of nitrate to lakes + rivers

Question 15

How do decomposrs feed?

Answer 15

By sabrobiontic nutrition. Secrete enzymes to break down carbon compounds in dead organic matter then absorb these products of digestion

Question 16

Why does the level of CO₂ fluctuate throughout the year? (4)

Answer 16

Due to gas’s involvement in respiration / photosynthesis.

Day:

• Daylight - both respiration & photosynthesis occurs
• More CO₂ in atmosphere surrounding plants at night than day

Yearly:

• Winter - cooler temps, shorter day lengths and loss of leaves reduces the level of photosynthesis in many plants
• In the summer it’s reversed

Crops:

• When they’re raised in greenhouse gases, the low levels of CO₂ can have a major impacct on productivity ∴ CO₂ levels are artificially raised

Burning natural gases:

• Raise temp of greenhouse gas but also raise CO₂ levels

Question 17

How have human impacts increased the levels of CO₂ in the atmosphere?

Answer 17

Linked to global warming because CO₂ is a greenhouse gas.

Extra CO₂ produced reflects even more heat back to earth so the earth becomes warmer

Question 18

How does deforestation have an impact on the carbon cycle? (2)

Answer 18

• Cutting treets reduces photosynthesis ∴ CO₂ uptake rates - reduces amount of atmospheric CO₂ removed by plants
• Trees contain a lot of CO₂ locked in their tissues. Releasing it all if burning them for fuel

Question 19

How does deforestation have an impact on the nitrogen cycle? (4)

Answer 19

• Most N is released into soil as the plants decompose
• I they’re burnt then N containing compounds will be in the ash and released immediately into the soil
• N content is then reduced by leaching - causes eutrophication
• N is removed as crops are harvested ∴ dropping in soil fertility as N is a finite resource that needs to be recycled