Nutrient cycle simplified:

Question 1

What are producers in nutrient cycles? Why?

Answer 1

Plants - as they are able to produce their own carbohydrates using carbon dioxide in the atmosphere or water.

Question 2

What happens to energy between each trophic level in the food web?

Answer 2

Most of the energy is lost due to respiration and excretion - remaining energy is used to form biomass.

Question 3

How can the amount of biomass in an organism be measured in terms of?

Answer 3

In terms of mass of carbon or dry mass of tissue per given area.

Question 4

Gross primary production:

Answer 4

Chemical energy store in plant biomass, in a given area or volume.

Total energy resulting from photosynthesis.

Question 5

Net primary production:

Answer 5

Chemical energy store in plant biomass taking into account the energy that will be lost due to respiration.

Question 6

What is the equation for NPP?

Answer 6

NPP = GPP - R

Question 7

How do you work out the net production of consumers?

Answer 7

N = I - F + R

I = ingested food
F = faeces and urine
R = respiratory losses

Question 8

What units do rates of productivity have?

Why?

Answer 8

kJ m-1 year-1

To standardise results to enable comparison of environments. Per year takes into account impact seasons will have - provides an annual average.

Question 9

Mycorrhizae

Answer 9

Fungal associations between plant roots and beneficial fungi.

Question 10

How are mycorrhizae beneficial?

Answer 10

• provide larger SA for plant roots and improve water and mineral absorption.

Question 11

The relationship between mycorrhizae and plants is what?

Answer 11

Mutualistic - as plants also provide fungi with carbohydrates.

Question 12

What are the 4 key stages of the nitrogen cycle?

Answer 12

Nitrogen-fixation
Nitrification
Denitrification
Ammonification

Question 13

Describe nitrogen-fixation:

Answer 13

Nitrogen fixing bacteria break nitrogen gas in atmosphere and fix nitrogen into ammonium ions.

Question 14

Describe nitrogen fixing bacteria:

Answer 14

Free-living in soil or symbiotic and living in root nodules of plants.

Question 15

Describe nitrification:

Answer 15

Ammonium ions in soil are converted to nitrite and then nitrate ions in soil by nitrifying bacteria.

Two stage oxidation reaction.

Question 16

Describe denitrification:

Answer 16

Returns nitrogen in compounds back to nitrogen gas in atmosphere - cannot be absorbed by plants.

Conducted by anaerobic denitrifying bacteria.

Question 17

Describe ammonification:

Answer 17

Proteins, urea and DNA are decomposed by saprobionts. Returns ammonium ions into the soil.

Question 18

Saprobionts

Answer 18

Bacteria and fungi that can digest waster extracellularly.

Question 19

Why is phosphorus important?

Answer 19

Needed to create DNA, RNA, ATP and phospholipid bilayers.

Question 20

What is the main source of the phosphorus cycle?

Answer 20

Sedimentary rocks.

Question 21

Why are fertilisers added to soil?

Answer 21

To replace the lost nitrate and phosphate ions when plants are harvested and removed as crops.

Question 22

What are the two types of fertilisers?

Answer 22

Natural or artificial

Question 23

What are pros and cons of natural fertilisers?

Answer 23

+ Cheaper - often free

- Exact minerals and proportions cannot be controlled.

Question 24

Why are artificial fertilisers more impactful on the environment?

Answer 24

• Inorganic substances are more water soluble, so more ions dissolve into water surrounding soil.
• So, high solubility means larger quantities are washed away with rainfall.

Question 25

Leaching

Answer 25

Water-soluble compounds are washed away.

Question 26

What happens if nitrogen fertilisers leach into waterways?

Answer 26

Causes eutrophication

Question 27

Describe the process of eutrophication.

Answer 27

Nitrates leached from fertilised fields stimulate excessive growth of algae in ponds.

Algal bloom creates blanket on surface of water blocking out light.

Plants below surface cannot photosynthesis and so die.

Question 28

How can eutrophication results in the death of aquatic organisms?

Answer 28

Bacteria in water feed and respire on dead plant matter.

Results in an increase in bacteria, which all respire and use up oxygen within the water.

Fish and other aquatic organisms can die due to lack of dissolved oxygen in water.