Nutrient Cycles

Question 1

What is phosphorus used for in organisms?

Answer 1

-DNA/RNA
-ATP
-Phospholipid bilayer

Phosphorus is not found as a gas but is found in rocks in the form of phosphate so the phosphorus cycle is a slow process

Question 2

Describe the features of the phosphorus cycle

Answer 2

• (ABSORPTION) - Firstly there are dissolved phosphate ions in oceans and soils, and plants absorb these ions by active transport in the roots
• (FEEDING + DIGESTION) - Plants use the phosphate ions in DNA/RNA, ATP + phospholipids and animals eat plants and can use the ions for the same things
• (EXCRETION) - Some excretion contains phosphate ions which goes directly into oceans and soils
• (EXCRETION + DECOMPOSITION) - After animal dies, there is breakdown of material. Guano is in bird excretion and is rich in phosphorus as are shells and bones
• (EROSION) - Overtime the shells, bones + guano will erode, breakdown and release phosphate ions into oceans + soil
• (DEPOSITION) - Some goes towards creating phosphate ions in rocks
• (EROSION + USE OF FERTILISERS) - Rocks can be eroded and phosphate ions return to oceans + soil but also the addition of fertiliser to land allows runoff into oceans
• (SEDIMENTATION) - Sediment from oceans builds up, creating rocks over thousands of years + contains phosphate ions

Question 3

Why is the nitrogen cycle important?

Answer 3

78% of the air is nitrogen but plants + animals can’t obtain nitrogen through gas exchange. This is due to nitrogen containing a triple bond so it’s harder to break the bond, making it an inert gas. Microorganisms are needed to convert nitrogen gas into nitrogen containing substances that plants + animals can absorb.

Question 4

Outline the 3 processes responsible for Nitrogen Fixation

Answer 4

1) Atmospheric fixation by lightning- Lightning energy combines N2 + O2 into nitrates + rain makes nitrates fall to earth faster
2) Industrial fixation ( Haber process)- Uses catalyst under high temp + pressure to make masses of ammonia thats then used as fertilisers.
3) Mutualistic bacteria (Rhizobium) in root nodules of leguminous plants converts nitrogen to ammonia

Question 5

Explain the process ammonification

Answer 5

-Proteins are made by the plants and are eaten by animals and organic nitrogen compounds return to environment in faeces + urine.
-Fungi + bacteria break down molecules in excretions + dead organisms into ammonia

Question 6

Explain the process of nitrification

Answer 6

-Most of ammonia produced by decay is converted into nitrates
1) Bacteria (Nitrosomonas) oxidise ammonia to nitrites
2) Bacteria (Nitrobacter) oxidise nitrites to nitrates
-These 2 bacteria are called nitrifying bacteria

Question 7

Explain the process of denitrification

Answer 7

-Reduces nitrates to nitrogen gas so closes the cycle
-It happens in wet + waterlogged soil
-Pseudomonas ( denitrifying bacteria) live in anaerobic conditions (in soil) + turn nitrates into nitrogen

Question 8

Explain why fertilisers are needed in agricultural ecosystems

Answer 8

• Fertilisers are used to replace nitrates and phosphates lost by harvesting plants and removing livestock.
• Nitrogen is used to produce amino acids which can make proteins for growth

Question 9

Can you distinguish between natural and artificial fertilisers?

Answer 9

Natural (organic) fertiliser- derived from living things like manure + compost

Artificial (inorganic) fertiliser- derived from inorganic chemicals

Question 10

Explain how fertilisers increase productivity

Answer 10

Fertilisers are used to replace nitrates and phosphates lost by harvesting plants + removing livestock.
Nitrogen fertilisers greatly increase crop yield so help with demands of a growing human population

Question 11

What are the negative effects on the environment when using nitrogen-containing fertilisers?

Answer 11

• reducing biodiversity
• leaching
• eutrophication

Question 12

Explain leaching and eutrophication

Answer 12

• Leaching is the process where mineral ions dissolve in rainwater + are carried from soil into rivers + lakes
• Therefore eutrophication occurs which is when the nitrates stimulate the growth of algae, forming an algae bloom. This blocks out sunlight so plants can’t photosynthesise, so die + less O2 in water. Bacteria decompose dead plants which further reduces O2 as they respire aerobically leading to the collapse of an ecosystem due to lack of dissolved O2 in water.

Question 13

What are mycorrhizae + why are they beneficial for plant growth?

Answer 13

Mycorrhizae are fungal associations between plant roots + beneficial fungi
1) Fungi increase SA for water + mineral absorption
2) Mycorrhizae act like a sponge so holds water + minerals around the roots
3) This makes plants more drought resistant + able to take up more inorganic ions
Plants can photosynthesise + provide carbohydrates to fungus
This is a mutualistic relationship as both provide an advantage