3. nutrient cycles

Question 1

why do organisms need nitrogen

Answer 1

to make proteins and nucleic acids (DNA / RNA)

Question 2

nitrogen cycle

1. nitrogen fixation

Answer 2

NITROGEN GAS -> NITROGEN CONTAINING COMPOUNDS

1. nitrogen gas in atmosphere turned into nitrogen containing compounds
2. bacteria Rhizobium (found in root nodules) - turn nitrogen into ammonia which can be used by plants
3. mutualistic relationship - provide plant with nitrogen compounds, plant provides them with carbs

Question 3

nitrogen cycle

2. ammonification

Answer 3

NITROGEN COMPOUNDS -> AMMONIA -> AMMONIUM IONS

1. nitrogen compounds from dead organisms / animal waste turned into ammonia by saprobionts. forms ammonium ions in soil

Question 4

nitrogen cycle

3. nitrification

Answer 4

AMMONIUM IONS -> NITRITES -> NITRATES

1. nitrifying bacteria (nitrosomonas) change ammonium ions into nitrites
2. nitrifying bacteria (nitrobacter) change nitrites into nitrates
3. nitrates can then be used by plants

Question 5

nitrogen cycle

4. denitrification

Answer 5

NITRATES -> NITROGEN GAS

1. denitrifying bacteria use nitrates in soil to carry out respiration and produce nitrogen gas
2. anaerobic conditions e.g. waterlogged soil

Question 6

saprobionts

Answer 6

microorganisms such as bacteria or fungi that are decomposers

Question 7

importance of saprobionts

Answer 7

break down organic molecules into inorganic ions

Question 8

mycorrhizae

Answer 8

1. fungi symbiotic relationship with roots of plants
2. made up of long thin strands called hyphae which connect to plant roots increasing surface area
3. help plants absorb ions from soil which are scarce and increase uptake of water (in turn obtain organic compounds)

Question 9

why do organisms need phosphorus

Answer 9

phospholipids, DNA, ATP

Question 10

phosphorus cycle

Answer 10

1. phosphate ions (PO4 3-) in rocks released into soil by weathering
2. taken into plant through roots (with help of mycorrhizae)
3. transferred through food chain (plants eaten, consumers eaten)
4. lost from animal in waste products
5. when plants and animals die saprobionts break down organic compound releasing phosphate ions in soil for assimilation by plants. saprobionts also release from urine and faeces
6. weathering of rocks releases phosphate ions into sea, lakes, rivers. taken up by aquatic produces which is passed along food chain to birds
7. waste of sea birds (guano) high proportion of phosphate ions. returns phosphate ions to soils/ often used as natural fertiliser