paper 2: Nutrient Cycles

Question 1

why is nitrogen needed in organisms

Answer 1

nitrogen is needed to make ATP, amino acids, DNA, RNA, proteins etc.

Question 2

draw diagram so show nitrogen cycle

Answer 2

Question 3

how do animals in the food chain obtain thier nitrogen and wht do they use it for

Answer 3

• consumers eat other organisms which contain nitrogen-containing compounds e.g. proteins
• compounds are hydrolysed during digestion into their monomers e.g. amino acids, which can then me absorbed into the blood stream
• monomers are then assimilated to make new nitorgen containing compondsin the consumer e.g. amino acids make proteins

Question 4

what is the name of the process of how nitrogen returns to the enivironment from organisms in the food chain

Answer 4

ammonification

Question 5

describe the process of ammonification

Answer 5

• saprobiotic bacteria and fungi secrete extracellular enzymes onto dead organisms, faeces and urine
• these enzymes hydrolyse nitorgen compounds e.g. proteins and absorb the products e.g. amino acids
• ammonium ions are released into the soil

Question 6

what is the name of the process where nitrogen in the soil is converted into a form which plants can absorb

Answer 6

nitrification

Question 7

describe the process of nitrification and which bacteria are used

Answer 7

Well-aerated soil (containing oxygen) has nitrifying bacteria​

They oxidise ammonium ions to nitrate ions in two stages:​

Ammonium to nitrite ( NO2-) ions​

Nitrite ions to nitrate (NO3-) ions

Question 8

describe the process of nitrogen fixation and which bacteria are used

Answer 8

nitrogen gas is redcued to ammonium ions by:
1. nitrogen fixin bacteria in the soil
2. nitrogen fixing bacteria in the root nodules of legumes

Question 9

decsribe the process denitrification and whihc bacteria are used

Answer 9

Waterlogged soil has anaerobic conditions.

In these conditions, denitrifying bacteria grow well.

These reduce nitrate ions to nitrogen gas.

Question 10

why do farmers need to keep their soil well drained and regularly ploughed

Answer 10

To avoid waterlogged anaerobic fields so less denitrifying bacteria grow so less nitrate ions are reduced to nitrogen gas, so there are more nitrates for plants to absorb

Question 11

how to sapprobiotic bacteria carry out decomposition

Answer 11

saprobiotic bacteria and fungi secrete extracellular enzymes onto dead organsims. the enzymes hydrolyse the nitrogen compounds e.g. proteins and absorb the products e.g. amino acids. and ammonium ions are released into the soil

Question 12

what is mycorrhizal fungus and how does the plant and fungus benefit

Answer 12

• mycorrhizae are relationships between fungi and plant roots
• the hyphae of fungi increases the surface area for absorption of water and nitrates/ phosphates for plants
• fungus recieves carbohydrates from plant such as glucose
• example of mutualistic relationship

Question 13

why do organisms need phosphorous

Answer 13

• make phospholipids for new cell membranes
• make ATP from ADP
• used in sugarphosphate backbone of DNA nucleotides

Question 14

describe the phosphorous cycle

Answer 14

• phosphorous exists mainly as phosphate ions in rocks
• weathering and erosion causes phsophate ions to dissolve into soil and oceans/ lakes
• phosphate ions absorbed by plants and incorporated into biological molecules such as DNA, phospholipids and ATP
• consumers then eat the plants and hydrolyse biological molecules e.g. phospholipids via digestion and are assimilated into new tissue in consumer e.g. DNA nucleotides
• decomposers e.g. saprobiotic bacteria and fungi secrete extracellular enzymes which hydrolyse the phosphorous containing molecules e.g. DNA in dead organisms and urine releasing phosphates back into soil or water
• phosphate ions can form sedimentary rocks through decomposition, completing the cycle.

Question 15

draw diagram of phosphorous cycle

Answer 15

Question 16

explain how harvesting crops and removing livestock can cause nitrates and phosphates to be lost

Answer 16

• crops do not decompose to replace the nitrates/ phosphates thay have absorbed
• livestock no longer excrete/ egest replacing the nitrates/ phosphates thye have consumed from the plants they have eaten

Question 17

what is a natural fertilizer

Answer 17

compost and manure

Question 18

what is an artificial fertilizer

Answer 18

chemical compunds which can be added to the soil.

Question 19

what is leaching

Answer 19

removal of nitrated and phosphates from soil by rainwater into rivers and lakes

Question 20

explain why natural fertilisers take longer to provide plants with an absorbable form of nitrogen than artificial fertilisers

Answer 20

• atrificial fertilisers add nitrates and ammonium ions and phosphates stright into the soil
• wherease natural fertilisers need saprobiotic bacteria to hydrolyse the nitrogen- containing compounds e.g. proteins into ammonium ions first and then the phosphate containing compounds e.g. dna into phosphate ions

Question 21

explain why the addition of fertiliser at high concentrations decreases the productivity of the crop

Answer 21

• high conc.s of fertilliser lowers the water potentil of the soil
• plant root cells have a higher water potential than the soil
• water moves out of the plant root cells by osmosis
• plants have less water for metabolic reactions e.g. photosynthesis/ hydorlysis

Question 22

explain eutrophication

Answer 22

• nitrates and phosphates from leaching of fetilisers enters streams and rivers
• these increase growth of algae causing an algal bloom
• reduces light available to plant sin water so they stop photosyntheisising and die
• sapprobiotic bacteria reproduce rapidly and decompose dead plant matter using oxygen for aerobic respiration
• this reduces oxygen avaialbale for other organisms like fish so they cannot respire aerobically and die