Nutrient Cycles Questions

Question 1

Name the type of bacteria that convert nitrites into nitrates (1)

Answer 1

Nitrifying

Question 2

Other than spreading fertilisers, describe and explain how one farming practice results in addition of nitrogen containing compounds to a field (2)

Answer 2

Allow cattle to graze

Add dung/urine

Question 3

Purification ponds can be used in warm climates to break down sewage. Explain the advantage of having both algae and bacteria in a purification (4)

Answer 3

Breakdown of sewage by enzymes from bacteria

Nitrates used by algae to make proteins

Algae photosynthesise

Bacterial respiration uses O2

Increased reproduction of bacteria

Question 4

Purification ponds can be used in warm climates to break down sewage. The ponds contain bacteria and green algae. The ponds only work efficiently when ey are shallow and warm. Explain why (4)

Answer 4

Sufficient light penetration for photosynthesis of algae

Warm leads to faster enzyme activity

Faster bacterial respiration

Faster photosynthesis

Increased growth of bacteria

Question 5

Explain why the net production of an area does not represent the total amount of plant biomass formed per year by photosynthesis (2)

Answer 5

Biomass lost in respiration

Biomass lost as co2

Question 6

Explain the role of bacteria in making carbon in dead plant remains available to plants (4)

Answer 6

Decomposers

Release enzymes and digest detritus

Substances found in detritus

Absorb producers of digestion

Question 7

Explain how the activities of decomposers and nitrifying bacteria recycle the substances in fallen leaves for reuse by the trees (7)

Answer 7

Decomposers digest organic matter

Respiration

Release CO2

CO2 used in photosynthesis

Release nutrients

Nitrifying bacteria convert ammonium to nitrate

By oxidation

Nitrates used in protein synthesis

Question 8

Explain how the felling and burning of trees on a large scale could affect the concentration of carbon dioxide in the atmosphere (2)

Answer 8

Burning release co2

Less co2 removed from atmosphere by trees

Question 9

Both rapidly growing softwood trees and slow growing hard trees grow in tropical tai forests. The seeds of both kind of trees lie dormant on the floor of a mature forest and only germinate when exposed to light and warmth. However, the seedlings of many hardwood species grow more successfully beneath the protective canopy of the softwood tress. When a small area of trees has been cut down, it can return normally to tropical rainforest . Suggest and explain how reestablishment of the rainforest ecosystem may occur in such areas (6)

Answer 9

Cleared area tree seeds germinate/grow in light

Light for photosynthesis

Softwoods compete for light

Hardwoods can grow in low light

Canopy reduces impact of rainfall

Roots stabilise soil

Less leaching

Trees provide food for animal

Trees provide habitats

Question 10

A large lake is surrounded by fields. These are separated from each other by hedges. One hundred years ago the lake was a habitat for many plants, invertebrates and fish. Today the lake has no fish and few plants or invertebrates. Explain how increased use of inorganic fertilisers on the fields may have led to these changes.

Answer 10

Leaching of nitrates

Leads to increased growth of algae

Competition for light

Deeper plants die

Increases food supply for Decomposers

Respiration of microorganisms uses up oxygen

Fish/animals die due to lack of oxygen

Question 11

A large lake is surrounded by fields. These are separated from each other by hedges. Explain how the removal of hedges near the lake would increase the impact of fertilisers on the aquatic ecosystem (2)

Answer 11

Leads to soil erosion

Increase in run off carries more fertilisers

Soil (+fertilisers) blown into lake

Question 12

What is the prices by which nitrates turn to nitrogen (1)

Answer 12

Denitrification

Question 13

What is the process by which nitrogen turns to ammonia (1)

Answer 13

Nitrogen fixation

Question 14

Explain how farming practices might be responsible for the change in nitrate concentration in the water near their fields (2)

Answer 14

Excessive use of fertilisers

Run off/leaching

Question 15

Describe the effect of increased nitrate concentration in a river (5)

Answer 15

Growth of algae

Death of deeper plants due to less light reaching them

More Decomposers

Respiration

Decomposers remove oxygen

Animals die because of lack of oxygen

Question 16

Explain why an outbreak of pests is more of a problem in monoculture than where a mixture of crops is grown (3)

Answer 16

Weeds left in soil

Plentiful supply of sane food source for pest

Rapid reproduction of pesticides

Need to really same pesticide - resistance developed

Hence lower yield

Question 17

Other than resistance, give two disadvantages of using pesticides (2)

Answer 17

Kill beneficial organisms

Bioaccumulation

Residue left on crop

Can enter water/food chain

Question 18

Microorganisms make the carbon in polymers in a dead worm available to cells in a leaf. Describe how (5)

Answer 18

Microorganisms are saprobionts

Extracellular digestion

Absorb products of digestion

Respiration produce co2

Co2 taken into leaves

Question 19

Explain why deforestation reduces the diversity index of an area (2)

Answer 19

Removes many habitats/niches

Fewer species

Question 20

Use your knowledge of the nitrogen cycle to explain the potential benefit of adding fertiliser containing ammonium nitrate rather than one containing Potassium nitrate (3)

Answer 20

Ammonium nitrate contains more nitrogen per molecule

Ammonium converted to nitrate

By nitrifying bacteria

Question 21

Explain how high nitrate concentration increases the growth of algae (2)

Answer 21

More proteins

More nucleotides

Increased cell division

Question 22

Suggest how increased growth of algae could lead to the death of submerged plants (2)

Answer 22

Reduced light

Less photosynthesis

Question 23

Explain how the decay of dead plants results in reduced oxygen concentration and increased nitrate production (6)

Answer 23

Bacteria feed on dead matter saprobiotically

Bacteria multiply

Respiration uses oxygen

Converts proteins to amino acids

Then to ammonium compounds

Nitrifying bacteria

Convert ammonium compounds

Via nitrates

Question 24

Describe how the reduced oxygen concentration of the water will change the composition of the communities in the river (2)

Answer 24

Lower species diversity

Species tolerant to low oxygen concentrations thrive

Question 25

Heterocysts are thick walled cells that do not contain chlorophyll. Suggest how these features improve the process of nitrogen fixation (3)

Answer 25

Thick walls exclude oxygen

Contain no chlorophyll so do not produce oxygen

Do not produce oxygen

Oxygen would inhibit nitrogen fixation

Question 26

In China the fern is cultivated and ploughed into fields to act as an organic fertiliser. Explain how ploughing the fern plants into the soil results in an improvement in the growth of rice crops in these fields (5)

Answer 26

Decomposers in fields

Convert organic nitrogen into ammonium ions

Ammonium ions converted to nitrite

Nitrite converted to nitrate

By nitrifying bacteria

Decomposers respire and release co2

Used in photosynthesis by rice

Question 27

Describe the role of bacteria in making the nitrogen in dead leaves available to growing plants (5)

Answer 27

Saprobionts

Break down nitrogen containing substances

Extracellular digestion

Ammonium produced

Ammonia converted to nitrite to nitrate

By nitrifying bacteria

Question 28

Clearing the forests and burning the vegetation affects the carbon dioxide concentration in the atmosphere. Describe how and explain why (4)

Answer 28

Co2 concentration increases

Less vegetation so less photosynthesis

Less co2 removed from atmosphere

Burning/combustion release co2

Question 29

Name the type of bacteria which convert nitrogen in the air into ammonium compounds (1)

Answer 29

Nitrogen fixing