Q1

State in stages the sequence that

forms the basis of all nutrient cycles.

(4 Marks)

Answer 

-The nutrient is taken up by producers as simple inorganic molecules.

{1 Mark}

-The producer incorporates the nutrient into complex organic molecules.

{1 Mark}

-The nutrient is passed into the consumer once the producer has been eaten.

{1 Mark}

-When the producers and consumers die, their complex organic molecules are broken down by saprobiotic microorganisms (otherwise knows as the decomposers) that release the nutrient back into its original simple form.

{1 Mark} 

Q2

Name two human activities that have 

increased the global level of carbon

dioxide in the atmosphere and explain

how.

(3 Marks)

Answer

-The combustion of fossil fuels, such as coal, oil and peat, has released the carbon dioxide that was locked within thhese fuels back into the atmosphere.

{1 Mark}

-Deforestation, has removed enormous amounts of photosynthesizing biomass and so less carbon dioxide is being removed from the atmosphere.{1 Mark}

Q3

Microorganisms make the carbon in polymers

within a dead fox available to cells in a leaf.

Describe how.

(5 Marks)

Answer

1-Microorganisms are saprobionts;{1 Mark}

2-Secrete enzymes onto the dead tissue/use extracellular digestion;{1 Mark}

3-Absorb the products of digestion/smaller molecules/named relevant subtance;

{1 Mark}

4-Respiration by the microorganisms occurs producing carbon dioxide;{1 Mark}

5-Carbon dioxide is taken into the leaves;{1 Mark}

6-Through the stomata.{1 Mark}

Q4

Dead rutabagas contain starch. Describe how microorganisms make carbon in starch

available to plants.

(2 Marks)

Answer

-Extracellualr digestion/secretes enzymes;{1 Mark}

-Starch is broken into monosaccharides/glucose/sugars/smaller molecules;

{1 Mark}

-The microorganisms respire the product of digestion;{1 Mark}

-Therefore producing carbon dioxide through respiration{1 Mark}

Note* A Rutabaga is a cross between a turnip and a cabbage and is otherwise

known as the yellow turnip.

Q5

Name the four main stages in the nitrogen cycle.

(1 Mark)

Answer

Ammonification, Nitrification, Nitrogen Fixation and Denitrification{1 Mark}

Q6

Define The following terms:

-Ammonification

-Nitrification

-Nitrogen Fixation

-Denitrification 

(4 Mark)

Answer

Ammonification: The production of ammonia from organic ammonium-containing compounds such as urea.{1 Mark}

Nitrification: The oxidation reaction where ammonium ions are converted to nitrate ions by nitrifying bacteria.{1 Mark}

Nitrogen Fixation: The process by which nitrogen gas is converted into nitrogen-containing compounds.{1 Mark}

Denitrification: The conversion of soil nitrates into gaseous nitrogen by anaerobic denitrifying bacteria; usually occuring in areas where oxygen supply is short especially in waterlogged soils.{1 Mark}

Q7

Distinguish between natural and artificial

fertilisers.

(2 Marks)

Answer

Natural Fertilisers- Are organic and come from living organisms in the form of dead remains, urine or faeces(manure).{1 Mark}

Artificial Fertilisers- Are inorganic and are mined from rocks and deposits; They are then converted into different forms and blended together to give the desired balance of minerals.{1 Mark}

Q8

Give two advantages of using a natural 

fertiliser produced in a anaerobic digester

rather than an artificial fertiliser.

(2 Marks)

Answer

-Acts as soil conditioner/increases organic content of soil/aerates soil;

{1 Mark}

-Contains other elements/such as the micronutrients like iron and magnesium;

{1 Mark}

-Production of artificial fertiliser is energy consuming;{1 Mark}

-Less leaching when using the natural fertiliser due to its slow release of nutrients.{1 Mark}

Q9

Describe one way in which the use of

nitrogen fertiliser can have a detrimental

effect on the environment.

(2 Marks)

Answer

-Reduce species diversity,because nitrogen rich soils favour the growth of grasses, nettles and other rapidly growing species. This allows those species to outcompete any other species in the area.{2 Marks}

-Leaching, which may lead to pollution of watercourses.{2 Marks}

-Eutrophication, caused by leaching of fertiliser into watercourses.{2 Marks}

Q10

Describe the stages of eutrophication

that take place in a lake once it has experienced

leaching.

(5 Marks)

Answer

-Nitrate is no longer the limiting factor in growth for algae and plants;{1 Mark}

-Algae and plants grow exponentially;{1 Mark}

-Increase of algae causing algal bloom;{1 Mark}

-Light blocked out due to dense layer of algae at the top of water layer;{1 Mark}

-Plants in lower depths cannot photosynthesize due to lack of sunlight/plants and algae in bottom depths die;{1 Mark}

-Saprobionts (Saprobiotic Bacteria) feed off the dead organims;{1 Mark}

-Biological oxygen demand increases;{1 Mark}

-Concentration of oxygen in the water decreases and becomes the limiting factor for aerobic organisms such as fish causing them to die;{1 Mark}

-Anaerobic organisms grow exponentially due to lack of aerobic organisms/no competition;{1 Mark}

-The anaerobic organisms furhter decompose the dead material releasing more nitrates and toxic wastes such as hydrogen sulphide which turns the water putrid.{1 Mark}