Energy And Ecosystem

Question 1

The grass in an ecosystem has a gross primary productivity of 20,000 kJ m² per year
it loses 8000 KJ m² per year as heat from respiration
calculate the net primary productivity of the grass in this ecosystem

Answer 1

NPP = GPP - R

20,000 - 8000

NPP = 12,000 kJ m² per year

Question 2

The net primary productivity in an area of tundra is 2800 kJ metres squared per year
it loses 1250 kJ metres squared per year through respiration
calculate the gross primary product productivity of the area of tundra

Answer 2

GPP = NPP + R

2800 + 1250 = 4050 kJ m² per year

Question 3

Net production in consumers

Equation

Answer 3

N = I - (F + R)

I is chemical energy thats ingested

F is chemical energy thats lost in faeces and urine

R is energy thas lost thru respiration

Question 4

The rabbits in an ecosystem ingest 20,000 kJ m² per year of energy
But lose 12,000 kJ m² per year of it in faeces and urine
they lose a further 6000 kJ m² per year using energy for respiration
calculate the net productivity of the rabbits:

Answer 4

NPP = 20,000 - (12,000+6000)

Question 5

Efficiency of energy transfer

Answer 5

% efficiency of energy transfer = net production of trophic level / net production of previous trophic level x 100

Question 6

The rabbits receive 20,000 kJ m² per year and the net productivity is 2000 kJ m² squared per yer so the percentage efficiency of energy transfer is:

Answer 6

2000/20000 x 100

= 10%

Question 7

The scientist wanted to measure the biomass of a crop of wheat
to do so he took a sample of the wheat and measured its dry mass

describe how the scientist could have measured the dry mass of the wheat

once the scientist has a sample of dry mass decides to burn it in a colorimeter what will the results from this procedure tell him about the wheat

Answer 7

Dry in a oven at low temperature
Check weight everyday until it becomes constant
Weight constant means all water has been removed so this would b the dry sample

It will give him an estimate of the chemical energy stored in the wheat

Question 8

The mussels in an ecosystem ingest 57,153 kJ m² squared per year
34,292 kJ metres squared per year is ingestible lost through urine and 17,000 kJ m² squared per year is lost through respiration

calculate the net productivity of the mussels

the mussels provide food for crayfish which have a net productivity of 627 kJ m² squared per year

Calculate the energy transfer between the mussels and the crayfish

Answer 8

N = I (F+R) 
N = 57,153 (34,292 +17,000)
N= 5861 KJ m² per yr

New / previous x 100
(627 / 5861) x 100 = 10.7%

Question 9

Two reasons why the net productivity of the large fish is less than the net productivity of the small fish

Answer 9

Because some of the energy is lost to the environment through respiration or excretion of urine

Some parts of the small fish are indigestible and so are egested as faeces

Question 10

What is a plants biomass?

Answer 10

The chemical energy stored in the plant

Question 11

What is gross primary production?

Answer 11

The total amount of chemical energy converted from light energy by plants in a given area

Question 12

What is meant by respiratory loss?

Answer 12

The energy lost to environment as heat when organisms respire

Question 13

What is net production?

Answer 13

The energy is stored in the consumers biomass it’s also the energy available to organisms at the next trophic level

Question 14

The equation for net production

Answer 14

Net production = I - (F + R)

Question 15

A pig Farmer wants to maximise production on his farm
he collects data on three different breeds of pig as shown in the table on the right and in the graph below

           Meat yield (% of total body weight)  Breed 1.                        64 Breed 2.                        73 Breed 3.                        66

Calculate the rate at which breed 3 gained weight between 18 and 22 weeks

Which breed of pig would produce the most meat at 22 weeks?
Antibiotics can be used to treat bacterial diseases in a pigs

Suggest how using antibiotics may increase the net production of the pigs

Suggest and explain one other way the farmer could increase the net production of the pigs

Answer 15

Rate = change y / change in x

Meat yield / 100 x weight at 22 weeks

Breed 1 : 64 / 100 x 82 = 52 kg
Breed 2 : 73 / 100 x 76 = 55 kg
Breed 3 : 66 / 100 x 57 = 38 kg

Using antibiotics may mean that the pigs use less energy fighting the disease so they can use more energy to grow increasing their net production

Keep the pigs in pens to restrict the movement this will reduce the energy lost through respiration
keep the pigs indoors so that they are kept warm this will reduce the energy lost through generating body heat

Question 16

What does a food change show

Answer 16

Simple lines of energy transfer through an ecosystem

Question 17

Explain how simplifying a food web could increase the efficiency of energy transfer to humans

Answer 17

Simplifying the food web gets rid of food chains that don’t involve humans or pests this means that less energy is transferred to the pests increasing the efficiency of energy transfer to humans

Question 18

Give two examples of methods of pest control

Answer 18

Pesticides herbicides

Question 19

The table on the right shows the rate of nitrogen fixation by various sources in the early 1990s

Source of nitrogen fixation : rate of fixation (Tg N yr-1)

Lightning : 5.4
Bacteria in uncultivated land : 107
Bacteria in cultivated land : 31.5
Fertiliser manufacture : 86

What percentage of the total amount of nitrogen fixed by all sources was fixed by bacteria

1860, 120 Tf N per year was fixed by bacteria on uncultivated land.calculate the overall percentage decrease in the mass of nitrogen fixed per year by bacteria on uncultivated land between 1860 and the early 1990s

Suggest why the mass of nitrogen fixed in uncultivated land decreased between 1860 and the early 1990s

Using the table suggest one way in which the nitrogen cycle may have been altered by the action of humans

Answer 19

Percentage decrease = change / original x 100

(120-107) / 120 x 100 = 11%

More land was being cultivated in the 1990s than in 1860 so there was less uncultivated land

Thru the Manufacture of fertilisers

Question 20

Heavy rain combined with poor drainage can lead to soils becoming waterlogged.suggest and explain what might happen to the amount of nitrogen assimilated by a plant in waterlogged soils

Answer 20

It might decrease because waterlogged soils create anaerobic conditions this means that denitrifying bacteria convert nitrates in the soil back into nitrogen gas which the plants constant assimilate without nitrogen fixation

Question 21

Figure A and B below show simplified versions of the nitrogen and phosphorus cycles

In what form is phosphorus Assimilated by plants?

Name the process labelled x in figure A
(Living organism to soil)

Explain whats happening at the part labelled y in figure b

Give two ways in which phosphate ions r returned from living organisms to the soul

Answer 21

As phosphate ions dissolved in water

Ammonification (when n compounds turn into ammonia (saprobionts do this)

Phosphate ions dissolved in the oceans are assimilated by aquatic producers such as algae

Thru the death And decomposition of organisms and through the breakdown of compounds and faeces and urine

Question 22

Name two types of saprobiont

Answer 22

bacteria fungi

Question 23

How do saprobionts digest their food

Answer 23

The secrete Enzymes and digest food externally then absorb the nutrients they need

Question 24

What are mycorrhizae?

Answer 24

Mycorrhizae are symbiotic relationships between fungi and the roots of plants

Question 25

Explain how mycorrhizae increase water and mineral ion uptake by plants

Answer 25

The fungi have long thin strands called hyphae which connect to the plants roots.
the hyphae greatly increase the surface area of the plants roots system allowing the plants to absorb more water and mineral ions

Question 26

Name 4 processes in the nitrogen cycle

Answer 26

Nitrogen fixation
nitrification
denitrification and ammonification

Question 27

Describe the role of saprobionts in the phosphorus cycle

Answer 27

Saprobionts are involved in breaking down the organic compounds when plants and animals die releasing phosphate ions into the soil for assimilation by plants they also release the phosphate ions from urine and faeces

Question 28

What is guano

Answer 28

The waste produced by seabirds

Question 29

Why is guano important in the phosphorus cycle

Answer 29

Because it returns a significant amount of phosphate ions to the soil from the oceans

Question 30

Suggest an explanation for the increase in peak nitrate concentration between the first and second farm along the river

Answer 30

The second form uses a higher concentration of nitrate fertiliser on its land

Question 31

What are the results of the control river show

Answer 31

The nitrate concentration and algal content of the control river remain constant at 7 mgl-1 and 10,000 cells cm-3
this indicates that the nitrates concentration and Algal growth on rivers a and B were affected by the two farms and not due to any other environmental variable

Question 32

Describe and explain the possible consequences of the peaks in the algal content of river a at 200 m and 900 m

Answer 32

Large amounts of algae block lights from reaching the plants below
eventually the plants might die because they’re unable to photosynthesise enough bacteria would then feed on the dead plants matter
the increased number of bacteria reduces the oxygen concentration in the water by carrying out aerobic respiration this could reduce the number of fish and other aquatic organisms of the locations because there isn’t enough dissolved oxygen in the water

Question 33

Explain how mineral ions are lost from crop fields

Answer 33

Crops take in mineral ions from the soil as they grow
When crops are harvested they r removed from the fields where they’re grown rather than being allowed to die and decompose
this means the mineral ions that they contain for example phosphate and nitrates arent returned to the soil by decomposers in the nitrogen or phosphorus cycles

Question 34

Give an example of a natural fertiliser

Answer 34

Manure

Crop residue

Question 35

By what process do fertilisers get into waterways

Answer 35

Leaching

Question 36

Name the process that can occur as a result of excess fertilisers in waterways

Answer 36

Eutrophication

Question 37

Suggest environmental conditions under which the seedlings were grown which should have been controlled by the scientists

Answer 37

That should have controlled the temperature that the group of seedlings were kept at and the light intensity that the two groups of seedlings were exposed to

Question 38

Suggest an explanation for the differences between the mycorrhizae group and the control group shown in figure 2

Answer 38

The fungi are used to inoculate the mycorrhizae cultural group increase the surface area of the seedlings’ root systems compared to those in the control group
this increases the mycorrhizae group seedlings’ uptake of water and important mineral ions compared to the seedlings’ in the control group
this increases the growth of the seedlings in the mycorrhizae group

Question 39

When fertilisers are applied to fields next to a lake nitrogen-containing substances from the fertilisers get in to the lake
describe how the nitrogen-containing substances get into the lake

Answer 39

dissolve in soil water(leaching)

Question 40

It takes longer for the nitrogen-containing substances to get into the lake when an organic fertiliser is used than when an inorganic fertiliser is used explain why it takes longer when an organic fertiliser is used

Answer 40

Less soluble

Molecules require breaking down

Question 41

Describe how the presence of nitrates in a lake may eventually lead to the death of fish

Answer 41

Algal bloom
Blocks light 
Less photosynthesis 
Plants die
Increase in decomposers
Bacteria respire
Less oxygen

Question 42

Scientists investigatedthe effect of mycorrhizal fungus on the growth of pea plants with a nitrate fertiliser or ammonium fertiliser
the fertilisers were identical except for nitrate or ammonia
The scientists took pea seeds and sterilised their surfaces they planted the seeds in soil that had been heated to 85°C for two days
the soil was sand that contained no mineral ions useful to the plants

explain why the scientists sterilised the surfaces of the seeds and group them into soil but had it had been heated to 85°C for two days

Explain why it was important that the soil contained no mineral ions useful to the plants

Answer 42

To kill any fungus on surface of seeds
So only the added fungus has any effect

So that only nitrate or ammonium affects growth

Question 43

Describe the role of microorganisms in producing nitrates from the remains of dead organisms

Answer 43

Saprobionts break down remains into ammonia or ammonium

Ammonia ions to nitrite to Nitrate

By nitrifying bacteria/nitrification

Question 44

Nitrification

Answer 44

Ammonium ions to nitrates

Question 45

The diagram above include one process in which microorganisms add ammonium ions to soil describe another process carried out by micro organisms which adds ammonium ions to soil

Answer 45

Protein broken down into ammonia by Saprobionts

Question 46

Denitrification requires anaerobic conditions
ploughing aerates the soil
explain how ploughing would affect the fertility of the soil

Answer 46

Fertility is increased as more nitrate is produced

Less denitrification

Question 47

One farming practice used to maintain high crop yields is crop rotation
this involves growing a different crop each year in the same field
suggest two ways in which crop rotation may lead to high crop yields

Answer 47

Grow crops with nitrogen fixing bacteria

Different crops use different nutrient from the soil