Energy Flow and Nutrient Cycles

Question 1

What do food chains and food webs show?

Answer 1

How energy is transferred through an ecosystem.

Question 2

What do food webs show?

Answer 2

Lots of food chains in an ecosystem and how they overlap.

Question 3

Why is not all the energy transferred to the next trophic level?

Answer 3

• plants can’t use all of the light energy
• some parts of the organism are not eaten (eg. roots, bones…)
• some parts of the organism are indigestible (eg. cellulose)
• 30% of all losses from respiration

Question 4

What do pyramids of numbers show? What traits do they usually show?

Answer 4

The number of organisms in each trophic level

Not always pyramid-shaped

Question 5

What do pyramids of biomass show? What traits do they usually have?

Answer 5

The amount of biomass in each trophic level (dry mass per sqm) at a single moment in time.

Nearly always pyramid-shaped, except when based on plant plankton

Question 6

Why are pyramids of biomass based on a plant plankton population dumbbell shaped?

Answer 6

Plankton have a short life span and reproduce quickly. Therefore there is a small amount at a given time, but many over a period.

Question 7

What do pyramids of energy show? What traits do they usually show?

Answer 7

The amount of energy available in each trophic level thus the net productivity of each trophic level.

Always pyramid shaped.

Question 8

What is the basic premise of intensive farming and it’s purpose?

Answer 8

Controlling the abiotic and biotic conditions to make conditions more favourable for livestock or crop, thus increasing net productivity.

Question 9

Which three ways can intensive farming be undertaken?

Answer 9

1 - increasing the efficiency of energy conservation (so that more is used for growth)

2 - removing growth-limiting factors

3 - increasing energy input

Question 10

Chemical pesticides

Answer 10

Herbicides, fungicides and insecticides

Question 11

Environmental issues with chemical pesticides:

Answer 11

They may directly or indirectly (build-up) non-pest species.

Question 12

Economic issues with chemical pesticides:

Answer 12

They’re expensive and thus may not be profitable for some farmers.

Question 13

Biological pesticides

Answer 13

Natural predators, parasites and pathogenic bacteria.

Question 14

Environmental issues with biological pesticides:

Answer 14

They may become pests themselves, or could affect other non-pest species.

Question 15

Economic issues with chemical pesticides:

Answer 15

They may be less cost-effective than chemical pesticides; they may increase productivity less in the short term for the same amount of money.

Question 16

What are the advantages of integrated pest control?

Answer 16

• The combined effect reduces the pests more than one alone.
• It can reduce costs if one method is particularly expensive.
• It can reduce environmental impact as less is used of each one.

Question 17

What is the purpose of fertilisers?

Answer 17

To replace lost minerals, so that more energy from the ecosystem can be used to grow, increasing the efficiency of energy conservation.

Question 18

What are the types of fertiliser and give examples of them:

Answer 18

• Natural, i.e. organic matter (manure, sewer sludge…)

- Artificial, i.e. inorganic pure chemicals (ammonium nitrate…)

Question 19

What are the environmental issues surrounding fertiliser use?

Answer 19

• it can run off the land, causing eutrophication and killing plants and animals.
• it can change the balance of nutrients in the soil - too much of a particular nutrient can cause crops and other plants to die.

Question 20

What economic issues surround the use of fertilisers?

Answer 20

The farmer must get the balance perfect. Too much and it is washed away and wasted; too little and the productivity is not increased, thus the fertiliser is not economically viable.

Question 21

What is the basis of rearing livestock intensively, and to what end?

Answer 21

Controlling the living conditions, meaning that more energy is used for growth and less for other activities.

This increases the efficiency of energy conversion, thus more biomass is produced, so the productivity is increased.

Question 22

How can livestock be reared intensively?

Answer 22

• The animals are kept warm, indoors and with restricted movement so that less energy is kept keeping warm and moving around.
• The animals are given a feed higher in energy than natural food, increasing the energy input and thus making more energy available for growth.

Question 23

What are the benefits of rearing livestock intensively?

Answer 23

You can get more food in a shorter space of time, often at a lower cost.

Question 24

What ethical implications are there of intensive livestock rearing?

Answer 24

The conditions cause pain, distress and limits the animals’ natural behaviour.

Question 25

Cause of annual CO2 fluctuations.

Answer 25

Most plant life is found in the northern hemisphere, as there is more land; most plant growth occurs in the summer (as light intensity is greatest in the northern hemisphere), so more photosynthesis occurs, thus CO2 concentrations decrease in the summer and increase in the winter.

Question 26

What are the causes of increased CO2 concentrations?

Answer 26

The destruction of natural sinks and the burning of fossil fuels.

Question 27

What are the causes of increased methane concentrations?

Answer 27

More fossil fuels being extracted, there is more decaying waste, more cattle and thawing permafrost.

Question 28

What are the main causes of global warming?

Answer 28

- burning fossil fuels - farming - deforestation

Question 29

What will be the effects of global warming on crop yield?

Answer 29

Increased crop yield (as [CO2] is a limiting factor in photosynthesis)

Question 30

What will be the effects of global warming on insect pests?

Answer 30

- may affect the life cycle (some go through larval stage quicker) - may affect numbers (warmer, wetter summers increase some pest numbers in some areas (eg. Mosquitos in temperate regions) and decrease in others (eg. sensitive tropical species as too hot)

Question 31

What will be the effects of global warming on wild animals and plants?

Answer 31

- it may affect distribution (those that need warmer conditions may spread further, those that need cold will regress) - it may affect number (for a similar reason), eg. Boarfish and Polar Bears.

Question 32

Explain nitrogen fixation:

Answer 32

Nitrogen gas is converted to ammonia by Rhizobium bacteria found on root nodules of leguminous plants, via a mutualistic relationship, to be used by plants.

Question 33

Explain ammonificafion:

Answer 33

Nitrogen compounds from dead organisms and animal waste are converted to ammonium compounds by decomposers.

Question 34

Explain nitrification:

Answer 34

Ammonium compounds in the soil are converted into nitrogen compounds to be used by plants, in a two-step process: 1 - Nitrifying bacteria (eg. Nitrosomonas) change ammonium compounds into nitrites. 2 - Other nitrifying bacteria (Nitrobacter) change nitrites into into nitrates.

Question 35

Explain denitrifying bacteria:

Answer 35

Nitrates in the soil are converted into nitrogen gas by denitrifying bacteria, who use nitrates for respiration. This only occurs under anoxic conditions, eg. waterlogged soils.

Question 36

Leaching

Answer 36

When water-soluble compounds in the soil are washed away, usually into nearby ponds or rivers.

Question 37

Leaching of nitrogen fertiliser is called...

Answer 37

Eutrophication

Question 38

State the six steps of eutrophication:

Answer 38

1 - Nitrates stimulate the growth of algae in ponds and rivers 2 - The algal blooms block light from reaching the plants below 3 - The plants are unable to photosynthesise enough, so die 4 - Bacteria feed on the dead plant matter. 5 - The increased number of bacteria reduce the concentration of oxygen in the water by carrying out aerobic respiration. 6 - Fish and other organisms die because there isn't enough dissolved oxygen.