Topic 5B: Energy Transfer and Nutrient Cycles

Question 1

What are biotic factors?
Give an example

Answer 1

• Living
  e.g. predators, food availability, pathogens

Question 2

What are abiotic factors?
Give an example

Answer 2

• Non-living
  e.g. temperature, light availability, water availability, pH, salinity

Question 3

Define ecosystem

Answer 3

• All organisms and the biotic & abiotic factors in an area

Question 4

Define population

Answer 4

• All organisms of one species in a habitat

Question 5

Define community

Answer 5

• All organisms of all species in a habitat

Question 6

Define habitat

Answer 6

• The place an organism lives

Question 7

Define niche

Answer 7

• The role of a species in an ecosystem

Question 8

Define trophic level

Answer 8

• Each stage of a food chain

Question 9

What productivity values do plants have?

Answer 9

• GPP -> total amount of energy made by a producer (units = given area per unit time - kJ/m^2/yr)
• NPP -> biomass accumulated
• R -> respiratory losses

Question 10

How is NPP calculated?

Answer 10

NPP = GPP - R

Question 11

What productivity values to animals have?

Answer 11

• I -> total energy ingested
• R -> respiratory losses
• F -> faeces and urine
• N -> net productivity

Question 12

How is net productivity (N) calculated?

Answer 12

N = I - (R + F)

Question 13

How do you calculate energy transfer efficiency?

Answer 13

• N/I x100

Question 14

How is energy lost from the sun to a producer?

Answer 14

• Light reflected
• Not all light shines on photosynthetic areas

Question 15

How is energy lost between producers and primary consumers?

Answer 15

• Respiration
• Heat
• Not all of the producer eaten - e.g. deep roots
• Some not digested - e.g. cellulose

Question 16

How is energy lost between consumers?

Answer 16

• Respiration, heat
• Not all eaten - e.g. bones

Question 17

How do you make dry biomass?

Answer 17

• Put in an oven on a low temperature - prevent combustion
• Regularly measure the mass
• When the mass remains constant - all the water has been removed - now dry

Question 18

What unit do you measure dry biomass in?

Answer 18

kg/m^2

Question 19

Describe calorimetry

Answer 19

• Estimates the amount of energy stored in dry biomass
• Burn a sample of dry biomass completely to heat a known volume of water
• Change in temperature is used to calculate the chemical energy of the dry biomass

Question 20

What is mass of carbon?

Answer 20

• Organisms are made of organic compounds that contain carbon
• Mass of carbon is a good biomass indicator
• Very difficult to measure
• Mass of carbon is around 50% of dry biomass
• Measured in kg/m^2/yr - accounts for seasonal changes

Question 21

What are the two types of decomposers?

Answer 21

• Saprobiotic microorganisms -> extracellular digestion - secrete enzymes to hydrolyse molecules - then absorb the smaller molecules produced (fungi, bacteria etc)
• Detritivores -> feed on dead / decaying matter, digest in the body (earthworms, maggots etc)

Question 22

In farming what are 2 methods of reducing lost energy?

Answer 22

• reducing energy lost to other organisms
• reducing energy lost through respiration

Question 23

What are ways of simplifying food webs?

Answer 23

Chemical pesticides
- Insecticides -> kill pests, less biomass lost, grow more, inc NPP
- Herbicides -> kill weeds, removes direct competition, removes pest food sources
Biological agents
- Parasites -> Kill insect / reduces its function, live or lay eggs on pest, viruses / bacteria - kill pests

Question 24

How are these methods of simplifying food webs best used?

Answer 24

• As integrated systems
• Use both chemical and biological
• Reduces pest numbers further than one method alone
• Even more inc in NPP

Question 25

What are ways of reducing respiratory losses?

Answer 25

Controlling conditions
- Restrict movement -> Small pens, indoors, warm
- Less energy wasted on maintaining body temperature
- More biomass produced, inc NP and energy transfer efficiency

Question 26

What are the benefits of reducing respiratory losses?

Answer 26

• More food produced in less time
• Lower cost

Question 27

What are issues with methods of reducing respiratory losses?

Answer 27

• Ethics
• Pain, distress caused
• Restricts the natural behaviour of animals

Question 28

Why are fertilisers needed?

Answer 28

• Crops take in minerals from soil as they grow
• When they are harvested these are taken with them
• They do not die and decompose there - nutrients not recycled back in by decomposers
• Nutrients also lost as animals eat plants and are then moved away

Question 29

What do fertilisers do?

Answer 29

• Replace lost minerals and increase energy efficiency

Question 30

What are artificial fertilisers?

Answer 30

• Inorganic
• Pure chemicals
• Powders / pellets

Question 31

What are natural fertilisers?

Answer 31

• Organic matter
• Manure, composted vegetables, crop residue, sewage sludge

Question 32

What are issues with fertilisers?

Answer 32

• Too much applied - overflow leaches into waterways
• Happens when fertiliser applied before heavy rainfall
• Change the nutrient balance of the soil - can cause crop death

Question 33

How do natural fertilisers have less issues?

Answer 33

• Minerals are contained in organic molecules
• They need to be decomposed first
• Cause a more controlled release - less likely to leach away

Question 34

What nutrients are less likely to leach?

Answer 34

• Phosphates
• Less soluble

Question 35

What causes eutrophication?

Answer 35

• Excess nutrients

Question 36

Describe the process of eutrophication

Answer 36

1. Mineral ions from fields cause rapid algal growth
2. Algae blocks sunlight from reaching plants below
3. Plants die as they cannot photosynthesise
4. Bacteria feed on dead plants - aerobically respire reducing O2 concentration
5. Fish & aquatic organisms die - not enough dissolved O2

Question 37

How do fungi help plants?

Answer 37

• Form symbiotic relationships with plant roots - mycorrhizae
• Long, thin strands (hyphae) - inc SA to absorb ions and water
• Fungi gain compounds such as glucose from the plant

Question 38

Describe the nitrogen cycle

Answer 38

nitrification nitrification denitrification
[Ammonium ions] —-» [nitrites] —-» nitrate —-» N2 in air
^ feeding l absorption l
l (animals)«—– (plants)«———-
l death & excretion l l death nitrogen
——————————–(decomposers) fixation
ammonification

Question 39

What things contain nitrogen compounds?

Answer 39

• Proteins
• DNA

Question 40

What is nitrification?

Answer 40

• Ammonium ions to nitrogen compounds for plants - oxygen added
• Done by nitrifying bacteria

Question 41

What is denitrification?

Answer 41

• Nitrates in the soil are converted to nitrogen gas
• Done by bacteria
• In anaerobic conditions only –> aerate soil, not waterlogged

Question 42

What is nitrogen fixation?

Answer 42

• Nitrogen from the atmosphere turned to nitrogen containing compounds
• Done by bacteria in the root nodules of leguminous plants
• N2 -> ammonia -> ammonium ions
• Form a mutualistic relationship

Question 43

What is ammonification?

Answer 43

• Saprobionts turn nitrogen compounds from dead organisms into ammonia
• Also done to animal waste

Question 44

Describe the phosphorus cycle

Answer 44

(fish)—-»(birds) (plants)———–»(animals)
l l / \ / \
(algae) [guano]—-»[soil]«–(decomposers)«–[urine&]
l ^ [faeces]
[seas&] l
[lakes] «——————- [rock]

Question 45

What things contain phosphates?

Answer 45

• DNA
• ATP
• Phospholipids

Question 46

How are phosphates released from rocks?

Answer 46

• Weathering releases phosphates from rock to soil and bodies of water

Question 47

How do plants obtain phosphates?

Answer 47

• Absorb them through the roots from the soil

Question 48

How do phosphates travel from the sea to the soil again?

Answer 48

• Phosphates taken in by aquatic producers
• Passed along the food chain to fish and then sea birds
• Waste from sea birds - guano - high proportion of phosphates which are returned to the soil
• Often used as a natural fertiliser