13: Energy and ecosystems Flashcards
What is the ultimate source of energy for almost all organisms?
Sunlight
What are the three groups of organisms divided by how they obtain energy?
Producers
Consumers
Saprobionts (decomposers)
Define producers
Photosynthetic organisms that manufacture organic substances using light energy, H20, CO2, and mineral ions
Define consumers
Organisms that obtain their energy by consuming other organisms
Define primary consumers
Organisms that feed on producers
Define secondary consumers
Organisms that feed on primary consumers
Define tertiary consumers
Organisms that feed on secondary consumers
What is the alternative name for secondary/tertiary consumers?
Predators
Can be scavengers or parasite
Define saprobionts
Organisms that break down complex materials of dead organisms into simple ones
E.g fungi and bacteria
Why are saprobionts important?
Simple molecules such as minerals and elements can be absorbed by plants
This contributes to recycling
Define a food chain
Describes feeding relationships between different producers and consumers
Producers-> 1° consumers -> 2° consumers etc
What are the stages in a food chain called?
Trophic level
What are the arrows in food chains representing?
Direction of energy flow
Define a food web
Shows the links between different food chains
Usually involves most organisms in an ecosystem
Define biomass
Total mass of living material in a specific area at a given time
What is biomass measured in?
Dry mass per given area in a given time
g/m2 in dry area
g/m3 in a wet area
What is calorimetry?
Method to determine the energy store in dry mass
How is bomb calorimetry done?
Sample of dry material weighed and burnt in pure oxygen in sealed “bomb” chamber
Bomb surrounded by water, temp that water increases by is measured
Use equations to find energy released and kJ/kg
What is the % of light which is converted into energy in plants?
1-3%
Why is so little of the Sun’s energy absorbed by plants?
90% reflected into space by clouds or dust in the atmosphere
Not all λ absorbed
Light may not fall on chlorophyll (photosystem)
Other limiting factor may limit photosynthesis
Define gross primary production (GPP)
Quantity of chemical energy stored in plant biomass in a given area/volume
Define net primary productivity (NPP)
Chemical energy stores left after losses to respiration taken into account
What is the equation related to GPP, NPP and R?
NPP = GPP - R
NPP - net primary production
GPP - gross primary production
R - respiratory losses
What are the percentages of energy transferred from trophic levels?
Producer-> Primary consumer 10%
Primary consumer -> Secondary 20%
What are the reasons little energy is transferred between trophic levels?
Not all of the organisms consumed
Some parts consumed but not digested so it would be lost in faeces
Energy lost in excretory materials
Losses as heat from respiration to environment
Why are energy losses as heat from respiration high in mammals and birds?
High body temperature
Much energy needed to maintain body temp, and heat lost to the environment
What is the equation relating to net production and energy losses?
N = I - (F+R) N - net production I - chemical energy store of ingested food F - energy lost in faeces and urine R - energy lost in respiration
What does the inefficiency of energy transfer explain?
Most food chains only have 4 or 5 trophic levels as insufficient energy to support a large enough breeding population
Total mass of organisms in a particular place (biomass) is less at higher trophic levels
Less total amount of energy available is less at each level
What is the equation for % efficiency?
% efficiency = 100 x energy available after the transfer / energy available before the transfer
Why is it important nutrients are recycled?
No extraterrestrial source so must be conserved
What are the standard processes in the nutrient cycle?
Nutrient taken up by producers (simple, inorganic molecules)
Producer incorporates nutrients into complex organic molecule
Nutrient passes to consumers when eaten
Producers/consumers die and complex molecules broken down by saprobionts into simple inorganic molecules at the start
Why saprobionts important in nutrient cycles?
They allow for the nutrients to be converted into simple inorganic molecules
Why is nitrogen needed?
Manufacture of: proteins, nucleic acids and other nitrogen-containing compounds
In what form do plants take up nitrogen and where from?
Nitrate ions (NO3 -) from the soil
How are nitrate ions absorbed by plants?
Active transport into the roots
How do animals gain a source of nitrogen-containing compounds?
Eating and digesting plants and other consumers
Why and how are nitrogen concentrations restored in soil?
Needed as nitrate ions are very soluble and can be leached (washed) through the soil
Restored by recycling of nitrogen-containing compounds
How are nitrogen concentrations restored in agricultural soil?
Addition of fertilisers
What are the four main stages in the nitrogen cycle?
Ammonification
Nitrification
Nitrogen fixation
Denitrification
What is ammonification?
Production of ammonia from organic nitrogen-containing compounds
Done by saprobionts by such as fungi and bacteria
What is nitrification?
Conversion of ammonium ions to nitrite ions
Nitrite ions converted to nitrate ions
Done by nitrifying bacteria which requires oxygen, so aeration improves productivity
What is nitrogen fixation?
Nitrogen gas converted into nitrogen-containing compounds
Can be industrially or naturally
What are two main types of natural nitrogen fixation?
Free-living bacteria - reduce N2 to ammonia and manufactured into amino acids, nitrogenous compounds released when they die
Mutualistic bacteria - live on nodules of legumes, obtain carbohydrates from plant and the plant gets amino acids from bacteria
What is denitrification?
Different bacteria when waterlogged (low O2)
More anaerobic denitrifying bacteria
Convert soil nitrates into gaseous nitrogen
Why is denitrification bad for agricultural?
Reduces nitrogen-containing compounds for plants and therefore reduces plant growth
Learn the nitrogen cycle
Do it
p307
Why is phosphorus an important biological element?
Component of ATP, phospholipids and nucleic acids
What form is phosphorus usually found in the environment?
PO4 3-
Learn the phosphorus cycle
Do it
p309
How are phosphate ions transferred from soil to plants?
Absorption
How are phosphate ions transferred from plants to animals?
Feeding and digestion
How are phosphate ions transferred from animals to soils?
Excretion
How are phosphate ions transferred from animals to wastes and remains (bones etc.)?
Excretion and decomposition
How are phosphate ions transferred from bones to phosphates in rocks?
Deposition
How are phosphate ions transferred from rocks to soils and vice versa?
Rocks -> soils is erosion and use of fertilisers
Soils -> rocks is sedimentation
Define mycorrhizae
Associations between certain fungi and the roots of the majority of plants
Why are mycorrhizae important?
Increase SA:V ratio for absorption of minerals and water
Plant gets minerals and water, fungus receives organic compounds (sugars and amino acids)
What is a mutualistic relationship?
One which benefits both organisms
Why do agricultural ecosystems need to increase efficiency of energy transfer?
Increases the productivity meaning more money is made
Why are fertilisers are needed in agriculture?
Crops grown on the same land (intensive farming)
Mineral ions absorbed by crops and are not decomposed as removed
Faeces and urine rarely returned to same location
What are the two types of fertilisers?
Natural (organic) fertilisers
Artificial (inorganic) fertilisers
What are natural (organic) fertilisers?
Consist of dead and decaying remains of plants and animals (including their waste)
What are artificial (inorganic) fertilisers?
Mined from rocks and deposits, then converted into different forms and blended
Nitrogen, phosphorus and potassium always present
How do fertilisers increase productivity?
Minerals used to make compounds like proteins etc.
Needed for plant growth, increases rate of photosynthesis and improves crop productivity
What are the detrimental effects of nitrogen-containing fertilisers?
Reduced species diversity - plants that benefit from nitrogen rich soil out-compete the others, causing others to die
Leaching - may lead to pollution of watercourses and could lead to eutrophication
Define leaching
Process of nutrients being removed from the soil
Removed by water which dissolves soluble minerals and takes them into the lakes and rivers etc.
Why is leaching harmful?
Can lead to eutrophication
V. high conc of nitrate ions can cause health problems in drinking water
Define eutrophication
Process by nutrient conc increase in bodies of water and the natural processes which occur because of it
What are the steps of eutrophication?
V. low conc of nitrates in lakes/rivers, limiting factor for plant growth
Increase of nitrate conc caused by leaching causing plants/algae populations to grow
Algae become densely populated “algal bloom” which absorbs light
Light becomes limiting factor for growth at lower depths
Saprobiont populations increase due to death of plants
Saprobionts use O2 for respiration, reducing O2 conc and nitrates released from dead organisms
Aerobic organisms die (lack of O2)
Anaerobic populations rise and decompose dead materials, which increases nutrient conc in water
