Section 5- Energy and ecosystems Flashcards
How is most energy lost?
Lost as heat
Leaves the environment as thermal energy
How is the energy content of organisms measured?
Measuring dry biomass
Why is dry biomass used to measure the energy content of organisms?
There is no energy in water
Water content of an organism can vary
What is used to measure energy content of organisms?
Calorimeter
What is an autotroph?
Plants
What is a heterotroph?
Organism that gets energy from other organsisms
How do you calculate energy efficiency?
Net production of trophic level
/Total energy of previous trophic level
x100
How is the Net production (N) calculated in heterotrophs?
N = I - (F + R)
I = Energy ingested F = Losses in faeces R = Losses in respiration
How is the Net Primary Product (NPP) calculated in autotrophs?
NPP = GPP - R
GPP = gross primary production R = respiration losses
Suggest how the efficiency of energy transfer in cattle could be improved?
Keep the cattle in sheds
Less energy used in movement
Less energy used in keeping warm
More energy available for growth
What is the nitrogen cycle?
Cycling of nutrients including nitrogen involved saprobiotic micro-organisms
What does saprobiotic mean?
Digesting extracellularly
Release enzymes, digestion occurs outside of the cell and the digested products are absorbed
What is ammonification and nitrification in the nitrogen cycle?
Dead organic matter contains nitrogen in proteins, DNA, RNA and ATP
Nitrogen is also found in urea and faeces
Bacteria will convert nitrogen into:
Ammonia -> nitrite -> nitrate
What is nitrogen fixation?
Nitrogen fixing bacteria take nitrogen gas and convert it to ammonia or nitrates
Many bacteria live in root nodules of leguminous plants
Bacteria makes nitrates for the plant which provides glucose and amino acids for the bacteria
What do mycorrhizae do in the nitrogen cycle?
Fungi which grow on roots of many plants
Extend the roots further into the soil and across a wider area
Provides plants with greater surface area for absorbing nutrients and water
Fungi get a source of glucose from the plant
What is denitrification?
Occurs when the soil becomes anaerobic (water-logged)
Denitrifying bacteria removes oxygen from nitrates for respiration
Releases nitrogen as nitrogen gas
-Quickly makes soil fertile
What is assimilation in the nitrogen cycle?
Uptake of ammonium ions and nitrates by plant roots and their incorporation into plant protein and nucleic acids
What are 2 reasons for the stunted growth of plants in a field?
Lack of nitrates due to denitrification
Little oxygen for respiration to provide energy for active transport
Why are composts rich in cellulose likely to be poor in nitrogen-containing ions?
Cellulose doesn’t contain nitrogen, neither do decomposed products
What is eutrophication?
When excess nitrates and phosphates are leached (washed) from soil into rivers and lakes, algal bloom occurs
What is the problem with eutrophication?
Algal bloom blocks light from reaching photosynthetic aquatic organisms, leading to their death
Decomposers use up oxygen in water, leading to death of aerobic animals
Only anaerobic bacteria survives- water becomes stagnant
What are the stages of the phosphorus cycle?
- Weathering
- Runoff
- Assimilation
- Decomposition
- Uplift
Why is the phosphorus cycle a slow process?
Phosphorus has no gas phase
No atmospheric cycle
What happens during weathering and runoff in the phosphorus cycle?
Phosphate compounds from sedimentary rocks leach into surface water and soil
What happens during uplift in the phosphorus cycle?
Sedimentary layers from oceans are brought up to land over many of years
What are the 4 main stages of the nitrogen cycle?
- Nitrogen fixation
- Ammonification
- Nitrification
- Denitrification
Why can’t organisms use nitrogen directly from the atmosphere?
N2 is very stable due to strong covalent triple bonds
How can the risk of eutrophication be reduced?
Use phosphate-free detergent
Pumping nutrient-enriched sediment out of water
Sewage treatment marshes on farms
What are 2 environmental issues caused by the use of fertilisers?
Eutrophication- algal bloom causes water sources being putrid
Leaching- nitrates dissolve in rainwater and runoff into water sources
What are the 2 categories of fertilisers?
Organic- decaying organic matter & animal waster
Inorganic- minerals from rocks, usually containing nitrogen, phosphorus, potassium
What are the advantages of planting a different crop on the same field each year?
Different crops use different proportions of certain ions
Different crops have different pathogens
Nitrogen-fixing crops make soil more fertile
How do plants use the sugars from photosynthesis?
Primarily as respiratory substrates
To synthesise other biological molecules
What is biomass?
Total dry mass of tissue or mass of carbon measured over a given time in a specific area
What is gross primary production?
Total chemical energy in plant biomass within a given volume or area
What is net primary productivity?
Total chemical energy available for plant growth, reproduction and energy transfer to other trophic levels after respiratory losses
Why is most of the suns energy not converted to organic matter?
Most absorbed by atmosphere or reflected by clouds
Photosynthetic pigments cannot absorb some wavelengths of light
Not all light falls directly on a chlorophyll molecule
Lost as heat during respiration/ photosynthesis
Why does biomass decrease along a food chain?
Energy lost in nitrogenous waste and faeces
Some of organisms not consumes
Energy lost to surroundings as heat
What are some common farming practices used to increase efficiency of energy transfer?
Exclusion of predators
Artificial heating
Restriction of movement
Feeding is controlled at the optimum
What are 2 nitrogen-containing molecules that are found in plants and animals?
DNA
ATP
What is the role of microorganisms in nitrogen fixation?
Converts nitrogen gas to ammonia ions
What is the role of microorganisms in denitrification?
Converts ammonia ions into Nitrogen gas
What are 2 advantages of using treated sewage sludge on farmland, rather than inorganic fertilisers?
Improves soil quality
Ensures it is anaerobic
Cheaper for farmers to use it
Why is there no build-up of phosphate ions when they enter chloroplasts?
Used in phosphorylation of ATP in the light-dependent reaction
Catalysed by ATP synthase
What do the arrows in a food web show?
The direction of energy flow
What is the general name to describe the bacteria and fungi that will break down death matter?
Saprobionts/ decomposers
What are 3 reasons for the small percentage of energy transferred at each trophic level?
Some of the organism is not eaten
Some parts are not digested and so are lost as faeces
Some energy is lost as excretory materials
Some energy is lost as heat
Why do most food chains rarely have more than four trophic levels?
After 4 trophic levels there is insufficient energy to support a large enough breeding population
Why does biomass show little increase after 100 years?
Net productivity = gross productivity - respiratory loss
Decrease in gross productivity
Why does gross productivity decrease as woodland matures?
Less light = more competition for light
Reduced photosynthesis
How do nitrogen-containing substances get into a lake from a field?
Runoff
How is nitrogen taken up by plant roots?
Uptake by roots involves active transport
Requires ATP
How does the presence of nitrates in a lake eventually lead to the death of fish? [4]
Algal bloom
Blocks light = less photosynthesis
Plants die
Less oxygen for fish
What is the role of microorganisms in producing nitrates from the remains of dead organsisms?
Saprobiotic break down dead material
Ammonium -> nitrite -> nitrate
By nitrifying bacteria
What is leaching?
Fertiliser dissolves in soil water
What are mycorrhizae and how do they benefit many plants?
Fungi that live in close association with plant roots
Increase water uptake
How does hedge removal result in the removal of nitrogen-containing compounds?
Leaching of nitrates
Why are leguminous plants important in succession?
Able to grow in nitrate poor soil
It will provide more nitrate when it dies
- these can be used by other species
What happens to the energy reaching producers that is not converted to growth?
Lost to surroundings as heat
Reflected off the plant
Why would percentage energy transfer between producers and primary consumers be less than the transfer between primary consumers and secondary consumers?
Producers have cell walls
Difficult to digest
Much cannot be eaten
What are 2 disadvantages of using biological pest control?
Risk of migration
Slow to work
May eat crop
What is a way in which nitrogen in the air can be converted directly into nitrate ions?
Lightning
Why might farmers grow plants containing root nodules on fields during periods when crop plants are not growing?
Nodules contain nitrogen-fixing bacteria
Increase amount of nitrogen containing compounds, increases amount of nitrogen available for next crop to use
What is one source of phosphate in a lake?
Fertilisers, detergents, sewage, faeces
Explain how a change in the phosphate concentration in a lake may have resulted in a decrease in fish population? [6]
Increased phosphate causes algal bloom
Plants cover surface, blocking light so plants underneath die - causes increase in decomposers
Decomposers use up oxygen in respiration
Plants unable to photosynthesise so less oxygen produced
