✅13 - Energy And Ecosystems Flashcards
What are producers?
Photosynthetic organisms that manufacture organic substances using light energy, water, CO2 and mineral ions
What are consumers?
Organisms that obtain their energy by feeding on other organisms rather than using the energy of the sunlight directly
What are saprobionts?
A group of organisms that break down the complex materials in dead organisms into simple ones, releasing valuable minerals and elements that can be absorbed by plants
What is a food chain?
A feeding relationship in which the producers are eaten by primary consumers
What is a trophic level?
Each stage in the food chain
What are food webs?
The way that different food chains link together
What is biomass?
The total mass of living material in a specific area at a given time
What is biomass measured in?
Grams per square metre of dry mass
Why is most of the sun’s energy not converted into organic matter?
Over 90% of it is reflected back to space by clouds and dust
Not all wavelengths of light can be absorbed by chlorophyll
Light may not fall on a chlorophyll molecule
Other factors such as low CO2 levels may limit the rate of photosynthesis
What is gross primary production?
The total quantity of chemical energy stored in plant biomass in a given area or volume in a given time
What is net primary productivity?
Gross primary production - respiratory losses
Why is the percentage of energy transferred at each trophic level low?
Some of the organism is not consumed
Some parts are consumed but cannot be digested
Some energy is lost in excretory materials eg urine
Some energy loss occurs from heat and respiration etc
What is the net production of consumers calculated as?
I-(F+R)
I = chemical energy ingested
F = energy lost in faeces and urine
R = energy lost in respiration
Why do most food chains only have four or five trophic levels?
Because insufficient energy is available to support a large enough breeding population at trophic levels higher than these
What intensive farming practices are used to conserve energy?
Movement restricted to reduce energy used for muscle contraction
Environment kept warm to reduce energy used for heat
Feeding controlled so that maximum growth and little wastage occurs
Predators excluded
What is the general pattern that all nutrient cycles follow?
Nutrient taken up by producers
Producer converts into complex organic molecule
Producer eaten, passes into consumer
Passes along food chain where animals eaten by other consumers
Complex molecules broken down by saprobiontic microorganisms
Why do living organisms require nitrogen?
To produce organic molecules such as proteins and nucleic acids
How do plants take up nitrogen?
As nitrate, NO3-, from the soil by active transport
How is nitrate concentration of soil increased in agriculture?
Through fertilisers
What are the four main stages on the nitrogen cycle?
Ammonification, nitrification, nitrogen fixation and denitrification
What do all the main stages of the nitrogen cycle involve?
Saprobionts
What is nitrogen fixation?
Conversion of nitrogen in the atmosphere into ammonium ions or ions
What is nitrification?
Turning ammonium ions into nitrite and then nitrate ions
What is ammonification?
The production of ammonia from organic nitrogen containing compounds
What type of reaction is nitrification?
Oxidation
What are the two main types of nitrogen fixing bacteria?
Free-living nitrogen-fixing bacteria
Mutualistic nitrogen-fixing bacteri
What are free-living nitrogen-fixing bacteria?
Bacteria that reduce gases nitrogen to ammonia which they use to manufacture amino acids. Nitrogen compounds released from them when they die and decay
What are mutualistic nitrogen-fixing bacteria?
Bacteria that live in nodules on the roots of plants such as legumes. They obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria
What do denitrifying bacteria do?
Convert soil nitrates into gaseous nitrogen
Why must soils be kept well aerated?
To prevent build up of denitrifying bacteria which reduce the availability of nitrogen containing compound for plants
Why do denitrifying bacteria build up in less aerated soil?
Because they carry out denitrification in anaerobic conditions, while nitrifying and nitrogen-fixing bacteria work in aerobic conditions
What is phosphorus used for?
ATP, phospholipids and nucleic acids
What does the phosphorus cycle lack?
A gaseous phase
What does phosphorus mostly exist as?
Phosphate ions, PO4 3-, in sedimentary rock deposits
What helps phosphate ions to become dissolved?
The weathering of rocks
What are dissolved phosphate ions absorbed by?
Plants
How does excretion of phosphate occur?
In the waste products of plants and animals as well as when they die
How can phosphate ions reach the oceans, lake and soils?
Erosion of rocks
Use of fertilisers
Excretion
What are mycorrhizae?
Associations between certain types of fungi and the roots of the vast majority of plants
How do mycorrhizae benefit the plants?
They increase the total surface area for the absorption of water and minerals and act like sponges to hold water and minerals around the plants even in drought
How do mycorrhizae play a part in nutrient cycles?
The improve the uptake of relatively scarce ions such as phosphate
What the the mycorrhizal relationship between plants and fungi?
Mutualistic
How do the fungi benefit from mycorrhizal relationships?
They gain sugars and amino acids form the plant
What is intensive food production?
Concentrated on specific areas of land that are used repeatedly to achieve maximum yield form the crops and animals on them
Why do concentrations of mineral ions on agricultural land fall?
The crop is harvested rather than dying back, and the urine, faeces and dead remains of the consumer are rarely returned to the same area of land
Why are fertilisers necessary?
To replenish mineral ions on the land
What are natural/organic fertilisers?
Consist of dead and decaying remains of plants and animals as well as animal waste
What are artificial/inorganic fertilisers?
Mined from rocks and deposits then converted into different forms and blended together to give the appropriate balance of minerals for a crop
What has the greatest long term increase in productivity?
A mixture of natural and artificial fertilisers
How do fertilisers increase productivity?
When more ions available, plants are likely to develop earlier, grow taller and have greater leaf area for more photosynthesis, increasing crop productivity
What are the effects of nitrogen containing fertilisers?
Reduced species diversity
Leaching
Eutrophication
Why is species diversity reduced by nitrogen containing fertilisers?
Nitrogen rich soils favour the growth of grasses, nettles and other rapidly growing species, which out compete others and they die as a result
What is leaching?
The process in which nutrients are removed from the soil and rainwater dissolves soluble nutrients, carrying them deep into the soil and potentially reaching water courses
What is eutrophication?
The process by which nutrient concentrations increase in bodies of water
What is the sequence of events that causes eutrophication?
Low concentration of mineral ions is limiting factor of algal growth in water bodies
As nitrate ion concentration increases as a result of leaching, plant and algal growth increases - algal bloom
Light prevented from reaching lower layers of water
Plants at bottom of water die
Saprobiontic bacteria use dead organisms as food, use oxygen for respiration
Oxygen concentration decreases, aerobic organisms die
Anaerobic organisms increase in number, water toxic
