13. ENERGY & ECOSYSTEMS Flashcards
Where does the energy in ecosystems originally come from?
The sun
In which direction does the arrow go in a food chain?
In the direction of energy flow
What is each level in a food chain called?
A tropic level
List the trophic levels in a food chain
Producer, primary consumer, secondary consumer, tertiary consumer and quaternary consumer.
Why are plants producers?
Because they produce their own food in photosynthesis.
What percentage of the sun’s rays will be absorbed by a plant?
1-3%
Why will only 1-3% of the sun’s rays be absorbed by a plant?
Some will be reflected / absorbed by the atmosphere, some is the wrong wavelength to be absorbed by chlorophyll
How much energy is converted to new biomass in each trophic level?
5-20%
Why does the amount of biomass decrease at each trophic level?
Not all of the organism will be consumed, some parts of the organism are undigestable, some energy is lost as heat, and some energy is lost in respiration
Describe how to measure the biomass at a trophic level
Put organisms into an oven at a high temperature (100-150 degrees Celsius) until the water has evaporated. Then weigh the dry biomass.
How can you ensure all the water is evaporated when drying organisms?
Record the mass at intervals until it is constant
Describe how you can measure the energy within biomass
Use bomb calorimetry to burn the sample and record the temperature change of a known mass of water. Then use E = m x c x ∆T
What does the productivity of an ecosystem depend on?
Biotic factors such as plants, animals, fungi, and bacteria
Biotic factors are living things that have an impact on another population of living things/environment
Abiotic factors such as light intensity, temperature, availability of nutrients, soil pH, water
Abiotic factors are non living variables that affect the distribution of organisms in an ecosystem
Abiotic and biotic factors together make up an ecosystem
Define GPP
The total chemical energy store in a plant, in a given area or volume
What three other ways can you describe GPP?
The total biological molecules produced from photosynthesis, the total light energy absorbed by chlorophyll, and the total energy produced from photosynthesis
Name three factors that might affect the GPP of a plant at a given time
Light intensity, temperature and carbon dioxide concentration
Recall the equation to calculate NPP
NPP = GPP - R
Define NPP
The chemical energy store in a plant after respiratory losses
Recall the equation for N
N = I - (F + R)
Define N
It is the net production of consumers
Recall the units for productivity
kJ ha-1 year-1
Recall the equation for ecological efficiency
% efficiency = energy or biomass available after transfer / energy or biomass available after transfer x 100
Define ecological efficiency
The efficiency of energy transfer between trophic levels
Recall the factors that farmers may control to increase ecological efficiency
Light intensity, water availability, temperature, nutrient availability, pests, disease, energy lost as heat or in movement
Describe how farmers would increase light intensity
Use artificial lamps
Describe how farmers would increase water availability
Irrigating crops
Describe how farmers would control temperature of indoor crops
Use heaters to heat greenhouses to the optimum temperature
Describe how farmers would control temperature of animal pens
Use heaters to heat pens to the optimum temperature
Describe how farmers would increase available nutrients to crops
Fertilisers
Describe how farmers would increase available nutrients to animals
Provide nutrient rich food
Describe how farmers would reduce pests on crops
Spraying pesticides
Describe how farmers would reduce disease on crops
Spraying fungicides
Describe how farmers would reduce disease in animals
Antibiotics
Describe how farmers would reduce energy lost in animal movement
Keeping them in pens
Name one thing farmers might want to know about a new practice before they adopt it
Cost, side effects, whether the substances will affect other organisms, method of application (labour)
Name phosphate-containing organic compounds
ATP/ADP, DNA/RNA, phospholipids, GP & TP
What are saprobiotic bacteria?
Aerobic bacteria that decompose dead organic matter
Why do plants grow more when more phosphates are available in the soil?
Because they can absorb more phosphates and use them to produce more phosphate-containing molecules for growth
Describe the effect on the soil of removing harvested crops
Harvesting crops removes the minerals contained in the plant biomass from the ecosystem, depleting the soil
How do farmers replenish mineral depleted soil?
Artificial fertilisers and / or natural fertilisers (manure)
Why are artificial and natural fertilisers absorbed differently by plants?
Artificial fertilisers contain minerals in a form that is readily absorbed, whereas manure must be decompsed by saprobiotic bacteria first as the minerals are contained in organic matter
Why might farmers choose to alternate the use of fields between grazing animals and growing crops?
Because the urine and manure from the grazing animals would re-enrich the soil
Name nitrogen-containing organic compounds
Amino acids, ATP/ADP, DNA/RNA, NADP+
Why do plants grow more when more phosphates are available in the soil?
Because they can absorb more nitrogen and use them to produce more nitrogen-containing molecules for growth
Name the molecules involved in the nitrogen cycle
N2 (atmospheric nitrogen)
Name the ions involved in the nitrogen cycle
NH4+ (ammonium), NO2- (nitrite), NO3- (nitrate)
Which is the only form plants can absorb nitrogen in?
NO3- (nitrate)
Name the four processes involved in the nitrogen cycle
Nitrogen fixation, nitrification, decomposition and denitrification
Write an equation to show what happens in nitrogen fixation
N2→NH4+
Which bacteria carry out nitrogen fixation?
Nitrogen fixing bacteria
Name the two places nitrogen fixing bacteria live
Free living in the soil, and in root nodules of leguminous plants
Nitrogen fixing bacteria have a mutualistic relationship with leguminous plants. What does this mean?
Both the bacteria and the plant benefit from the relationship. The bacteria gain sugars from the plant for respiration, and the plant gains nitrogen fixed by the bacteria
What type of reaction is nitrogen fixation?
Reduction
Write an equation to show what happens in nitrification
NH4+→NO2-→NO3-
Which type of bacteria carry out nitrification?
Nitrifying bacteria
What type of reaction is nitrification?
Oxidation
Write an equation to show what happens in decomposition
Organic compounds→NH4+
What type of bacteria carry out decomposition?
Saprobiotic bacteria
Name the conditions necessary for saprobiotic bacteria to carry out decomposition
Aerobic
Write an equation to show what happens in denitrification
NO3-→N2
Which type of bacteria carry out denitrification?
Denitrifying bacteria
What type of reaction is denitrification?
Reduction
How would farmers use leguminous plants to re-enrich depleted soil?
They would grow them as a crop, then plough them into the soil
Why would farmers grow leguminous crops on depleted soil, then plough them in?
To increase nitrogen fixation (because of the nitrogen-fixing bacteria on the root nodules). The plant would also be decomposed when ploughed in, increasing available minerals in the soil
How could selective breeding produce a more efficient crop plant?
You could breed plants for increased nutrient uptake
Why would ploughing the soil increase available nutrients?
It would aerate the soil, increasing decomposition
Why would growing the same crops on a field eventually deplete it?
Crops absorb one particular nutrient more than most, therefore the soil would become deficient in this nutrient as the crops were harvested
Why does rotating crops reduce soil nutrient depletion?
Because different crops absorb different nutrients, preventing the soil becoming depleted in one particular mineral
What is leaching?
When rain washes fertiliser into rivers and lakes
Why does leaching happen more from a fallow field?
Crops absorb some of the fertiliser, and the soil becomes more compact when crops are grown in it
Name the process that causes organisms in a lake to die because of leaching
Eutrophication
What is the first thing that leaching produces in rivers and lakes?
An algae bloom
What does an algae bloom cause?
Aquatic producers die because light cannot penetrate into the lake, so they can’t photosynthesise
What happens when the aquatic producers in rivers and lakes die?
Saprobiotic bacteria decompose them, using up oxygen in the lake
What does the oxygen depletion in the lake cause?
It causes aerobic organisms e.g. fish to die
How does the death of aerobic organisms in rivers and lakes perpetuate eutrophication?
Because more decompsition occurs, which means the saprobiotic bacteria use up even more of the oxygen
