Section 5: Energy and Ecosystems + Nutrient Cycles Flashcards
How do different types of autotrophs (producers) to synthesise their own food
- Photoautotrophs use light energy and chemoautotrophs use inorganic molecules
How can biomass be measured?
- Mass of carbon
- Dry mass of tissue per given area
How is dry mass of tissue obtained?
- Sample of organism dried in an oven set to a low temperature
- Sample reweighed at regular intervals
- All water is removed when mass remains constant
- Mass of carbon is 50% of dry mass
How is dry mass more representative
- Because water content of sample varies
How do you measure the chemical energy stored in dry biomass using calorimetry
- Sample of dry biomass is burnt
- Energy released is used to heat a known volume of water
- Change in temperature of water is used to calculate the chemical energy
What is gross primary production?
- Chemical energy store in plant biomass in a given area/ volume in a given time
What is net primary production?
- Chemical energy store in plant biomass after respiratory losses to the environment
- NPP - GPP - R
- NPP is available for plant growth and reproduction
- The NPP is also available to other trophic levels in the ecosystem
What is net primary production?
- Chemical energy store in plant biomass after respiratory losses to the environment
- NPP - GPP - R
- NPP is available for plant growth and reproduction
- The NPP is also available to other trophic levels in the ecosystem
How do you work out the net production of consumers?
- N = I - (F+R)
- I = The chemical energy store in food
- F = The chemical energy lost to the environment as faeces and urine
- R = Respiratory losses
What are the units of rate productivity
KJ ha-1year-1
- KJ = unit of energy
- Per unit area (ha) = different environments vary in size
- Per year = more representative as it takes into account the effect of seasonal variation on biomass so environments can be compared
Why is the energy transfer between the sun and producer inefficient
- Wrong wavelength of light
- Light does not hit chlorophyll
- Light is reflected back into space
- Lost as heat
Why is the energy transfer between producer - primary consumer - secondary consumer inefficient
- Respiratory loss - for metabolism
- Lost as heat
- Not all plant/ animal eaten e.g bones
- Some food not digested - faeces
What are some farming practices that increase energy efficiency in crops?
- Simplifying food webs to reduce energy/ biomass losses to non-human food chains
- Herbicides - kill weeds - less competition - more energy to create biomass
- Fungicides
- Pesticides
- Fertilisers
What are some farming practices that increase energy efficiency in livestock?
- Restrict movement
- Keep warm
- Slaughter when young
- Selective breeding
- Treated with antibiotics to prevent loss of energy due to pathogens
What is the role of saprobionts in recycling chemical elements?
- Feed on remains of dead plants/ animals and their waste products and break down organic molecules
- By secreting enzymes for extracellular digestion - absorb soluble nutrients
What is the role of mycorrhizae in recyling chemical elements
- Symbiotic relationship between fungi and roots of plants = mycorrhizae
- Fungi acts as an extension of the plant roots - increase surface area - absorption of water
- Mutualistic relationship - plant provides fungi with carbs
What are the main stages of the nitrogen cycle?
- Nitrogen Fixation
- Ammonification
- Nitrification
- Denitrification
What is Nitrogen Fixation?
- Nitrogen gas converted to nitrogen containing compounds e.g ammonia
- By nitrogen fixing bacteria
- Can be free living in the soil
- Or mutualistic - nodules on roots of legumes. Plant gets amino acids and bacteria gets carbs
What is ammonification?
- Nitrogen containing compounds e.g proteins from dead organisms is broken down
- Converted to ammonia which forms ammonium ions
- By saprobionts
What is Nitrification?
- Ammonium ions in the soil turn into nitrites then nitrates by nitrifying bacteria
- Bacteria need oxygen
- Nitrates absorbed by plant root hair cells by active transport
- Adding more O2 - nitrifying bacteria increases and denitrifying to decrease
What is denitrification?
- Nitrates in the soil - nitrogen gas by denitifying bacteria - anaerobically respire
What is the importance of the nitrogen cycle?
- Nitrogen gas is unreactive and not easily converted into other compounds
- Nitrates can be used to make proteins and nucleic acids for growth
What are the stages of the Phosphorous cycle?
- Phosphate ions in the rocks released by erosion/weathering
- Phosphate ions taken up by plants into their biomass
- Phosphate ions transferred through food chain
- Some phosphate ions lost in waste products - saprobionts decompose
- Weathering of rocks can release phosphate into seas, lakes and rivers
