5 - Population Size and Ecosystems (C1) Flashcards
What is gross primary productivity? (GPP)
The rate at which plants fix energy into organic molecules, by photosynthesis, in a given area and time
What is net primary production? (NPP)
The rate at which energy in organic molecules present in plants is made available for herbivores in a given area and time
What is the equation linking GPP and NPP?
NPP = GPP - respiration
What is succession?
The change in structure and species composition of a community over time as the environment improves or better adapted species survive
What are seral stages?
The different stages in a succession when particular communities dominate
What are the 4 phases of growth?
- Lag phase - Exponential phase - Stationary phase - Death phase
What happens during the lag phase?
- Bacteria are adapting and preparing for growth - Organisms like rabbits are waiting to reach sexual maturity and find mates
What happens during the exponential phase?
- Bacterial cells divide at a constant rate and the population doubles per unit time - More organisms become ready for reproduction
What happens during the stationary phase?
- Rate of increase slows as there is less space, food, etc. - Birth rate = death rate - Population has reached the carrying capacity for that particular environment
What happens during the death phase?
- The factors that slow down population growth at the end of the lag phase become more significant - Population size decreases until death rate > birth rate - Graph will have negative gradient
What are density dependent factors?
When the population density increases, the effect is increased (biotic factors)
What are density independent factors?
When the population density increases, the effect is the same (abiotic factors)
What is the carrying capacity?
The maximum number of individuals that an area can support
What is the source of energy for most food chains?
The sun
What are some reasons why energy in plants may not be passed on to animals that eat them?
- Animals only eat a small amount of the plants - Cellulose is difficult for animals to digest - Energy is lost in respiration
What are some reasons why energy in animals may not be passed on to animals that eat them?
- Energy released by respiration is used for movement - ENergy is lost as waste, such as in faeces - Predators only consume small amounts of animal as some parts are not digestible
What happens to the energy present in faeces and dead plants and animals?
It’s consumed or processed into useful nutrients by microorganisms that use digestive enzymes to break down complex molecules into simpler nutrients
Why are pioneer plants often xerophytes that can fix nitrogen?
Xerophytes are adapted to decrease water loss and have long roots to absorb as much water as possible. They fix nitrogen as there are few nutrients available
What are pioneer species?
The first species to colonise a new area in an ecological succession
Why is energy in GPP less than the energy available from the sun?
- Light energy misses the plant - Light reflects off leaves - Light passes through leaves - Light is absorbed by non-photosynthetic parts - Only red and blue light can be used in photosynthesis
What is the order of groups in the food change?
- Primary producers - Primary consumers - Secondary consumers - Tertiary consumers
What is meant by the trophic level?
The number of stages that an organism is from the start of the food chain
What is meant by the term carbon footprint?
The amount of CO2 released into the atmosphere per year as a result of the activities of a particular individual, organisation or community
What is the name of the group of plants that have a large number of root nodules on their roots?
Legumes
What is the advantage for legumes by having root nodules?
- Contain nitrogen fixing bacteria - Some nitrogenous compounds pass to the plant - Allows the plant to grow in poor soil
Why are nitrogen and phosphorus needed for plant growth?
- Nitrogen is needed for protein production - Phosphorus maintains the phospholipid bilayer
What is an example of a biological molecule that contains sulphur?
Amino acid
What is the definition of a population?
An interbreeding group of organisms of the same species in one area at one time
What is the definition of a community?
Interacting populations of 2 or more species in the same habitat at the same time
What is the definition of an ecosystem?
A characteristic community of interdependent species interacting with the abiotic components of their environment
What is the definition of niche?
The role of an organism within the place where it lives (what it eats, etc)
What is the definition of an abiotic factor?
A part of the environment of an organism that is non-living e.g. O2 availability
What is the definition of a biotic factor?
A part of the environment of an organism that is living e.g. pathogens, predators
What is the definition of immigration?
The movement of individuals into a population of the same species
What is the definition of emigration?
The movement of individuals out of a population of the same species
What is the definition of an equilibrium species?
Species that control their population by competition rather than by reproduction and dispersal
What does a pyramid of numbers show?
The number of organisms at each trophic level
What does a pyramid of biomass show?
The mass of organisms present at each trophic level
What does a pyramid of energy show?
The energy present in the biomass produced in a year at each trophic level
What is intraspecific competition?
Competition between individuals of the same species
What is interspecific competition?
Competition between individuals of different species
Why is intraspecific competition more intense than interspecific competition?
Because individuals have more needs in common
What is facilitation?
When a species which occurs in a succession grows more readily when another species is present
What is commensalism?
When one species benefits from the presence of another without affecting the other
What happens in nitrification?
Nitrosomonas oxidises ammonia to nitrite, and Nitrobacter oxidises nitrite to nitrate - Requires aerobic well-drained soil (as the nitrogen atom in the ammonium ion progessively loses hydrogen atoms and gains oxygen atoms)
What happens in denitrification?
- Removal of O2 from nitrate producing nitrogen, by denitrifying bacteria (e.g. pseudomonas) so they may respire - Occurs in anaerobic, water-logged soil
What happens in ploughing?
- Soil is aerated - Increases nitrification, decreases denitrification
What is ammonification / putrefaction?
- Decomposition of dead material, urine and faeces to ammonium ions by bacteria and fungi
- Bacteria and fungi secrete enzymes: proteases digest proteins into amino acids, deaminases reduce amino acids to ammonium ions
What are disadvantages of the nitrogen cycle?
- Nitrates are very soluble and are washed out of the soil in a process called leaching - Nitrates are washed into rivers, lakes and the sea leading to eutrophication
What is eutrophication?
- Nitrate (NO3) causes algae to grow on surface of water = algal bloom - No light reaches plants on stream bed so they die - Aerobic decomposing bacteria use up available O2 as they multiply - Lack of O2 kills fish etc.
What is secondary productivity?
The rate at which consumers accumulate energy in the form of cells or tissue
What is primary succession?
The change in structure and species composition of a community over time in an area that has not previously been colonised
What is secondary succession?
The recolonisation of a habitat previously occupied by a community, following disturbance or damage
What is the name of the fungi involved in the breakdown of leaf litter?
Saprotrophic fungi
What is the definition of ecology?
The study of the interaction of organisms with their natural environment
What is the definition of abundance?
The number of individuals in a species in a given area or volume
Why can’t quadrats be used to measure animal populations, and what method is used?
- They’re motile - Mark and recapture: * Catch, count and mark animals * Repeat * Find total pop = (no. marked x total in 2nd catch) div. by no. marked in 2nd catch
What is the nitrogen cycle?
The flow of organic and inorganic nitrogen within the abiotic and biotic components of an ecosystem where there is an interchange between certain nitrogenous bases and atmospheric nitrogen
What is the definition of distribution?
The area or volume in which the organisms of a species are found
Which organisms start decomposition and which ones finish it?
- Detrivores, e.g. earthworms and woodlice, start the process - Decomposers, e.g. bacteria and fungi, complete the process
What is the definition of primary productivity?
The rate at which energy is converted by producers into biomass
What is the definition of secondary productivity?
The rate at which consumers convert the chemical energy of their food into biomass
What are problems with using pyramids of numbers?
- They don’t consider the size of organisms - Don’t differentiate between young and adult forms
What are problems with using pyramids of biomass?
- Biomass is difficult to measure, e.g. plant roots must be included - Organisms contain structures with mass that aren’t transferred to the next trophic level e.g. bones, beaks - Don’t show the energy flow
What is the definition of a climax community?
A stable, self-perpetuating community that has reached equilibrium with its environment, and no further changes occur
What is a xerosere sequence?
Pioneers -> herbs and grasses -> shrubs and small trees -> large trees
What is mutualism?
An interaction between organisms of 2 species from which both derive benefit
Why does decomposition produce CO2?
Dead animals and plants have taken in carbohydrates, fats and proteins which are released as CO2 when they’re decomposed by detritivores and saprobionts
What are the 2 main causes of climate change?
- Burning fossil fuels
- Deforestation (as it releases O2 stored in trees, and reduces photosynthesis)
What is global warming?
The increase of average global temperature, in excess of the greenhouse effect, caused by the atmosphere’s historical conc of CO2
What is the greenhouse effect?
- Gases such as Co2, methane and CFCs surround the earth
- They allow solar radiation to pass to the Earth’s surface, much of which is absorbed by Earth, which warms and re-radiates infra-red radiation
- This is absorbed and trapped by the greenhouse gases which re-radiate it back to Earth, heating it more
What are some consquences of global warming?
- Melting of polar ice resulting in flooding in coastal areas
- More extreme weather conditions e.g. droughts, hurricanes
- Increase in CO2 in oceans decreases the PH, distrubting marine life
- Increased freq of forest fires
What are the 3Rs, publicised to reduce the production of greenhouse gases?
Reduce, reuse, recycle
What is nitrogen fixation?
- Reduction of nitrogen molecules to ammonium ions by Azotobacter and Rhizobium
- Nitrogenase catalyses the reduction using energy from ATP
- Lots of energy is required so nitrogen-fixing organisms are often aerobic
- NF requires reduction reactions and is poisoned by oxidising conditions so root nodules contain leg-haemoglobin which binds molecular O2 in the nodules and protects the reactions from oxidation
What are 3 processes that impact the nitrogen cycle?
- Application of agricultural fertilisers adds nitrogen to soil
- Lightning adds a small amount of nitrogen to soil
- Leaching of minerals removes nitrogen from soil
How does ploughing improve the circulation of nitrogen?
It favours:
- Aerobic organisms, such as nitrogen fixers, enhancing the formation of ammonium ions in soil
- Nitrifying bacteria and so enhances the conversion of ammonium into nitrites and nitrates
- Plant roots respire aerobically and generate ATP, which fuels their active uptake of minerals
What human activities improve the circulation of nitrogen in agricultural soils?
- Ploughing
- Draining land
- Artificial nitrogen fixation e.g. Haber process
- Putting animal waste onto soil
What problems can the use of nitrogen-containing fertilisers cause?
- Reduces species diversity on grassland
- Fertilisers increase the growth of grasses and plants which shade smaller plants
- Eutrophication in lakes and rivers
How does draining land and ploughing fields prevent denitrification?
Increase aeration so anaerobic bacteria can’t compete with aerobic bacteria
