populations and energy flow Flashcards
what happens during the ‘lag phase’?
period of adaption to environment/time to reach sexual maturity
what happens during the ‘log phase’?
no.s increase exponentially as there are no limiting factors (reproductive rate>death rate)
what happens during the ‘stationary phase’?
carrying capacity is reached- pop. will fluctuate due to environmental changes and availability of resources (reproductive=death)
what happens during the ‘death phase’?
factors reducing pop. growth become more significant (death>reproductive)- cause pop. CRASH
define ‘carrying capacity’
the maximum population size that can be sustained over a period of time
define ‘species’
a group of organisms which can interbreed to produce fertile offspring
define ‘population’
the total no. of organisms of a single species occupying a particular area
define ‘ecosystem’
a characteristic community of interdependent species interacting with the abiotic components of their habitat (are dynamic- constantly changing in size)
what is meant by a ‘biotic factor’?
(factor being a feature that restricts population growth)
a part of the environment of an organism that is living (eg. pathogens/ predators)
what is meant by a ‘abiotic factor’?
a part of the environment of an organism that is non-living (eg. temp, oxygen availability)
what things cause environmental resistance?
- competition for food and space
- predation
- parasitism
- disease
- accumulation of toxic waste
- climate
what are the two types of factors that reduce population?
density DEPENDENT (biotic): pop. size increases, effect of factor increases- leads to slow down of pop. growth
density INDEPENDENT (abiotic): pop. size has no effect on factors so all members equally affected- can lead to pop. crash
what are the possible reasons for population fluctuation?
- changes in light intensity/temp (due to time of year)
- shortage of nutrients due to exceeding carrying capacity (effect of densitiy dependent factor increases, mortality increases)
- once pop. falls below certain point, environmental resistance relieved
- lack of natural predators/disease
- build-up of toxic by-products
what are the two types of competition?
- inTRAspecific: competition between individuals of SAME species (limits pop. size- natural selection)
- inTERspecific: competition between individuals of DIFFERENT species
what practical is carried out to measure plant abundance?
- use random no. generator to select random co-ordinates in a 10x10 area
- put quadrat down at co-ordinate
- count no.s of different species in area (how many squares contain it)
- calculate % cover
LIMITATIONS: small sample area, mis-identification of species
what practical is carried out to measure animal abundance?
- kick sampling (use simpson’s diversity index to calculate)
LIMITATIONS: organisms may not dislodge from bed, invertebrate’s too small so escape through mesh) - capture-mark-recapture (then count how many marked from before in now sample)
LIMITATIONS: difficult to identify all species as similar-looking
what practical is carried out to measure distribution?
- line transect
- lay out line of tape across area, place quadrat at regular intervals of distance
- count no./% cover of specific plant in each quadrat
- draw kite diagram
why does not all light that lands on producer get absorbed?
light can reflect off plant/ transmit through or is absorbed by non-photosynthetic parts
why is energy lost between producers and primary consumers?
cellulose may not be able to be digested, not all of plant is eaten
why is energy lost between primary and secondary consumers?
- energy used in respiration (needed for synthesis of ATP, muscle contraction, temp regulation)
- lost as urea
- not all animal can be eaten (eg. bones) - some present in faeces
what do food chains not show?
- all the species at each trophic level (leads to calculated efficiency of energy transfer being low)
- decomposers/denitrivores which are often a greater biomass
- omnivores/organisms feeding at several levels
what is meant by photosynthetic efficiency?
a measure of how well a plant is able to catch light energy
GPP/light energy falling on plant x 100
what is meant by GPP?
Gross Primary Productivity
-rate of production of chemical energy in organic molecules by photosynthesis in a given area
what is meant by NPP?
Net Primary Production
- the chemical energy available to primary consumers in an ecosystem
what is the equation that links GPP and NPP?
NPP= GPP-R (energy used by plant in respiration)
why are herbivores less efficient than carnivores in energy transfer?
- cellulose (and lignin) is more difficult to digest than protein
- much more energy used in digestion of it
- much more energy left in faeces of herbivore
what do pyramids of numbers show?
- no. organisms at each level (producer at bottom)
- doesn’t take size into account (can be inverted)
what do pyramids of biomass show?
- show total weight of organisms
- slightly more accurate
- however difficult to measure as many organisms contain biomass that will not transfer to next trophic level)
- doesn’t take lifespan into account
what do pyramids of energy show?
amount of energy (eg. in J) transferred from one level to the next
define ‘succession’
the change in structure and composition of species in a community over time
what is ‘primary succession’?
succession in a habitat that has never before been colonised
what is ‘secondary succession’?
the re-introduction of organisms into a habitat that was previously occupied by plants/animals before being destroyed/disturbed
what are the different stages in a succession called?
seral stages
what is meant by a ‘pioneer species’?
the first plants to grow in a new habitat (often highly adapted to harsh environment- xerophytes- and are nitrogen-fixing)
what is meant by ‘climax community’?
the final, stable collection of plants and animals that succession produces and are the best adapted to those conditions
why may the climax community have less biodiversity than the pioneer species?
the environment is dominated by a specific collection of species
what occurs in the environment as succession occurs?
- biomass increases: more soil allows bigger plants to grow
- soil depth increases: plants die and create humus (dead accumulated plant matter)
- soil nutrient and water content increases: increased depth means soil can hold onto more
- biodiversity increases: more niches (roles of an organism in an ecosystem)
what are the differences between primary and secondary succession?
- p: surface is bare, s: soil is present
- p: takes longer time to reach climax community (soil has to be created), s: quicker to reach
what do the terms 1. ‘mutualism’ and 2. ‘commensalism’ mean?
- an interaction between organisms of two species from which both derive benefit
- an interaction between organisms of two species from which one benefits but the other is not affected
what are the effects of human activity on the greenhouse effect, leading to the enhanced greenhouse effect?
- cattle produce methane by belching
- CFC’s in aerosol propellants/ coolants in fridges
- deforestation/ combustion of fossil fuels releases CO2/ less trees taking it in (contributes to climate change)
explain the greenhouse effect
- radiation from sun reaches earth, some reflected back by atmosphere or is re-emitted back into space after hitting earth, and some is absorbed
- reflected/re-emitted is then absorbed by insulating layer of greenhouse gases
- this traps the heat in between the layer and earth
- contributes to global warming
what are the effects of global warming?
- melting polar ice-> sea level rise-> coastal erosion and flooding OR desertification
- increase in temp/ extreme weather events-> habitat changes-> migration/extinction
- CO2 dissolves in ocean-> ocean acidification-> interferes with coral reefs and enzyme reaction in aquatic organisms
- crop yield reductions-> farmers may need to move
describe and explain the process of eutrophication
- soluble nitrates (from use of nitrogen-rich fertiliser in farming) wash into water from fields
- NO3- is leached from soil
- causes an algal bloom due to excess nutrients in water
- algae use up all nutrients and die, blocking light from penetrating water (plants can’t photosynthesise so die)
- decomposed by saprotrophic bacteria which uses up all oxygen
- more animals/plants die from lack of oxygen, causing a decrease in biodiversity
which bacteria has a symbiotic relationship with the root nodules of leguminous plants?
rhizobium
which bacteria is free-living in the soil?
azotobacter
which bacteria is present during nitrification? (in order)
nitrosomonas, nitrobacter
which bacteria is present during denitrification?
pseudomonas
