biology 4
a2 aqa biology
- Created by: rebecca
- Created on: 07-06-12 09:29
Populations - definitions
Ecosystems - a species occupies a niche, goverened by adaptations to abiotic and biotic factors
Community - all the species of a habitat
Population - all the organisms of one species in a habitat
birth rate = (no births per year/pop in same year) x 1000
death rate = (no deaths per year/pop in same year) x 1000
% pop growth rate = (pop change / pop at start) x 100
immigration - individuals joining a pop
emmigration - individuals leaving a pop
life expectancy - the average life expectancy is that age at which 50% of the individuals in a particular pop are still alive
populations - definitions
increasing population - birth rates > death rates
decreasing population - birth rates < death rates
stable population - death rate = birth rate - no change in pop size
pop growth = (B+I) - (D+E)
investigating ecosystems
random sampling
- quadrats - consider size of quadrat, number of sample needed & position of each quadrat
- transects - abundance & distribution of a species
- quantative data
abundance
- percentage cover - estimate the area within a quadrat that a species covers
- frequency - the likelihood of a species occuring in a quadrat
mark-release-recapture
- estimated pop size = (total in 1st sample x total in 2nd sample)/no marked in 2nd
- no immigration/emmigration
- few births/deaths
- mark not rubbed off
variation in pop size
predation
- one organism consumed by another
- predator-prey relationships: predator eats prey & decreases no of prey. more competiton for fewer prey. predator pop decreases. fewer predators = fewer prey eaten. prey pop increases. predator pop increases.
interspecific competition - individuals of DIFFERENT species
intraspecific competition - individuals of SAME species
abiotic factors
- temperature - enzymes & optimum
- light - energy source for ecosystems
- pH - affects enzyme activiy
- water & humidity - affects transpiration in plants
inheritance & selection
inheritance
- genotype: genetic constitution of an organism
- phenotype: observable characteristics
- gene: a section of DNA that determines a single characteristic. exists in 2 or more forms
- allele: one of the different forms of a gene. only one can occur
speciation
- the evolution of a new species from an existing species
- geographical isolation: physical barrier prevents 2 pops breeding with each other, conditions in 1 area change, mutations arise & are passed down generations. LONG period of time new species evolves, & is unable to produce fertile offspring with original species
inheritance & selection
sex linkage
- controlled by recessive alleles
- on X or Y chromosome
Multiple alleles
- only 2 can be present in an individual
- more than 2 alleles for a gene
codominance
- two alleles are dominant
- both expressed in phenotype
selection
stabilising
- environmental conditions remain same
- phenotype closest to mean favoured
- eliminates extremes
directional
- if environmental conditions change phenotypes needed to survive will change
- phenotypes at extremes are favoured
hardy-weinberg
p + q = 1
p2 + 2pq + q2 = 1
- used to predict the frequencies of the alleles of a particular gene in a population
- predicts that the proportion of dominant & recessive alleles remain the same for each generation
can only be used if:
- population is large
- no mutations
- population is isolated
- no selection
- mating is random
energy & ecosystems
energy transfer
- photosynthesis: main route that energy enters the ecosystem
- energy transferred through trophic levels
- energy transfer = (energy available after / energy available before) x 100
Pyramids
- numbers - no account of size, may not be pyramid shape/ may be inverted, maybe impossible to represent on same scale
- biomass - gm-2, only organisms at a particular time are shown, total mass of the plants/animals at a particular place
- energy - most accurate, energy stored in organisms, difficult & complex
energy & ecosystems - food production
Pest control
- pest = organism that competes with humans for food - may be a danger to health
- effective pesticide should: be specific, biodegrade, be cost effective, not accumulate
- biological control: pests don't develop resistance, control organism may become a pest, doesn't work quickly (time lag), controls the pest - doesn't eradicate it, reproduces itself, specific
- chemical pesticides: pests develop genetic resistance - new pesticides need to be developed, must be reapplied at intervals - expensive, always has some effect on non-target species
- integrated pest-control systems: removal of pests mechanically-time, using biological control, pesticides as last resort.
- pests & productivity - monoculture crop allows rapid spread, pests create a limiting factor, photosynthesis reduces. ∆ productivity decreases.
energy & ecosystems - food production
intensive rearing
- reduce energy losses: feeding controlled, predators excluded, selective breeding, hormones used to increase growth, animals confined, movement reduced - less energy lost in muscle contraction, temperature controlled - reduced heat losses
agricultural ecosystems
- energy input: food for workers, fossil fuels for machinery
- natural ecosystem only input is sun & productivity is low
- agricultural: productivity increased - reducing effect of limiting factors - reducing competition
net productivity = gross productivity - respiratory losses
net productivity: kJm-2year-1, area of ground covered by leaves of crop, efficiency of photosynthesis
succession
primary pioneer species
barren land->primary colonisers->secondary->tertiary--shrub land->climax
hostile, instable
community less hostile, more stable & higher biodiversity
secondary(faster): land altered due to fire/disease/grazing/agriculture - re-colonisation to climax community
- non-living environment becomes less hostile
- a greater number and variety of habitats
- increased biodiversity
- more complex food webs
- increased biomass
conservation of habitats
- management of Earths natural resources
- managing succession & preventing next stage
- why? - ethical(some species here before humans) -economic -cultural & aesthetic(habitats & organisms enrich our lives
fertilisers
natural/organic
- dead & decaying remains
- animal waste
artificial/inorganic
- mined from rocks & deposits
- converted into different forms
- blended together to form appropriate balance for particular crop
leaching
nutrients removed from soil
rain water dissolves nitrates & carries them beyond reach of roots
find way to watercourse
eutrophication
little nitrate in lakes & rivers = limiting factor
nitrate conc increases, not limiting factor, plant & algae grow on surface & absorb light
no light to lower depth
light limiting factor for deeper plants, plants die
lack of dead plants not limiting factor so saprobiotic microorganisms grow
increased demand for oxygen - conc decreases - limiting factor - aerobic organisms die
less competition for anaerobic organisms - populations increase
anaerobic organisms decomposed - more nitrates released
global warming
consequences
- extinction of organisms
- rise in sea level
- higher temp & less rainfall = failure of crops
- greater rainfall & intense storms = life cycles & pop of insects alters
- methane produced by decomposers
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