Summary WJEC (England) Eduqas Biology A-Level 1. Energy for Life - 5. Population size & ecosystems
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Course
1. Energy for life
Institution
WJEC
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a. Population: all members of one species (capable of sexually reproducing fertile offspring) in habitat at same time
Ecology: study of interactions between organisms & environment
Niche: feeding role of organism in ecosystem
Equilibrium species: species that control their population by competition
Environment: set of external conditions surrounding organism – biotic & abiotic factors
b. population growth: immigration + reproduction rate > emigration + death rate
lag phase: slow rate of reproduction/division but high metabolic activity
limited no. individuals of reproductive age – time to reach sexual maturity / find mate
synthesise enzymes/proteins / replicate DNA
stationary phase: reproduction rate = death rate
carrying capacity: maximum population size sustained by environment indefinitely – fluctuates around set point
negative feedback: more competition & predation increases deaths = reduces competition = population can rise
- predator-prey relationships
prey decrease – less food for predators – predators decrease – less predation – prey increase
environmental resistance: reduce growth rate – reduce birth rate / increase death rate
concentration of waste becomes toxic
biotic factors = living
predation abiotic factors = non-living
competition soil pH
o intraspecific: same species light intensity
o interspecific: different species temperature
parasitism oxygen availability
food availability water availability
disease – pathogen space/habitat availability
death phase: nutrients deplete / toxins accumulate – rapid decline = population crash
c. population density = population/area
density dependent factor (biotic): higher death rate / affect greater proportion of larger populations
density independent factor (abiotic): death rate / affect same proportion of all populations – regardless of size
d. sampling techniques
, e. ecosystem: characteristic community of interdependent species interacting with environment
dynamic & subject to change – energy flows, nutrients cycle, succession, species composition, population size
very small –> very large
f. sun (light energy trapped by photosynthesis) = ecosystem energy source
g. habitat: region where organism usually lives/breeds/feeds
community: all organisms of all species in habitat at same time – interact with each other
h. biomass: mass of biological material in organisms – transferred between organisms in food chains/webs
trophic (feeding) levels: position of organism in food web – number of times energy transferred
transfer efficiency % = output / input
lots lost: limits chain length – can’t sustain another trophic level
- aquatic = longer – ectothermic: lose less energy from respiration – don’t need to keep warm (like endotherms)
- small organisms = less efficient – large SA:V ratio: lose more heat & have to respire at higher rate to keep warm
reduce energy losses – agriculture
- autotrophs with higher GPP
- animals with higher transfer efficiency
o reduce respiration – keep warm & reduce movement
o feed: high protein, less cellulose, high energy supplements
Producers: plants = autotrophs – convert energy from sun to chemical energy in organic molecules by photosynthesis
Gross Primary Productivity: rate of light to chemical energy conversion by photosynthesis by producers kJm-2year-1
photosynthesis efficiency % = light fixed/fallen
Loss – majority of light not absorbed by plant
- wrong wavelength
- reflected by leaf waxy cuticle
- transmitted through leaf – doesn’t hit chloroplast
Net PP = GPP–R (of organic molecules): organic molecules assimilated = energy in plants biomass available to consumers
highest in tropical: high rainfall / light intensity / temperature
Consumers: animals = heterotrophs – depend on existing nutrients &digestion to use – pass energy in organic molecules
Primary: herbivore – cellulose/lignin not efficiently digested = large energy loss in egestion
Secondary: carnivore – protein/fat efficiently digested = little energy lost in egestion – higher efficiency
Loss
- egestion (indigestible) & excretion (urea: high-energy organic molecule)
- respiration: energy for movement = produce heat
o high in endotherms: need maintain body temperature – ectotherms more efficient
- inedible parts: roots / bones / feathers
Ecological pyramids of trophic levels: as energy lost, fewer individuals can be supported – bar area ∝
pyramid of number
hard to draw bar for large number
can be inverted: doesn’t consider size of organism
pyramid of biomass (dry mass – not affected by water loss/uptake) – more accurate
can be inverted: taken at one time = doesn’t indicate productivity (biomass over year) – some have rapid
reproduction/productivity
hard to calculate (mass in roots?) & lots not be transferred (inedible)
pyramid of energy – most accurate but
hard to calculate
none can show that some organisms operate at several trophic levels
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