populations and energy flow

Question 1

what happens during the ‘lag phase’?

Answer 1

period of adaption to environment/time to reach sexual maturity

Question 2

what happens during the ‘log phase’?

Answer 2

no.s increase exponentially as there are no limiting factors (reproductive rate>death rate)

Question 3

what happens during the ‘stationary phase’?

Answer 3

carrying capacity is reached- pop. will fluctuate due to environmental changes and availability of resources (reproductive=death)

Question 4

what happens during the ‘death phase’?

Answer 4

factors reducing pop. growth become more significant (death>reproductive)- cause pop. CRASH

Question 5

define ‘carrying capacity’

Answer 5

the maximum population size that can be sustained over a period of time

Question 6

define ‘species’

Answer 6

a group of organisms which can interbreed to produce fertile offspring

Question 7

define ‘population’

Answer 7

the total no. of organisms of a single species occupying a particular area

Question 8

define ‘ecosystem’

Answer 8

a characteristic community of interdependent species interacting with the abiotic components of their habitat (are dynamic- constantly changing in size)

Question 9

what is meant by a ‘biotic factor’?
(factor being a feature that restricts population growth)

Answer 9

a part of the environment of an organism that is living (eg. pathogens/ predators)

Question 10

what is meant by a ‘abiotic factor’?

Answer 10

a part of the environment of an organism that is non-living (eg. temp, oxygen availability)

Question 11

what things cause environmental resistance?

Answer 11

• competition for food and space
• predation
• parasitism
• disease
• accumulation of toxic waste
• climate

Question 12

what are the two types of factors that reduce population?

Answer 12

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

Question 13

what are the possible reasons for population fluctuation?

Answer 13

• 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

Question 14

what are the two types of competition?

Answer 14

• inTRAspecific: competition between individuals of SAME species (limits pop. size- natural selection)
• inTERspecific: competition between individuals of DIFFERENT species

Question 15

what practical is carried out to measure plant abundance?

Answer 15

• 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

Question 16

what practical is carried out to measure animal abundance?

Answer 16

• 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

Question 17

what practical is carried out to measure distribution?

Answer 17

• 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

Question 18

why does not all light that lands on producer get absorbed?

Answer 18

light can reflect off plant/ transmit through or is absorbed by non-photosynthetic parts

Question 19

why is energy lost between producers and primary consumers?

Answer 19

cellulose may not be able to be digested, not all of plant is eaten

Question 20

why is energy lost between primary and secondary consumers?

Answer 20

• 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

Question 21

what do food chains not show?

Answer 21

• 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

Question 22

what is meant by photosynthetic efficiency?

Answer 22

a measure of how well a plant is able to catch light energy
GPP/light energy falling on plant x 100

Question 23

what is meant by GPP?

Answer 23

Gross Primary Productivity
-rate of production of chemical energy in organic molecules by photosynthesis in a given area

Question 24

what is meant by NPP?

Answer 24

Net Primary Production
- the chemical energy available to primary consumers in an ecosystem

Question 25

what is the equation that links GPP and NPP?

Answer 25

NPP= GPP-R (energy used by plant in respiration)

Question 26

why are herbivores less efficient than carnivores in energy transfer?

Answer 26

- 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

Question 27

what do pyramids of numbers show?

Answer 27

- no. organisms at each level (producer at bottom) - doesn't take size into account (can be inverted)

Question 28

what do pyramids of biomass show?

Answer 28

- 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

Question 29

what do pyramids of energy show?

Answer 29

amount of energy (eg. in J) transferred from one level to the next

Question 30

define 'succession'

Answer 30

the change in structure and composition of species in a community over time

Question 31

what is 'primary succession'?

Answer 31

succession in a habitat that has never before been colonised

Question 32

what is 'secondary succession'?

Answer 32

the re-introduction of organisms into a habitat that was previously occupied by plants/animals before being destroyed/disturbed

Question 33

what are the different stages in a succession called?

Answer 33

seral stages

Question 34

what is meant by a 'pioneer species'?

Answer 34

the first plants to grow in a new habitat (often highly adapted to harsh environment- xerophytes- and are nitrogen-fixing)

Question 35

what is meant by 'climax community'?

Answer 35

the final, stable collection of plants and animals that succession produces and are the best adapted to those conditions

Question 36

why may the climax community have less biodiversity than the pioneer species?

Answer 36

the environment is dominated by a specific collection of species

Question 37

what occurs in the environment as succession occurs?

Answer 37

- 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)

Question 38

what are the differences between primary and secondary succession?

Answer 38

- 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

Question 39

what do the terms 1. 'mutualism' and 2. 'commensalism' mean?

Answer 39

1. an interaction between organisms of two species from which both derive benefit 2. an interaction between organisms of two species from which one benefits but the other is not affected

Question 40

what are the effects of human activity on the greenhouse effect, leading to the enhanced greenhouse effect?

Answer 40

- 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)

Question 41

explain the greenhouse effect

Answer 41

- 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

Question 42

what are the effects of global warming?

Answer 42

- 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

Question 43

describe and explain the process of eutrophication

Answer 43

- 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

Question 44

which bacteria has a symbiotic relationship with the root nodules of leguminous plants?

Answer 44

rhizobium

Question 45

which bacteria is free-living in the soil?

Answer 45

azotobacter

Question 46

which bacteria is present during nitrification? (in order)

Answer 46

nitrosomonas, nitrobacter

Question 47

which bacteria is present during denitrification?

Answer 47

pseudomonas