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Biology A-level > Population size and ecosystems. > Flashcards

Population size and ecosystems. Flashcards

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1
Q

Population definition.

A

A group of organisms of the same species.

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2
Q

Factors affecting population fluctuation.

A

-Births
-Deaths
-Immigration
-Emigration(decreases).
Birth+immigration=deaths+emigration(in a stable population).

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3
Q

Density independent factors.

A

Abiotic
Affect death rate
Kill members of small and large populations to the same extent
E.g. Wildfires.

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4
Q

Density dependent factors.

A

Biotic
Affect population more greatly(proportionally) if population is larger & denser
E.G. Larger pop=more food comp, more predation, more diseases, higher spreading of parasites etc.

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5
Q

Phases of a population growth curve for bacterium/yeast grown in nutrient broth.

A

Lag- Enzymes synthesised, DNA replicated
Exponential- Population doubles every unit of time, nutrients abundant
Stationary- Competition of nutrients=death and cell reproduction are equal rates
Death/decline- Nutrient depletion, toxin accumulation=death rate higher than cell reproduction.

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6
Q

Carrying capacity meaning.

A

The maximum number of individuals of a species that the environment can support indefinitely.

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7
Q

Phases of a population growth curve for a more complex organism e.g. grey squirrel.

A

Lag- Population limited by the low numbers to reproduce
Exponential- Doubling of numbers with abundant resources and low predation
Stationary phase- Fluctuation as increase in competition for resources, predation= death rate can become higher than birth rate(when pop increases
When pop decreases, competition reduced–> increases again
Continues indefinitely
Set point of fluctuation=carrying capacity of the environment.

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8
Q

Ecosystem definition.

A

An area that has a particular community of plants and animals interacting with their environment.

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9
Q

Community definition.

A

All of the organisms of all species in an ecosystem.

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10
Q

Habitat definition.

A

The place in an ecosystem where an organism lives.

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11
Q

Niche definition.

A

An organism’s role in an ecosystem
Applies particularly to it’s feeding role.

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12
Q

Direction of energy flow along food chains in an ecosystem.

A

Sunlight
Producers (autotrophs)
Primary consumer (herbivores)
Secondary consumers (carnivores)
May be more trophic levels.

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13
Q

Photoautotrophs meaning.

A

Use light energy from the sun
To fix CO2 into organic molecules (via photosynthesis)
Gross Primary Production (GPP)= rate at which this happens.

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14
Q

Net Primary Production (NPP).

A

Some organic molecules made during photosynthesis used in respiration
What is left=NPP
NPP=plant’s biomass that can be consumed by the next trophic level (herbivores).
NPP=GPP-R.

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15
Q

Why is not all sunlight used in photosynthesis?

A

May be wrong wavelength
Transmitted through leaf
Reflected
Energy is lost at every level due to respiration.

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16
Q

What do decomposers feed on?

A

Dead organism
Faeces
Urine.

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17
Q

Why is the number of trophic levels limited?

A

Because of energy losses
Eventually will not be enough left to sustain another level.

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18
Q

Efficiency of a transfer calculation.

A

little number/big number
x100.

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19
Q

General efficiency transfers facts.

A

Sun–>plant=0.2%
Plant–>herbivore=10%

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20
Q

Why do herbivores lose a lot of energy as faeces?

A

High cellulose levels
Relatively indigestible.

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21
Q

Why are endotherms less efficient than ectotherms?

A

Higher respiratory rates to produce heat
So more energy lost because of this
One reason why aquatic food chains tend to be longer.

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22
Q

Methods used in agriculture to reduce energy losses.

A

Keeping animals warm
Reducing movement
High protein feed.

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23
Q

Succession definition.

A

Change in a community and species composition over time.

24
Q

Stages of primary succession.

A

Starts from bare rock- no organism living
Pioneer species colonise bare rock- blown in as spores
Lichens erode rock
Die then decay
Eroded rock builds up in cracks= mosses colonise (blown in as spores)
Soil accumulates= grasses, herbaceous plants, shrubs, woodlands(climax community) become established.

25
Q

Climax communities.

A

Stable, end point of succession- no further changes
High species diversity.

26
Q

Factors affecting speed of succession.

A

Temperature
Proximity to a source of seeds and spores to be blown in.

27
Q

Sere meaning.

A

A stage of succession
Characterised by particular communities.

28
Q

How can succession be deflected?

A

Grazing
Mowing
Burning
Maintaining particular sub climax communities.

29
Q

Secondary succession.

A

Starts from cleared land
Where communities have lived before
Faster due to seeds, roots and soil to support the plants
After forest fires.

30
Q

Random sampling method.

A

Used on a uniform area
Grid area
Generate random numbers to select co-ords
Place quadrats at co-ords
Use to asses cover %/number of organisms.

31
Q

What to measure in fieldwork?

A

Abiotic factors that may affect results
E.g. pH, light intensity, soil, water
Use Simpson’s diversity index (counted species/organisms).

32
Q

Method w/ transects.

A

Use when there is a change in conditions
Place quadrats at regular intervals along a line
Count/use % cover
Present data as a kite diagram.

33
Q

Practical work- risks.

A

Biting/stinging insects
Slippery conditions
Sunburn
Hypothermia.

34
Q

Methods to insure fairness/ accuracy of fieldwork.

A

Use correct sized grid
preliminary investigation to determine this
Carry out enough repeats
Different times of year
Successive years?

35
Q

What recycles nutrients in a nutrient cycle?

A

Decomposers- bacteria/fungi
Use organic molecules and convert them to inorganic compounds.

36
Q

Autotrophs function.

A

Use energy from sunlight/chemicals
Convert inorganic compounds to organic ones
Then passed along food chain.

37
Q

Carbon cycle steps.

A

1) Plants take in CO2, use it in photosynthesis, make organic molecules, passed through food chain
2) Plants and animals respire and secrete CO2
3) Combustion releases CO2
4) Decomposers respire= releases CO2.

38
Q

Carbon footprint definition.

A

Total amount of CO2 released attributable to an individual, product or service over the course of a year.

39
Q

Human impacts on the carbon cycle.

A

Deforestation- less CO2 absorbed
Combustion of fossil fuels- releases ‘locked in’ CO2 to atmosphere.

40
Q

Effect of CO2.

A

Traps heat
Raises global temperatures
Global warming.

41
Q

Effects of global warming.

A

Species distribution- species pushed further north and south as equator gets warmer
Agricultural practices- may need to have drought resistant crops, may need crops that can survive w/ excess rain.

42
Q

Factors affecting rate of decomposition.

A

Colder= slower
pH, more acidic= slower
O2 availability: slower when less oxygen available.

43
Q

Nitrifying bacteria.

A

Nitrosomonas-converts ammonium to nitrite
Nitrobacter-convert nitrite to nitrate.

44
Q

Nitrogen fixing bacteria.

A

Convert nitrogen gas to ammonium:
Azotobacter-free living in soil
Rhizobium-in root nodules of legumes, symbiotic.

45
Q

Dentrifying bacteria.

A

Convert nitrate to nitrogen gas
Pseudomonas-thrive in water logged soils.

46
Q

Rhizobium.

A

-Symbiotic relationship w/ legumes
-Fixes N gases to ammonium ions
-Makes amino acids
-Exports them to legumes
-Legume makes root nodule for Rhiz
-Gives it carbs, micro-anaerobic conditions(for nitrogen fixation).

47
Q

Dentrification.

A

Nitrogen released back into atmosphere
From dentrifying bacteria
Nitrate to N gas
Anaerobic conditions, water-logged soils
Slows nitrification=nitrate poor soil.

48
Q

Insectivorous plants.

A

Water-logged areas
Insect proteins–>amino acids.

49
Q

Ploughing in agriculture.

A

Introduces air to soil
Encourages nitrification.

50
Q

Drainage in agriculture.

A

Reduces water logging
Reduces dentrification.

51
Q

Leaching meaning.

A

Soluble ammonium, nitrite and nitrate ions dissolve in ground water and drain away
Loss in nitrites.

52
Q

Eutrophication.

A

Excess nutrients in lakes and rivers from leaching.

53
Q

Algal bloom.

A

Microscopic algae undergoing a population bloom
As a result of eutrophication
Blocks light from bottom-dwelling plants=die
Algae die=decomposer increase=use more oxygen in water=increased biological oxygen demand
Fish and invertebrates die and are decomposed.

54
Q

What do plants do with nitrates and ammonium ions?

A

Absorb them and use to synthesise nitrogen containing compounds
Key components in amino acids, proteins, nucleic acids, chlorophyll=photosynthesis(CO2+water).

55
Q

Negatives of draining land.

A

Loss in species rich wetlands
Reduces species diversity.

56
Q

Benefit of using wide borders around fields.

A

Support wild flowers(favour poor soil), pest predators, pollinators
Fertiliser=reduction in wild flowers&pollinators–>reduce species diversity.

Biology A-level (27 decks)

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