Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

a level biology > 3.5 population size and ecosystems > Flashcards

3.5 population size and ecosystems Flashcards

1
Q

population definition

A

the total number of organisms of a single species interbreeding within a habitat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is the population size equation?

A

population size = birth size + immigration - death rate + emigration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

the number of individuals in a population changes over time

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

immigration definition

A

the movement of individuals into a population

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what happens to the number of organisms in the lag phase?

A
  • there is a period of slow growth

(in sexually reproducing organisms e.g rabbits, this represent the time taken to reach sexual maturity and gestating young)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what happens to the number of organisms in the log phase?

A
  • (growth phase)
  • numbers increase logarithmically as there are no factors limiting growth
  • this cannot be maintained indefinitely as environmental resistance reduces growth (e.g biotic + abiotic factors)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

biotic factors definition

A
  • a living factor that can influence the population
  • e.g a predator or pathogen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

abiotic factors definition

A
  • a non-living factor which can influence the population
  • e.g oxygen availability or air temperature
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are some examples of biotic factors that limit growth?

A
  • predation
  • competition
  • parasitism
  • disease
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what are some examples of abiotic factors that limit growth?

A
  • soil pH
  • light intensity
  • temperature
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what happens to the number of organisms in the death phase?

A
  • birth and death rates are equal
  • the population has reached its maximum size/carrying capacity
  • numbers will fluctuate around this in response to environmental changes
  • this is often due to predator-prey relationships, where negative feedback regulates, i.e no. of prey decreases so there is less food so no. of predators decrease, which reduces predation, so prey number increases, and so on.
  • these fluctuations exist over months, even years as population responses are slow
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what happens to the number of organisms in the death phase?

A
  • factors that have reduced population growth become more significant and the population size decreases
  • death exceeds birth
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q
  • when writing about population growth, it is important to consider the organism
  • bacteria are not born, mammals are
  • the death phase in bacteria occurs largely due to build up of toxic waste products; which cannot be said about a population of rabbits
A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

carrying capacity definition

A
  • the maximum number around which a population fluctuates in a given environment
  • (varies depending on biotic and abiotic factors)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

negative feedback definition

A
  • occurs in an equilibrium where the corrective mechanism is in the opposite direction to the direction change
  • e.g if population numbers increase, negative feedback results in a decrease and vice versa
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is a log scale used for?

A
  • used to show very large numbers which a linear scale would be unable to do
  • with log10, the scale increases by a factor of ten times each time
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what are density-dependent factors? examples?

A
  • factors that have an increased effect on larger population sizes (denser population)
  • are biotic factors
  • e.g predation and disease. in larger populations, disease is more easily spread, and a predator can find more prey more easily
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what are density-independent factors? examples?

A
  • abiotic
  • their effect is the same regardless of the population density
  • e.g light intensity, temperature, fire
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is the abundance of a species?

A
  • a measure of how many individuals exist in a habitat
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q
  • physical features like soil type, pH and temperature will influence the range of organisms that can live there
  • where conditions are optimal, e.g warm, good rainfall, high sunlight intensity, then many plants will be found supporting many other animals
A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

why should sampling be at random?

A

to eliminate sampling bias

(can be done by creating a square grid and generating random coordinates)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what are some methods to estimate the number of individuals of each species in a given area?

A
  • mark-release-recapture
  • kick sampling + simpson’s index
  • quadrats + transects
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what type of species does the mark-release-recapture technique work on?

A

terrestrial animals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what is the method for mark-release-recapture (lincoln index)?

A
  • animals are captured and marked (important that they are not harmed or made more visible to predators) and then released
  • once animals have had chance to reintegrate with the population, e.g 24hours, the traps are reset
  • the total population size can be estimated using the number of individuals captured in sample 2, and the number in the sample that are marked (i.e caught before)
  • pop size = (no. in sample 1 x no. in sample 2) / no. marked in sample
  • have to assume that no births/death/immigration/emigration, have occurred during the time between collecting both samples
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what is the equation to determine population size using the capture-recapture method?

A

population size = (no. in sample 1 x no. in sample 2) / no. marked in sample

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what do you have to assume when doing the capture-recapture technique?

A
  • that no births/deaths/immigration/emigration have occurred during the time between collecting both samples
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what type of species does kick-sampling and Simpson’n index work for?

A

freshwater invertebrates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what is the method for kick-sampling?

A
  • collect and identify invertebrates from a given area using a quadrat and a net
  • kick or rake the area e.g 0.5m^2 for a set period e.g 30seconds, and collect invertebrates in a net downstream
  • release invertebrates carefully
  • use simpson’s index to calculate diversity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

what type of species does quatrats and transects work for to estimate population size?

A

plants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what is the method for using quadrats and transects to estimate population size?

A
  • estimate % area cover of different plants using a quadrat divided into 100 sections
  • measure plant density by counting number of plants in a quadrat e.g 1m^2
  • a transect is a tape measure that is used to measure intervals along an environmental gradient e.g distance from a woodland, along which quadrats can be placed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

ecosystem definition

A
  • a community in which energy and matter are transferred in complex interactions between the environment and organisms, involving biotic and abiotic elements
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

what are some examples of ecosystems?

A
  • tropical rainforest
  • temperate deciduous forest
  • tundra
  • desert
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

the abiotic and biotic features vary from ecosystem to ecosystem

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

what does a food chain represent?

A

the energy flow through an ecosystem

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

what is the ultimate source of energy for a food chain?
what is it converted into? by what?

A

sunlight
- which is converted into chemical energy by producers via photosynethesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

most of the energy available at each trophic level is released in _____ and incorporated into other molecules or into electrochemical gradients

A

respiration

  • this means that often less than 10% is incorporated into biomass and is availability to the next trophic level, which ultimately limits the length of food chains
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

producer definition (food chain)

A
  • the autotrophic organism at the start of a food chain converts light energy into chemical energy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

trophic level definition

A

the feeding level within a food chain and shows the number of times that energy has been transferred to successive organisms along a food chain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

biomass definition

A

the mass of biological material in living, or recently living organisms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

what does a typical food chain look like?

A

SUN —> producer —> primary consumer —> secondary consumer —> tertiary consumer (all consumers —> detritivores and decomposers)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

what are primary consumers?

A
  • herbivores and feed on producers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

what do secondary and tertiary consumers include?

A
  • carnivores and feed on the trophic level below
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

what are food webs?

A
  • more complex energy flow diagrams
  • as some tertiary consumers feed at more than one trophic level
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

what are detritivores?

A
  • organisms that feed on detritus (the remnants of dead organisms and fallen leaves)
  • e.g earthworms and woodlice
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q
  • decomposition involves detritivores, which feed on detritus and decomposers, that feed via external digestion (saprotrophism) completing the process started by the detritivores
  • they therefore feed on all trophic levels
A
  • when decomposers die they are fed on by other decomposers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

what are some examples of decomposers?

A
  • bacteria
  • fungi
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

the majority of light falling on a plant (60%) may not be absorbed by the pigments within the chloroplasts because it is:

A
  • the wrong wavelength
  • reflected by the leaf surface
  • transmitted through the leaf without striking a chlorophyll molecule
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

roughly what % of energy from sunlight is available to the next trophic level as biomass?

A

0.5%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

how can photosynthetic efficiency be calculated?

A

efficiency = (quantity of light energy fixed by plant / quantity of light energy falling on plant ) x100

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

gross primary productivity (GPP) definition

A
  • the energy produced by green plants (photosynthesis) in a given area over a given time
  • measure in kJ m^-2 year^-1
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

net primary productivity (NPP) definition

A
  • the energy in the plant’s biomass which is actually available to primary consumers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

what equation can represent the NPP (net primary productivity)

A

NPP = GPP - R
where R = respiration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

does the NPP (net primary productivity) vary according to the ecosystem?

A

yes
- tropical rainforests have a very high NPP due to plentiful rainfall, high light intensity and warm temperature
- tundra has a much lower NPP due to the environment being cold, with much lower light intensities

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

only part of the NPP in an ecosystem is transferred to the primary consumers due to low conversion efficiency

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

the transfer of energy in the form of biomass from one trophic level to the next is relatively low at around ___% or less

A

10% or less

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

in a primary producer, how is energy typically lost?

A
  • in excretion and egestion (urine and faeces)
  • lost as heat in respiration
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

what is the secondary production?

A
  • the proportion of chemical energy of food which consumers convert into biomass
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

why is the secondary production (proportion of chemical energy of food which consumers convert into biomass) much higher in carnivores)

A
  • due to the fact that they can digest their protein-rich diet more efficiently
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

what is the equation to calculate the % efficiency of energy transfer?

A

% efficiency = ( energy produced as biomass / energy available to next trophic level ) x100

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

only a pyramid of ____ shows true energy flow through an ecosystem

A

energy

(not pyramid of numbers or biomass)

61
Q

pyramid of numbers info:
adv/disadv?

A
  • relatively easy to construct
  • shows the energy flow through a food chain: as energy is lost at each stage, fewer individuals can be supported
  • but doesn’t take into account the size of organisms e.g a few wheat plants can support large numbers of greenfly, and so the pyramid inverts at this trophic level
  • when dealing with very large numbers e.g aphids, it is difficult to draw the bars to scale
62
Q

pyramid of biomass info:
adv/disadv?

A
  • more accurate than pyramid of numbers
  • but difficult to measure
  • pyramids may also be inverted, which can happen when organisms have a rapid life cycle and so numbers are replenished very quickly e.g phytoplankton, where total biomass over a year is considerably higher than at any given time
  • pyramids also difficult to calculate (e.g how do u measure the mass of tree roots)
63
Q

pyramid of energy info:
adv/disadv?

A
  • most accurate way of representing feeding relationships
  • show more clearly the energy lost at each level
  • but are difficult to calculate
64
Q

however, no pyramid can show that some organisms operate at several trophic levels

A
65
Q

succession definition

A
  • the change in the structure and species composition of a community over time
66
Q

ecosystems are dynamic and subject to change over time. the change in the composition of a community over time is referred to as succession, and occurs over tens to thousands of years depending upon the starting point

A
67
Q

what is each stage in succession known as?

A
  • a seral stage
  • where different communities dominate as they outcompete pre-existing species as conditions are more favourable for them
68
Q

when does primary succession occur?

A
  • when organisms invade spaces that did not previously support life
  • e.g bare rocks, sand dunes, volcanic flows

(where an area previously devoid of life is colonised by pioneer species)

69
Q

what changes as succession progresses?

A
  • soil depth increases
  • nutrient content increases
  • humus content increases ∴ water content increases
  • species diversity increases
  • stability of community increases
70
Q

what is secondary succession?

A

the reintroduction of organisms into a habitat previously occupied by plants and animals

  • soil is present
  • disrupted from succession by event such as fire/flooding/cultivation
71
Q

climax community definition

A

a stable community that undergoes no further change

72
Q

pioneer species definition

A
  • the first species to colonise a new area in an ecological succession
  • e.g mosses and lichens in primary succession
73
Q

primary succession from bare rock example:

A
  • weathering creates small cracks in the rocks and small particles
  • mosses and lichens begin to colonise. organic matter builds up slowly
  • legumes begin to grow as they are able to fix atmospheric nitrogen to supplement the poor nutrient soil. as they die soil becomes enriched
  • grasses and ferns start to grow, sheltering the soil from the elements. soil, and its moisture content increases
  • large shrubs and small trees colonise. leaf litter greatly increases fertility and humus content of the soil. habitats created for nesting birds and soil invertebrates so diversity increases
  • climax woodland is reached. this is usually oak, beech, hazel or lime species but is largely deciduous in southern UK. ground flora includes bracken, shrubs and bluebells
74
Q

when does a deflected or disclimax arise?

A
  • when the climax community is not reached due to practices such as monoculture, or grazing i.e human intervention
  • heather moors are managed to increase grouse numbers routinely burning large areas every twelve years to remove old growth and encourage new pioneer species which provide food for grouse
75
Q

comparison of primary and secondary succession:

A

primary vs secondary
- surface is bare vs soil present
- pioneer organisms are lichens and mosses vs pioneer organisms are typically small weedy plants
- takes a long time to reach climax community bc soil must be created through physical and biotic interactions vs quicker to reach climax community

76
Q

niche definition

A

the role and position a species has in its environment including all interactions with the biotic and abiotic factors

77
Q

mutualism definition

A
  • an interaction between organisms of two species from which both derive benefit
  • two species in a relationship that is beneficial to both
78
Q

commensalism definition

A
  • an interaction between organisms of two species from which one benefits but the other is not affected
79
Q
  • the immigration of spores and seeds into an area are important in the recolonisation of an area
  • as new species are introduced, competition exists for resources at all the seral stages because, e.g legumes can outcompete mosses as the soil content increases
A
80
Q

what does competition exist between?

A
  • different species (interspecific competition) where each may occupy a different niche
  • individuals of the same species (intraspecific competition) which is density dependent in.e competition increases with population size
81
Q

can two species occupy the same niche?

A

no
- when two species occupy the same habitat, one will out-compete the other

82
Q

what is an example of commensalism?

A
  • the small fish that attach themselves to larger fish for locomotion and food scraps
83
Q

microorganisms are important in the recycling of a number of nutrients e.g. carbon and nitrogen, which cycle between the biotic and abiotic components of an environment

A
84
Q

how is carbon (+carbon dioxide) absorbed in the carbon cycle?

A
  • carbon is absorbed from the atmosphere during photosynthesis
  • carbon dioxide is dissolved in aquatic ecosystems as HCO3 - ions
    (and undergoes similar processes as in the atmosphere, except that it forms calcium carbonate in mollusc shells and arthropod skeletons. when these organisms die, and their shells settle on the ocean bed, compression over millions of years forms chalk, limestone and marble, from these carbonates which act as a longer-term store (or sink) for carbon
85
Q

how is carbon dioxide released into the atmosphere in the carbon cycle?

A
  • returned to the atmosphere during respiration
  • during combustion of fossil fuels, but decreasing amounts are being removed by photosynthesis as large area of forests are being deforested, resulting in unprecedented rises in atmospheric carbon dioxide levels
  • detritivores and decomposers feed on every trophic level, and as they respire, CO2 is returned to the atmosphere
  • erosion of these rocks made from shells of organisms that contain co2 return carbon dioxide back to the atmosphere
86
Q

what are some human impacts on the carbon cycle?

A
  • deforestation
  • burning of fossil fuels
87
Q

how has deforestation impacted on the carbon cycle?

A
  • it significantly reduces volume of carbon dioxide removed from the atmosphere through photosynthesis
88
Q

how has the burning of fossil fuels impacted on the carbon cycle?

A
  • increase in carbon dioxide emissions over recent decades has led to an enhanced greenhouse effect
89
Q

carbon dioxide is a greenhouse gas which absorbs ____ radiation and re-radiates it back towards the earth’s surface rather than allowing it to escape into space

A
  • infrared radiation
90
Q

why do we need a natural greenhouse effect?

A

or temperatures would fluctuate too widely to support life

91
Q

what are some other gases that act as strong greenhouse gases?

A
  • methane
  • nitrous oxide
  • ozone
  • water vapour
  • CFCs
92
Q

the process of photosynthesis (increases/decreases) CO2 levels?

A

decreases

93
Q

the process of respiration (increases/decreases) CO2 levels?

A

increases

94
Q

the process of combustion (increases/decreases) CO2 levels?

A

increases

95
Q

the process of deforestation(increases/decreases) CO2 levels?

A

increases

96
Q

desertification definition

A

the process by which fertile land becomes desert as it loses water, vegetation and wildlife

97
Q

rising carbon dioxide levels lead to:

A
  • global warming
  • climate change
98
Q

what happens to the earth as global temperatures rise?

A
  • polar ice melts, resulting in sea levels rising and coastal flooding
  • higher temperatures increases the incidence of forest fires, and lead to desertification
99
Q

climate change is a consequence of ____

A

global warming
- as changes to regional climate patterns, average temperature, wind patterns and rainfall become more noticeable, and extreme weather conditions e.g drought and hurricanes, become more frequent

100
Q

how is the earth affected by climate change?

A
  • as the climate changes, plants and animals may not be able to adapt or migrate and many will become extinct
  • there is a risk from both global warming and the associated change in climate that many areas will suffer crop yield reductions and failed harvests, unless farming practices are changed e.g through use of drought-tolerant crops
  • acidification of oceans due to increased dissolved co2 will affect many aquatic organisms: fish gills produce mucus in response to increasing acidity which reduces gas exchange, and crustaceans lose calcium carbonate from their exoskeletons as it is soluble in acid
101
Q

what does the carbon footprint represent?

A

the equivalent amount of carbon dioxide produced in one year by an individual or activity

102
Q

how does agriculture induce a carbon footprint?

A
  • whilst removing co2 via photosynthesis, energy is needed to produce insecticides and fertilisers, fossil fuels power farming machines and produce needs to be transported to markets
103
Q

how can we reduce energy consumption and hence our carbon footprint?

A
  • reduce use of products
  • reuse products more
  • recycling
104
Q

what does the nitrogen cycle involve?

A
  • the flow of nitrogen atoms between the atmosphere and inorganic and organic nitrogen compounds in the soil or water
105
Q

why is nitrogen needed by plants?

A

to synthesise nucleic acids and proteins

106
Q

why must nitrogen gas be absorbed by plants in some other form?

A
  • because nitrogen gas is inert
  • usually nitrate ions in solution via their roots
107
Q

how do animals obtain a source of nitrogen?

A

by digesting plant and animal proteins

108
Q

what are the 4 main processes in the nitrogen cycle?

A
  • ammonification (putrefaction)
  • nitrification
  • denitrification
  • nitrogen fixation
109
Q

what is ammonification in the nitrogen cycle?

A
  • bacteria and fungi digest extracellularly dead organisms, faeces and urine
  • proteases hydrolyse proteins to amino acids and deaminases reduce the amino groups to ammonium ions (NH4 +)

(by decomposers)

110
Q

what is nitrification in the nitrogen cycle?

A
  • the addition of nitrates to the soil by the conversion of ammonium ions to nitrites by Nitrosomonas bacteria and then the conversion of nitrites to nitrates by Nitrobacter bacteria
  • the first reaction involves the loss of hydrogen atoms and both result in the gain of oxygen, meaning both reactions are oxidation and require aerobic conditions
111
Q

what is denitrification in the nitrogen cycle?

A
  • the loss of nitrate ions from the soil by anaerobic bacteria Pseudomonas, to atmospheric nitrogen gas
112
Q

what is nitrogen fixation in the nitrogen cycle?

A
  • the reduction of atmospheric nitrogen molecules to ammonium ions
  • this is accomplished by two genera of bacteria:
    • Azotobacter free living in the soil accounts for most nitrogen fixation
    • Rhizobium is a mutualistic bacterium found in the root nodules of leguminous plants e.g pea and clover. nitrogen gas diffuses into the nodules where nitrogenase enzyme produced by the bacteria reduces nitrogen (N2) to ammonium ions (NH4 +) in an anaerobic process. the ammonium ions are converted to organic acids and amino acids for the bacteria, and some enter the phloem for use by the plant
113
Q

nitrogen-fixing bacteria reduce ______ to _____ in an anaerobic process

A
  • atmospheric nitrogen (N2) to ammonium ions (NH4 +)
114
Q

human impact on the nitrogen cycle:

A
  • to maximise yields, farmers use pesticides to reduce damage to crops, and use nitrogen-based fertilisers e.g ammonium nitrate, to improve plant growth
  • farmers regularly plough and drain soils to increase soil aeration, which favours the aerobic processes of nitrogen fixation and nitrification, whilst inhibiting denitrification, which is anaerobic
  • (this also allows air to reach the roots of plants, as nitrates and other minerals are taken up by active transport, which requires ATP)
  • manure and slurry are also added to soils to improve soil structure and nitrogen content
  • major consequence of using water-soluble nitrate fertilisers is that they can be washed off (leached) into water courses - eutrophication
  • phosphates used in washing powders entering the water course further compound the problem
  • the increase in nitrates and phosphates lead to an algal bloom which blocks out light to aquatic plants
  • as plants and algae die, they form detritus, which is decomposed aerobically, using up dissolved oxygen in the water, which cause other aerobic organisms e.g fish, to die, further adding to the detritus
  • eventually all the oxygen is used up and only anaerobic bacteria survive, releasing ammonia, methane and hydrogen sulphide into the water creating an environment toxic to most aerobic organisms
115
Q

what is biological oxygen demand (BOD)?

A
  • the amount of dissolved oxygen needed by organisms to break down organic material present in a given water sample at certain temperature over a specific time period
  • when this is high, microorganisms are respiring aerobically depleting the dissolved oxygen in the water
116
Q

what can farmers do to reduce fertiliser run-off?

A
  • apply fertilisers when plants are actively growing. this increases their uptake reducing build up in the soil
  • not apply fertilisers within 10 meters of watercourses
  • dig drainage ditches to collect any run off
117
Q

ecology definition

A

the study of the relationships among organisms and their environment

118
Q

community definition

A

all of the populations of different species living together in a habitat

119
Q

what is a habitat?

A
  • the region where an organism normally lives
120
Q

what do population numbers depend on?

A
  • birth rate
  • death rate
  • immigration
  • emigration
121
Q

birth rate definition

A

the number of offspring born per thousand of population per year

122
Q

death rate definition

A

the number of deaths per thousand of population per year

123
Q

what is emigration?

A

the number of individuals leaving a region per thousand of population per year

124
Q

when do population sizes increase?

A

when births and immigrants are greater than deaths and emigrants

125
Q

what is distribution?

A

the spread of living organisms in an ecosystem

126
Q

suggest different ways abundance can be quantified:

A
  • percentage area cover
  • percentage frequency
  • density
127
Q

what is systematic sampling?

A
  • sampling technique used to determine the abundance and distribution if organisms along an area at periodic intervals e.g along a belt transect
  • commonly used in ecosystems where some form of gradual change occurs
128
Q

what is biomass? how is it transferred? how can we measure this?

A
  • total weight of living matter in a certain area
  • transferred up trophic levels through consumption
  • measured in terms of mass of carbon, or dry mass of tissue
129
Q

why is some energy never taken in at each trophic level?

A
  • some parts of food arent consumed
  • some parts of food are indigestible
  • plants cant use all light energy as some is the wrong wavelength
130
Q

summarise the process of primary succession:

A
  • pioneer species colonise the area
  • they die, decompose and add nutrients to the ground
  • over time, this allows more complex organisms to survive
131
Q

what are seres?

A
  • various intermediate stages in succession in an ecosystem progressing towards a climax community
132
Q

how does succession affect species diversity and the stability of a community?

A

succession increases species diversity and the stability of the community

133
Q

describe extracellular digestion by saprotrophs

A
  • they release enzymes which catalyse the breakdown of dead plant and animal material into simpler organic matter
134
Q

describe the stages of the carbon cycle:

A
  • photosynthesising plants remove CO2 from the atmosphere
  • eating passes carbon compounds along a food chain
  • respiration in plants and animals returns CO2 to the atmosphere
  • organisms die and decompose. saprotrophs break down dead material and release CO2 via respiration
  • combustion of materials (e.g wood, fossil fuels) releases CO2
135
Q

what is the greenhouse effect?

A
  • the increase of global temperatures caused by the trapping of solar heat by gases in the atmosphere
136
Q

how might global warming affect the natural world?

A
  • temperature, rainfall, light levels etc all affect survival
  • habitats may be destroyed by deforestation or flooding
  • species may need to change their habitat, or face extinction
137
Q

how do plant roots take up nitrogen?

A
  • taken up via active transport and facilitated diffusion as ammonium (NH4 +) and nitrate ions (NO3 -)
138
Q

name the four types of bacteria involved in the nitrogen cycle

A
  • nitrogen-fixing bacteria
  • nitrifying bacteria
  • denitrifying bacteria
  • decomposers
139
Q

give some examples of nitrifying bacteria

A
  • azotobacter - lives freely in the soil
  • rhizobium - lives inside the root nodules of leguminous plants
140
Q

name the 2 types of nitrifying bacteria and state their functions

A
  • nitrosomonas - oxidises ammonium compounds into nitrites
  • nitrobacter - oxidises nitrites into nitrates
141
Q

what are denitrifying bacteria?

A
  • anaerobic microorganisms
  • found in waterlogged soils
  • responsible for the reduction of nitrate ions to nitrogen gas
142
Q

describe the economic importance of the nitrogen cycle

A
  • maximises plant growth and crop yield, increasing food production
143
Q

how can farmers increase the nitrate content of soil?

A
  • ploughing and drainage to aerate the soil
  • application of fertilisers
  • growing legumes
144
Q

what are fertilisers?

A

natural or artificial materials that are added to soils to provide essential nutrients and improve plants growth

145
Q

give some example of natural fertilisers

A
  • manure
  • compost
  • treated sewage
146
Q

give an example of an artificial fertiliser

A

ammonium nitrate

147
Q

what is eutrophication?

A
  • the process by which pollution by nitrogen-containing fertilisers results in algal blooms and subsequent oxygen level reduction in bodies of water
148
Q

describe how fertilisers can cause eutrophication

A
  • fertilisers run-off into rivers and lakes
  • nutrients buildup in water
  • algal bloom blocks sunlight
  • aquatic plants cannot photosynthesise therefore less oxygen produced
  • they die and decompose
  • decomposers further deplete oxygen levels
  • animals can no longer respire aerobically so die
149
Q

how does digging drainage ditches affect habitats?

A
  • habitat loss
  • reduced biodiversity
  • may lead to eutrophication

a level biology (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions