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Biology Alevel > energy and ecosystems > Flashcards

energy and ecosystems Flashcards

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1
Q

why is dry biomass more accurate than wet biomass

A
  • organisms contain different amounts of water in their tissues
  • dry biomass allows for compasrison between biomass of different organisms
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2
Q

What is biomass

A

Biomass is the total mass of living material / mass of carbon /dry mass in a specific area at a given time

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3
Q

What is biomass

A

Biomass is the total mass of living material / mass of carbon /dry mass in a specific area at a given time

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4
Q

Why can you not use fresh mass to measure biomass

A

Varying water levels make it unreliable as water content of a sample varies

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5
Q

What are the units for dry mass

A

Grams per square metre of grams per cubic metre

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6
Q

Why are only small samples taken for dry mass

A

Organisms must be killed

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7
Q

How do you obtain dry mass

A

dry by heating Heat at 100* or over , to confirm your sample is dry repeat until mass stops decreasing - heat until constant mass. low temperature is used to avoid burning

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8
Q

How do you then calculate the biomass from dry mass

A

1) burn dry biomass in pure oxygen in a calorimeter,with a known volume of water this breaks the bonds and released the energy as heat which increases the temp of water
2) measure temperature increase
3) calculate energy transferred
= SHC water x water volume x temp change / mass of dry biomass

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9
Q

What does biomass contain

A

Chemical energy store , which is produced during photosynthesis

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10
Q

What is gross primary production( GPP)

A

GPP is the chemical energy stored in plant biomass in a given area or volume in a given time

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11
Q

How much of this energy is used for respiration

A

20-50%

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12
Q

What is net primary production (NPP)

A

The chemical energy stored in plant biomass after respiratory losses to the environment

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13
Q

An area of vegetation 5m by 5m produces 40000kj energy in a year . Calculate GPP

A

Area =25 m2
40000/25 =1600 kjm-2year-1

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14
Q

Why does NPP vary

A

Environmental temperature
Type of plants growing and their density
Day length and light intensity
Availability of soil nutrients

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15
Q

What happens when rate of photosysnethesis increases

A

More carbon (biomass enters the food chain

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16
Q

What is NPP also known as

A

The energy left over that is available to ththe plant to create new biomass - available to the next tropic level in a foodweb

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17
Q

How do you work out the net production of consumers

A

N=I-(F+R) where N= net production , I= chemical energy store in ingested food , F= chemical energy lost to environment in faeces and urine and R= respiratory losses

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18
Q

What are the units for rates of productivity and why

A

Kjha-1year-1.
Kj for energy
Ha-1 is an area , we have to standardise the results to enable the environments to be compared l- it takes into account that different environments will vary in size
Per year - takes into account the impact seasons will have on rain , light and heat ( affecting soil quality , nutrients etc )- it provided an annual average to allow fair comparisons between environments

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19
Q

How do you work out % efficiency

A

Energy available after transfer / energy available before the transfer
X100

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20
Q

what are the issues with bomb calorimetry

A
  • organisms must be killed
  • normally only made on a small sample which may not be representative
  • can take a long time to fully dehydrate a sample as the sample has to be heated at a relatively low temperature to ensure it doesnt burn
  • prescice equiptment is needed which might not be available
    ( prescise digital balance for the mass of the plant samoke and a precise thermometer too)
    -
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21
Q

why is their air surrounding the bomb calorimeter

A
  • draught excluder - decreases amount of heat lost to enviroment . air reduces loss of heat
    insulation reduces gain of heat
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22
Q

what is the purpose of the copper container

A

transfers heat from burning sample to water

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23
Q

why do we use a crucible

A

it is a heat proof container

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24
Q

what is the point of a stirrer

A

distributes heat energy so ensures even temperature - no hot spots

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25
Q

what are ignition wires used for ( only in certain models )

A

electrical current is passed through causing the sample to burn

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26
Q

what is the point of the vessel with oxygen

A

ensures all of the sample is burnt

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27
Q

what are autotrophs

A

producers

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28
Q

how do autotrophs grow

A

they use energy from sunlight to produce glucose

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29
Q

why does a mouse have a higher respiratory rate than an elephant

A
  • higher surface area to volume ratio and therefore more heat is lost to surroundings and it needs to maintain this
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30
Q

how is energy lost between the sun and a producer

A
  • light is reflected back into the atmosphere
    -light may not fall on a chlorophyll molecule so is transmitted straight through the cells
    -not all wavelengths of light can be absorbed and used by chlorophyll for photosynthesis
    -a limiting factor eg low c02 levels may limit the rate of photosynthesis ( so biomass is not gained)
31
Q

what are heterotrophs

A

consumers

32
Q

how do heterotrophs obtain their carbon

A

by eating other organisms for growth

33
Q

what are saprobionts

A

microorganisms that feed by releasing enzymes outside of their body and then absorbing the digested food. decay is caused by saprobionts .

34
Q

what is the order for the food web

A

sun - producer - primary consumer ( herbivore)- secondary consumer ( predators) - tertiary consumer and so on

35
Q

what does an arrow represent in a food web

A

the energy transfer

36
Q

why is biomass lost between the primary and secondary consumer

A
  • energy is lost through respiration ( energy lost through heat ) , faeces ( some parts can be eaten but not digested ), not all parts can be eaten ( eg roots and bones ). excretory materials eg urine. maintaining high body temperature
37
Q

why do most food chains only have four to five trophic levels

A
  • there is insufficient energy to support a large enough breeding population at levels higher than these
38
Q

what is a trophic level

A

trophic levels describe the position of an organism in a food chain , web or pyramid

39
Q

why can organisms not get nitrogen from the air

A

nitrogen is pretty unreactive ( contains a triple bond ) so we have a nitrgogen cycle instead

40
Q

what is the first stage in the nitrogen cycle

A

nitrogen fixation - this is a reduction reaction and can occur via nitrogen fixing bacteria in plant roots , on root nodules of leguminous plants ( beans and peas )
or it can occur via soil bacteria
- using enzymes nitrogen gas is converted into ammonia / ammonium ions in the soil.

  • lightning also fixes atmopsheric nitrogen
41
Q

why are the bacteria on root nodules “mutalistic”

A
  • they obtain carbohydrates from the plant and the plant aquires amino acids ect from the bacteria
42
Q

what is the next stage in the carbon cycle

A

-nitrification is an oxidation reaction and releases energy ( as gain of oxygen and loss of hydrogen )
- which converts ammonium ions to nitrite ions ( NO2-) and then converts nitrite ions to nitrate ions (NO3-) , this is done by free living nitrifying bacteria which are aerobic so plently of oxygen is required for this conversion

43
Q

what is the next stage in the nitrogen cycle

A

assimilation - plants absorb these nitrate ions by active transport on root hair cells which are then converted into nitrogen - containing compounds like amino acids , proteins , dna ect

44
Q

what is ammonification

A
  • after plants and animals obtain their nitrogen ( animals eat the plants and nitrates are taken up) some ammonia / ammonium ions are recycled back into the soil through faeces/ waste and death.
    this is done by saprobionts( fungi and bacteria) which decompose / digest and breakdown proteins and amino acids and dna and urea ( nitrogen containing compounds ) from the dead organic matter
45
Q

what is denitrification

A

nitrate ions in the soil are converted back into nitrogen gas .
this occurs when soil becomes waterlogged and has a low oxygen concentration as these bacteria are anaerobic and are called denitrifying bacteria .this reduces the amount of nitrifying and nitrogen fixing bacteria as they respire aerobically

46
Q

why is denitrification bad

A
  • not wanted in agriculture as it is a way you are losing nitrogen and nitrogen containing compounds from the soil and therefore plants have less nitrate ions to grow
47
Q

how can farmers prevent denitrification

A
  • ploughing / aerating the soil to increase o2 concentration
  • good drainage
48
Q

what is secondary production

A

like producers , the chemical energy in their biomass is also stored in consumers

49
Q

what is the rate of production known as

A

productivity, either measured as energy per unit or mass per unit area

50
Q

how do farmers increase agricultural productivity

A

increase biomass

51
Q

how can farmers increase production

A
  • high energy feed
    -low fibre diet ( less energy is used for digestion)
    -antibiotics
    -growth hormones
    -excluding predators
    -fetiliser
    -pesticides ( stop crops being eaten and losing biomass
    either insecticides which kills insect pets that eat and damage crops or herbicides that kills weeds that compete with the crops for sunlight and water)
    -monoculture - use of weed killers
    -selective breeding - to promote specific desired characterisitcs
  • crop rotation - different crops use different nutrients
    -ploughing - increases 02 conc by aerating soil so more oxygen for nitrogen fixing bacteria and fewer denitrifying bacteria)
52
Q

how can farmers reduce respiratory losses

A
  • rear animals in barns which are heated
  • reduce movement
    this lowers energy loss through respiration
53
Q

what are the issues with farming

A
  • intensive rearing causes a poor quality of life as animals have a lack of space
  • selective breeding could increase harmful recessive characteristics
    -genetic modification affects natural animals
    -spread of disease
  • use of drugs causing antibiotic resistance
54
Q

what are some enviromental impacts

A
  • eutrophicatoon and killing unintended organisms resulting in reduced biodiviserty
  • removal of hedgerows and adjacent woofland copse resulting in reduced biodiversity
  • monocultures - reduced biodiviserity
  • absence of crop rotation- poor soil structure
  • human activities increases atmospheric greenhouse gas levels , increases the greenhouse effect , increases atmospheric temperature , climate change because fuels , machinery , heating , producing fertilisers , producing meat , clearing land for farming
55
Q

why are fertilisers added to soil

A
  • to replace the nitrates and phosphates which are lost when plants are harvested ( removed from the cycle and take the nutrients with them)
  • either natural fetilisers ( manure )
  • or artificial ( inorganic chemicals)
56
Q

what are the benefits / downsides of natural fertilisers

A
  • cheaper and often free if a farmer owns animals , however the exact minerals and proportions in the manure cannot be controlled
57
Q

what are the benefits / downsides of chemical fetilisers

A

created to contain ecact proportions of minerals however
they are very soluble in water therefore will dissolve in rainwater and leach into nearby lakes and rivers

58
Q

what is leaching

A

when water soluble compounds are washed away , often into rivers or ponds

59
Q

describe and explain the results in yeild of wheat vs amount of fertiliser

A

initially as fertiliser application increases , so does yield
this is because nutrients are a limiting factor in determining growth of wheat as soil is deficient in nutrients
- then yeild plateus because nutrients are no longer limiting growth / nutrients have reached optimum for growth
- eventually yeild decreases with more fertiliser application as nutrients are at toxic levels

60
Q

how does an increase in algae cause a decrease in fish in a lake

A
  • more saprobionts which decompose the algae and these saprobionts respire aerobically therefore will be less oxygen available for fish , causing some of the fish to die
61
Q

what is fertiliser

A

a chemical or natural substance added to soil or land to increase its fertility

62
Q

what ions / minerals are important in fertilisers

A

nitrogen , phosphorous and potassium

63
Q

why do we need fertilisers

A

excretement and remains are rarely recycled back to the same area of land

64
Q

why do we use artifical fertilisers

A
  • more accurate / measured concentration
  • easier to apply
    -easier to transport / store
    -fast release
    -risk of leaching and eutrophication due to high solubility
65
Q

why do we use natural fertilisers

A
  • cheaper / free (manure)
    -slower release
  • bulky and more difficult to apply
66
Q

what are the downsides / effects of fertiliser usage

A
  • reduced species diversity : nitrogen - rich compounds favour the growth of grasses and nettles and too much of a particular nutrient can cause crops and other plants to die
  • large populations of these compete with others
  • leaching( fertilisers dissolved in soil water are carried away into ground water or surface water )
    -eutrophication
67
Q

what is eutrophication

A
  • nitrates and phosphates dissolve in water and accumulate in bodies of water through leaching / surface run off
  • this allows rapid growth of algae causing algae bloom
    -algae bloom blocks sunlight for plants below
  • these plants use up oxgyen present and die as cannot photosynthesise
  • more saprobionts , decompose dead algae and plants which use oxygen for respiration , decreasing oxgyen concentration in the lake,river and the plants die due to lack of oxygen
68
Q

where is phosphorous mainly found

A
69
Q

what are the steps to the phosphorous cycle

A
  • phosphate ions in rocks are released into the soil or sea by weathering / erosion
    -plants and aquatic plants take in phosphate ions through roots and incourporate into their biomass
  • animals feed off and digest plants incourpourating phosphate ions in their biomass.
  • exretion of these animals can go directly into rivers and lakes - putting phosphate ions back in or decomposition of dead organisms by saprobionts can be released into the soil
  • ## or guano which can either erode into the sea or forming rocks by deposition
70
Q

what is mycorrhizal fungi

A
  • rate of absorption is increased by mycorrhizae , you find these fungi attached to the roots of plants and they act as extensions increasing the surface area to absorb more water and ions like phosphate
  • this is a mutualistic relationship as fungi get dissolved sugars and plants get more water and minerals . phosphates are more soluble than nitrates
  • mycorrhizae acts like a sponge and so holds water and ions , enabaling the plant to better resist draught
71
Q

why are mycorrhizae fungi so important

A

phosphates do not stay in the soil for long so these fungi help a plant absorb more before it leaches out

72
Q

what biological molecules contain phosphorous

A
  • phospholipids
  • dna
    -rna
    -nadp
    atp
73
Q

what is a difference between the phosphorous cycle and nitrogen cycle

A

the phosphorous cycle does not contain a gaseous phase

Biology Alevel (17 decks)

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