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A - Biology > Topic 5B - Energy transfer and nutrient cycles ARN * > Flashcards

Topic 5B - Energy transfer and nutrient cycles ARN * Flashcards

Energy transfer in ecosystems farming practices and production nutrient cycles fertilisers and eutrophication

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1
Q

what does an ecosystem include?

A

all the organisms living in a particular area and all the non-living conditions

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2
Q

what are producers?

A

organisms that make their own food, e.g. plants and algae through photosynthesis

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3
Q

how do plants make their own food?

A

they use energy from sunlight and carbon dioxide to make glucose and other sugars in photosynthesis

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4
Q

where do plants get carbon dioxide from?

A 
land-based = the atmosphere
aquatic = dissolved in water
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5
Q

what are sugars produced from plants used for?

A

some used in respiration to release energy for growth
rest is used to make other biomols like cellulose
these biomols make up the plant’s biomass

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6
Q

what is biomass?

A

chemical energy stored in the plant
the mass of living material
biological molecules make up the biomass

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7
Q

what is the food chain?

A

energy is transferred through the living organisms of an ecosystem when organisms eat other organisms
producers are eaten by primary consumers
primary by secondary consumers
and then tertiary consumers

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8
Q

how can biomass be measured?

A

in terms of the mass of carbon that an organism contains or the dry mass of its tissue per unit area
g/m^2 on land
g/m^3 in water

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9
Q

what is dry mass?

A

the mass of the organism with the water removed

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10
Q

how is dry mass measured?

A

a sample of the organism is dried, often in an oven set to a low temperature.
the sample is weighed at regular intervals until constant, this is when all water is removed
sample must be dead, usually small samples

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11
Q

how can the dry mass (biomass) of the total population in an area be measured?

A

the dry mass calculated for a single sample can be scaled up

units : Kg/m^2

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12
Q

how to find the mass of carbon in an organism?

A

50 % of the dry mass

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13
Q

how can the amount of chemical energy stored in biomass be calculated?

A

burning the biomass in a calorimeter.

the amount of heat given off tells you how much energy is in it (joules / kilojoules)

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14
Q

how is biomass burnt in a calorimeter?

A

a sample of dry biomass is burnt using a hot wire
the energy released is used to heat a known volume of water (1kg)
the change in temperature of the water is used to calculate the chemical energy of the dry biomass
4184 J to heat 1kg of water by 1*C

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15
Q

what is gross primary production?

A

GPP is the total amount of chemical energy converted from the light energy by plants (stored in pant), in a given area, in a given time

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16
Q

what is respiratory loss? (R)

A

the amount of GPP that is lost to the environment as heat when the plants respire
approx. 20 - 50%

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17
Q

what is the net primary production?

A

the energy available to the plant for growth and reproduction
also energy available to organisms at next stage of the food chain (herbivores and decomposers)

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18
Q

how to calculate NPP?

A

NPP = GPP - R

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19
Q

what is primary productivity?

A

when primary production is expressed as a rate

kJ/m^2/yr

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20
Q

how do consumers get energy?

A

by ingesting plant material, or animals that have eaten plant material

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21
Q

how is energy lost when energy is transferred from consumers food to their biomass?

A

not all food is eaten, so the energy it contains is not taken in
some parts are indigestible, so are egested as faeces. so chemical energy stores is lost to environment
energy is lost to environment through respiration or excretion of urine
approx. 90% energy is lost

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22
Q

what is the equation for net production of consumers?

A 
N = I - (F + R)
N = net production
I = chemical energy in ingested food
F = chemical energy lost in waste
R = energy lost through respiration
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23
Q

how to calculate how efficient energy transfer from 1 trophic level to the next is?

A

divide consumer NPP by producer NPP and multiply by 100 to find % efficiency

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24
Q

what do food chains and webs show?

A

how energy is transferred through an ecosystem
chain - simple lines of energy transfer, each stage is a trophic level
web - lots of food chains in an ecosystem and how they overlap

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25
Q

what are decomposers?

A

they break down dead or undigested material, allowing nutrients to be recycled

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26
Q

what do farming practices do?

A

increase the amount of energy available for human consumption by:
reducing energy lost to other organisms (pests)
reducing energy lost through respiration

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27
Q

how to increase energy available to humans by reducing energy lost to pests?

A

in a food web containing a crop grown for human consumption, simplifying the food web to remove any chains that don’t involve humans (e.g. getting rid of pests)

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28
Q

how can farmers reduce pest numbers?

A

chemical pesticides
biological agents
integrated systems combining both

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29
Q

what are examples of a chemical pesticide?

A

insecticides kill insect pests that eat and damage crops. less biomass is lost, they grow to be larger, NPP is greater
herbicides kill weeds. this removes direct competition with the crop for sunlight, it can also remove preferred habitat for pests

30
Q

what are examples of biological agents to reduce the number of pests?

A

parasites live in or lay eggs on pest insect. parasites kill insect or reduce its ability to function
pathogenic bacteria and viruses can kill pests

31
Q

how can farmers increase NPP of livestock?

A

controlling conditions livestock live in so more energy is used for growth and less is lost through respiration

32
Q

how are respiratory losses reduced?

A

movement increases respiration so animals kept in pens where movement is restricted
warm indoor pens so less energy wasted by generating body heat

33
Q

what are the benefits of increasing NPP of livestock?

A

more food can be produced in a shorter space of time, often at low costs

34
Q

what are the disadvantages of increasing NPP of livestock?

A

ethical issues
intensively reared animals kept in conditions that cause them pain, distress or restrict their natural behaviour, so it shouldn’t be done

35
Q

what is a natural ecosystem?

A

one that hasn’t been changed by human activity.

nutrients are recycled though the food webs, but human activity often disrupts the cycling of nutrients

36
Q

what are saprobionts?

A

(type of decomposer) microorganisms, such as bacteria and fungi that feed on the remains of dead plants and animals and on their waste products, breaking them down to obtain energy.

37
Q

why are saprobionts important?

A

they allow important chemical elements in the remains to be recycled

38
Q

what is extracellular digestion?

A

saprobionts secrete enzymes and digest their food externally, then absorb the nutrients they need.

39
Q

what is saprobiotic nutrition?

A

obtaining nutrients from dead organic matter via extracellular digestion. e.g. during extracellular digestion by saprobionts organic molecules are broken down into inorganic ions.

40
Q

what are mycorrhizae?

A

symbiotic relationships between fungi and the roots of plants

41
Q

what is involved in mycorrhizae?

A

fungi made up of hyphae, which connect to plant’s roots
they greatly increase SA of plant’s root system, helping it absorb water and ions that are usually scarce from soil
the fungi obtain organic compounds e.g. glucose from the plant

42
Q

what is nitrogen needed for in plants and animals?

A

amino acids
DNA/RNA nucleotides
ATP
NAD/NADP

43
Q

what are the stages of the nitrogen cycle?

A

nitrogen fixation
ammonification
nitrification
denitrification

44
Q

what is nitrogen fixation?

A

nitrogen gas in atmosphere turned into nitrogen-containing compounds via bacteria (e.g. Rhizobium)
they form ammonia which makes ammonium ions in solution for plants
N2 in air –> ammonium compounds in plants —> ammonium compounds in animals via feeding
N2 in air –> ammonium ions in soil

45
Q

where are Rhizobium?

A

found inside root nodules of leguminous plants, they form a mutualistic relationship with plants
they swap nitrogen compounds for carbohydrates

46
Q

what is ammonification?

A

nitrogen compounds from dead organisms and animal waste turned into ammonia via saprobionts, which form ammonium ions in soil

47
Q

what is nitrification?

A

ammonium ions in soil changed into nitrogen compounds to be used for plants (nitrates) via nitrifying bacteria
nitrosomonas change ammonium ions into nitrites
nitrobacter change nitrites into nitrates

48
Q

what is denitrification?

A

nitrates in the soil are converted into nitrogen gas by denitrifying bacteria - use nitrates in respiration to produce nitrogen gas
under anaerobic conditions

49
Q

what other ways of nitrogen getting into an ecosystem are there?

A

lightning - fixes atmospheric nitrogen

artificial fertilisers - produced from atmospheric nitrogen on an industrial scale in the Haber process

50
Q

what is phosphorus needed for in plants and animals?

A

to make biological molecules like:
phospholipids for cell membrane
DNA
ATP

51
Q

where is phosphorus found?

A

in rocks and dissolved in the oceans in the form of phosphate ions (PO4 3-)

52
Q

what is the phosphorus cycle?

A

phosphate ions in rocks released into soil via weathering (erosion/ use of fertilisers)
PI taken into plants through roots via absorption
PI transferred through food chain as animals eat the plants and are eaten by other animals
PI lost in waste products and dead organisms
saprobionts release PI into soil for assimilation by plants
weathering of rocks release PI into seas, lakes and rivers. taken in by aquatic producers and passed along food chain to birds
guano contains high proportion of PI which is returned to soils as a natural fertiliser

53
Q

what do mycorrhizae do in the phosphorus cycle?

A

greatly increase the rate at which phosphorus can be assimilated

54
Q

what does assimilated mean?

A

absorbed and used to make more complex molecules

55
Q

how are nutrients removed from an ecosystem in farming of crops?

A

crops take in minerals from the soil as they grow and use them to build their own tissues.
when harvested, they are not allowed to die and decompose in the field so mineral ions aren’t returned to the soil by decomposers

56
Q

how are nutrients removed from an ecosystem in farming of animals?

A

minerals are lost from the system when animals or animal products are removed from the land. animals eat plants, taking in their nutrients.
the nutrients aren’t replaced through their remains or waste products as its removed to be slaughtered

57
Q

how is lost nutrients from the soil replaced?

A

adding fertilisers replaces lost minerals, so more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer

58
Q

what are artificial fertilisers?

A

they are inorganic, they contain pure chemicals as powders or pellets

59
Q

what are natural fertilisers?

A

organic matter - they include manure, composted vegetables, crop residues and sewage sludge

60
Q

why does using fertilisers raise environmental issues?

A

more fertiliser applied than plants need
so they leach into waterways
leading to eutrophication
fertilisers change balance of nutrients in soil - too much of a particular nutrient can cause crops and other plants to die

61
Q

what is leaching?

A

when water-soluble compounds in the soil are washed away e.g. by rain or irrigation systems. often into nearby ponds and rivers

62
Q

when is leaching more likely?

A

if the fertiliser is applied just before heavy rainfall

63
Q

why are inorganic fertilisers more dangerous than organic?

A

inorganic ions in chemical fertilisers are relatively soluble. this means excess minerals that are not used immediately are more likely to leach.
natural fertilisers - minerals still contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed, so release of ions is more controlled, leaching is less likely

64
Q

which minerals are more likely to be leached?

A

phosphates are less soluble in water than nitrates so less likely to be leached

65
Q

what happens in eutrophication?

A

mineral ions leached from fertilised fields stimulate rapid growth of algae in ponds and rivers
blocking light to plants below
plants unable to photosynthesise and die
saprobionts feed on dead plant matter and respire aerobically, reducing oxygen concentration in water
fish and other aquatic life die because there isn’t enough dissolved oxygen

66
Q

why is fresh mass not accurate for biomass?

A

this is the mass of a living organism, its easier to measure but varying water content makes it unreliable

67
Q

how much energy do producers get from the sun?

A

1 - 3%

68
Q

why do producer get so little energy from the sun?

A

over 90% of sun is reflected by clouds back into space
not all wavelengths of light can be absorbed by the plant
light may not fall on a chlorophyll pigment molecule
limiting factors might prevent energy storage

69
Q

what farming methods can be put in place to put less strain on soil?

A

crop rotation
fallow year - grass followed by ploughing
fallow year - clover/ legumes followed by plowing
allow animals to graze - faeces, organic fertiliser

70
Q

how do enzymes produced by plants kill bacteria?

A

they hydrolyse the murein in the cell wall of the bacteria

A - Biology (21 decks)

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