5B - energy transfer and nutrient cycles Flashcards
1
Q
what is an ecosystem?
A
all the organisms (biotic factors) and non-living components in an area (abiotic factors such as temperature and rainfall)
2
Q
ecosystems & primary producers
A
all ecosystems include and depend on primary producers
3
Q
what are primary producers?
(+ examples)
A
organisms that make their own glucose
(plants and algae)
4
Q
ecosystems and photosynthesis:
A
in ecosystems where sunlight and water is available, photosynthesis enables plants to synthesise organic compounds (glucose and other sugars) from carbon dioxide
5
Q
sources of carbon dioxide for different plant:
A
in terrestrial ecosystems:
plants use CO2 from the atmosphere
in aquatic ecosystems:
plants use CO2 dissolved in the water
6
Q
what does the process of photosynthesis do?
A
transforms light energy into chemical energy held in biological molecules
↳ chemical energy in these biological molecules can then be used by other organisms in the community (consumers)
7
Q
what are primary consumers?
A
(herbivores or omnivores) feed on producers
8
Q
what are secondary consumers?
A
(carnivores or omnivores) feed on primary consumers
9
Q
what are tertiary consumers?
A
(carnivores or omnivores) feed on secondary consumers
10
Q
simple food chains
(example)
A
tropic level 1 - producer
grass
→
trophic level 2 - primary consumer
grasshopper
→
trophic level 3 - secondary consumer
frog
→
trophic level 4 - tertiary consumer
python
→
trophic level 5 - quartenary consumer
eagle (apex predator)
11
Q
what do arrows in food chain show?
A
how the chemical energy originally produced by the primary producer is transferred to other organisms in the community
12
Q
what are the sugars synthesised by plants used as?
A
-most are used as respiratory substrates
-the remaining sugars (not used in respiration) are used to make other groups of biological molecules needed by plants
13
Q
what is a respiratory substrate?
A
a molecule that can be used in respiration
14
Q
examples of biological molecules made from sugars:
A
-starch
-cellulose
-lipids
-proteins
15
Q
what is starch?
A
a complex carbohydrate molecule (formed from many glucose molecules) that acts as a short-term energy storage molecule
16
Q
what is a cellulose?
A
a complex carbohydrate molecule (formed from many glucose molecules) that acts as a structural component of plant cell walls
17
Q
what is a lipid?
A
it acts as another type of (longer-term) energy storage molecule
18
Q
how are protein made from sugars synthesised in plants?
A
sugars can be combined with nitrates to make amino acids, which can then be used to produce proteins
19
Q
biological molecules & biomass:
A
these different groups of biological molecules (all formed from the sugars synthesised by plants during photosynthesis) make up the biomass of the plants
20
Q
what is biomass?
A
the mass of living material / the chemical energy that is stored within the plant
21
Q
how can biomass be measured?
A
-the dry mass of an organism or tissue
-the mass of carbon that an organism or tissue contains
22
Q
how does the mass of carbon link to dry mass?
A
the mass of carbon that a sample contains is generally taken to be 50% of the dry mass of the sample
23
Q
what is dry mass?
A
the mass of the organism or tissue after all the water has been removed
24
Q
what can the dry mass of an organism be used to calculate?
A
the dry mass of a sample can be used to calculate the biomass of a total population of organisms / the biomass of organisms in an area
(dry mass of 1 organism x number of organisms)
(dry mass per m² x whole field size)
25
does biomass stay the same?
it can change over time
26
examples of changing biomass & implications:
the biomass of deciduous trees decreases over autumn and winter as they lose their leaves
↳ biomass is sometimes given with units of time as well
27
biomass & time units
including units of time shows the average biomass of an organism within a given area over that time period
28
what can calorimeter be used to do?
estimate the chemical energy stored in dry biomass
29
steps of calorimetry:
1) burn the sample of dry biomass in a calorimeter
2) the burning sample heats a known volume of water
3) the change in temperature of the water provides an estimate of the chemical energy the sample contains
30
apparatus of finding the dry mass and energy value of plant biomass:
-crucible
-oven
-digital balance
-calorimeter
31
what is a crucible?
a heat-proof, open-topped container
↳ it needs to be able to withstand the temperatures inside the oven
↳ it’s open-topped to let any moisture leaving the sample escape and evaporate
32
what is the oven used for?
to slowly dry the sample
33
what is the digital balance used for?
-for monitoring the mass of the plant sample as it dries out
-needs to have a high level of precision to detect small changes in the mass of the sample
34
what is a calorimeter?
these can be simple and inexpensive or very precise and expensive → bomb calorimeters (more commonly found in professional scientific laboratories)
35
method of finding the dry mass of a sample:
1) weigh the crucible container without the sample first
2) place the sample in the crucible &
place the crucible in the oven
3) set the oven to a low temperature (if the temperature is too high the sample may burn, which would cause it to lose biomass)
4) remove and weigh the crucible at regular intervals during the drying process
5) once the mass of the crucible (and sample) stops decreasing / becomes constant, the sample is fully dehydrated (all the water has been removed)
6) take the original mass of the crucible (withoit sample) away from this final constant mass to find the dry mass of the sample
36
steps of finding the energy released by a sample of plant biomass:
1) use a calorimeter
2) a calorimeter burns the dried sample and uses the energy released to heat a known volume of water
3) measure the change in temperature of the water
4) this temperature change can be used to estimate the chemical energy stored within the sample (this energy is measured in joules (J) or kilojoules (kJ)
5) 1 joule is the energy needed to raise the temperature of 0.24 g of water by 1 °C
37
limitations of chemical energy calorimetry:
-all of the sample may not be burnt
-some of the heat released will be lost to the surroundings.
-some of the heat released will be used to heat the beaker / container holding the water
-the water may not be pure, so the specific heat capacity may not be 100% accurate
38
limitations of calorimetry:
-It can take a long time to fully dehydrate a plant sample to find its dry mass →
because the sample has to be heated at a relatively low temperature to ensure it doesn’t burn → the drying process could take several days
-precise equipment is needed, which may not be available
-the more simple and basic the calorimeter, the less accurate the estimate will be as heat energy from the burning sample will be lost / not being transferred efficiently to the water
39
what is GPP?
(gross primary production)
the amount of chemical energy stored in the carbohydrates within plants (during photosynthesis)
40
how much of the light falling on a plant is used during photosynthesis?
roughly only 1% of the light falling on a plant is used in photosynthesis to produce glucose → the quantity of energy now stored in glucose is the gross primary production
41
how is the majority of light falling on a plant wasted?
99% of the light either…
-passes through the leaf without hitting chloroplasts
-is reflected off of the leaf
-is transferred to heat energy
-is transmitted through the leaf
42
how can gross primary production be measured? (units)
units of energy per unit area:
J m^–2 (joules per square metre)
kJ km^-2 (kilojoules per square kilometre)
units of mass per unit area:
g m^–2 (grams per square metre)
kg km^-2 (kilograms per square kilometre)
in aquatic environments, it may be more suitable to measure gross primary production per unit volume:
kg m^-3 (kilograms per cubic metre)
kJ m^-3 (kilojoules per cubic metre)
43
where is there gross primary production?
where there are primary producers → if there are no primary producers present in this area of land, there will be no gross primary production)
44
what is gross primary productivity?
the rate at which plants are able to store chemical energy via photosynthesis
45
how is gross primary productivity expressed?
using units of energy/mass per unit area per unit time
eg:
Mj m^–2 y^-1 (megajoules per square metre per year)
kg km^-2y^-1 (kilograms per square kilometre per year)
46
what is the difference between gross primary production and gross primary productivity?
gross primary production is not a rate so does not need to include time
47
the total biomass of the grass that grows in a 200 m² field is found to be 1,000 kg. calculate the gross primary production of the grass field. give appropriate units.
step 1: calculate the total yearly biomass of grass in 1 m² of the field
1,000 ÷ 200 = 5kg
step 2: give the appropriate units
5 kg m²
48
on average, a patch of rainforest covering an area of 1 km² is estimated to contain 1,500 kg of biomass. calculate the gross primary production of this rainforest patch. give your answer in g m^-2.
step 1: calculate the average biomass of 1 m² of the rainforest patch (1 km² = 1,000,000 m²)
1,500 ÷ 1,000,000 = 0.0015kg
step 2: convert this into grams
0.0015 × 1,000 = 1.5 g m^-2
49
the biomass of aquatic algae in a tank is estimated to contain a total of 5,440 joules of chemical energy. the tank has a volume of 4 m³. calculate the gross primary production of this aquatic algae. Give appropriate units.
step 1: calculate the chemical energy of the biomass of aquatic algae in 1 m³
5,440 ÷ 4 = 1,360 (J)
step 2: give the appropriate units
1,360 J m^-3
50
what is net primary production?
(net primary production)
the chemical energy stored in plant biomass after respiratory losses have been taken into account
51
how much energy is used for photosynthesis and how much passes from producers to herbivores?
-of total energy trapped in glucose during photosynthesis, 90% of this energy will be released from glucose to create ATP for the plant
-the plant uses most of its glucose to fuel active cellular processes
-a significant percentage of the energy originally captured will not be used to create new plant cells and therefore will not be able to be passed on to herbivores via eating
52
NPP formula:
NPP = GPP - R
53
how is NPP expressed?
it is expressed in units of energy per unit area or volume
for example:
J m–2 (joules per square metre)
J m–3 (joules per cubic metre)
54
why is NPP important?
-it represents the energy that is available to organisms at higher trophic levels in the ecosystem
-it is available for plant growth and reproduction.
55
how is net primary productivity expressed?
using units of energy/mass per unit area per unit time (time must be included as it is a rate)
for example:
Mj m^–2 y^-1 (g per square metre per year)
kg km^-2 y^-1 (kilograms per square kilometre per year)
56
what is a trophic level?
the position of an organism in a food chain, web or pyramid
57
how can trophic levels be represented?
by numbers or by the name of that trophic level e.g. plants and algae are in trophic level 1 (producers)
58
how many trophic levels can an organism be on?
organisms can belong to more than one trophic level
59
what are decomposers?
they break down dead plant and animal material and gain the chemical energy still stored in the dead matter
60
main decomposers:
bacteria and fungi
61
how do decomposers break down and absorb dead plant and animal material?
-they secrete digestive enzymes onto the surface of the dead organism
-these enzymes break down the dead matter into small soluble food molecules
-these molecules are then absorbed by the decomposers
62
how is decomposition beneficial?
it helps to release organic nutrients back into the environment (eg. the soil) which are essential for the growth of plants and other producers
63
what is primary production?
the storing of chemical energy (converted from light energy during photosynthesis) in the biomass of primary producers
64
how can primary production be expressed?
units of mass per unit area / units of energy per unit area
for example:
kg ha–1 (kilograms per hectare) l
kJ ha–1 (kilojoules per hectare)
65
conversion of hectare
1 hectare = 10,000 m²
(i.e. 100m × 100m)
66
what happens when consumers ingest producers?
the chemical energy in the biomass of the producers is transferred to the consumers → the consumers also store this chemical energy in their biomass
↳ secondary production / **the production of consumers**
67
the importance of productivity:
when measuring the production of producers or consumers, it can be useful to measure the average production over a period of time
for example:
a farmer’s crops might grow very fast in the summer but very slow in the winter (the production of producers varies during the year due to abiotic factors)
↳ it may be useful to the farmer to know the average growth rate of his crops per month or year so that they can estimate how much crop biomass they can expect to harvest
a cattle farmer may want to know the average biomass they can expect their cows to produce per month or year
68
which type of productivity would a cattle farmer want to know compared to a plant farmer?
-the crop farmer needs to know the primary productivity of his crops
-the cattle farmer needs to know the secondary productivity of his cows
69
a company that produces sunflower oil wants to know the primary productivity of their sunflower crop. the record the primary production of the crop each year for five years. this information is provided in the table below. [TABLE IN CAMERA ROLL] calculate the primary productivity of the sunflower crop, giving appropriate units. draw a graph of the data provided, adding a line showing the primary productivity of the sunflower crop over the five year period.
step 1: calculate the mean primary production per year
150 + 200 + 175 + 150 + 225 = 900
900 ÷ 5 = 180
step 2: give the appropriate units
180 kJ ha-1 yr-1
step 3: draw a graph of the data provided, adding a line showing the primary productivity of the sunflower crop over the five year period
70
how much chemical energy in the consumers’ food is transferred to the consumer?
only around 10% of the energy is available to the consumer to store as new biomass (only 10% passes between trophic levels)
71
why isn’t all of the chemical energy in the consumers’ food is transferred to the consumer?
-not all of the biomass of the food is eaten (e.g. the roots of plants or the bones of animals) → the chemical energy this biomass contains is lost to the environment
-consumers are not able to digest 100% of the food they ingest, so some is always egested as faeces → the chemical energy in this undigested biomass is also lost to the environment
-lots of chemical energy is lost to the environment as heat when consumers respire and during the excretion of waste products (e.g. urine)
72
what is the net production of consumers?
the energy that is left for the consumer to store as biomass after these losses to the environment (N)
73
formula for net production of consumer:
N = I - (F + R)
I = the chemical energy store in ingested food
F = the chemical energy lost to the environment in faeces and urine
R = the respiratory losses to the environment
74
in a patch of woodland, caterpillars ingest 2,000 kJ m⁻² yr⁻¹ of chemical energy from the biomass of oak leaves. the caterpillars lose 1,200 kJ m⁻² yr⁻¹ of this energy in faeces and urine. They lose a further 600 kJ m⁻² yr⁻¹ of this energy through respiration. calculate the net production of the caterpillars.
step 1: write out the equation and substitute in the known values
N = I - (F + R)
N = 2,000 - (1,200 + 600)
step 2: Calculate the net production (N) and give appropriate units
N = 2,000 - 1,800
N = 200 kJ m⁻² yr⁻¹
75
what is the efficiency of energy transfers?
the percentage of energy that is transferred from the sun to producers / the percentage of energy that is transferred from one trophic level to a higher trophic level
76
equation for efficiency of energy transfers:
% efficiency =
(gross primary productivity ÷ light energy falling on the producer) × 100
OR
% efficiency = (chemical energy in consumer ÷ chemical energy in ingested food) × 100
77
how efficiency links to producers:
(+ equation)
if a producer is being ingested, the chemical energy in the ingested food = net primary productivity of the producer and the chemical energy in the consumer = net productivity of the consumer
% efficiency = (net productivity of consumer ÷ net primary productivity ) × 100
78
how efficiency links to consumers:
(+ equation)
if it is a consumer being ingested (e.g. a primary consumer being ingested by a secondary consumer), the chemical energy in the ingested food is the same as the net productivity of the consumer being ingested and the chemical energy in the consumer is the same as the net productivity of the consumer (that is doing the ingesting)
% efficiency = (net productivity of secondary consumer ÷ net productivity of primary consumer) × 100
79
a wheat farmer’s crops are being damaged by insect pests. the net primary productivity of the wheat is 112,500 kJ m-2 yr-1. the net production of the insect pests is 10,000 kJ m-2 yr-1.
calculate the percentage efficiency of energy transfer from the wheat to the insects.
Step 1: srite out the equation for % efficiency and substitute in the known values
% Efficiency = (chemical energy in consumer ÷ chemical energy in ingested food) × 100
% efficiency = (10,000 / 112,500) × 100
step 2: Calculate the efficiency
% efficiency = (0.089) × 100
% efficiency = 8.9%
80
the wheat farmer decides to use biological control against insect pests that are eating the wheat. The farmer introduces a species of toad. by eating the insect pests, the toads ingest 10,000 kJ m-2 yr-1 of energy but lose 2,000 kJ m-2 yr-1 of this energy in faeces and urine. They lose a further 7,000 kJ m-2 yr-1 using energy for respiration.
calculate the percentage efficiency of energy transfer from the insects to the toads.
step 1: calculate the net production of the toads
N = I - (F + R)
N = 10,000 - (2,000 + 7,000)
N = 10,000 - 9,000
N = 1,000 kJ m-2 yr-1
step 2: write out the equation for % efficiency and substitute in the known values
% efficiency = (chemical energy in consumer ÷ chemical energy in ingested food) × 100
step 3: calculate the efficiency
% efficiency = (1,000 / 10,000) × 100
% efficiency = (0.1) × 100
% efficiency = 10%
81
what is yield?
how much of a useful product is obtained
82
what is crop yield?
a measure of how much crop can be obtained from an area of agricultural land
83
strategies that farmers use to increase yield:
-by simplifying food webs to reduce energy losses / reducing energy losses from crops to other organisms by removing pests
-by reducing respiratory energy losses from livestock (restricting their movement and keeping them warm / indoors)
84
methods of increasing yield in animals:
-keep livestock in smaller pens with regulated temperatures, reduces the energy they need for movement and temperature regulation and so maximises their size and yield
-they are often fed antibiotics in their food to prevent diseases
85
increasing yield refers to…
-increasing the net primary production of crops
-increasing the net production of livestock
86
what is theoretical yield?
the amount of crop or livestock biomass that is theoretically possible to produce, given the ideal conditions
87
what is actual yield?
the amount of crop or livestock biomass) that is actually produced, given the actual conditions the crops or livestock are kept under
88
what is percentage yield?
the actual yield achieved, given as a percentage of the theoretical yield possible
89
equation for percentage yield:
(actual yield / theoretical yield) × 100
90
the maximum theoretical net primary production of wheat crops is approximately 200 kg m⁻² yr⁻¹. A wheat farmer finds that her crops have a net primary production of only 50 kg m⁻² yr⁻¹. calculate the percentage yield of her wheat crops and explain why the percentage yield is not 100%.
step 1: write out the equation and substitute in the known values
yield = (actual yield ÷ theoretical yield) × 100 → (50 / 200) × 100
step 2: calculate the % yield
% yield = 0.25 × 100
% yield = 25%
explain why the percentage yield is not 100:
-the theoretical yield can only be obtained if the conditions are perfect
(abiotic factors, such as temperature, water availability and light availability )
(biotic factors, such as a lack of pest species competing with the crop)
91
a cattle farmer estimates that over a five year period, the final biomass of his herd of cattle should be 15,000 kg. At the end of the five years, when the cattle are ready for human consumption, the farmer calculates that the percentage yield is an impressive 90%. calculate the actual biomass of the herd of cattle at the end of the five years.
step 1: rearrange the equation
% yield = (actual yield / theoretical yield) × 100
actual yield = (% yield × theoretical yield) ÷ 100
step 2: substitute in the known values and calculate the actual yield
actual yield = (90 × 15,000) ÷ 100
actual yield = 1,350,000 ÷ 100
actual yield = 13,500
step 3: Give the appropriate units
13,500 kg
(15000 x 0.9 = 13,500)
92
reducing energy loss to other organisms:
(crops & pests)
-in a food web containing corn, a weed, a harvest mouse and a caterpillar they a all considered pests (ex corn) because they reduce the energy available for the growth of the crop
-this means they reduce the net primary production (NPP) of the corn
-this, reduces the amount of energy available to humans (who consume the corn)
93
reducing energy loss to other organisms:
(crops & pests → solution)
corn farmers can simplify the food web by getting rid of the pest species → this reduces the energy lost by the corn to these organisms → this will cause the NPP of the corn to increase
94
how can pest species be removed?
pest control methods:
-use chemical pesticides
-use biological agents to reduce the number of pests
(often, farmers will use both these methods (chemical and biological) together to reduce pest numbers more effectively)
95
chemical pesticides:
-insecticides are chemicals that kill insect pests that eat and damage crops,
-herbicides are chemicals that kill weeds that compete with crops for sunlight and water
96
using biological agents to reduce the number of pests
consumers of the pests can be used / parasites can be introduced /
pathogenic bacteria and viruses that kill pests can be used
97
what is the objective of reducing energy loss through respiration?
-careful control of the conditions that the livestock are raised in → the energy lost through respiration is minimised → the energy available for growth is maximised
98
methods of intensive farming of animals:
-respiration rate is increased when animals move, so keeping livestock in pens where their movement is restricted lowers energy loss through respiration
-respiration rate is increased when animals need to generate body heat to keep warm, so keeping livestock indoors and in heated pens also lowers energy loss through respiration
99
benefits of intensive farming of animals:
-more chemical energy is stored as biomass in the livestock, net production increases
-more energy is available for human consumption
-in a given period of time, a greater amount of food can be produced, even at a lower cost
100
drawbacks of intensive farming of animals:
some people think it is unethical to keep livestock in cramped, unnatural conditions where their movement is restricted and they may have a lower quality of life
101
the importance of nutrients:
living organisms require nutrients from their environments for growth and other processes (e.g. reproduction)
102
what happens to nutrients over time?
1) nutrients are returned to the environment when organisms produce waste or die and decompose
2) this is because the waste products of dead organisms are digested/decomposed by microorganisms
3) the products of this decomposition are available to plants as nutrients in the soil
4) these plants can then sustain organisms in higher trophic levels (consumers)
103
nutrients in stable communities:
the processes that remove nutrients (eg. plant growth) are balanced by the processes that return these nutrients (e.g. decomposition of dead plants and animals)
this means these nutrients are constantly being cycled in ecosystems
104
two examples of nutrient cycles are:
-the nitrogen cycle
-the phosphorous cycle
105
what does the nitrogen cycle show?
how nitrogen is recycled in ecosystems
106
why plants need nitrogen?
to produce proteins and nucleic acids (DNA and RNA)
107
how do plants obtain nitrogen?
-about 78% of the atmosphere is nitrogen gas but plants and animals cannot access the nitrogen in gaseous form
-they need nitrogen-fixing bacteria to convert nitrogen gas into nitrogen-containing compounds, which can be taken up by plants
108
what are the four key processes in the nitrogen cycle and what is different about them?
(they are carried out by different types of bacteria)
1) nitrogen fixation
2) ammonification
3) nitrification
4) denitrification
109
what happens during nitrogen-fixation?
atmospheric nitrogen gas is converted into nitrogen-containing compounds
110
nitrogen fixation steps:
1) nitrogen-fixing bacteria convert nitrogen (N2) into ammonia (NH3), which forms ammonium ions (NH4) that can then be used by plants
2) the bacteria have a symbiotic (mutually beneficial) relationship with these plants
↳ the bacteria provide the plants with nitrogen-containing compounds
↳ the plants provide the bacteria with organic compounds such as carbohydrates
111
where is nitrogen fixing bacteria found?
-inside the root nodules of leguminous plants (peas, beans and clover)
-in soil
112
examples of nitrogen fixing bacteria:
rhizobium (found in the root nodules of leguminous plants)
113
steps of ammonification:
1) nitrogen compounds in waste products (e.g. urine and faeces) and dead organisms are converted into ammonia by saprobionts
2) this ammonia forms ammonium ions in the soil
114
what are saprobionts?
a type of decomposer including some fungi and bacteria
115
steps of nitrification:
1) ammonium ions in the soil are converted by nitrifying bacteria into nitrogen compounds that can be used by plants (nitrates / NO3-)
2) first, nitrifying bacteria convert ammonium ions into nitrites,
different nitrifying bacteria then convert these nitrites into nitrates
116
steps of denitrification:
1) denitrifying bacteria use nitrates in the soil during respiration
2( this process produces nitrogen gas, which returns to the atmosphere
3) this process occurs in anaerobic conditions (when there is little or no oxygen available, such as in waterlogged soil
117
how does the nitrogen cycle support life on earth?
-it provides organisms with the nitrogen they need to grow and produce essential organic compounds, such as proteins and DNA (nitrogenous bases)
-the nitrogen cycle also helps regulate the amount of nitrogen in the environment, ensuring that it is not depleted or accumulated in harmful amounts
118
what does the phosphorous cycle show?
how phosphorus is recycled in ecosystems
119
why do organisms need phosphorous?
to produce biological molecules such as phospholipids (for cell membranes), nucleic acids (DNA and RNA) and ATP
120
steps of the phosphorous cycle:
1) phosphorus in rocks is slowly released into soil and water sources in the form of phosphate ions (PO₄³⁻) by the process of weathering
2) phosphate ions are taken up from the soil by plants through their roots or absorbed from water by algae
3) phosphate ions are transferred to consumers during feeding
4) phosphate ions in waste products and dead organisms are released into the soil or water during decomposition by saprobionts
5) the phosphate ions can now be taken up and used once again by producers or may be trapped in sediments that, over very long geological time periods may turn into phosphorus-containing rock once again
121
what is weathering?
the slow breaking down and erosion of rocks over time
122
how are nutrients recycled in natural ecosystems?
through food webs
↳ the nutrients get passed on from producers to primary consumers when they feed on the producers and from primary consumers to secondary consumes when they feed on primary consumers
123
why are microorganisms important?
they ensure that nutrients that are within dead organisms and in the waste products of organisms (faeces and urine) are recycled and made available to producers once again
(decomposition)
124
what are true decomposers are known as?
saprobionts
125
what are saprobionts mainly made up of?
fungi and bacteria
126
how do saprobionts decompose?
1) they secrete a wide range of digestive enzymes onto their food (dead organisms and waste material), then digest the material externally
↳ extracellular digestion
2) the products of this external digestion are then absorbed by the saprobionts
127
what is saprobiotic nutrition?
the method of obtaining nutrients from dead or waste organic matter via extracellular digestion
128
what do the digestive enzymes that saprobionts secrete allow them to do?
they allow them to hydrolyse a large variety of biological molecules & release a large range of nutrients
(eg: ammonium and phosphate ions)
129
what happens to the products of extracellular digestion?
-not all of the products of extracellular digestion get absorbed by saprobionts
-many remain in the surrounding environment (e.g. the soil) and are available to be absorbed by other organisms
130
what would happen without saprobionts?
nutrients would end up locked up in dead and waste matter would never be made available again → producers such as plants would not have access to sufficient nutrients
131
additional benefits of saprobionts:
some saprobionts excrete important nutrient mineral ions as waste products from their own metabolism
132
what have many plants evolved with fungi?
many plants have evolved symbiotic (mutually beneficial) relationships with fungi
133
what are fungi composed of?
long, thin filaments known as hyphae, which interact with the roots of the plants
134
what is the benefit of hyphae for plants?
they greatly increase the surface area of the root systems of the plants
↳ they increase the amount of water and mineral ions (e.g. nitrates and phosphates) that can be absorbed by the plants' roots
135
what do the micorrhizal fungi receive from plants?
in return, the fungi receive organic compounds (e.g. glucose) from the plant
136
these relationships between plant roots and fungi are known as…
mycorrhizae
137
definition of a mutualistic relationship:
a type of symbiotic relationship where all species involved benefit from their interactions
138
what happens to nutrients in agricultural ecosystems?
-crops and livestock take in nutrients from the soil (or from the grass that grows in the soil) as they grow and use these nutrients to generate biomass
-however, agricultural ecosystems are not like natural ecosystems because the crops or livestock are eventually removed from the fields instead of dying and decomposing there naturally
↳ as a result, the mineral ions now contained in the biomass of these crops or livestock are not returned to the soil by microorganisms
139
what is the result of agricultural farming? (nutrients)
-it interrupts the crucial processes of nutrient recycling
-if the interruption of these nutrient cycles occurs over a long enough time period, the concentration of nutrients in the soil will decrease, eventually leading to a decrease in crop yields or meat and milk yields from livestock
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what is a way to replace the minerals lost from agricultural ecosystems?
adding fertilisers → it ensures that crops and livestock can continue to grow and increase in biomass as normal, ensuring yields remain high
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what are examples of the minerals that fertilisers can add to the soil?
nitrogen, phosphorus and potassium ions
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what are the two types of fertilisers?
-natural fertilisers
-artificial fertilisers
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what are natural fertiliser made up of?
organic matter → the dead and decomposing remains of organisms and their waste products
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examples of nature fertilisers:
manure, composted vegetables, sewage & crops residues (crop parts left over after harvesting)
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what are other benefits of natural fertilisers?
they can improve soil structure, which helps in reducing soil erosion and increase the water-holding ability of the soil
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limitations of natural fertilisers:
-nutrients from natural fertilisers are released over long time periods
-the nutrients present are not very concentrated so relatively large amounts are needed
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what are artificial fertilisers made up of?
inorganic matter in the form of powders or pellets that contain pure chemical compounds
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strengths of artificial fertilisers:
-the exact chemical composition is known so it is easier to how know much to apply and the effects they will have on crop yields
-the nutrients present are concentrated so smaller amounts are needed → transport costs are lower
-these fertilisers are easy to apply evenly and are clean, making them easy to handle
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what are some issues with the way that artificial fertilisers are applied?
as fertilisers are very effective in ensuring high crop yields, they are often applied to fields by farmers in greater quantities than are actually needed by the crop plants
↳ as the crop plants are unable to use all the fertiliser provided, the soluble nitrate and phosphate ions in the excess fertiliser are not taken up by the crop plants and remain in the soil water
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what can happen to soluble mineral ions that remain in soil water?
the mineral ions can be transported by rainwater or the water from irrigation systems into nearby bodies of water (such as ponds and lakes) or waterways (such as streams and rivers)
(leaching)
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when is leaching more likely to occur?
if fertilisers are applied just before heavy rainfall
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why is leaching more likely when using artificial fertilisers?
the inorganic ions are readily soluble and if they are not used immediately by crop plants, they can quickly leach into waterways
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why is leaching less likely when using natural fertilisers?
-the minerals are contained within organic matter that must first be decomposed by microorganisms before the mineral ions can be absorbed by crop plants
-this means the release of the mineral ions into the soil is slower and more controlled, making leaching less likely
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TIP: APPROPRIATE LANGUAGE
minerals - nitrogen and phosphorus
ions - nitrate and phosphate ions
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which mineral leaching is more common?
in general, phosphate leaching occurs to a lesser extent than nitrate leaching, as phosphates are less soluble in water
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what can leaching lead to?
eutrophication
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what is eutrophication?
a process in which nutrients accumulate in a body of water and there is an increased growth of organisms that may deplete the oxygen in the water
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steps of eutrophication:
1) mineral ions from excess fertiliser leach from farmland into waterways and cause rapid growth of algae at the surface of the water (algal bloom)
2) this blocks sunlight, aquatic plants below the surface of the water start to die as they can no longer photosynthesise
3) the algae also start to die when competition for nutrients becomes too intense
4) as aquatic plants and algae die in increasing numbers, saprobionts feed on the dead organic matter and also increase in number
5) the decomposing bacteria respire aerobically & use up the dissolved oxygen in the water
6) the amount of dissolved oxygen in the water rapidly decreases, so aquatic organisms such as fish and insects may be unable to survive
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TIP: leaching vs eutrophication
leaching itself is not a damaging process but the knock-on effects of this (i.e. eutrophication) can be very damaging to aquatic ecosystems, which often contain organisms that are very sensitive to dissolved oxygen levels, such as fish and aquatic insects and their larvae
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how do other human activities impact the nitrogen cycle?
-the burning of fossil fuels, and deforestation, can have a significant impact on the nitrogen cycle
-these activities can alter the balance of nitrogen in the environment, leading to the overproduction of nitrogen compounds and the release of harmful pollutants, such as nitrogen oxides
