3.5- Chapter 13- Energy and Ecosystems Flashcards
3.5.3 Energy and Ecosystems, 3.5.4 Nutrient Cycles
1
Q
Explain the importance of energy
A
- Life depends on continuous transfers of energy.
- Organisms found in any ecosystem rely on a source of energy to carry out all their activities.
2
Q
What is an ecosystem?
A
All the organisms living in a particular area and all the non-living abiotic conditions.
3
Q
Describe the stages that energy goes through in an ecosystem.
A
- The ultimate source of energy is sunlight- conserved as chemical energy by plants.
- In any ecosystem, plants are producers and during photosynthesis use energy from sunlight to synthesise organic compounds from atmospheric or aquatic (dissolved in water) carbon dioxide.
- Organic compounds- glucose and other sugars- mostly used by plants as respiratory substrates to release energy.
- Other organic compounds/ sugars- are used to make other biological molecules- e.g. cellulose- form the biomass of the plant- chemical energy store- means by which energy is passed between other organisms.
- Energy is transferred through the living organisms of an ecosystem when organisms are consumed by other organisms.
- In communities, the biological molecules produced by photosynthesis are consumed by other organisms, including animals, bacteria and fungi. Some of biological molecules are used as respiratory substrates by these consumers.
4
Q
What are the three groups of organism
A
- Producers- photosynthetic organisms- manufacture organic substances using light energy, water, carbon dioxide and mineral ions. Occur in all organisms.
- Consumers- organisms that obtain energy by feeding on other organisms- consumption rather than using energy of sunlight directly. Animals are consumers.
- Saprobionts- decomposers- usually fungi and bacteria- organisms that break down complex materials in dead organisms into simple ones- release valuable minerals and elements in a form that can reabsorbed by plants and so contribute to recycling.
5
Q
What are the types of consumer.
A
- Primary consumers- eat producers directly.
- Secondary consumers- animals eating primary consumers- usually predators but could also be scavengers/ parasites.
- Tertiary consumers- animals eating secondary consumers- usually predators but could also be scavengers/ parasites.
- May also be quaternary consumers but energy transfers get too inefficient to reach higher levels of the food chain.
6
Q
What do food chains and food webs do?
A
Show how energy is transferred through an ecosystem.
7
Q
What is a food chain?
A
- Shows simple energy transfers
- Shows feeding relationships.
- Demontrates the consumer each organism is eaten by starting at the producer.
- Arrows represent direction of energy flow.
8
Q
What is a trophic level?
A
A stage in the food chain.
9
Q
What are food webs.
A
- Linking of food chains within a habitat- shows how they overlap.
- Highly complex- all organisms within a habitat are likely to be linked to others in the food web.
- Decomposers can also be part of food webs- break down dead or undigested material allowing nutrients to be recycled.
10
Q
What are the dietary groups of consumers and destribe what trophic levels they are at.
A
- Herbivores- animals that eat plants (producers)- primary consumer.
- Carnivore- animal that eats animals- secondary or tertiary consumer.
- Omnivore- animal that eats plants and animals- primary consumer and also a secondary or tertiary consumer.
11
Q
What is biomass.
A
Total mass of living material in a specific area at a given time.
12
Q
How may biomass be measured.
A
- Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area.
13
Q
Describe why fresh mass and height are not used as a measure of biomass.
A
- Fresh mass- easy to assess but due to variance of the water content in living tissue- unreliable, so dry mass is more preferably used.
- Biomass- not proportional to height of organism- biomass may be put into roots/ some increase in height is due to water gain
14
Q
What is dry mass and why is it useful?
A
- Dry mass- mass of an organism with its water removed.
- Measuring mass of carbon/ dry mass- **prevents varying amounts of water so that only measures organic material. **
- Because the organism must be killed, it usually is made on a sample- may not be representative.
- You may be asked how to carry out investigations to find the dry mass of plant samples or the energy released by samples of plant biomass.
15
Q
How do you measure dry mass?
A
- The sample of the organism is dried in an oven set to a low temperature.
- The sample is weighed and the mass is recorded at regular intervals.
- The sample is reheated until the mass becomes constant- all the water is removed.
- Once the dry mass of the sample has been measured, the result can be scaled up to give the dry mass of the total population or area investigated.
16
Q
How is the mass of carbon measured from dry mass.
A
The mass of carbon present is usually taken as 50% of the dry mass (you may usually be given the proportion of carbon present in the question).
17
Q
Describe the units used to measure biomass.
A
- Measured using dry mass per given area in a given time- grams per square metre- gm-2- when an area is being sampled.
- If volume is being sampled e.g. a pond or an ocean- measured in grams per cubic metre gm-3.
18
Q
How is the chemical energy store in biomass estimated.
A
- The chemical energy store in dry biomass can be estimated using calorimetry. Involves burning the biomass in a calorimeter.
- The amount of heat given off by the mass gives how much energy is in it- measured in joules or kilojoules.
19
Q
Describe how you use calorimetry.
A
- Bomb calorimetry- sample of dry material weighed and burned in pure oxygen within a sealed chamber (called a bomb).
- Bomb- surrounded by a water bath with a known volume of water- heat of combustion causes small temperature rise in this water.
- Know the volume and specific heat capacity of the water- know how much energy is required to raise temperature of 1g of water by 1°C. Use the temperature rise to calculate the energy (heat) released from the mass of burnt biomass in kJkg-1.
20
Q
Draw an annotated diagram to illustrate calorimetry.
A
Answer on revision card.
21
Q
Explain why photosynthesis is not 100% efficienct
A
- Sun- source of energy for ecosystems but usually 1-3% of sunlight energy may be converted by green plants into organic matter and made available to organisms in the food chain.
- Over 90% of the Sun’s energy is reflected back into space by clouds and dust or absorbed by the atmosphere.
- Not all wavelengths of light can be absorbed/ used for photosynthesis.
- Light- may not fall on a chlorophyll molecules.
- Low carbon dioxide levels or other factors may limit the rate of photosynthesis.
22
Q
What is Gross Primary Production?
A
- Gross primary production (GPP) is the chemical energy store in plant biomass, in a given area or volume.
- GPP measures the amount of chemical energy converted by plants in a given area.
23
Q
What does R represent with regards to primary production.
A
Respiratory losses to the environment (R)- 20-50% of energy is used for respiration and is lost as heat.
24
Q
What is Net Primary Production.
A
- Net primary production ( NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account.
- **High NPP means low respiration. High NPP is advantageous as it means more growth/ biomass/ colonisation. **
25
Q
What is the equation for net primary production.
A
- Net Primary Production= Gross Primary Production – Respiratory losses to the environment
- NPP= GPP-R
26
Q
How is primary production expressed?
A
- Often expressed as a rate- total amount of chemical energy/ biomass in a given area in a given time- usually kJ m-2 yr-1 (kilojoules per square metre per year).#
- When primary production is expressed as a rate- called the primary productivity.
27
Q
How can Net Primary Produciton be measured.
A
Net Primary Productivity can be measured using biomass because it represents the dry mass- mass of carbon, and represents gross production minus respiratory losses.
28
Q
What is net primary production available for use as?
A
- Net primary production- available for plant growth and reproduction as stored in the plant’s biomass.
- Net primary production also available to other trophic levels in the ecosystem such as herbivores and decomposers.
29
Q
How do consumers get energy.
A
- Consumers store chemical energy in their biomass.
- Consumers get energy by ingesting plant material or animals that have eaten plant material.
30
Q
Describe the efficiency of energy transfers within ecosystems.
A
- Photosynthesis and respiration are not 100% efficient.
- The transfer of biomass and its stored chemical energy in a community from one organism to a consumer is also not 100% efficient.
- Organisms- pass only a small fraction of energy they receive to each successive stage in the food chain.
- Less than 10% of net primary production in plants can be used by primary consumers for growth. 90% of the energy is lost in various ways.
- Secondary and tertiary consumers- transfer about 20% of the energy available from their prey.
31
Q
Why are low percentages of energy transferred at each stage of the food chain.
A
- Some of the organism is not consumed – e.g. roots, bones.
- Parts are consumed but cannot be digested- egested in faeces.
- Energy lost in excretory materials e.g. urine.
- Energy losses occur as heat from respiration- lost to the environment- losses high in mammals and birds because of high body temperature- energy needed to maintain body temperature when heat is lost to the environment constantly.
32
Q
What does the relative inefficiency of energy transfer between trophic levels explain.
A
- Most food chains only have 4/5 trophic levels because insufficient energy is available to support a large enough breeding population at higher trophic levels.
- Total biomass- less at higher trophic levels.
- Total amount of energy available less at each level up the food chain.
33
Q
What is net production.
A
Energy left after loss of energy to the environment in consumers- stored in the consumers biomass and available to the next trophic level.
34
Q
How is net production calculated?
A
- N= I- (F+R).
- N= net production.
- I= chemical energy store of ingested food.
- F= chemical energy lost to the environment in faeces and urine.
- R= energy lost in respiration to the environment.
35
Q
What does data on net production often show?
A
Often shows the amount of energy available at each trophic level- usually measured by kilojoules per square metre per year.
36
Q
What is important to remember when calculating net produciton.
A
- It is important to remember that energy cannot be created or destroyed- total amount of energy entering the system must equal the amount of energy in the system plus the amount leaving the system.
- Energy loss is always to the environment.
37
Q
What is net production also known as.
A
The net production of consumers can also be called secondary production or secondary productivity when expressed as a rate.
38
Q
How do you calculate net productivity.
w
A
- You may be asked to calculate the net productivity of producers or consumers from given data.
- Primary and secondary productivity is the rate of primary or secondary production, respectively.
- It is measured as biomass in a given area in a given time eg kJ ha–1 year–1 .
39
Q
How do you calculate the efficiency of energy transfers within ecosystems.
A
Use percentage efficiency= net production of trophic level/ net production of previous trophic level x100.
40
Q
What is the equation for percentage efficiency
A
Percentage efficiency= net production of trophic level/ net production of previous trophic level x100.
41
Q
Describe the distribution of the efficiency of energy transfers in the food chain.
A
- Further up the food chain- energy transfer usually becomes more efficient.
- Efficiency of energy transfer from producer to consumer may be 5-10% but from consumer to consumer may be 15-20%, as plants contain more indigestible matter than animals.
42
Q
What do farming practices aim to do.
A
- Farming practices- aim to increase amount of energy available for human consumption.
- Farmers increase yields by increasing efficiency of energy transfer along food chains which produce food.
- Farmers aim to increase the net primary production (NPP) of crops and net production (NP) of livestock.
43
Q
How is production altered by farming practices.
A
- Production is affected by farming practices designed to increase the efficiency of energy transfer by:
- Simplifying food webs to reduce energy losses to non-human food chains
- Reducing respiratory losses within a human food chain.
44
Q
How is reducing respiratory loss beneficial to farmers.
A
- Energy passes along the food chain- only a small percentage passes from one organism to the next- most lost as heat during respiration.
- Practices that reduce respiratory losses in a human food chain reduce energy loss and increase yield.
45
Q
How is intensive rearing of livestock beneficial to farmers.
A
- Intensive rearing of domestic livestock- converts the smallest possible quantity of food energy into the greatest quantity of animal mass.
- Minimise energy losses from domestic animals during their lifetime- more of the food energy taken in by animals- converted into body mass- passed onto humans.
- Energy conversion- made more efficient ensuring as much energy from respiration as possible goes into growth rather than other activities.
46
Q
How is respiratory loss reduced in livestock.
A
- Farmers control conditions in which livestock live in so more of their energy is used for growth and less is lost through respiration and activities that increase the rate of respiration.
- Achieved by keeping animals in confined spaces such as small enclosures, barns or cages- to reduce their movement- factory farming.
- Pens are often indoors and kept warm so less energy is wasted by generating body heat.
- Enhancing net production by keeping animals in pens raises ethical issues- causes animals pain, distress and restricts natural behaviour.
47
Q
How does farming increase the energy-conversion rate.
A
- Movement is restricted- less energy is used in muscle contraction.
- Environments- kept warm to reduce heat loss from the body.
- Feeding- controlled so animals receive optimum amount and type of food for maximum growth with no wastage.
- Predators are excluded- no loss to other organisms in the food web.
- More biomass is produced and more chemical energy can be stored- increases the net production and efficiency of energy transfer to humans.
- More food is produced in a shorter time at a lower cost.
48
Q
How do farmers simplify food webs.
A
Reducing or eliminate organisms that are part of a food web which compete with the plant or animal being farmed.
49
Q
What are pests?
A
- Organisms that reduce the amount of energy available for creating biomass and crop growth and therefore net primary production of crops.
- The reduced NPP reduces the amount of energy available for humans.
- By simplifying the food web- getting rid of pests in food chains that don’t involve humans- energy losses will be reduced and the NPP of the crop increases.
50
Q
How do you identify pests in the food web.
A
- Identify which organisms are eating the crop or competing with it for energy.
- See revision card for example.
51
Q
What are the different types of pest.
A
- Weeds- compete with crop plants for limited resources- amount taken by them means less available for the crop plant.
- Insect pests- may damage leaves of crops- limiting photosynthesising ability and reducing productivity, also may be in direct competition with humans eating the crop itself.
- Pests of domesticated animals- cause disease- animals may to grow as rapidly, be unfit for human consumption or die, reducing productivity.
- Crops grown in monoculture- enables insect and fungal pests to spread rapidly.
52
Q
Describe what pest control is and the issues.
A
- Pest control- simplifies the food web to limit the effects of pests on productivity to a commercially level.
- Need to balance ethical and practical costs of pest control with the commercial benefits.
- Two conflicting interests- cheap food and conservation of natural resources.
53
Q
Describe the different forms of pest control.
Hint: 5 points
A
- Insecticides- chemical pesticides that kill inspects- less biomass is lost from crops- grow larger- greater NPP.
- Herbicides- chemical pesticides that kill weeds- remove direct competition with crop for energy from the sun. Also removes the preferred habitat/ food source of the insect pests- further reducing their numbers and simplifying the food web.
- Parasites- biological agents- kill the insect or reduce ability to function. Reduces the number of pests so crops lose less energy and biomass, increasing the efficiency of energy transfer to humans.
- Pathogenic bacteria and viruses- biological control- used to kill pests.
- Farmers often use integrated systems that combine chemical and biological methods- combined effect of using both can reduce pest numbers more than either method alone- NPP is further increased.
54
Q
What is the equation for percentage yield.
A
Percentage yield= actual yield/ theoretical yield x100
55
Q
Describe how the movement of energy through an ecosytem is linear.
A
- Energy enters an ecosystem as sunlight and is lost as heat.
- Heat- can’t be recycled- flow of energy in an ecosystem is therefore linear.
- Sun- continues to supply energy to Earth- linear flow not a problem.
56
Q
Describe the movement of nutrients through an ecosystem.
A
- Nutrients- don’t have extraterrestrial source- limited availability of ions in a usable form- important that carbon, nitrogen and phosphorus and recycled.
- While rock weathering releases inorganic ions, the rate is inadequate to sustain most communities so recycling of inorganic ions is essential.
- Flow of nutrients within an ecosystem- mostly cyclical.
- Nutrients are recycled within natural ecosystems, exemplified by the nitrogen cycle and the phosphorus cycle.
57
Q
Describe the generic process of nutrient cycles.
Hint: 5 steps
A
- The nutrient is taken up by producers as simple inorganic molecules.
- The producer incorporates nutrients into complex organic molecules.
- When the producer is eaten- the nutrient passes into consumers.
- Nutrient- then passes along food chain when these animals are eaten by other consumers.
- When producers and consumers die- complex molecules broken down by saprobiontic microorganisms (decomposers)- release the nutrient into its original simple form.
58
Q
Describe the importance of microorganisms in nutrient cycles.
A
Microorganisms play a vital role in recycling chemical elements such as phosphorus and nitrogen.
59
Q
What is the role of saprobionts in decomposition.
A
- Feed on the remains of dead plants and animals and on their waste products, breaking them down.
- Decomposition allows important chemical elements in the remains and waste to be recycled.
- Secrete enzymes and digest their food externally, then absorb the nutrients they need- extracellular digestion. Break organic molecules into inorganic ions.
- Saprobionts ensure nutrients are released for reuse and not part of complex molecules that can’t be taken up and used again by plants.
60
Q
What is saprobiontic nutrition.
A
Obtaining nutrients from dead organic matter and animal waste using extracellular digestion.
61
Q
What are mycorrhizae?
A
Associations between certain types of fungi and the roots of the vast majority of plants- symbiotic relationship.
62
Q
How do mycorrizae facilitate the uptake of water and inorganic ions by plants.
A
- Fungi- made up of long, thin strands called hyphae- act as extensions of plants roots and increase the total surface area for absorption of water and scarce ions.
- Mycorrhizae- act like a sponge- hold water and minerals around roots- enables plants to better resist drought and to take up inorganic ions more readily.
- Mycorrhiza- play a part in nutrient cycles by improving the uptake of scarce ions such as phosphate ions.
- Mycorrhizal relationship between plants and fungi- mutualistic.
- Plants- benefit from improved water and inorganic ion uptake.
- Fungi receive organic (carbon-containing) compounds- carbohydrates and amino acids from the plant.
63
Q
What is the role of nitrogen in living organisms?
A
- Living organisms- require nitrogen to manufacture proteins, nucleic acids and other nitrogen-containing compounds.
- Biological molecules containing nitrogen include amino acids, proteins, DNA, RNA, ATP, NAD, NADP, ADP, cAMP, chlorophyll (but don’t combine similar molecules e.g. NADP, NAD, ATP, ADP, amino acids, protein).
64
Q
What are the main nuitrogen-containing ions/ molecules.
A
Nitrogen-containing ions/ molecules include nitrites, nitrates and ammonias.
65
Q
In the carbon and nitrogen cycles where does each element originally come from.
A
- Carbon and nitrogen cycles- main reservoir of each element is in the atmosphere.
- 78% of the atmosphere is nitrogen but few organisms can use nitrogen gas directly.
66
Q
What is the importance of bacteria in the nitrogen cycle.
A
- 78% of the atmosphere is nitrogen but few organisms can use nitrogen gas directly.
- Bacteria within ecosystems convert nitrogen in the atmosphere into nitrogen-containing compounds.
67
Q
How do plants obtain nitrogen?
A
- Plants- gain most of their nitrogen in the form of nitrate ions from the soil (NO3-)
- Nitrate ions- absorbed into plants using active transport by the roots- where nitrogen enters the living components of the ecosystem.
- In many ecosystems, the availability of nitrates is the factor that limits plant growth- plants are the primary producers- nitrate availability affects the whole ecosystem.
68
Q
How do animals obtain nitrogen.
A
Obtain nitrogen-containing compounds by eating and digesting plants.
69
Q
How does nitrogen travel through natural ecosystems.
A
- Nitrate concentrations restored by recycling nitrogen containing compounds.
- Plants/ animals die- decomposition begins- microorganisms replenish the nitrate concentrations in the soil.
- Release of nitrate ions by decomposition- important- in natural ecosystems- few nitrate ions available from other sources.
- Nitrate ions- soluble and easily leach through the soil- beyond the reach of plant roots.
- Nitrogen cycle- shows how nitrogen is converted into a usable form and then passed between different living organisms and the non-living environment.
70
Q
How does nitrogen reach agriculutural ecosystems.
A
Concentration of soil nitrate further increased by artificial fertilisers- produced from atmospheric nitrogen on an industrial scale in the Haber process).
71
Q
What are the steps of the nitrogen cycle you need to know.
A
- Describe the role of bacteria in the nitrogen cycle to illustrate the processes of saprobiontic nutrition, ammonification, nitrification, nitrogen fixation and denitrification.
- The nitrogen cycle also includes food chains- as nitrogen is passed on when organisms are eaten.
72
Q
Draw the nitrogen cycle.
A
Answer on revision card.
73
Q
Describe ammonification.
A
- Stage saprobionts used in.
- Production of ammonia by saprobionts from organic nitrogen-containing compounds- including urea (produced form the breakdown of excess amino acids), proteins, RNA, DNA and vitamins found in faeces and dead organisms.
- Saprobiontic microorganisms- fungi and bacteria- feed on faces and dead organisms’ material- releasing ammonia- forms ammonium ions in the soil.
- Nitrogen returns to the non-living component of the ecosystem through ammonium ions.
74
Q
Describe nitrification.
A
- The ammonium ions in the soil are changed into nitrogen compounds that can be used by plants- nitrates.
- Plants use light energy to produce organic compounds but some bacteria obtain their energy from chemical reactions involving inorganic ions.
- Nitrifying bacteria- gain energy from the conversion of ammonium ions into nitrate ions in an oxidation reaction (releasing energy).
- Conversion occurs in two stages by different bacteria:
- Oxidation of ammonium ions to nitrite ions (NO2-).
- Oxidation of nitrite ions to nitrate ions (NO3-).
75
Q
Describe the conditions required for nitrification to occur.
A
- Nitrifying bacteria require oxygen for the oxidation of ammonium ions to nitrite and nitrate ions.
- Nitrifying bacteria- require oxygen for reaction- require soil with air spaces.
- Important for farmers to keep soil well aerated by ploughing.
- Good drainage- prevents air spaces being filled with water forcing air out of the soil.
76
Q
Describe nitrogen fixation.
A
- Nitrogen gas is converted into nitrogen-containing compounds.
- Can be carried out industrially in the production of artificial fertilisers produced from atmospheric nitrogen in the Haber process- and also occurs naturally when lightning passes through the atmosphere.
- Most important form of nitrogen fixation- carried out by microorganisms- two main types:
- Free-living nitrogen-fixing bacteria- reduce gaseous nitrogen to ammonia- used to manufacture amino acids- nitrogen-rich compounds are released when they die and decay.
- Mutualistic nitrogen-fixing bacteria- live in nodules on the roots of leguminous plants e.g. peas and beans- obtain carbohydrates from the plant and the plant acquires nitrogen compounds from the bacteria.
77
Q
Describe denitrification. #
A
- Denitrifying bacteria- convert soil nitrates into gaseous nitrogen.
- Reduces availability of nitrogen-containing compounds for plants.
78
Q
Describe the conditions under which denitification occurs.
A
- Denitrification requires anaerobic conditions - no oxygen.
- Anaerobic conditions- more denitrification occurs- more nitrate ions reduced/ converted to nitrogen gas.
- E.g. waterlogged soil- low oxygen concentration- type of microorganism present changes. Fewer aerobic nitrifying and nitrogen-fixing bacteria and an increase in anaerobic denitrifying bacteria.
- Soils crops grow on must be kept well aerated to prevent the build-up of denitrifying bacteria.
- This balance could be upset by human activities.
79
Q
Describe the importance of phosphorus.
A
- Phosphorus- important biological element- used to produce ATP, ADP, phospholipids, DNA, RNA, RuBP, TP and GP. #
- Life depends on phosphorus being recycled.
80
Q
What is the main source in phosphorus in the phosphorus cycle.
A
- Phosphorus cycle- main reservoir is in mineral form rather than from the atmosphere.
- Phosphorous- mostly exists as phosphate ions (PO43-) dissolved in oceans and in sedimentary rock deposits which originate in oceans.
- Phosphate ions disoolved in water in soil can be assimilated (absorbed and used to make more complex molecules) by plants and other producers.
81
Q
What are the steps of the phosphorus cycle.
A
- Weathering and erosion of rocks- enables phosphate ions to become dissolved in the soil.
- Dissolved phosphate ions in water in the soil can be absorbed by plants- incorporate them into their biomass.
- Phosphate ions are absorbed through plants roots- mycorrhizae greatly increase the rate phosphorous can be assimilated.
- Phosphate ions- pass through the food chain into animals which feed on plants, and other animals which are secondary and tertiary consumers.
- Excess phosphate ions- excreted by animals- accumulate in waste material e.g. guano from the excretory products of sea birds.
- Death of plants and animals, alongside excreted products- saprobionts break down organic compounds- release phosphate ions into the water or soil for assimilation by plants.
- Some phosphate ions- remain in parts of animals- such as bones/ shells- slow to breakdown.
- Phosphate ions in excretion, released by decomposition and dissolved from rocks- transported by streams and rivers into lakes and oceans- form sedimentary rocks- completes the cycle.
- Some phosphate ions in water sources such as lakes, oceans and rivers, are taken up by aquatic producers such as algae and passed along the food chain to birds.
- Waste produced by sea birds- guano- contains high amounts of phosphate ions- returns them to soils, particularly in coastal areas and used as natural fertiliser.
82
Q
Draw the phosphorus cycle
A
Answer on revision card.
83
Q
Describe the features of agricultural ecosystems.
A
- Agricultural ecosystems increase the efficiency of energy transfer along human food chains- improve productivity e.g. using fertilisers.
- Food production- developed world- intensive- concentrated on specific areas of land used repeatedly to achieve maximum yield from crops and animals- crops are used as food or as fodder for animals.
84
Q
Explain why agricultural ecosystems need mineral ions restored.
A
- All plants need mineral ions- especially nitrates.
- Natural ecosystems- minerals returned when plant is decomposed. However, once the crop is harvested it is transported from its point of origin for consumption.
- Crops absorb mineral ions from the soil as they grow and use them to build their tissues.
- The crops are removed from the field rather than dying or decomposing and urine, faeces, and remains of the consumer rarely return to the same area of land.
- The mineral ions crops contain aren’t returned to the soil by decomposers in the nitrogen or phosphorous cycle.
- Animal products also remove nutrients from land- animals eat grass and other plants taking in nutrients, and are taken elsewhere for slaughter or transferred to a different field- nutrients aren’t replaced through remains or waste products.
- As concentrations of mineral ions in agricultural land fall- important to replenish minerals because they become the limiting factor for plant growth and productivity will be reduced.
85
Q
How are minerals replentished in agricultural ecosystems.
A
Natural and artificial fertilisers are used to replace the nitrates and phosphates lost by harvesting plants and removing livestock, so more energy can be used for growth, increasing the efficiency of energy transfers.
86
Q
Describe the types of fertilisers.
A
- Natural fertilisers- organic- remains of plants and animals and animal waste (manure, slurry and bone meal).
- Artificial fertilisers- inorganic- mined from rocks and deposits, or converted from the atmosphere using the Haber process. Converted into different forms and blended together to give the right balance of minerals for a crop. Contain pure chemicals as powders or pellets. Compounds contain nitrogen, phosphorus and potassium.
87
Q
Describe the optimal balance of fertilisers.
A
- Combination of natural and artificial fertilisers- greatest long-term increase in productivity.
- Important that minerals are added in appropriate quantities as point reached where more fertilisers don’t increase productivity.
88
Q
When asked to devise investigations into teh effect of named minerals on plant growth what must you remember.
A
- **State which mineral/ fertiliser is the most/ least effective.
- Compare data to the control.
- Note where there is no increase in growth after a certain concentration.
- Compare the different fertilisers.
- State at which concentration effectiveness decreases.
- State the effect on plant growth- whether it increases/ reduces plant growth, and for which plants it increases/ decreases, and for which fertilisers it increases/ decreases- compare to the control.**
- State the limitation in the study- e.g. only shows the results for one type of crop, small timeframe e.g. only 20 weeks, small sample, not testing for all growth- e.g. **root growth not known. **
- State what benefit the fertiliser/ mineral gives e.g. **nitrogen helps as a source for protein. **
- Note if there’s **no statistical test to determine the significance. **
- If there is a statistical test- note the significance.
- Soil and seeds may be sterilised to kill any fungus or bacteria on the surface of seeds or in soil so only added fungus/ bacteria has an effect.
- Think about factors to control- e.g. contains no extra mineral ions, so that only the tested type of fertiliser affects growth.
- Explain how groups act as controls-** so that the effects of only the factor alone can be seen (may need to mention two factors).**
89
Q
What is the importance of fertilisers with regards to productivity.
A
Increased productivity- provides cheaper food. Use of fertilisers increased agricultural food production in the UK by 100% since 1955. Nitrogen fertiliser is the main fertiliser used to increase crop productivity.
90
Q
How do fertilisers increase productivity.
A
- Plants- require minerals for growth.
- Nitrogen- needed for amino acids to form proteins, ATP and nucleotides for plant growth.
- If nitrate ions are available- plants develop earlier, grow taller and have greater leaf surface area- increases the rate of photosynthesis and improves crop productivity.
91
Q
What are the environmental issues with the use of fertilisers
A
- The environmental issues arising from the use of fertilisers include leaching and eutrophication as the main factors.
- Another environmental issue is reduced species diversity- nitrogen-rich soils favour growth of grasses, nettles and other rapidly growing species- out-compete other species. If meadows get contaminated biodiversity declines.
92
Q
Describe leaching
A
- More fertiliser is applied than the plants needs or are able to use at a particular time.
- Using fertilisers- change the balance of nutrients in the soil. Too much of a particular nutrient- can cause crops and other plants to die.
- As inorganic ions in chemical fertilisers are relatively soluble, excess minerals that aren’t used immediately are more likely to leach into waterways.
- Nutrients are removed from the soil- rainwater dissolves and carries nutrients deep into the soil out of the reach of plant roots.
- Leaching- water soluble compounds in the soil are washed away- e.g. by rain or irrigation systems- often washed into nearby ponds and rivers.
- Leached nitrate ions- enter waterways- streams and rivers- drain into freshwater lakes.
- Harmful effects if source of drinking water as high nitrogen content is toxic to humans.
- Often leads to eutrophication.
93
Q
Describe the factors that make leaching more likely to occur.
A
- More likely to occur if the fertiliser is applied before heavy rainfall.
- Leaching is less likely to occur with natural fertilisers- nitrogen and phosphorous contained in inorganic molecules that need to be decomposed by microorganisms before they can be absorbed by plants- release in the soil for uptake by plants more controlled.
- Leaching of phosphates is less likely than the leaching of nitrates because phosphates are less soluble in water.
94
Q
Describe eutrophication.
A
- Caused by leaching of fertiliser into watercourses:
- Occurs in freshwater lakes and rivers. Caused by sewage and natural fertilisers leaching, but mainly artificial fertilisers.
- Caused by excess nutrients.
95
Q
Describe hte setps of eutrophocation
A
- Low concentration of mineral ions in most lakes and rivers- so mineral ions are a limiting factor for plant and algal growth.
- Mineral ion concentration increases- due to leaching from fertilisers- no longer a limiting factor for growth of plants and algae- stimulates populations of algae to grow rapidly.
- Algae- form algal bloom on the upper layer of the water- absorbs light and stops it from reaching plants at lower depths.
- Light- becomes limiting factor to plants at lower depths. The plants die because they aren’t able to photosynthesise enough.
- Saprobiontic bacteria- limiting factor of lack of dead plants and algae no longer a problem- population grows as they feed on dead plant matter- increased demand of oxygen as require oxygen for aerobic respiration.
- Oxygen concentration of water is reduced and more mineral ions are released from decaying organisms.
- Oxygen loss- becomes limiting factor for aerobic organisms e.g. fish- organisms die as oxygen is used up.
- Without aerobic organisms- less competition from anaerobic organisms- populations now rise.
- Anaerobic organisms- decompose dead material- release more nitrates and toxic wastes- hydrogen sulphide- makes water putrid.
96
Q
What should you remember to mention when evaluating the use of fertiliser.
A
- Where the benefit of using more fertiliser stops.
- Potential environmental problems.
- ** Describe data.
- Use of more fertiliser but getting less response over time.
- Remember data showing correlation doesn’t mean causation- could be other factors.
- Cost effectiveness.**
