Ecosystems, Nutrient Cycles & Human Impact on the Environment (WJEC GCSE Science (Double Award): Biology): Flashcards
Exam code: 3430
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What do food chains and food webs show?
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What do food chains and food webs show?
The flow of energy through an ecosystem, transferred between organisms at different trophic levels.
Define producer.
An organism that makes its own carbon compounds, e.g. a plant using carbon dioxide and water to produce glucose by photosynthesis.
Name the organisms found at each of the first four trophic levels.
First: producers
Second: first stage consumers
Third: second stage consumers
Fourth: third stage consumers
Define herbivore.
An animal that feeds on producers, i.e. plants. Herbivores are first stage consumers.
Define carnivore.
An animal that feeds on other animals.
Define decomposer.
An organism such as a bacterium or fungus that breaks down dead organisms and waste products, releasing the energy stored in them.
What is the original source of energy for almost all ecosystems?
Radiation from the Sun.
How does energy first enter a food chain?
Producers convert light energy from the Sun into chemical energy stored in their biomass, during photosynthesis.
How is energy transferred from a producer to a first stage consumer?
The consumer digests the tissues of the producer and uses the products to build up its own tissues, so the chemical energy passes into its biomass.
Define biomass.
Living matter, such as the tissues of plant stems and leaves or animal muscle.
What is the difference between a food chain and a food web?
A food chain shows a single pathway of energy transfer.
A food web shows the interactions between many food chains in one ecosystem.
The arrows in a food chain show the direction in which ＿＿＿＿＿＿＿＿ is transferred.
The arrows in a food chain show the direction in which energy is transferred.
＿＿＿＿＿＿＿＿ such as bacteria and fungi break down dead organisms and waste products.
Decomposers such as bacteria and fungi break down dead organisms and waste products.
True or False?
An organism can belong to more than one trophic level in a food web.
True.
An omnivore, for example, may eat both producers and consumers, placing it at more than one level.
True or False?
Most of the light energy falling on a plant is converted into chemical energy in biomass.
False.
Only a small percentage is converted. Most light passes through the leaves, misses the chloroplasts or is lost as heat.
Roughly how much of the energy at one trophic level is passed on to the next?
Only a small proportion — roughly 10% in a typical food chain.
The exact figure varies, so in the exam calculate it from the data given rather than assuming 10%.
Name two ways energy is used at each stage of a food chain.
Repair of damaged cells
Cell maintenance and growth
Name two ways energy is lost from a food chain to the environment.
Heat generated during respiration
Waste materials, such as faeces and urine
Why is only some of the energy at each trophic level passed on?
Only the energy stored in biomass can be passed on.
Energy used for cell processes or transferred to the environment as heat and waste is not available to the next level.
Explain why food chains are usually relatively short.
Energy is lost at each stage.
Eventually the energy available at higher trophic levels becomes too small to support another level.
Energy is lost from a food chain as ＿＿＿＿＿＿＿＿ generated during respiration.
Energy is lost from a food chain as heat generated during respiration.
True or False?
All the energy eaten by a consumer is passed on to the next trophic level.
False.
Only a small proportion is passed on. The rest is used in repair, maintenance and growth, or lost as heat from respiration and in waste materials.
State the equation for the efficiency of energy transfer between trophic levels. (Higher Tier Only)
efficiency (%) = (energy passed to the next level ÷ energy received from the previous level) × 100
Plants store 50 000 kJ and the aphids feeding on them store 4 500 kJ. Calculate the efficiency of transfer. (Higher Tier Only)
efficiency = (4 500 ÷ 50 000) × 100
efficiency = 9%
How does the efficiency of energy transfer affect the number of organisms at each trophic level? (Higher Tier Only)
Because transfer is inefficient, there is less energy available at higher levels.
This means fewer organisms can be supported at higher trophic levels than at lower ones.
To calculate energy transfer efficiency, divide the energy passed on by the energy received and multiply by ＿＿＿＿＿＿＿＿. (Higher Tier Only)
To calculate energy transfer efficiency, divide the energy passed on by the energy received and multiply by 100.
In the efficiency calculation, which figure goes on the top of the fraction? (Higher Tier Only)
The energy stored in biomass at the higher trophic level, i.e. the energy available to be passed on.
The energy received from the level below goes on the bottom.
True or False?
There are always more individual organisms at lower trophic levels than at higher ones. (Higher Tier Only)
False.
Usually there are, but there are exceptions. A single tree, for example, can support many consumers.
Define pyramid of numbers.
A diagram showing the number of individual organisms present at each stage of a food chain.
Define pyramid of biomass.
A diagram showing the mass of living tissue present at each stage of a food chain.
Why can a pyramid of numbers vary in shape?
It counts individuals regardless of size.
Small organisms are many in number and large organisms are few, so a single large producer such as a tree can give an inverted shape.
Why is a pyramid of biomass always pyramid-shaped?
Energy is lost at each stage of the food chain, so there is less energy available to make new biomass at each higher trophic level.
What labels should a pyramid of numbers or biomass have?
The name of each trophic level
The number of individuals or the biomass represented by each bar
When should a pyramid be drawn to scale?
Whenever a grid is provided in the question. The size of each bar must then be proportional to the value it represents.
A pyramid of ＿＿＿＿＿＿＿＿ shows the mass of living tissue at each trophic level.
A pyramid of biomass shows the mass of living tissue at each trophic level.
A pyramid of ＿＿＿＿＿＿＿＿ shows how many individual organisms are at each trophic level.
A pyramid of numbers shows how many individual organisms are at each trophic level.
True or False?
A pyramid of numbers is always pyramid-shaped.
False.
Only a pyramid of biomass is always pyramid-shaped. A pyramid of numbers can be inverted, e.g. when one tree supports many insects.
True or False?
The producers are always shown at the bottom of the pyramid.
True.
The first trophic level, the producers, forms the base, with each consumer level stacked above it.
A food chain runs oak tree → caterpillars → birds. Describe the shape of the pyramid of numbers.
It would be inverted at the base.
There is only one oak tree but many caterpillars, so the bottom bar is narrower than the one above it.
For the same oak tree food chain, what shape would the pyramid of biomass be?
A normal pyramid shape.
Although there is only one tree, its biomass is far greater than the total biomass of the caterpillars feeding on it.
Why is a pyramid of biomass often more useful than a pyramid of numbers?
It reflects the actual amount of living material and therefore the energy at each level, rather than just counting individuals of very different sizes.
A food chain has biomass values 80, 30, 10 and 2 kg. Describe the pyramid you would draw.
Four bars stacked with the widest at the bottom.
The bars represent 80 kg, 30 kg, 10 kg and 2 kg, drawn to scale and each labelled with its trophic level.
Why do human needs increasingly conflict with the needs of wildlife?
A rapidly growing human population needs more agriculture, housing and industry.
This takes land and resources away from other species and produces more pollution.
Define environmental impact assessment.
A study of a proposed development site to identify local species, judge the site's value to wildlife, and put forward ways to reduce the impact of the development.
Give three possible outcomes of an environmental impact assessment.
Developers must modify their plans to protect a species
Permission is granted under conditions, e.g. planting trees or building new habitats
Permission is refused if the environmental damage cannot be reduced
How does the use of agricultural machinery increase yields?
It allows farmers to work larger areas of land and to monitor crop health, reducing losses to disease and ensuring harvesting happens at the right time.
Give two disadvantages of using large agricultural machinery.
Small fields are combined into large ones, destroying hedgerow habitats
Machinery usually runs on fossil fuels, and it may take jobs from people
State one advantage and one disadvantage of using chemical fertilisers.
Advantage: increases soil nutrient availability, giving larger crop yields
Disadvantage: fertiliser can run off into water, causing plant and algal overgrowth and killing aquatic life
State one advantage and one disadvantage of using pesticides and herbicides.
Advantage: kills pests and reduces competition from weeds, giving larger yields
Disadvantage: may kill non-target species and lead to the evolution of resistance
How does battery farming of livestock increase meat production?
Animals are kept in small, temperature-controlled spaces.
This reduces energy lost through movement and keeping warm, so more energy goes into growth.
Give two disadvantages of battery farming.
Concerns about the welfare of the animals
Disease spreads easily in crowded conditions, which can be costly for farmers
Why can using antibiotics to prevent disease in livestock be a problem?
Overuse increases the chance of antibiotic-resistant strains of bacteria emerging.
Antibiotics may also be present in the meat.
＿＿＿＿＿＿＿＿ farming aims to produce more food from reduced energy and land inputs.
Intensive farming aims to produce more food from reduced energy and land inputs.
Before a development goes ahead, an environmental ＿＿＿＿＿＿＿＿ assessment must be completed.
Before a development goes ahead, an environmental impact assessment must be completed.
True or False?
Growing a single crop variety across large areas reduces biodiversity.
True.
Such monocultures support fewer species and the crop itself has low genetic variation, so it adapts poorly to change.
True or False?
An environmental impact assessment can result in planning permission being refused.
True.
If the environmental damage cannot be reduced or mitigated, permission may be refused altogether.
Suggest why farmers may still choose intensive methods despite the drawbacks.
They produce more food per unit of land and energy, which is needed to feed a growing population and to keep farming economically viable.
Define indicator species.
A species whose presence or absence gives information about the level of pollution in a habitat.
Name two invertebrates whose presence indicates clean, unpolluted water.
Stonefly larvae
Freshwater shrimps
Name two invertebrates whose presence indicates heavily polluted water.
Bloodworms
Mosquito larvae
Explain why stonefly larvae disappear from a polluted stream.
Pollution causes microorganisms to increase in number.
As they respire they use up the dissolved oxygen, and stonefly larvae are highly sensitive to low oxygen.
Besides indicator species, which two measurements can be used to assess pollution in a stream?
Oxygen concentration, measured with an oxygen meter; low levels indicate pollution
pH, tested on water samples; changes in pH can be a sign of pollution
Which organism is used as an indicator of air pollution, and what is it sensitive to?
Lichens, which are highly sensitive to sulfur dioxide concentration in the air.
Where does the sulfur dioxide that affects lichens come from?
The combustion of fossil fuels, released from car exhausts and power stations.
What do bushy lichens and crustose lichens each indicate about air quality?
A high abundance of bushy lichens indicates very clean air
A high abundance of crustose lichens with no leafy lichens indicates more polluted air
＿＿＿＿＿＿＿＿ can be used as indicator species for air pollution because they are sensitive to sulfur dioxide.
Lichens can be used as indicator species for air pollution because they are sensitive to sulfur dioxide.
The presence of ＿＿＿＿＿＿＿＿ larvae in a stream indicates that the water is not polluted.
The presence of stonefly larvae in a stream indicates that the water is not polluted.
Give two limitations of using indicator species to assess pollution.
They do not give quantitative measurements of pollution levels
Their distribution can be affected by factors other than pollution
Why should several indicator species be studied rather than just one?
Any single species may be affected by other environmental factors.
Using several species makes any pattern in the data far more reliable.
True or False?
Finding bloodworms but no stonefly larvae suggests a stream is heavily polluted.
True.
Bloodworms tolerate low oxygen, while stonefly larvae cannot survive it. That combination points to heavy pollution.
True or False?
A low dissolved oxygen reading in a stream suggests high levels of pollution.
True.
Pollutants cause microorganisms to multiply, and their respiration uses up the dissolved oxygen.
Lichen data show crustose lichens far from any city. Suggest a reason.
The air pollution may come from a source other than a city, such as nitrogen released from agriculture.
This shows indicator species must be interpreted with care.
Name two sources of heavy metal pollution.
Industrial processes such as mining
Chemical pesticides
Name three heavy metals that can pollute the environment.
Lead
Arsenic
Copper
How do heavy metals enter a food chain?
They are washed from mining sites and farmland into the environment.
They are then taken up by plants and passed on to animal consumers that eat them.
Define bioaccumulation.
The build-up of a pollutant inside the tissues of an organism over time.
Why do heavy metals build up inside organisms rather than being removed?
Heavy metals do not degrade inside cells, so they accumulate in the tissues over extended periods.
What are the effects of heavy metals reaching a toxic concentration?
They can cause loss of fertility and death in affected organisms.
Why are organisms higher up a food chain most at risk from heavy metals?
Each consumer eats many organisms from the level below, so it receives a larger combined dose of the metal.
Heavy metals do not ＿＿＿＿＿＿＿＿ inside cells, so they build up in an organism's tissues.
Heavy metals do not degrade inside cells, so they build up in an organism's tissues.
The build-up of a pollutant in an organism's tissues over time is called ＿＿＿＿＿＿＿＿.
The build-up of a pollutant in an organism's tissues over time is called bioaccumulation.
True or False?
Heavy metals are always immediately toxic to living organisms.
False.
They may be harmless in small doses, but become toxic once they have accumulated to higher concentrations.
True or False?
Heavy metals can enter food chains through plants.
True.
Plants take up the metals from polluted soil and water, and they are then passed on to the animals that eat them.
Suggest why a top predator in a polluted lake may die while small fish survive.
The predator eats many fish, each carrying accumulated heavy metal.
The metal builds up in the predator to a toxic concentration, while the level in each individual fish stays below that threshold.
Why is it a problem that some pesticides contain heavy metals?
The pesticide is spread over farmland and washes into the environment.
The metals then enter food chains and accumulate in organisms, where they can reach toxic levels.
Name two habitats into which heavy metals are commonly washed.
Lakes
Ponds and other bodies of fresh water
Name two pollutants that can run off into water and cause rapid plant growth.
Untreated sewage
Fertilisers
Describe the sequence of events when fertiliser runs off into a lake.
The fertiliser is high in nitrogen, causing rapid growth of plants and algae at the water surface.
Light is blocked, so plants below the surface die.
Decomposers break them down and increase in number.
Their respiration uses up the dissolved oxygen, so aquatic animals suffocate and die.
Why does fertiliser cause such rapid growth of algae?
It is high in nitrogen, an essential mineral for plant growth.
Why do submerged plants die when algae grow rapidly at the surface?
The surface growth blocks the light, so the plants below can no longer photosynthesise.
Why does the level of dissolved oxygen fall in a polluted lake?
Decomposers feeding on the dead plants increase in number.
Their increased respiration uses up the oxygen dissolved in the water.
Why do fish and other aquatic animals die as a result of fertiliser run-off?
The water no longer contains enough dissolved oxygen to support them, so they suffocate.
Name two types of organism that act as decomposers in this process.
Bacteria
Fungi
Fertilisers running into water are high in ＿＿＿＿＿＿＿＿, which causes rapid growth of plants and algae.
Fertilisers running into water are high in nitrogen, which causes rapid growth of plants and algae.
The increased respiration of decomposers uses up the dissolved ＿＿＿＿＿＿＿＿ in the water.
The increased respiration of decomposers uses up the dissolved oxygen in the water.
True or False?
Aquatic animals die because the fertiliser itself is poisonous to them.
False.
They die because the water runs out of dissolved oxygen, used up by the decomposers breaking down dead plant material.
True or False?
You must use the word 'eutrophication' to gain marks on this topic.
False.
The term is not required. You must instead describe the sequence of events that follows fertiliser run-off.
Suggest one way farmers could reduce fertiliser run-off into rivers.
Apply less fertiliser, or avoid applying it just before heavy rain or close to watercourses, so less is washed into the river.
Why does the number of decomposers increase after the plants die?
There is a large supply of dead plant material for them to feed on, so they can reproduce rapidly.
Explain why this process affects animals even though the pollutant only affects plant growth at first.
The extra plant growth eventually dies and decomposes.
The decomposers' respiration removes the oxygen the animals need, so the effect passes on to them indirectly.
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