5. Energy And Ecosystems Flashcards
What are producers?
Photosynthetic organisms which manufacture organic substances using light energy, water and carbon dioxide
What are consumers?
Organisms that derive their energy from eating plants and other organisms rather than through photosynthesis
What is a decomposer?
Organisms such as detritivores that break down complex molecules into simple components
What is each stage in a food chain called?
Trophic level
What do the arrows on food chains represent?
The flow of energy
What is the source of energy in all ecosystems?
The sun
How much of the sun’s energy available to them do plants convert into organic matter by photosynthesis?
Why is so little converted into organic matter?
Between one percent and three percent.
- 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 for use in photosynthesis
- Light may not fall on a chlorophyll molecule
- There may be factors limiting the rate of photosynthesis such as carbon dioxide concentration
What is the total amount of energy plants in a community convert to organic matter called?
Gross production
What is the rate at which plants store energy called?
Net production
What is the equation for net production?
Net production = gross production - respiratory losses
Why is there such a low percentage of energy transferred at each stage?
- Not all of the organism is eaten
- Not all of the organism can be digested (therefore lost in faeces)
- Energy lost in excretory materials such as urine
- Energy losses as heat from respiration
How is the efficiency of energy transfer calculated? (equation)
Energy transfer = (energy available after the transfer)/ (energy available before the transfer) x100
What are the drawbacks of using a pyramid of numbers to describe a food chain?
- No account is taken of size (eg oak tree is massive but still only counts as 1)
- Number of individuals can be so great that it is hard to represent them on the same scale as other organisms
Why can pyramids of biomass be unreliable if done incorrectly?
-The fresh mass can be easily calculated however in different organisms there are different levels of water so the mass will vary
-Therefore you must use the dry mass by heating in an oven
>However organisms must be killed so therefore only a few measurements can be taken which means the results may not be representative of the population.
-Only valid at the time of sampling- doesn’t take into account seasonal changes
What is the unit for biomass in the context of pyramids of biomass?
gm^-2
or gm^-3 when a volume is being sampled
What is the most accurate representation of flow through an ecosystem?
Pyramids of energy (measuring energy stored in organisms)
What is the unit used for energy flow in the context of pyramids of energy?
kJm^-2year^-2
Why are the results of a pyramid of energy much more reliable than a pyramid of biomass?
Organisms with the same dry mass may contain different amounts of stored energy eg fat stores more energy than carbohydrate, even though their biomasses are equal
What is the purpose of an agricultural ecosystem?
Ensure as much of the available energy from the sun is transferred to humans (increasing the productivity of the human food chain)
What factors is net productivity affected by?
- Efficiency of the crop carrying out photosynthesis
- Area of ground covered by the leaves of the crop
In which ways does an agricultural ecosystem differ to a natural ecosystem?
- There is additional energy input into an agricultural ecosystem (eg energy from food (labour) and fossil fuels (machinery and transport))
- Higher productivity
- Less species diversity
- Less genetic diversity within a species
- Populations are controlled both by natural means and by use of pesticides and cultivation
- Prevented from reaching a climax community
- Natural recycling limited and supplemented by the addition of artificial fertilisers
What are the qualities of a good pesticide?
- Cost-effective because development costs are high an pesticides only remain efficient for a limited amount of time as pests become resistant
- Does not accumulate (eg bioaccumulation)
- Biodegradable- break down into harmless substances in the soil
- Specific- only toxic to the pest that it is trying to control- harmless to humans and other organsisms
What is the aim of a biological control?
To reduce the numbers of the pest below the economic injury level but NOT eradicate the pest
What are the advantages of using biological control rather than chemical pest control?
Biological control
- Very specific
- Once introduced the control organism reproduces itself
- Pests to not become resistant
What are the disadvantages of chemical pest control?
- May affect species other than the target species
- Must be reapplied regularly (expensive)
- Pests develop genetic resistance and so new pesticides need to be developed.
What are the disadvantages of using biological pest control?
- The control species may become a pest itself
- Do not usually act very quickly- lag between the time of application and the reduction of the pest.
What is an integrated pest control?
Using all forms/ a combination of pest controls
- Mechanical
- Chemical
- Biological
How can maximum yield of product be achieved through intensive farming?
-Limiting movement (keeping in confined spaces)
-Keeping environment warm to reduce heat loss
-Optimum food quantity and food type so there is as little waste as possible
-Predators excluded so no loss to other organisms in the food web
This all limits the energy losses through respiration so there is more energy available for growth/ milk production etc…
Describe ways other than intensive farming that can increase the energy conversion rate.
- Using hormones to increase growth rate
- Selective breeding to produce varieties that are more efficient at converting the food they eat into body mass.
(5 marks)
The Amazonian forest today contains a very high diversity of bird species.
-Over the last 2 000 000 years, long periods of dry climate caused this forest to
separate into a number of smaller forests.
-Different plant communities developed in each of these smaller forests.
-Each time the climate became wetter again, the smaller forests grew in size and
merged to reform the Amazonian forest.
Use the information provided to explain how a very high diversity of bird species has
developed in the Amazonian forest.
1. No interbreeding / gene pools are separate / geographic(al) isolation; 2. Mutation; 3. Different selection pressures / different foods/niches/habitats; 4. Adapted organisms survive and breed / differential reproductive success; 5. Change/increase in allele frequency/frequencies;
(2 marks)
Sampling 2 types of lizzard to see the effect of malaria parasites on competition between the two species
The population number of both species of lizard varied at different times of the year.
Suggest two reasons why.
- Breeding (of lizards);
- Food source/prey;
- Predator;
- Variation in malarial infection;
- Temperature variation;
- Availability of water eg
drought/’rainy season’
(2 marks)
The malarial parasite of Anolis lizards destroys both red and white blood cells.
Suggest how an increase in the percentage of A. gingivinus infected with malaria could
result in A. wattsi having a competitive advantage.
1. Reduced immunity / increased susceptibility to disease; 2. Reduced oxygen transport/uptake/respiration / reduced activity/movement;
(6 marks)
Rather than use chemical pesticides or biological agents, farmers often use an
integrated system of chemical pesticides and biological agents to control agricultural
pests. Explain the advantages of using an integrated system to control agricultural
pests.
(Biological Agents) 1. Only needs one application/ reproduces; 2. Specific; 3. Keeps/maintains low population; 4. Pests do not develop resistance; 5. Can use less chemicals / reduces chemical residues / no bioaccumulation; (Chemical pesticides) 6. Acts quickly; 7. Can apply to specific area; 8. Kills all/most/greater variety of pests;
(4 marks)
Explain how the intensive rearing of domestic livestock increases net productivity
1. Slaughtered when still growing/before maturity/while young so more energy transferred to biomass/tissue; 2. Fed on concentrate /controlled diet / so higher proportion of food absorbed/digested/assimilated / used for biomass/tissue / lower proportion lost in faeces; 3. Movement restricted so less heat/energy/respiratory loss; 4. Heating/Kept warm/ inside so less heat/energy/respiratory loss/maintain body temperature; 5. Genetically selected / selective breeding (for high productivity);
(2 marks)
l Experiment 1 – Hydrilla left untreated l Experiment 2 – Hydrilla treated with the fungus
l Experiment 3 – Hydrilla treated with fluridone
l Experiment 4 – Hydrilla treated with both fluridone and the fungus
The treatment in experiment 4 was the most effective. Use your knowledge of
integrated pest control systems to suggest why the treatment in experiment 4 was the
most effective
1. Fluridone/chemical acts quickly / quickly reduces Hydrilla; 2. Fungus/biological control keeps Hydrilla in low numbers; 3. Fungus/biological control works over a long time/can reproduce 4. Resistance does not develop against fungus/biological control;
(2 marks)
l Experiment 1 – Hydrilla left untreated l Experiment 2 – Hydrilla treated with the fungus
l Experiment 3 – Hydrilla treated with fluridone
l Experiment 4 – Hydrilla treated with both fluridone and the fungus
The scientists isolated the fungus from the tissue of Hydrilla growing in its country of
origin. Suggest two possible advantages of using this fungus as the biological
control agent.
1. Is specific / grows/survives in Hydrilla/habitat; 2. Can reproduce / only one application required; 3. Does not become a pest;
(1 mark)
l Experiment 1 – Hydrilla left untreated l Experiment 2 – Hydrilla treated with the fungus
l Experiment 3 – Hydrilla treated with fluridone
l Experiment 4 – Hydrilla treated with both fluridone and the fungus.
Experiment 1 acted as a control. Explain why the scientists carried out experiment 1.
To compare/see effect with/without
fungus/fluridone/control agent/s;
(2 marks)
Upwelling is a process where water moves from deeper parts of the sea to the
surface. This water contains a lot of nutrients from the remains of dead organisms.
Upwelling often results in high primary productivity in coastal waters.
Explain why some of the most productive fishing areas are found in coastal waters
- Nitrate/phosphate/named ion/nutrients for growth
of/absorbed/used by plants/algae/producers; - More producers/consumers/food so more fish /
fish reproduce more / fish grow more / fish move
to area;
(2 marks)
Hydrilla (Hydrilla verticillata) is an aquatic plant which has become a major pest of
waterways in parts of the USA. Hydrilla is not a native species of the USA. It was
introduced into natural habitats from aquariums. In many freshwater habitats it has
rapidly become the dominant plant species.
In many freshwater habitats Hydrilla has rapidly become the dominant plant species.
Suggest two reasons why.
- No/few consumers/pests/pathogens;
- Outcompetes/better competitor for
resources/light/CO2/abiotic factor /
ideal niche;
(2 marks)
Hydrilla (Hydrilla verticillata) is an aquatic plant which has become a major pest of
waterways in parts of the USA. Hydrilla is not a native species of the USA. It was
introduced into natural habitats from aquariums. In many freshwater habitats it has
rapidly become the dominant plant species.
The spread of Hydrilla has had economic consequences for commercial activities and
for the government’s environmental agency.
Suggest two economic consequences of the spread of Hydrilla
- (Cost of) control/removal;
- (Cost of) restoring habitat /
conservation; - (Loss of income) from fishing;
- (Loss of income) from
boating/tourism/recreation;
(2 marks)
Scientists investigated the effect of a pesticide called malathion on the survival of
tadpoles of species of toads found in the USA. The scientists determined the LC50 for
the tadpoles of each species over a 16-day period in an aquarium. The LC50 is the
concentration of malathion that killed 50 percent of a population of tadpoles. The
scientists also investigated whether the presence of a predator of tadpoles changed
the effect of malathion.
Suggest two advantages of using the LC50 to determine the effect of a pesticide
- Provides a standard/benchmark;
- Can compare (different
pesticides/chemicals); - Does not kill all the
tadpoles/organisms/population;
(3 marks)
The scientists looked at previous studies on the effects of various pesticides on
tadpoles.
They found that most of these studies:
- were carried out on tadpoles of the African clawed toad
- measured the LC50 of each pesticide over 1 to 4 days in the absence of any
biotic factor.
The scientists concluded that these previous studies were of limited use when trying to
assess the effects of malathion on the tadpoles of toads found in the USA. Suggest
why the scientists reached this conclusion.
1. Only carried out on one species of toad/African toad / not carried out on USA toads/tadpoles/species; 2. Only tested for 1-4 days/short term / not 16 days/long term; 3. Did not look at effect of predator/predation; 4. Used various pesticides / may not have used malathion;
(2 marks)
Adult toads spend most of their time on land but lay their eggs in water. These eggs
hatch into tadpoles, which live in water and develop into adults. The tadpoles are
much smaller than adult toads. Use this information to explain why the tadpoles are
affected more rapidly by pesticides in water than adult toads.
1. Large surface area to volume ratio; 2. Rapid/more diffusion / shorter diffusion pathway; 3. Longer time exposure to pesticide / adults/toads live in and out of water / tadpoles remain/stay in water;
(2 marks)
When malathion is used as a pesticide, it is often sprayed onto aquatic habitats at
concentrations of 0.1 to 1.6 mg dm–3. The scientists tested the effect of malathion at
concentrations of 0.001 to 10 mg dm–3.
Suggest why.
- Link between using less
(pesticide) and cost/less effect on
environment/organisms; - Pesticide/malathion diluted (in
water); - Concentrated due to evaporation;
- Concentrated in food
chains/webs/tadpoles/habitat;
(5 marks)
Describe the reasons for the low efficiency of energy transfer through ecosystems.
1. Some light is reflected / not of appropriate wavelength; 2. Some light misses leaves/ photosynthetic tissue/chloroplasts/chlorophyll; 3. Heat loss; 4. (Energy loss via) respiration; 5. Loss via faeces/undigested food/part of organism not eaten; 6. Excretion/named excretory product;
(1 mark)
Give one advantage of using natural fertiliser produced in the digester rather than an
artificial fertiliser
- Acts as soil conditioner/improves drainage/ aerates
soil/increases organic content of soil; - Contains other elements/named element/wider range of
elements; - Production of artificial fertiliser energy-consuming;
- Less leaching / slow release (of nutrient);
(2 marks)
In some countries, pigs are reared in intensive units in which the temperature is
controlled. Agricultural scientists investigated the effect of temperature on pig growth
and on the efficiency with which the pigs converted food to biomass.
In the investigation, the scientists used pigs of the same breed, with similar genotypes.
Explain why
- Same breed so similar alleles;
- Controls/removes variable/so
genes not a factor / only
temperature affects results /
rate of growth affected by
genes;
(2 marks)
In some countries, pigs are reared in intensive units in which the temperature is
controlled. Agricultural scientists investigated the effect of temperature on pig growth
and on the efficiency with which the pigs converted food to biomass
The pigs were allowed to eat as much food as they wanted.
How could this have decreased the reliability of any conclusions drawn from the
investigation?
1. Different growth rates / gained different biomass / grew different amount; 2. Not due to temperature / the independent variable;
(2 marks)
In some countries, pigs are reared in intensive units in which the temperature is
controlled. Agricultural scientists investigated the effect of temperature on pig growth
and on the efficiency with which the pigs converted food to biomass
Pigs can survive at temperatures above 35 oC. Use the data to suggest why scientists
did not carry out any investigations at temperatures higher than 35 oC.
1. Growth rate decreasing / conversion staying same/ decreasing; 2. (Scientists would be) looking for high growth rate/ conversion / data shows unlikely to improve growth/yield; 3. Wastes time/resources/would not relate to farming conditions;
(2 marks)
The efficiency of conversion of food to biomass is lower at 0 oC than it is at 20 oC.
Suggest an explanation for the lower efficiency.
1. Will lose more heat / not as much energy used to maintain body temperature; 2. Heat resulting from respiration/more respiration; 3. More food used in respiration;
