Ecosystems Flashcards
1
Q
Define the term “ecosystem”.
A
All living organisms and the non-living conditions in an area.
2
Q
Define the term “community”.
A
All the populations of living organisms in a particular habitat.
3
Q
Define the term “habitat”.
A
An area inhabited by a species.
4
Q
Define the term population.
A
A group of organisms of one species that live in the same place at the same time.
5
Q
Define the term species.
A
A group of organisms which have a common ancestor and can interbreed to produce fertile offspring.
It is the smallest and most specific taxonomic group.
6
Q
Define the term ecology.
A
A branch of biology that deals with the distribution, abundance, and interactions of living organisms at the level of communities, populations and ecosystems as well as at a global scale.
7
Q
Explain what is meant by the phrase “ecosystems are dynamic”.
A
They are constantly changing.
8
Q
Define the term “biotic factor”.
A
The living components of an ecosystem.
9
Q
Define term abiotic factor.
A
The non-living conditions in a habitat.
10
Q
Give some examples of biotic factors.
A
- presence of organism (as predator or prey)
- the size of the populations of organisms
- the competition between organisms.
11
Q
Give some abiotic factors.
A
- amount of rainfall
- yearly temperature range
- availability of light
- availability of water
- availability of oxygen
- salinity
- PH
12
Q
Define the term “edaphic factor”.
A
the soil factors - the type and condition of the soil.
13
Q
Give three examples of edaphic factors.
A
Clay - this has fine particles, is easily waterlogged, and forms clumps when wet
Loam - this has different-sized particles, it retains water and but does not become water logged.
Sand - this has coarse, well-separated particles that allow free draining, sand soil does not retain water and is easily eroded.
14
Q
Define the term “food web”
A
Food webs are systems of interlinked food chains used to show the transfer of biomass, and therefore energy, through the organisms in an ecosystem.
15
Q
Define the term “food chain”.
A
Chains used to show the transfer of biomass and therefore energy through organisms in an ecosystem. Each stage in the chain is known as a trophic level.
16
Q
Define the term “trophic levels”.
A
The stages in a food chain. Starting with a producer, the rest are consumers.
17
Q
Define the term “heterotroph”.
A
Organisms that acquire nutrients by the ingestion of other organisms.
18
Q
Explain what the arrows represent in a food web.
A
The transfer of energy, they point in the direction that the energy is being transfered.
19
Q
Define the term “consumer”.
A
Organisms that attain their energy by feeding on other organisms.
20
Q
Define the term producer.
A
Organism that converts light energy into chemical energy.
21
Q
Define the term “detritivore”. Give two examples and explain their role in food webs.
A
Organism that speeds up decay by breaking down detritus into smaller pieces.
- Woodlice, breaks down wood.
- Earthworms, breaks down dead leaves.
Detritivores increase the surface area of organic material for decomposers to work on. They perform internal digestion.
22
Q
Define the term “decomposer”. Give 2 examples of and explain their role in food webs.
A
Organism that breaks down dead organisms, releasing nutrients back into the ecosystem.
They are primarily microscopic fungi and bacteria e.g oyester mushrooms which decompose wood.
Decomposers obtain their energy by saprobiotic nutrition. This means that they digest waste externally by secreting enzymes. This process releases stored inorganic compound and elements back into the environment.
23
Q
Define the term “biomass”.
A
The mass of living material.
24
Q
Define the terms “dry mass”.
A
The mass of living material without its water content.
25
Explain why dry mass is a better indicator of biomass than fresh mass.
Dry mass excludes fluctuating water concentrations which could affect the overall mass.
26
Explain how to calculate the dry mass of each trophic level in a food chain.
1) Kill the organism and then place it in an oven at 80oC until all water has evaporated.
2) Weigh the organism to find the dry mass.
3) Multiply the dry mass present in each organism by the total number of organisms in that trophic level.
27
Explain how to experimentally measure the energy content of organic matter.
The energy available at each trophic level is measured in kilojoules per metre sqaured per year.
28
Suggest suitable units for the biomass in an ecosystem (both terrestrial and aquatic).
g/m2 - terrestrial
| g/m3 - aquatic
29
Explain how pyramids of numbers, biomass and energy represent data about an ecosystem and the relative merits of each.
Pyramid of numbers - producers are always placed at the bottom of the diagram with subsequent trophic levels added above. Shows the actual number of organims in each trophic level.
Sometimes misleading as the shapes will not consistently get smaller the further up the pyramid you go.
Pyramid of biomass - usually a pyramid shape, because each trophic level normally has less biomass than the trophic level before it.
Pyramid of energy - very similar to biomass so will likely show a pyramid. Level of energy is roughly equal to level of biomass.
Neither pyramid of biomass nor pyramid of energy will be representative of the number of individuals at each trophic level.
30
Suggest suitable units for the energy at each trophic level in a food chain and explain why these units are appropriate.
kJ m-2 yr-1 (kilojoules per metre squared per year)
31
Explain how energy is transferred from one trophic level to the next.
When animals eat, only a small proportion of food they ingest is converted into new tissue. It is only this part of the biomass (and hence energy) that is available to be transferred to the next trophic level.
32
Define the term “ecological efficiency” and write an equation to calculate it.
The efficiency with which energy or biomass is transferred from on trophic level to the next.
Calculate:
(Energy or biomass available after the transfer / energy or biomass available before the transfer) x100
33
Explain 3 reasons why only 1-3% of the sunlight producers receive is converted into chemical energy.
- Not all of the solar energy available is used for photosynthesis (approx 90% is reflected, some is transmitted through the leaf and some is of an un-useable wavelength.)
- A proportion of energy is lost as it used for photosynthetic reactions.
- Other factors may limit photosynthesis.
34
Define the terms “gross production”.
The total solar energy that plants convert to organic matter.
35
Define the term “net production”.
The energy that is converted into the organism's biomass. This is the energy that will be available in the next trophic level when the organism is eaten.
36
Define the term “respiratory losses”.
Energy lost in respiration (heat?)
37
Write an equation to link “gross production”, “net production” and “respiratory losses”.
Net production = gross production - respiratory losses
38
Define the term “primary production”.
The generation of biomass within a producer
39
Define the term “secondary production”.
The generation of biomass within a consumer.
40
Give four reasons why not all the energy the form the organisms biomass is transferred to the next trophic level when the organism is ingested.
- Not all of the biomass of an organism is eaten, for example, plant roots or animal bones may not be consumed.
- Some energy is transferred to the environment as metabolic heat, as a result of movement and respiration.
- some parts of an organism are eaten but are indigestable, these parts (and their energy content) are egested as faeces.
- some energy is lost from the animal in excretory materials such as urine.
41
Draw, label and annotate, a diagram showing the flow of energy through trophic levels and out of the food chain.
Look at pg 613.
- 1-3% of light energy is absorbed by producers
- 5-10% of energy from producers is passed to primary consumers
- 15-20% goes to secondary
- 15-20% goes to tertiary consumers.
42
Explain why biomass decreases at each trophic level in a food chain.
Energy is lost along the way.
43
Explain why food chains with more than 4 trophic levels are rare.
There is not sufficient biomass/ stored energy left to support any further organisms.
44
Describe how humans have manipulated energy transfer through trophic levels in the farming of plants and animals to our advantage.
Plants are provided with the abiotic conditions they need to thrive. Competition from other species is removed (i.e. with pesticides) as well as the threat of predators (creating protective barriers).
Agriculture creates simple food chains with only two or three trophic levels - this means very little energy is lost as there are fewer trophic levels present than in the natural ecosystem, and as much energy as possible is transferred into the biomass to be eaten by humans.
45
Compare the movement of energy through an ecosystem with the movement of elements such as nitrogen and carbon.
- Energy has a linear flow through an ecosystem. It enters the ecosystem from the sun and is ultimately transferred to the atmosphere as heat. As long as the sun continues to supply the earth with energy, life will continue.
- In constrast, nutrients constantly have to be recycled throughout ecosystems in order for plants and animals to grow. This is because they are used up by living organisms and there is no large external source constantly replenishing nutrients in the way the sun supplies energy.
46
Draw, label and annotate a diagram of the nitrogen cycle.
The processes of nitrogen fixation, nitrification, denitrification and ammonification all form part of the nitrogen cycle.
47
Describe how humans have manipulated energy transfer through trophic levels in the farming of plants and animals to our advantage.
Plants are provided with the abiotic conditions they need to thrive. Competition from other species is removed (i.e. with pesticides) as well as the threat of predators (creating protective barriers).
Agriculture creates simple food chains with only two or three trophic levels - this means very little energy is lost as there are fewer trophic levels present than in the natural ecosystem, and as much energy as possible is transferred into the biomass to be eaten by humans.
48
Compare the movement of energy through an ecosystem with the movement of elements such as nitrogen and carbon.
- Energy has a linear flow through an ecosystem. It enters the ecosystem from the sun and is ultimately transferred to the atmosphere as heat. As long as the sun continues to supply the earth with energy, life will continue.
- In constrast, nutrients constantly have to be recycled throughout ecosystems in order for plants and animals to grow. This is because they are used up by living organisms and there is no large external source constantly replenishing nutrients in the way the sun supplies energy.
49
Draw, label and annotate a diagram of the nitrogen cycle.
The processes of nitrogen fixation, nitrification, denitrification and ammonification all form part of the nitrogen cycle.
50
Explain the importance of decomposers and detritivores in the recycling of matter in ecosystems
Decomposition is a chemical process in which a compound is broken down into smaller molecules or its constituent elements. These are often essential elements e.g. nitrogen or carbon, which could not be used before in their organic, before decomposition.
Detritivores help to speed up the process of decay, they break down the dead organic material into smaller pieces so that the surface area for decomposition is increased.
51
Define the term “nitrogen fixation”.
The conversion of nitrogen gas to ammonium compounds.
52
Define the term “nitrification”.
Conversion of ammonium compounds into nitrites and nitrates.
53
Define the term “denitrification”.
Conversion of nitrates to nitrogen gas
54
Define the term “ammonification”.
Conversion of nitrogen in dead organic matter or waste to ammonium compounds by decomposers.
55
Name the micro-organisms involved in the nitrogen cycle and state the nitrogen-containing molecule they use and the nitrogen-containing molecule they produce.
- Nitrogen fixing bacteria: Azotobacter and Rhizobium contain the enzyme nitrogenase, which combines atmospheric nitrogen with hydrogen to produce ammonia (NH3).
- Nitrifying bacteria: Nitrosomonas, oxidise ammonium compounds into nitrites. Nitrobacter, oxidise nitrites into nitrates.
- Denitrifying bacteria: converts nitrates in the soil back to nitrogen gas, denitrification, only happens in anaerobic conditions.
- Decomposer: convert nitrogen-containing molecules in dead organic matter into ammonium compounds.
56
Draw, label and annotate a diagram of the carbon cycle.
There are five stores of carbon.
1) Atmosphere.
2) Producers (plants).
3) Consumers (animals).
4) Waste organic matter/ compost.
5) Fossil fuels.
- Carbon is transferred from producers to consumers by feeding. When they die/ excrete, carbon from both sources goes to organic waste matter. Can become fossilised to form fossil fuels.
- Carbon in this organic waste matter is released by the action of decomposers like fungi and bacteria. The carbon is released into the atmosphere as carbon dioxide gas as the decomposers respire.
- Consumers and producers also released CO2 from respiration.
- Producers remove CO2 from the atmosphere as they photosynthesise.
- Fossil fuels release carbon dioxide in combustion reaction when they are burned for energy.
57
Define the term “sampling” and explain why it is important.
Taking measurements of a limited number of individual organisms present in a particular area.
Sampling can be used to estimate the number of organisms in an area without having to count them all.
Can also be used to measure a particular characteristic of an organism e.g. the height plants.
58
State the two general ways in which sampling can be undertaken.
- Random sampling.
| - Non-random.
59
Define the terms “random sampling”.
Studying a representative sample of organisms in their natural habitat. Each organism has an equal chance of being selected.
60
Define the term “non-random sampling”.
The sample of organisms is not chosen at random, it can be opportunistic or stratified, or systematic. Some organisms have more chance than others of being selected for the sample.
61
Outline how to randomly sample an area.
Random sampling uses a quadrat.
1. Mark out a grid with xy axises on the area you are sampling and choose random co-ordinates from this grid.
2. Place the quadrat according to the first set of co-ordinates.
3. Use an identification key to identify the species present within the quadrat.
4. Record identified species and th abundance of each species in a suitable table and repeat until enough data is collected to calculate a reasonable estimation of the population size of each species within the area.
62
Name and describe the 3 main techniques of non-random sampling.
Opportunistic sampling - Samples whatever organisms are conveniently available. Weakest form as it is not always representative of the population.
Stratified sampling - some populations can be divided into a number of strata (subgroups) based on their characteristics. A random sample is then taken from each of these strata proportional to its size.
Systematic sampling - different areas within an overall habitat are identified which are then sampled separately.
63
Define the term “frame quadrat”.
A square rigid structure of a fixed size used to identify an area to be sampled, it is usually divided into a grid of equal sections.
64
Define the term “point quadrat”.
A horizontal bar set at intervals with 10 long pins, which can be lowered to the ground to take a sample. Every species that the pins touch is recorded as present for that particular sample.
This method uses the ACFOR scale to measure the abundance of each species.
65
Define “line transect”.
This involves marking out a line along the ground between two poles and taking samples at specified points.
66
Define the term “belt transect”.
Two parallel lines are marked and samples are taken from the area between the two lines. Provides more information than the line transect.
67
Define the term “interrupted belt transect”.
Uses a frame quadrat at specific intervals along a belt transect.
68
Explain why carbon dioxide levels in the atmosphere may vary throughout a 24 hour period, seasonally and over many years.
- Photosynthesis only takes place in light and so during the day photosynthesis removes carbon dioxide from the atmosphere.
- Respiration is carried out through day and night. Therefore, carbon dioxide levels are higher at night than during the day.
- CO2 levels are lower on a summer's day than on a winters day, because photosynthesis rates are higher.
69
Suggest two reasons why carbon dioxide levels in the atmosphere have increased significantly over the last 200 years.
- the combustion of fossil fuels: released co2 back into the atmosphere which had previously been trapped in fossil for millions of year.
- deforestation: has removed significant quantities of photosynthesising biomas from the earth, as a result less carbon dioxide is removed from the atmosphere.
- positive feedback effect: co2 raises global temperature. The amount of co2 dissolved into seas and oceans is affected by the temperature of water, the higher temperature the less co2 is dissolved. Therefore global warming reduces the carbon bank in oceans and releases more co2 into the atmosphere. L
70
Define the term “succession”.
The progressive replacement of one type of species or community by another in an ecosystem until a stable climax community is reached.
71
Define the term “primary succession”.
The predictable change in a community of organisms over time, starting in location where terrestrial life has not previously colonised. For example, newly formed land and exposed bare rock. There is no soil or organic material present.
72
Define the term “secondary succession”.
The predictable change in a community of organisms over time, starting in a location where terrestrial life had previously colonised but the larger plant and animal life is no longer present.
73
Define the term “deflected succession”.
Succession is prevented from proceeding due to some external factor, usually human activity. Succession is halted before it reaches the climax community.
74
Define “pioneer species”.
The first organisms to colonise an area.
75
Define “seral or sere stage”.
The steps in succession.
76
Define “climax community”.
The final stage in succession, where the community is said to be in a stable state. No further succession occurs as long as the abiotic conditions remain the same.
77
Define “plagioclimax”.
Stage in succession where artificial or natural factors prevent the natural climax community from forming. Plagioclimax is the final stage in deflected succession.
78
Give 5 adaptations that some species have for being pioneer species.
- ability to produce large quantities of seeds or spores, which are blown away by the wind and deposited on 'new land'.
- seeds that germinate rapidly.
- the ability to photosynthesize to produce their own energy - light, rainfall and air are often the only abiotic factors present.
- tolerance to extreme environments
- the ability to fix nitrogen from the atmosphere
79
Describe the effect pioneer species have on the environment.
Their presence helps to the abiotic/biotic conditions of the area, so that it can support other forms of life.
When organisms of the pioneer species die and decompose small organic products are released into th soil. This organic component of the soil is called humus. The soil becomes able to support the growth of secondary colonisers.
In some cases, pioneer species also provide a food source for consumers.
80
Describe how the conditions of the soil change as succession occurs (and why).
- Over time, weathering of bare rocks produces particles that form the basis of soil, but it cannot support life on its own.
- However, when organisms of the pioneer species die and decompose small organic products are released into the soil.
- This organic component of the soil is called humus. The soil becomes able to support the growth of secondary colonisers, as it contains minerals such as nitrates and is able to retain some water.
81
Explain how succession occurs.
- The arrival of a pioneer species in a previously un-colonised land improves environmental conditions by making the soil fertile and providing a food source for consumers.
- As environmental conditions continue to improve, new species arrive. As these species die and decompose they contribute to a deeper and nutrient-rich soil.
- Conditions become more favourable to support life, and so the greater species biodiveristy which is acheived creates competition.
- At each seral stage of succession some species are better adapted to conditions than others, these organisms outcompete many of the species that were previously present and become the dominant species (by mass) present in the ecosytem.
- Eventually a climax community is attained.
82
Define the term “dominant species”.
The most abundant species in an ecosystem at a given time.
83
Describe and explain the change in niche number and number of species (and so biodiversity) present as succession progresses.
A general increase in biodiversity because abiotic conditions become less harsh and so more plant species can survive, so more plants provide different food sources for primary consumers. More primary consumers provide more different food sources for secondary consumers etc
More food sources provide more niches and more species arrive to fill each niche, increasing biodiversity.
But often biodiversity decreases as succession reaches the climax community as a dominant species is out competing pioneer and other species, resulting in their elimination. The more successful the dominant species the less biodiversity in a given ecosystem.
84
Explain why secondary succession is likely to occur more quickly than primary succession.
Soil is already present for secondary succession so there doesn't need to be time for soil to develop up to the condition required for a climax community. Often there are seeds already present in the soil so chance colonisation doesn't need to occur. Often then location of sites of secondary succession are near sites that are already colonised so colonisation of this site is quick.
85
Give 3 reasons why deflected succession may occur.
- grazing and trampling of vegetation by domesticated animals.
- removing existing vegetation (such as shrub land) to plant crops, the crop becomes the final community.
- burning as a means of forest clearance, this often leads to an increase in biodiversity as it provides space and nutrient-rich ash for other species to grow, such as shrubs.
86
Describe how the abundance of plants can be estimated (and then how population size can be calculated from this).
To measure the abundance of plants quadrats are placed randomly in the area. The abundance of the organisms in that area is measured by counting the number of individual plants contained with the quadrat.
Estimated population number (m-2) = number of individuals in the sample/ area of sample (m2)
87
Describe the capture-mark-release-recapture technique can be used to estimate the population size of an animal species.
1) Capture as many individuals as possible in the sample area.
2) Mark or tag the individuals in a way that is not detrimental to it.
3) Release the marked animals back into the sample area and allow time for them to redistribute themselves throughout the habitat.
4) Recapture as many individuals as possible in the original sample area.
5) Record the number of marked and unmarked individuals present in the sample. (release all individuals present back into their habitat).
6) Use lincoln's index to estimate population size.
88
Write the equation for the Lincoln index to estimate the population size of an animal species.
Estimated population size = (number of individuals in first sample x number of individuals in the second sample) / number of recaptured marked individuals.
