Ecosystems

Question 1

Define the term “ecosystem”.

Answer 1

All living organisms and the non-living conditions in an area.

Question 2

Define the term “community”.

Answer 2

All the populations of living organisms in a particular habitat.

Question 3

Define the term “habitat”.

Answer 3

An area inhabited by a species.

Question 4

Define the term population.

Answer 4

A group of organisms of one species that live in the same place at the same time.

Question 5

Define the term species.

Answer 5

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.

Question 6

Define the term ecology.

Answer 6

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.

Question 7

Explain what is meant by the phrase “ecosystems are dynamic”.

Answer 7

They are constantly changing.

Question 8

Define the term “biotic factor”.

Answer 8

The living components of an ecosystem.

Question 9

Define term abiotic factor.

Answer 9

The non-living conditions in a habitat.

Question 10

Give some examples of biotic factors.

Answer 10

• presence of organism (as predator or prey)
• the size of the populations of organisms
• the competition between organisms.

Question 11

Give some abiotic factors.

Answer 11

• amount of rainfall
• yearly temperature range
• availability of light
• availability of water
• availability of oxygen
• salinity
• PH

Question 12

Define the term “edaphic factor”.

Answer 12

the soil factors - the type and condition of the soil.

Question 13

Give three examples of edaphic factors.

Answer 13

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.

Question 14

Define the term “food web”

Answer 14

Food webs are systems of interlinked food chains used to show the transfer of biomass, and therefore energy, through the organisms in an ecosystem.

Question 15

Define the term “food chain”.

Answer 15

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.

Question 16

Define the term “trophic levels”.

Answer 16

The stages in a food chain. Starting with a producer, the rest are consumers.

Question 17

Define the term “heterotroph”.

Answer 17

Organisms that acquire nutrients by the ingestion of other organisms.

Question 18

Explain what the arrows represent in a food web.

Answer 18

The transfer of energy, they point in the direction that the energy is being transfered.

Question 19

Define the term “consumer”.

Answer 19

Organisms that attain their energy by feeding on other organisms.

Question 20

Define the term producer.

Answer 20

Organism that converts light energy into chemical energy.

Question 21

Define the term “detritivore”. Give two examples and explain their role in food webs.

Answer 21

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.

Question 22

Define the term “decomposer”. Give 2 examples of and explain their role in food webs.

Answer 22

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.

Question 23

Define the term “biomass”.

Answer 23

The mass of living material.

Question 24

Define the terms “dry mass”.

Answer 24

The mass of living material without its water content.

Question 25

Explain why dry mass is a better indicator of biomass than fresh mass.

Answer 25

Dry mass excludes fluctuating water concentrations which could affect the overall mass.

Question 26

Explain how to calculate the dry mass of each trophic level in a food chain.

Answer 26

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.

Question 27

Explain how to experimentally measure the energy content of organic matter.

Answer 27

The energy available at each trophic level is measured in kilojoules per metre sqaured per year.

Question 28

Suggest suitable units for the biomass in an ecosystem (both terrestrial and aquatic).

Answer 28

g/m2 - terrestrial

g/m3 - aquatic

Question 29

Explain how pyramids of numbers, biomass and energy represent data about an ecosystem and the relative merits of each.

Answer 29

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.

Question 30

Suggest suitable units for the energy at each trophic level in a food chain and explain why these units are appropriate.

Answer 30

kJ m-2 yr-1 (kilojoules per metre squared per year)

Question 31

Explain how energy is transferred from one trophic level to the next.

Answer 31

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.

Question 32

Define the term “ecological efficiency” and write an equation to calculate it.

Answer 32

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

Question 33

Explain 3 reasons why only 1-3% of the sunlight producers receive is converted into chemical energy.

Answer 33

• 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.

Question 34

Define the terms “gross production”.

Answer 34

The total solar energy that plants convert to organic matter.

Question 35

Define the term “net production”.

Answer 35

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.

Question 36

Define the term “respiratory losses”.

Answer 36

Energy lost in respiration (heat?)

Question 37

Write an equation to link “gross production”, “net production” and “respiratory losses”.

Answer 37

Net production = gross production - respiratory losses

Question 38

Define the term “primary production”.

Answer 38

The generation of biomass within a producer

Question 39

Define the term “secondary production”.

Answer 39

The generation of biomass within a consumer.

Question 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.

Answer 40

• 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.

Question 41

Draw, label and annotate, a diagram showing the flow of energy through trophic levels and out of the food chain.

Answer 41

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.

Question 42

Explain why biomass decreases at each trophic level in a food chain.

Answer 42

Energy is lost along the way.

Question 43

Explain why food chains with more than 4 trophic levels are rare.

Answer 43

There is not sufficient biomass/ stored energy left to support any further organisms.

Question 44

Describe how humans have manipulated energy transfer through trophic levels in the farming of plants and animals to our advantage.

Answer 44

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.

Question 45

Compare the movement of energy through an ecosystem with the movement of elements such as nitrogen and carbon.

Answer 45

• 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.

Question 46

Draw, label and annotate a diagram of the nitrogen cycle.

Answer 46

The processes of nitrogen fixation, nitrification, denitrification and ammonification all form part of the nitrogen cycle.

Question 47

Describe how humans have manipulated energy transfer through trophic levels in the farming of plants and animals to our advantage.

Answer 47

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.

Question 48

Compare the movement of energy through an ecosystem with the movement of elements such as nitrogen and carbon.

Answer 48

• 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.

Question 49

Draw, label and annotate a diagram of the nitrogen cycle.

Answer 49

The processes of nitrogen fixation, nitrification, denitrification and ammonification all form part of the nitrogen cycle.

Question 50

Explain the importance of decomposers and detritivores in the recycling of matter in ecosystems

Answer 50

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.

Question 51

Define the term “nitrogen fixation”.

Answer 51

The conversion of nitrogen gas to ammonium compounds.

Question 52

Define the term “nitrification”.

Answer 52

Conversion of ammonium compounds into nitrites and nitrates.

Question 53

Define the term “denitrification”.

Answer 53

Conversion of nitrates to nitrogen gas

Question 54

Define the term “ammonification”.

Answer 54

Conversion of nitrogen in dead organic matter or waste to ammonium compounds by decomposers.

Question 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.

Answer 55

• 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.

Question 56

Draw, label and annotate a diagram of the carbon cycle.

Answer 56

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.

Question 57

Define the term “sampling” and explain why it is important.

Answer 57

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.

Question 58

State the two general ways in which sampling can be undertaken.

Answer 58

• Random sampling.

- Non-random.

Question 59

Define the terms “random sampling”.

Answer 59

Studying a representative sample of organisms in their natural habitat. Each organism has an equal chance of being selected.

Question 60

Define the term “non-random sampling”.

Answer 60

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.

Question 61

Outline how to randomly sample an area.

Answer 61

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.

Question 62

Name and describe the 3 main techniques of non-random sampling.

Answer 62

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.

Question 63

Define the term “frame quadrat”.

Answer 63

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.

Question 64

Define the term “point quadrat”.

Answer 64

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.

Question 65

Define “line transect”.

Answer 65

This involves marking out a line along the ground between two poles and taking samples at specified points.

Question 66

Define the term “belt transect”.

Answer 66

Two parallel lines are marked and samples are taken from the area between the two lines. Provides more information than the line transect.

Question 67

Define the term “interrupted belt transect”.

Answer 67

Uses a frame quadrat at specific intervals along a belt transect.

Question 68

Explain why carbon dioxide levels in the atmosphere may vary throughout a 24 hour period, seasonally and over many years.

Answer 68

• 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.

Question 69

Suggest two reasons why carbon dioxide levels in the atmosphere have increased significantly over the last 200 years.

Answer 69

• 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

Question 70

Define the term “succession”.

Answer 70

The progressive replacement of one type of species or community by another in an ecosystem until a stable climax community is reached.

Question 71

Define the term “primary succession”.

Answer 71

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.

Question 72

Define the term “secondary succession”.

Answer 72

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.

Question 73

Define the term “deflected succession”.

Answer 73

Succession is prevented from proceeding due to some external factor, usually human activity. Succession is halted before it reaches the climax community.

Question 74

Define “pioneer species”.

Answer 74

The first organisms to colonise an area.

Question 75

Define “seral or sere stage”.

Answer 75

The steps in succession.

Question 76

Define “climax community”.

Answer 76

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.

Question 77

Define “plagioclimax”.

Answer 77

Stage in succession where artificial or natural factors prevent the natural climax community from forming. Plagioclimax is the final stage in deflected succession.

Question 78

Give 5 adaptations that some species have for being pioneer species.

Answer 78

• 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

Question 79

Describe the effect pioneer species have on the environment.

Answer 79

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.

Question 80

Describe how the conditions of the soil change as succession occurs (and why).

Answer 80

• 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.

Question 81

Explain how succession occurs.

Answer 81

• 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.

Question 82

Define the term “dominant species”.

Answer 82

The most abundant species in an ecosystem at a given time.

Question 83

Describe and explain the change in niche number and number of species (and so biodiversity) present as succession progresses.

Answer 83

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.

Question 84

Explain why secondary succession is likely to occur more quickly than primary succession.

Answer 84

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.

Question 85

Give 3 reasons why deflected succession may occur.

Answer 85

• 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.

Question 86

Describe how the abundance of plants can be estimated (and then how population size can be calculated from this).

Answer 86

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)

Question 87

Describe the capture-mark-release-recapture technique can be used to estimate the population size of an animal species.

Answer 87

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.

Question 88

Write the equation for the Lincoln index to estimate the population size of an animal species.

Answer 88

Estimated population size = (number of individuals in first sample x number of individuals in the second sample) / number of recaptured marked individuals.