Ecosystems & Energy Transfer (Edexcel A Level Biology (A) SNAB): Flashcards
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Define habitat.
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Define habitat.
A habitat is the place where an organism lives, which can be large (a desert) or small (a single tree).
Define population.
A population is all the individuals of one species living in a habitat.
Define community.
A community is all the populations of different species living and interacting in the same area.
Define ecosystem.
An ecosystem is a community and its interactions with the non-living (abiotic) parts of its habitat.
Define abundance.
Abundance is the number of individuals of a species living in a habitat.
Define distribution.
Distribution is where a species lives within a habitat.
What is the difference between a habitat specialist and a generalist?
A specialist can only survive in a very specific habitat.
A generalist can survive in a range of habitats.
Why are generalist species more likely to become invasive?
They can survive in a range of habitats.
This makes it easier for them to invade and take over a new habitat.
What two types of component make up an ecosystem?
Biotic (living) components.
Abiotic (non-living) components.
Multiple populations living and interacting in the same area form a .
Multiple populations living and interacting in the same area form a community.
True or False?
An ecosystem is completely self-contained.
False.
No ecosystem is fully self-contained — organisms such as birds can move between ecosystems.
What two things happen within an ecosystem?
There is a flow of energy through it.
Nutrients within it are recycled.
Define biotic factor.
A biotic factor is a living factor that influences a community, arising from the activity of other organisms.
Define abiotic factor.
An abiotic factor is a non-living factor that influences a community, such as temperature or pH.
Give four examples of biotic factors.
Any four of:
Predation
Food availability
Competition (intraspecific or interspecific)
Disease or parasitism
Give four examples of abiotic factors.
Any four of:
Light intensity
Temperature
pH of soil or water
Oxygen or carbon dioxide concentration
What is the difference between intraspecific and interspecific competition?
Intraspecific competition is between individuals of the same species.
Interspecific competition is between individuals of different species.
What determines the abundance and distribution of a species?
A combination of biotic and abiotic factors in the habitat.
Give an example of how a biotic factor could reduce a population.
An increase in a predator or disease.
Either would reduce the number of individuals surviving in the population.
Give an example of how an abiotic factor could affect a plant population.
A change in light intensity or soil pH.
Plants not suited to the new conditions would grow less well or die.
Competition between individuals of the same species is called competition.
Competition between individuals of the same species is called intraspecific competition.
True or False?
Temperature is a biotic factor.
False.
Temperature is an abiotic (non-living) factor.
Is disease a biotic or abiotic factor?
A biotic factor, as it results from the activity of living organisms (pathogens).
Define water turbidity.
Water turbidity is the cloudiness of water — an abiotic factor that affects how much light reaches aquatic organisms.
Define niche.
A niche is the role of a species within its habitat, including what it eats, when it is active and exactly where it lives and feeds.
What happens if two species try to occupy the same niche?
They compete directly for resources.
One out-competes the other, which then dies out in that habitat.
How does the niche a species fills affect its abundance?
If two species have similar niches they compete, so their populations stay smaller.
This lowers the abundance of each.
How does a species' niche affect its distribution?
A species can only survive where it is well adapted to the biotic and abiotic factors.
This determines where it is found.
How can two species appear to share a niche but still coexist?
There are subtle differences in their roles.
For example, they may feed at different times or on different foods.
Define abundance in the context of a niche.
Abundance is the number of individuals of a species living in a habitat.
Give three things that a species' niche includes.
What it eats and which species eat it.
When it is active and where in the habitat it lives and feeds.
No two species can occupy the same within a habitat.
No two species can occupy the same niche within a habitat.
True or False?
A species' niche has no effect on its distribution.
False.
A species' niche determines where it can survive, and so its distribution.
Why might a species' distribution change over time?
If it is not well suited to a habitat's biotic and abiotic factors.
It may move to a more suitable habitat.
How do warbler species feeding in the same tree avoid direct competition?
They feed at different locations within the tree.
This gives each a slightly different niche.
True or False?
Two species competing for a similar niche will each have a lower abundance.
True.
Competition keeps both populations smaller, lowering the abundance of each.
Define sampling.
Sampling is a method of estimating the abundance and distribution of species by studying small representative parts of a habitat.
What is the difference between random and systematic sampling?
In random sampling, sample points are chosen at random.
In systematic sampling, sample points are placed at fixed intervals.
Why is random sampling used?
To avoid bias by the person sampling.
Bias could make a habitat seem more or less diverse than it really is.
When is systematic sampling more appropriate than random sampling?
When investigating how species change along a gradient or near an environmental feature.
For example, sampling along a transect away from a river.
How are random sample sites selected?
Lay a grid over the area.
Generate random number coordinates and sample the matching grid squares.
Define transect.
A transect is a line laid across a habitat along which samples are taken to study how species change along a gradient.
What is measured by percentage cover in a quadrat?
The percentage of the quadrat that is covered by a particular species.
When would you use a point quadrat rather than a frame quadrat?
In areas with dense plant cover, where the ground is hard to study.
Pins are lowered and species touching them are recorded.
What is the difference between a line transect and a belt transect?
A line transect records species touching the line.
A belt transect uses quadrats placed along the line.
Define kite diagram.
A kite diagram is a graph that shows both the distribution and abundance of species along a transect.
On a kite diagram, how are distribution and abundance shown?
Distribution is shown by the position along the transect (x-axis).
Abundance is shown by the width of the kite shape.
Sampling at fixed intervals across a habitat, rather than at random points, is called sampling.
Sampling at fixed intervals across a habitat, rather than at random points, is called systematic sampling.
Define succession.
Succession is the process of ecosystem change over time, during which the biotic and abiotic conditions change.
Define primary succession.
Primary succession is succession that occurs on newly formed or newly exposed land with no soil, such as bare rock.
Define pioneer species.
A pioneer species is the first to colonise bare land, such as lichens or mosses, able to withstand harsh conditions.
How do pioneer species help soil to form?
They break apart the rock surface and, when they die, add dead organic matter.
Together these form a basic soil.
How do small plants and grasses change the environment during succession?
Their roots stabilise the soil and help it hold water and nutrients.
When they die, the soil becomes deeper and more nutrient-rich.
Define climax community.
A climax community is the final, stable community that forms at the end of succession, dominated by large species such as trees.
Why do pioneer species often disappear from a climax community?
They are poor competitors, well adapted only to harsh conditions.
Later species out-compete them for light and resources.
How does secondary succession differ from primary succession?
Secondary succession occurs on previously occupied land where soil is already present.
So it begins at a later stage, e.g. after a fire.
How can humans prevent a climax community from developing?
By activities such as mowing or grazing livestock.
These stop woody plants and trees becoming established.
Define plagioclimax.
A plagioclimax is a stable community that results from human intervention preventing succession reaching its natural climax, such as heathland.
The first species to colonise bare land during succession are called species.
The first species to colonise bare land during succession are called pioneer species.
True or False?
A climax community is always the most biodiverse stage of succession.
False.
A climax community is stable but not necessarily the most biodiverse stage.
Define gross primary productivity (GPP).
GPP is the rate at which producers convert light energy into chemical energy (carbohydrates) during photosynthesis.
Define net primary productivity (NPP).
NPP is the rate at which energy is stored as plant biomass, after respiratory losses (GPP minus respiration).
State the equation linking NPP, GPP and respiration.
NPP = GPP − R
Why is NPP less than GPP?
Some of the energy fixed in photosynthesis is released in respiration by the plant.
Only the remainder is stored as new biomass.
Why is NPP important for an ecosystem?
It represents the energy stored in plant biomass.
This is the energy available to primary consumers and decomposers at higher trophic levels.
Grass has a GPP of 17 500 kJ m⁻² yr⁻¹ and respires 14 000 kJ m⁻² yr⁻¹. Calculate its NPP.
NPP = GPP − R
= 17 500 − 14 000 = 3 500 kJ m⁻² yr⁻¹
How would you rearrange NPP = GPP − R to find GPP?
GPP = NPP + R
In what units is NPP usually expressed?
Energy per unit area (or volume) per unit time.
For example, kJ m⁻² yr⁻¹ (or J m⁻³ yr⁻¹ for aquatic habitats).
Net primary productivity is the rate at which energy is stored in plant .
Net primary productivity is the rate at which energy is stored in plant biomass.
True or False?
NPP is the total energy fixed by a plant before any respiratory losses.
False.
That is GPP. NPP is what remains after respiratory losses.
Why would volume-based units be used for NPP in some habitats?
For aquatic habitats.
Producers such as algae are distributed through a volume of water rather than over an area.
Define producer.
A producer is an organism, such as a plant, that converts light energy into chemical energy by photosynthesis.
Define trophic level.
A trophic level is a stage in a food chain, such as producer, primary consumer or secondary consumer.
Roughly what percentage of energy is transferred between trophic levels?
Only about 10%.
Around 90% is lost to the environment at each level.
Give three reasons energy is lost between trophic levels.
Not all of an organism is eaten.
Some food is not digested and is egested as faeces.
Energy is lost as heat from respiration.
Give two reasons much of the Sun's energy is unavailable to producers.
Light passes through or is reflected off leaves, or hits non-photosynthetic parts.
Only certain wavelengths of light are absorbed for photosynthesis.
State the equation for the efficiency of energy transfer.
energy efficiency = (net productivity ÷ energy received) × 100
Toads receive 10 000 kJ m⁻² yr⁻¹ and lose 9 000 in respiration, faeces and urine. Calculate the efficiency of energy transfer.
Net productivity = 10 000 − 9 000 = 1 000
Efficiency = (1 000 ÷ 10 000) × 100 = 10%
State the equation for the efficiency of biomass transfer.
efficiency of biomass transfer = (biomass transferred ÷ biomass intake) × 100
A bush of 35 kg dry mass is eaten by aphids of 4.1 kg dry mass. Calculate the efficiency of biomass transfer.
Efficiency = (4.1 ÷ 35) × 100
= 11.7%
Why is dry biomass used rather than wet biomass?
The water content of tissues varies.
Drying removes this variation, giving a fair comparison.
How is the dry biomass of a sample measured?
Dry it in an oven at low heat and weigh at intervals until the mass is constant.
The constant mass is the dry biomass.
Energy is lost as to the environment when organisms respire.
Energy is lost as heat to the environment when organisms respire.
True or False?
Calculating biomass transfer efficiency gives essentially the same information as energy transfer efficiency.
True.
Biomass is effectively a measure of the chemical energy stored in an organism.
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