Ecosystems and Interdependence - Worksheets, Questions and Revision

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KS3 · Biology

K5 Ecosystems and Interdependence

AQA KS3 AQA KS3 Science (Activate 2) · Calculator allowed · about 95 minutes

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Ecologists use precise scientific vocabulary to describe ecosystems.

(a)Define the term 'habitat'.(1)

(b)Define the term 'population'.(1)

(c)Define the term 'community'.(1)

(d)Define the term 'ecosystem'.(1)

(e)Define the term 'niche'.(1)

Every ecosystem is shaped by biotic (living) factors and abiotic (non-living) factors. Classify each of the following factors as biotic or abiotic.

(a)Rainfall.(1)

(b)Presence of parasites.(1)

(c)Oxygen concentration dissolved in pond water.(1)

(d)Competition for nesting sites.(1)

(e)Soil pH.(1)

(f)Availability of prey.(1)

Organisms in a food chain have different feeding roles.

(a)State what is meant by a 'producer', giving one example.(1)

(b)State what is meant by a 'consumer', giving one example.(1)

(c)State what is meant by a 'decomposer', giving one example.(1)

In a farmland ecosystem, wheat is eaten by field mice, which are in turn eaten by barn owls.

(a)Construct a food chain for wheat, field mice and barn owls, using arrows to show the direction of energy transfer.(1)

(b)Identify the producer, the primary consumer and the secondary consumer in this food chain.(3)

A freshwater pond food web contains the following feeding relationships, where an arrow points from the organism eaten to the organism that eats it: pondweed -> tadpole -> perch -> heron; algae -> water flea -> stickleback -> heron.

(a)Identify the two producers in this food web.(1)

(b)Name a predator of the water flea.(1)

(c)Explain why the heron can be described as occupying two different trophic levels in this food web.(1)

(d)If the tadpole population in this pond were wiped out by a disease, name one organism whose population would most directly lose a food source.(1)

In a grassland ecosystem, the producers store a total of 500 000 kJ/m²/year of energy. On average, only 10% of the energy available at one trophic level is transferred to the next trophic level.

(a)Calculate the energy available to the primary consumers.(2)

(b)Calculate the energy available to the secondary consumers.(2)

(c)Explain two reasons why not all of the energy available at one trophic level is transferred to the next trophic level.(2)

A single bramble bush can support several thousand aphids feeding on its sap. These aphids are eaten by a much smaller number of ladybirds. If the numbers of organisms at each level were simply counted, a pyramid of numbers for this food chain would have an unusual, non-pyramid shape (narrow at the bottom, very wide in the middle). Explain why building a pyramid of biomass, rather than a pyramid of numbers, would give a more realistic true-pyramid shape for this food chain.

(3)

Organisms have adaptations that help them survive in their habitat. Adaptations may be structural (a feature of the body), behavioural (a way an organism acts) or physiological (a process inside the body).

(a)Classify each of the following adaptations as structural, behavioural or physiological: (i) a polar bear's thick layer of blubber and fur, (ii) emperor penguins huddling together in large groups in Antarctic winter, (iii) a camel's ability to produce very concentrated urine to conserve water, (iv) a stick insect's body shape and colour resembling a twig.(4)

(b)Explain how the camel's ability to produce very concentrated urine helps it to survive in a hot desert habitat.(2)

Grey squirrels were introduced to the UK from North America in the 19th century. They now compete with the native red squirrel for the same woodland food and nesting sites.

(a)Define 'intraspecific competition'.(1)

(b)Define 'interspecific competition'.(1)

(c)Using the idea of competition, explain why the introduction of grey squirrels has led to a decline in red squirrel populations in many parts of the UK.(2)

Required practical: Freya investigated the percentage cover of creeping buttercup in a paddock with a total area of 750 m². She used a 0.5 m x 0.5 m quadrat and placed it randomly 8 times, recording the percentage cover of buttercup inside the quadrat each time. The mean percentage cover from her 8 quadrats was 35%.

(a)Explain why Freya should use randomly generated coordinates to position her quadrat, rather than choosing the positions herself.(1)

(b)State one variable, other than quadrat position, that Freya should keep the same each time to make her method valid.(1)

(c)Calculate the estimated total area of the paddock covered by creeping buttercup.(2)

(d)Suggest one way Freya could improve the reliability of her estimate.(1)

(e)Freya's quadrat has a grid dividing it into 100 equal smaller squares. Explain why using this grid to estimate percentage cover is more precise than simply judging the cover by eye.(1)

Required practical: Olamide used the capture-mark-recapture method to estimate the population of snails in a garden. On day 1 he caught and marked 60 snails with a small dot of non-toxic paint, then released them. On day 2 he caught 45 snails, of which 9 had a marked dot.

(a)State the formula used to estimate the total population using the capture-mark-recapture method.(1)

(b)Calculate an estimate of the total snail population in the garden. Show your working.(2)

(c)State one assumption that must be true for this population estimate to be valid.(1)

In coastal waters off the west coast of Scotland, sea otters prey on sea urchins, and sea urchins graze on kelp, a large seaweed that forms dense underwater 'kelp forests' used as habitat by many other species. Predict and explain what would happen to the sea urchin population and the kelp forest if sea otters were hunted until almost none remained in the area.

(4)

Carbon moves between the atmosphere, living organisms and fossil fuels as part of the carbon cycle.

(a)State the name of the process by which green plants remove carbon dioxide from the atmosphere.(1)

(b)State the name of the process by which plants and animals release carbon dioxide back into the atmosphere.(1)

(c)State the name of the process by which decomposers break down dead organisms and waste material.(1)

(d)State one human activity that releases carbon dioxide stored in fossil fuels back into the atmosphere.(1)

(e)Explain why decomposers are essential for recycling nutrients such as carbon back to producers in an ecosystem.(2)

A large area of forest is cleared (deforestation) to create farmland.

(a)Explain how removing trees can lead to increased soil erosion on the cleared land.(2)

(b)Explain how removing trees from a large area can reduce rainfall in that local area.(2)

Some pesticides do not break down easily and build up in the bodies of organisms, becoming more concentrated at each trophic level. This is called bioaccumulation. In a river ecosystem, algae contain a pesticide at a concentration of 0.2 ppm (parts per million). Small fish that eat the algae have a pesticide concentration of 1.0 ppm, a five-fold increase.

(a)Herons feed on the small fish. Assuming the same five-fold increase applies at this next trophic level, calculate the pesticide concentration in the herons.(2)

(b)Calculate the overall factor by which the pesticide concentration has increased from the algae to the herons.(1)

(c)Explain why top predators, such as herons, are usually at the greatest risk from bioaccumulation of pesticides.(2)

A large area of tropical rainforest in Indonesia is cleared and burned to plant palm oil trees for a plantation. Explain the effects that this deforestation could have on the local ecosystem and on the wider global carbon cycle.

(6)

Required practical: Aisha and Ravi set up a transect on a rocky shore, from the low water mark up to the top of the shore, to investigate how the distribution of barnacles is affected by the time each part of the shore spends exposed to air between tides. They placed a 0.25 m² quadrat at 5 m intervals up the shore and counted the number of barnacles in each quadrat.
Distance up the shore from the low water mark (m): 0, 5, 10, 15, 20
Number of barnacles per quadrat: 45, 38, 22, 10, 3

(a)Name the sampling technique Aisha and Ravi used to investigate the distribution of barnacles up the shore.(1)

(b)State the independent variable in this investigation.(1)

(c)Calculate the mean number of barnacles per quadrat across the 5 sampling points. Give your answer to 1 decimal place.(2)

(d)Describe the pattern shown by the results, and suggest an explanation for it in terms of an abiotic factor.(2)

In a woodland food chain, the producers have a total biomass of 15 000 kg. The primary consumers that feed on them have a total biomass of 1500 kg. The secondary consumers that feed on the primary consumers have a total biomass of 90 kg.

(a)Calculate the percentage efficiency of energy transfer from the producers to the primary consumers.(2)

(b)Calculate the percentage efficiency of energy transfer from the primary consumers to the secondary consumers.(2)

(c)Explain two reasons why the efficiency of energy transfer between trophic levels is usually well below 20%.(2)

Callum was estimating the population of dandelions in a school field using a 1 m x 1 m quadrat, but for convenience he only placed the quadrat at points close to the car park at the edge of the field. Explain why this sampling method could make his population estimate inaccurate, and suggest one change Callum could make to improve his method.

(4)

Since the 1970s, Dutch elm disease, spread by elm bark beetles, has killed most of the mature elm trees in many UK woodlands. The white-letter hairstreak butterfly lays its eggs only on elm trees, and its caterpillars feed exclusively on elm leaves.

(a)Predict what will happen to the population of white-letter hairstreak butterflies in a woodland as its elm trees die from the disease, and explain your reasoning.(2)

(b)Explain why a woodland containing many different tree species is likely to cope better with a disease like Dutch elm disease than a woodland made up almost entirely of elm trees.(3)

Mark scheme · K5 Ecosystems and Interdependence

Question 1

(a) B1 the place where an organism normally lives oe
(a) Answer: The place where an organism normally lives.
(b) B1 all the organisms of one species living in the same habitat at the same time oe
(b) Answer: All the organisms of one species living in the same habitat at the same time.
(c) B1 all the populations of different species living and interacting in the same habitat oe
(c) Answer: All the populations of different species living and interacting together in the same habitat.
(d) B1 a community of organisms together with the non-living (abiotic) conditions in the area, and the way they all interact oe
(d) Answer: A community of organisms together with the non-living (abiotic) conditions in that area, and the way they all interact.
(e) B1 the specific role and position of an organism within its habitat, including what it eats, where it lives and how it interacts with other organisms oe
(e) Answer: The specific role and position of an organism within its habitat, including what it eats and how it interacts with other species.

Question 2

(a) B1 abiotic cao
(a) Answer: Abiotic.
(b) B1 biotic cao
(b) Answer: Biotic.
(c) B1 abiotic cao
(c) Answer: Abiotic.
(d) B1 biotic cao
(d) Answer: Biotic.
(e) B1 abiotic cao
(e) Answer: Abiotic.
(f) B1 biotic cao
(f) Answer: Biotic.

Question 3

(a) B1 an organism that makes its own food by photosynthesis, e.g. a green plant or algae oe
(a) Answer: A producer makes its own food by photosynthesis, for example grass or a green plant.
(b) B1 an organism that gets its energy by eating other organisms, e.g. any named animal oe
(b) Answer: A consumer gets its energy by eating other organisms, for example a rabbit or a fox.
(c) B1 an organism that breaks down dead organisms and waste material, releasing nutrients back into the environment, e.g. bacteria or fungi oe
(c) Answer: A decomposer breaks down dead organisms and waste, releasing nutrients back into the environment, for example bacteria or fungi.

Question 4

(a) B1 wheat -> field mouse -> barn owl, with arrows pointing from organism eaten to organism that eats it
(a) Answer: wheat -> field mouse -> barn owl
(b) B1 producer = wheat
(b) B1 primary consumer = field mouse
(b) B1 secondary consumer = barn owl
(b) Answer: Producer: wheat. Primary consumer: field mouse. Secondary consumer: barn owl.

Question 5

(a) B1 pondweed and algae, both required
(a) Answer: Pondweed and algae.
(b) B1 stickleback cao
(b) Answer: Stickleback.
(c) B1 the heron eats perch (a secondary consumer, making the heron a tertiary consumer in that chain) and also eats stickleback (also a secondary consumer, so the same trophic level applies), but because it can feed at more than one point in the web its overall trophic level is not fixed oe; accept: heron eats both perch and stickleback, which places it at more than one feeding level depending on the chain followed
(c) Answer: The heron feeds on both perch and stickleback, which are reached by different length chains, so it does not sit at a single fixed trophic level across the whole food web.
(d) B1 perch cao
(d) Answer: Perch.

Question 6

(a) M1 500 000 x 0.1 (or 500 000 x 10/100) seen
(a) A1 50 000 kJ/m²/year cao
(a) Answer: 50 000 kJ/m²/year
(b) M1 50 000 x 0.1 seen (ft from part a)
(b) A1 5000 kJ/m²/year cao (ft)
(b) Answer: 5000 kJ/m²/year
(c) B1 energy is lost as heat through respiration, used for movement and keeping warm oe
(c) B1 energy is lost in body parts not eaten (e.g. bones, fur) or in waste that is egested (faeces) or excreted (urine) oe
(c) Answer: Energy is lost as heat from respiration (for movement and staying warm), and in uneaten body parts or waste material such as faeces and urine.

Question 7

B1 a pyramid of numbers only counts individual organisms, without taking into account how large or small they are oe
B1 one bramble bush is a single, very large organism, but is counted the same as one tiny aphid, even though it has far more mass oe
B1 a pyramid of biomass measures the total mass of living material at each level, which reflects the huge difference in size between the bush and the aphids, so it gives a true pyramid shape oe
Answer: A pyramid of numbers treats the huge bramble bush as equal to one tiny aphid, giving a misleading shape; a pyramid of biomass measures total mass instead, correctly showing that the bush has far more biomass than the aphids, so it forms a true pyramid.

Question 8

(a) B1 (i) structural
(a) B1 (ii) behavioural
(a) B1 (iii) physiological
(a) B1 (iv) structural
(a) Answer: (i) structural, (ii) behavioural, (iii) physiological, (iv) structural.
(b) B1 producing very concentrated urine means less water is lost from the body when waste is excreted oe
(b) B1 this helps the camel conserve water, which is important for survival where water is scarce and hard to find in the desert oe
(b) Answer: By producing very concentrated urine, the camel loses much less water when excreting waste, helping it conserve water in a habitat where water is scarce.

Question 9

(a) B1 competition between organisms of the same species for the same resources, e.g. food, mates or territory oe
(a) Answer: Competition between organisms of the same species for the same resources, such as food, mates or territory.
(b) B1 competition between organisms of different species for the same resources oe
(b) Answer: Competition between organisms of different species for the same resources.
(c) B1 grey squirrels compete with red squirrels for the same food and nesting sites (interspecific competition) oe
(c) B1 grey squirrels are generally more successful in this competition, leaving fewer resources for red squirrels, so fewer red squirrels survive and reproduce and their population falls oe
(c) Answer: Grey and red squirrels compete for the same food and nesting sites; grey squirrels tend to out-compete red squirrels for these resources, so fewer red squirrels survive and reproduce, causing their population to decline.

Question 10

(a) B1 choosing positions herself could introduce bias, e.g. by picking areas that look more or less covered in buttercup, which would not represent the whole paddock fairly oe
(a) Answer: Choosing positions herself could bias the results, for example by picking spots that look especially covered or bare, so random coordinates give a fairer sample of the whole paddock.
(b) B1 any valid controlled variable, e.g. size of quadrat, time of day, date/season the sampling is carried out
(b) Answer: The size of the quadrat used each time (or the date/time of sampling).
(c) M1 750 x 0.35 (or 750 x 35/100) seen
(c) A1 262.5 m² cao
(c) Answer: 262.5 m²
(d) B1 any valid improvement, e.g. use a larger number of quadrats (a bigger sample size)
(d) Answer: Use a larger number of quadrats across the paddock.
(e) B1 each small square represents 1% of the quadrat, so counting the squares containing buttercup gives a more precise numerical value than an estimate made by eye oe
(e) Answer: Each of the 100 small squares represents exactly 1% of the quadrat, so counting how many contain buttercup gives a precise percentage rather than a rough estimate by eye.

Question 11

(a) B1 population estimate = (number caught and marked in sample 1 x total number caught in sample 2) / number of marked individuals recaptured in sample 2 oe
(a) Answer: Population estimate = (number marked in sample 1 x number caught in sample 2) / number of marked individuals recaptured.
(b) M1 60 x 45 (= 2700) seen
(b) A1 300 (snails) cao, from 2700 / 9
(b) Answer: 300 snails
(c) B1 any valid assumption, e.g. no snails are born, die, enter or leave the garden between the two samples, or the marked snails mix randomly back into the population and the mark does not affect survival
(c) Answer: The population must not change (through births, deaths, migration in or out) between the two samples, and the marked snails must mix randomly with the rest of the population.

Question 12

B1 with otters removed, sea urchins are no longer preyed upon (predation pressure is reduced), so the sea urchin population increases oe
B1 more sea urchins means more grazing pressure on the kelp oe
B1 the kelp is eaten faster than it can regrow, so the kelp forest declines/is destroyed oe
B1 this affects other species that depend on the kelp forest for food or shelter, showing how the organisms in this ecosystem are interdependent oe
Answer: Sea urchin numbers increase because predation by otters has stopped; the urchins then over-graze the kelp, so the kelp forest declines, which in turn harms other species that depend on the kelp forest for food and shelter, showing the interdependence of the ecosystem.

Question 13

(a) B1 photosynthesis cao
(a) Answer: Photosynthesis.
(b) B1 respiration cao
(b) Answer: Respiration.
(c) B1 decomposition cao
(c) Answer: Decomposition.
(d) B1 any valid answer, e.g. burning fossil fuels (coal, oil or gas) in power stations, vehicles or homes; combustion oe
(d) Answer: Burning fossil fuels, for example coal, oil or gas in power stations or vehicles.
(e) B1 decomposers break down dead organisms and waste, releasing carbon dioxide into the air (by respiration) and other nutrients into the soil oe
(e) B1 producers can then take up this recycled carbon dioxide (for photosynthesis) and nutrients (for growth); without decomposers these nutrients would stay locked up in dead material oe
(e) Answer: Decomposers break down dead material, releasing carbon dioxide and nutrients that would otherwise stay locked away; producers can then take up this recycled carbon dioxide and nutrients for photosynthesis and growth.

Question 14

(a) B1 tree roots normally hold/bind soil particles together oe
(a) B1 with the roots gone, the exposed soil is more easily washed away by rain (or blown away by wind) oe
(a) Answer: Tree roots normally bind soil particles together; once the trees and roots are removed, the exposed soil is far more easily washed away by rain or blown away by wind.
(b) B1 trees take up water from the soil and release water vapour into the air through transpiration oe
(b) B1 with fewer trees, less water vapour enters the atmosphere, which can reduce local cloud formation and reduce rainfall oe
(b) Answer: Trees release large amounts of water vapour into the air through transpiration; with far fewer trees, less water vapour enters the atmosphere, which can reduce local cloud formation and rainfall.

Question 15

(a) M1 1.0 x 5 seen
(a) A1 5.0 ppm cao
(a) Answer: 5.0 ppm
(b) B1 25 (times) cao, from 5.0 / 0.2, ft from part a
(b) Answer: 25 times
(c) B1 the pesticide is not easily broken down or excreted, so it builds up in the body (often in fatty tissue) of each organism that eats contaminated prey oe
(c) B1 because the concentration increases at each trophic level, and top predators eat many organisms from lower levels over their lifetime, they accumulate the highest concentrations, which can reach harmful/toxic levels oe
(c) Answer: Because the pesticide is not broken down or excreted easily, it builds up in body tissue at every trophic level; top predators eat many contaminated organisms over their lifetime, so they end up with the highest, potentially toxic, concentrations.

Question 16

Level 1 (1-2): Basic, isolated statement(s), e.g. that animals lose their homes, or that carbon dioxide levels rise. Little or no linking between ideas. Limited use of scientific terms.
Level 2 (3-4): Some logical chain of reasoning given, linking habitat/biodiversity loss to reduced photosynthesis or increased atmospheric carbon dioxide. Most scientific terms used correctly, but the chain through to the greenhouse effect/climate change may be incomplete.
Level 3 (5-6): A clear, logically ordered chain of reasoning links habitat and biodiversity loss, reduced photosynthesis from losing producers, direct release of stored carbon by burning, the resulting rise in atmospheric carbon dioxide, and the enhanced greenhouse effect/climate change. Scientific terms used accurately throughout.
Indicative content:
- Clearing the rainforest destroys the habitat of many species, e.g. birds, insects and mammals.
- Loss of habitat reduces local biodiversity, and some species may become locally extinct.
- Removing producers (trees) means less photosynthesis takes place in that area.
- Less photosynthesis means less carbon dioxide is removed from the atmosphere.
- Burning the cleared trees releases the carbon stored in them directly into the atmosphere as carbon dioxide.
- These effects together increase the concentration of carbon dioxide in the atmosphere.
- Carbon dioxide is a greenhouse gas, so a higher concentration enhances the greenhouse effect, contributing to global warming and climate change.
- Clearing the forest for a single crop also disrupts existing food webs and the interdependent relationships between species in the ecosystem.

Question 17

(a) B1 a (line/belt) transect
(a) Answer: A (line) transect.
(b) B1 distance up the shore from the low water mark oe (or exposure time to air)
(b) Answer: Distance up the shore from the low water mark.
(c) M1 45 + 38 + 22 + 10 + 3 (= 118) seen
(c) A1 23.6 awrt (1 d.p.), from 118 / 5
(c) Answer: 23.6 barnacles per quadrat
(d) B1 the number of barnacles decreases as distance up the shore (from the low water mark) increases oe
(d) B1 higher up the shore, the rock is exposed to air for longer between tides, so there is a greater risk of the barnacles drying out (desiccation); barnacles are less able to survive this further up the shore oe
(d) Answer: The number of barnacles falls steadily further up the shore; this is because higher points are exposed to air for longer between tides, increasing the risk of the barnacles drying out, so fewer survive there.

Question 18

(a) M1 (1500 / 15 000) x 100 seen
(a) A1 10% cao
(a) Answer: 10%
(b) M1 (90 / 1500) x 100 seen
(b) A1 6% cao
(b) Answer: 6%
(c) B1 a large amount of energy is lost as heat through respiration (used for movement, keeping warm and other life processes) oe
(c) B1 energy is also lost in material that is not eaten (e.g. bones, fur, roots) or not digested (egested as faeces, or excreted in urine) oe
(c) Answer: Much of the energy is lost as heat from respiration, and further energy is lost in uneaten body parts or in undigested waste such as faeces and urine, so only a small fraction is ever converted into new biomass.

Question 19

B1 only sampling near the car park is not random, so the field is not sampled fairly/representatively oe
B1 conditions near the car park (e.g. more trampling, compacted soil, more light or disturbance at the field edge) may differ from the rest of the field, so dandelion numbers there may not represent the whole field oe
B1 this introduces bias into the results, so the population estimate calculated from this sample is likely to be inaccurate for the field as a whole oe
B1 improvement: use randomly generated coordinates (e.g. from a random number generator) to place the quadrat across the whole field, not just near the car park oe
Answer: Sampling only near the car park is not random and conditions there (e.g. trampling, compacted soil) may differ from the rest of the field, so the sample is biased and the resulting estimate is unlikely to be accurate for the whole field; Callum should use randomly generated coordinates to place his quadrat across the entire field instead.

Question 20

(a) B1 the white-letter hairstreak population would be predicted to decrease sharply oe
(a) B1 because the caterpillars rely entirely on elm leaves as their only food source, and adults need elm trees to lay eggs, so as elms die there is nowhere for eggs to be laid or for caterpillars to feed, and few new butterflies survive oe
(a) Answer: The white-letter hairstreak population would fall sharply, because its caterpillars feed only on elm leaves and its eggs are laid only on elm trees, so as elms die there is nowhere left for them to feed or reproduce.
(b) B1 in a mixed woodland, other tree species survive even though the elms die, so most of the tree cover and habitat remains oe
(b) B1 fewer other species in the food web depend entirely on elm, so the overall impact of losing elm on the wider community is smaller oe
(b) B1 in a woodland made up mostly of elm, almost all of the trees would be lost, causing much greater loss of habitat and food sources, with far bigger knock-on effects across the whole food web oe
(b) Answer: In a mixed woodland, other tree species survive the disease so most habitat remains, and fewer species depend entirely on elm, limiting the wider impact; in an elm-dominated woodland almost all the trees would be lost, causing far greater habitat and food loss with much bigger knock-on effects through the food web.

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Ecosystems and Interdependence - Worksheets, Questions and Revision

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