Revision Library

revisionlibrary.co.uk

GCSE · Biology

B7a Ecosystems, Adaptation and Feeding Relationships

AQA 8464 · Calculator allowed · about 80 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Useful Equations - B7a Ecosystems

Original text written for Revision Library.

Some useful equations for field-sampling calculations:

population estimate = mean number of organisms per quadrat x (total area of habitat / area of one quadrat)

percentage cover = (number of squares in a quadrat containing the organism / total number of squares in the quadrat) x 100

percentage energy (or biomass) transfer between trophic levels = (energy available to the next trophic level / energy available at the current trophic level) x 100

In most ecosystems, only around 10% of the energy taken in by an organism is transferred to the trophic level above it; the rest is lost, mainly through respiration, movement, and materials that are not eaten or not digested.

Ecosystems can be described using several levels of organisation.

(a)State what is meant by the term 'population'.(2)

(b)State what is meant by the term 'community'.(1)

(c)The terms 'organism', 'population', 'community' and 'ecosystem' each describe a different level of organisation. Write these four terms in order, starting with the smallest level of organisation and ending with the largest.(2)

(Total for Question 1 is 5 marks)

Six factors that can affect the organisms living in an ecosystem are listed below.
1 soil pH
2 number of predators
3 concentration of dissolved oxygen in a pond
4 wind intensity
5 presence of a new pathogen
6 competition for mates
Classify each factor as abiotic or biotic.

(Total for Question 2 is 3 marks)

Lesser celandine is a small woodland plant. It grows most of its leaves and produces its yellow flowers in early spring, then dies back to underground tubers by early summer, once the leaves on the deciduous trees above it have fully grown. Use your knowledge of light intensity and photosynthesis to explain why lesser celandine grows and flowers mainly in early spring.

(Total for Question 3 is 4 marks)

Give one biotic factor, other than predation, that could cause the population of wild rabbits in a field to decrease. Explain how this factor could reduce the rabbit population.

(Total for Question 4 is 2 marks)

Six adaptations that help animals survive in cold environments are listed below.
1 a thick layer of blubber under the skin
2 hibernating during the coldest months
3 producing antifreeze proteins in the blood
4 having white fur for camouflage
5 migrating to a warmer climate for winter
6 having a lower resting metabolic rate to conserve energy
Classify each adaptation as structural, behavioural or functional.

(Total for Question 5 is 3 marks)

Polar bears live in the Arctic, where air temperatures can fall below -30 C. Explain how two structural adaptations help polar bears to survive these cold conditions.

(Total for Question 6 is 4 marks)

Camels store fat in a hump on their back, rather than as a layer spread evenly under the skin like many other mammals. Suggest why storing fat in this way is an advantage for camels living in hot desert conditions.

(Total for Question 7 is 2 marks)

State what is meant by the term 'extremophile', and give one example of an extreme environment in which extremophiles live.

(Total for Question 8 is 2 marks)

Some bacteria that live in hot springs at temperatures of around 80 C produce enzymes that continue to work at this temperature, unlike the enzymes of most other organisms, which would denature. Suggest one reason why these heat-tolerant enzymes are useful in industrial or scientific processes.

(Total for Question 9 is 2 marks)

Priya grows vegetables in her garden. She notices the following feeding relationships: cabbage plants are eaten by caterpillars; caterpillars are eaten by blue tits; blue tits are eaten by sparrowhawks.

(a)Use these four organisms to construct a food chain. Use arrows to show the direction of energy transfer.(2)

(b)Identify the producer and the tertiary consumer in this food chain.(2)

(c)The caterpillars in the garden have a total of 6200 kJ of energy stored in their biomass. Only 10% of this energy is transferred to the blue tits that eat them. Calculate the energy transferred to the blue tit population.(2)

(d)Explain why less than 100% of the energy available in the caterpillars is transferred to the blue tits.(3)

(Total for Question 10 is 9 marks)

In a farmland food web: cereal seeds are eaten by field voles and by wood mice; field voles and wood mice are both eaten by kestrels and by barn owls. A cold, wet spring causes a sharp decline in the wood mouse population. Predict two effects this could have on the population of kestrels, and explain your answers.

(Total for Question 11 is 4 marks)

Explain why a food web gives a more complete picture of the feeding relationships in an ecosystem than a single food chain does.

(Total for Question 12 is 2 marks)

The table shows estimated snowshoe hare and Canada lynx population sizes, in the same area of forest, over a 10-year period.
Year 1: hares 20000, lynx 800
Year 2: hares 55000, lynx 1200
Year 3: hares 90000, lynx 3000
Year 4: hares 60000, lynx 4500
Year 5: hares 25000, lynx 3500
Year 6: hares 15000, lynx 1500
Year 7: hares 30000, lynx 900
Year 8: hares 65000, lynx 1400
Year 9: hares 95000, lynx 3200
Year 10: hares 55000, lynx 4200

(a)Describe the relationship shown between the changes in the hare population and the changes in the lynx population.(2)

(b)Explain why changes in the population of Canada lynx lag behind changes in the population of snowshoe hares.(6)

(Total for Question 13 is 8 marks)

Aaliyah wanted to compare the abundance of creeping buttercup plants in a sunny, open part of the school field with a shaded part underneath a large oak tree. She used a quadrat measuring 1 m x 1 m.

(a)Describe how Aaliyah should use the quadrat to collect random samples of creeping buttercup in each part of the field.(3)

(b)In the sunny area, Aaliyah counted the number of creeping buttercup plants in 10 quadrats. Her results were: 8, 12, 6, 10, 14, 8, 10, 8, 12, 12. Calculate the mean number of creeping buttercup plants per quadrat.(2)

(c)The area of the sunny part of the field is 250 m^2. Estimate the total population of creeping buttercup plants in this part of the field.(3)

(d)Explain why using randomly generated coordinates to position the quadrats, rather than Aaliyah choosing positions by eye, gives a more valid estimate of the buttercup population.(2)

(Total for Question 14 is 10 marks)

Callum thought that light intensity affected where white clover grew in a field bordered by a tall, dense hedge. He wanted to investigate how the percentage cover of white clover changed with distance from the hedge.

(a)Name the sampling technique Callum should use to investigate how the percentage cover of white clover changes with distance from the hedge.(1)

(b)Describe how Callum could use this technique, together with a light meter, to collect suitable data.(4)

(c)At one point along the transect, a quadrat was divided into 100 equal squares. White clover was present in 37 of these squares. Calculate the percentage cover of clover at this point.(2)

(d)Callum's results showed that the percentage cover of white clover was much lower close to the hedge than in the open field. Use your knowledge of photosynthesis to suggest an explanation for this pattern.(3)

(Total for Question 15 is 10 marks)

Mark scheme · B7a Ecosystems, Adaptation and Feeding Relationships

Question 1

(a) B1 refers to all the organisms of one species (oe)
(a) B1 living in the same area (habitat) at the same time (oe)
(a) Answer: All the organisms of one species living in the same area (habitat) at the same time.
(b) B1 all the populations of different species living in the same area (habitat) at the same time (oe)
(b) Answer: All the populations of different species living in the same area (habitat) at the same time.
(c) B1 organism placed first (smallest) and ecosystem placed last (largest)
(c) B1 population placed before community, as the second and third terms respectively
(c) Answer: organism, population, community, ecosystem

Question 2

B3 5 or 6 factors correctly classified (abiotic: soil pH, dissolved oxygen concentration, wind intensity; biotic: number of predators, presence of a new pathogen, competition for mates)
B2 3 or 4 factors correctly classified
B1 1 or 2 factors correctly classified
Answer: Abiotic: soil pH, concentration of dissolved oxygen, wind intensity. Biotic: number of predators, presence of a new pathogen, competition for mates.

Question 3

B1 in early spring, the deciduous trees above have no leaves (bare branches), so light intensity reaching the woodland floor is high
B1 lesser celandine can absorb more light for photosynthesis at this time, allowing it to produce enough glucose to grow quickly and flower
B1 by early summer, the tree leaves have fully grown and form a canopy that blocks/absorbs much of the light
B1 light intensity reaching the woodland floor falls, limiting the rate of photosynthesis, so the plant cannot produce enough glucose to keep growing above ground and instead survives as an underground tuber, oe
Answer: In early spring there is high light intensity on the woodland floor because the trees have no leaves, allowing lesser celandine to photosynthesise quickly and grow/flower; once the tree canopy is in full leaf by summer, light intensity falls, limiting photosynthesis, so the plant dies back and survives underground as a tuber instead.

Question 4

B1 a suitable biotic factor named, e.g. a new disease/pathogen spreading through the population, or increased competition (with other rabbits or another herbivore species) for food
B1 a linked explanation, e.g. disease increases the death rate/reduces reproduction in the population; or competition means less food is available per rabbit, reducing survival and reproduction rates, oe
Answer: For example, a new disease spreading through the population (a biotic factor) could increase the death rate and reduce the rabbits' ability to reproduce, lowering the population.

Question 5

B3 5 or 6 adaptations correctly classified (structural: thick blubber, white fur; behavioural: hibernating, migrating; functional: antifreeze proteins, lower metabolic rate)
B2 3 or 4 adaptations correctly classified
B1 1 or 2 adaptations correctly classified
Answer: Structural: thick layer of blubber, white fur. Behavioural: hibernating, migrating to a warmer climate. Functional: antifreeze proteins, lower resting metabolic rate.

Question 6

B1 adaptation 1 named: a thick layer of fat (blubber) under the skin
B1 explanation: the blubber acts as an insulating layer, reducing the rate of heat loss from the body, oe
B1 adaptation 2 named: a compact, rounded body shape with small ears (a relatively small surface area)
B1 explanation: this gives a small surface area to volume ratio, which reduces the rate of heat loss from the body, oe
Answer: A thick layer of blubber under the skin insulates the body and reduces heat loss; a compact, rounded body with small ears gives a small surface area to volume ratio, which also reduces heat loss.

Question 7

B1 if fat were spread evenly under the skin, it would act as an insulating layer over the whole body, trapping heat inside
B1 storing the fat in one place (the hump) leaves the rest of the body without this insulating layer, so heat can be lost more easily through the skin, helping the camel avoid overheating, oe
Answer: If fat were spread under the skin it would insulate the whole body and trap heat in; keeping it in a hump leaves the rest of the skin free to lose heat easily, helping the camel avoid overheating in the desert heat.

Question 8

B1 an organism (often a microorganism/bacterium) that is adapted to live in conditions of extreme temperature, pressure, salt concentration or pH, oe
B1 a suitable example environment, e.g. deep-sea hydrothermal vents, hot springs, or highly salty lakes
Answer: An extremophile is an organism adapted to live in conditions of extreme temperature, pressure, salt concentration or pH, for example in deep-sea hydrothermal vents or hot springs.

Question 9

B1 reactions that require a high temperature can be carried out without the enzyme denaturing, oe
B1 elaboration, e.g. the enzyme does not need to be replaced repeatedly during a long or repeatedly heated process (such as the polymerase chain reaction, PCR), making the process more efficient/reliable, oe
Answer: The enzyme will not denature at high temperatures, so reactions that need heat (for example, the repeated heating steps in the polymerase chain reaction, PCR) can be carried out without needing to keep replacing the enzyme.

Question 10

(a) B1 all four organisms included, in a logical feeding order
(a) B1 arrows drawn correctly, in the direction of energy transfer (from each organism to what eats it)
(a) Answer: cabbage plant -> caterpillar -> blue tit -> sparrowhawk
(b) B1 producer correctly identified: cabbage plant, ft from (a)
(b) B1 tertiary consumer correctly identified: sparrowhawk, ft from (a)
(b) Answer: Producer = cabbage plant. Tertiary consumer = sparrowhawk.
(c) M1 6200 x (10/100), oe
(c) A1 620 kJ cao
(c) Answer: 620 kJ
(d) B1 some energy is lost as heat, released during respiration (used for movement and, in the endothermic blue tits, to maintain a constant body temperature)
(d) B1 not all parts of the caterpillars are eaten, or are not digested, and are egested as faeces/waste material
(d) B1 some energy is used for the caterpillars' own life processes (e.g. movement, growth of body parts that are not eaten) before they are eaten, oe
(d) Answer: Energy is lost as heat from respiration (used for movement and, in blue tits, keeping warm), in undigested material egested as faeces, and in the caterpillars' own life processes before being eaten, so only a small proportion of the total energy is passed on.

Question 11

B1 effect 1: the kestrel population may fall (or some kestrels may struggle to find enough food)
B1 linked explanation: because there is less food available for kestrels overall, as one of their two prey species has declined, oe
B1 effect 2: the kestrel population might not change very much / may stay fairly stable
B1 linked explanation: because kestrels can instead eat more field voles (an alternative food source), so they are not solely dependent on wood mice, oe
Answer: The kestrel population could fall, because there is less food available overall with fewer wood mice; alternatively, it might stay fairly stable, because kestrels can rely more heavily on field voles as an alternative food source instead.

Question 12

B1 a food web shows that most organisms eat, and are eaten by, more than one other species, by combining several interconnected food chains, oe
B1 this means it also shows what could happen to a population if one of its food sources or predators changes/declines (e.g. alternative food sources are shown), which a single food chain cannot show, oe
Answer: A food web combines several interconnected food chains, showing that most organisms have more than one food source or predator; this means it can also show what might happen to a population if one food source or predator changes, unlike a single food chain.

Question 13

(a) B1 both populations rise and fall in a repeating (cyclical) pattern over the 10 years
(a) B1 the changes in the lynx population follow the same pattern as the hare population, but lag behind by about a year (e.g. hares peak in year 3, but lynx peak in year 4)
(a) Answer: Both populations show a repeating, cyclical rise-and-fall pattern, with the lynx population's changes lagging around a year behind the same changes in the hare population.
(b) L3 (5-6): A clear, logically sequenced explanation of the full predator-prey cycle, correctly linking food availability to changes in the lynx population and explaining the time lag in both the rise and the fall of lynx numbers.
(b) L2 (3-4): The explanation links food availability to changes in the lynx population and refers to a time lag, but the chain of reasoning is incomplete or not fully sequenced (e.g. only the rise, or only the fall, is explained fully).
(b) L1 (1-2): Basic, largely isolated statements are made about the link between hares and lynx (e.g. 'lynx eat hares'), with little or no reference to a time lag or mechanism.
(b) L0 (0): No relevant content.
(b) Answer: Levels of response question - no single correct answer; credit a clear, logically sequenced explanation covering how hare numbers affect lynx food supply and breeding success, and how the resulting change in lynx numbers (after a delay) then affects hare numbers through predation, completing the cycle. See indicative content.

Question 14

(a) B1 mark out a grid across each study area, e.g. by laying two tape measures at right angles, to create a set of coordinates
(a) B1 use a random number generator (or random number table) to generate pairs of coordinates
(a) B1 place the quadrat at each randomly generated coordinate and count/record the number of buttercup plants inside it, repeating for a suitably large number of quadrats (e.g. at least 10) in each area, oe
(a) Answer: Mark out a grid of coordinates across each area, use a random number generator to pick coordinate pairs, then place the quadrat at each randomly chosen point and count the buttercups inside, repeating for at least 10 quadrats in each area.
(b) M1 total = 100 (sum of the 10 counts), divided by 10
(b) A1 10.0 (buttercups per quadrat) cao
(b) Answer: 10.0 creeping buttercup plants per quadrat.
(c) M1 number of 1 m² quadrats needed to cover the whole area = 250 / 1 (= 250), ft from (b)
(c) M1 population estimate = mean count per quadrat x number of quadrats
(c) A1 2500 creeping buttercup plants, allow ecf from the student's mean in part (b)
(c) Answer: Approximately 2500 creeping buttercup plants.
(d) B1 choosing positions by eye could introduce bias, e.g. Aaliyah might unconsciously choose areas that look like they have more (or fewer) buttercups
(d) B1 random positioning means every part of the area has an equal chance of being sampled, so the sample is more likely to be representative of the whole area, giving a more valid estimate, oe
(d) Answer: Choosing quadrat positions by eye could introduce bias, for example by unconsciously picking areas with more or fewer buttercups; random coordinates give every part of the area an equal chance of being sampled, so the estimate is more likely to be representative and valid.

Question 15

(a) B1 a belt transect (accept 'transect')
(a) Answer: A belt transect.
(b) B1 lay a tape measure (or string) in a straight line from the hedge out into the open field
(b) B1 starting at the hedge, place a quadrat at regular intervals along the tape (e.g. every 2 m)
(b) B1 at each point, record the percentage cover of white clover within the quadrat, e.g. using a quadrat with a grid of numbered squares to help estimate cover
(b) B1 at each of the same points, measure and record the light intensity using a light meter/data logger, held at the same height and angle each time, oe
(b) Answer: Lay a tape measure in a straight line from the hedge into the field, and place a quadrat at regular intervals (e.g. every 2 m) along it. At each point, record the percentage cover of clover using a gridded quadrat, and measure light intensity with a light meter held at the same height and angle each time.
(c) M1 (37/100) x 100, oe
(c) A1 37% cao
(c) Answer: 37%
(d) B1 close to the hedge, the tall hedge blocks/shades light, so light intensity is lower there than further into the open field
(d) B1 light is needed, along with carbon dioxide and water, for photosynthesis, so a lower light intensity limits the rate of photosynthesis near the hedge
(d) B1 this means white clover near the hedge produces less glucose for growth, so fewer/smaller clover plants survive there, giving a lower percentage cover than in the open field, where higher light intensity allows a faster rate of photosynthesis and more growth, oe
(d) Answer: Close to the hedge, shading reduces light intensity, which limits the rate of photosynthesis; with less glucose produced for growth, fewer clover plants can survive there, giving lower percentage cover than further into the open field, where light intensity (and so photosynthesis and growth) is greater.

Ecosystems, Adaptation and Feeding Relationships - Worksheets, Questions and Revision