1.

Study the passage and data below and then answer the questions that follow. Grazing in the Serengeti grassland The Serengeti is a huge area of tropical grassland in Tanzania. Herds of grazing mammals, such as wildebeest, gazelle and zebra, roam freely. Every year, these herds migrate across the Serengeti, in search of fresh grassland. The grazing mammals affect the primary productivity of the grassland. Long-term research has found that the rate of primary production is linked to both the rainfall and the numbers of grazing mammals.

-

Figure 1 Map of Africa showing the location of the Serengeti

Figure 2 A wildebeast, one of the many types of grazing mammal found in the Serengeti

Grazing can increase the growth rate of many grass species. This is called compensatory growth. The grazing mammals remove the upper parts of the grass leaves and this increases the amount of light reaching the rest of the plant. The smaller leaf area reduces transpiration and this decreases the uptake of water by the roots. Researchers investigated compensatory growth of grasses in a region of the Serengeti. They fenced off several areas to prevent mammals from grazing the grass. During the annual migration, thousands of wildebeest moved into the study region where they grazed intensively for 4 days and then moved on. The researchers recorded the changes in the fresh biomass of the grasses in the grazed and ungrazed areas over the next 32 days (Figure 3). A further investigation studied the effect of grazing intensity on primary productivity (Figure 4).

1

Figure 3 Table showing the fresh biomass over a 32 day period on grazed and ungrazed grassland. Day I is the first day after the wildebeest moved on.

D ay G ra z e d 1 8 16 24 32 50 55 100 120 200

F re s h b io m a s s / g m

2

U n g ra z e d 430 420 380 350 300

Figure 4 Graph to show the effect of grazing intensity on the primary productivity of Serengeti grassland P ro d u c tiv ity / g m 900 800 700 600 500 400 300 200 100 0 0 .0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 0 .7 0 .82

year

1

G r a z in g in te n s ity / a r b itr a r y u n its

(a)

Define the terms biomass and productivity. Biomass ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... Productivity ..................................................................................................................................... .....................................................................................................................................(2)

(b)

(i) Using the data in Figure 3, calculate the mean rate of change of fresh biomass per day, for both the grazed and ungrazed grassland, between days 1 and 32. Show your working.

Grazed grassland......................................... Ungrazed grassland.....................................(4)

(ii)

Suggest why the fresh biomass of grass in the ungrazed area decreased. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)

3

(c)

Study the information provided in Figure 4 (i) What is the optimum grazing intensity for Serengeti grassland? ..........................................................................................................................(1)

(ii)

Suggest reasons for the very low levels of primary productivity at the highest grazing intensity (0.8 arbitrary units). ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)

(d)

In the Serengeti, lions are the top consumers. Suggest and explain how a fall in the number of lions could affect the Serengeti food chain and grassland productivity. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(3)

(e)

The grazing mammals have an important role to play in the recycling of nutrients on the grassland. Their dung is rich in organic nitrogen-containing compounds. Describe how these compounds are converted to nitrates. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(4) (Total 20 marks)

2.

Scientists estimate that the atmosphere holds 755 gigatonnes (Gt) of carbon, mostly as carbon dioxide. This value is increasing each year as a result of human activities, such as the burning of fossil fuels and of timber. The diagram below shows a simplified balance sheet of the carbon cycle for one year. 5 .5 G t B u r n in g o f fo s s il fu e ls V o lc a n ic e ru p tio n s 0 .1 G t A tm o s p h e ric c a rb o n (7 5 5 G t) 90 G t 1 .6 G t B u rn in g o f tim b e r 120 G t R e s p ira tio n P h o to s y n th e s is 121 G t 93 G t O c e a n ic p ro cesses

5

(a)

Calculate the increase in atmospheric carbon during this year. Show your working.

Answer ..............................................................(3)

(b)

Describe and explain how carbon can be removed from the terrestrial (land based) part of the cycle for long lengths of time. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................(4)

(c)

By reference to the information in the cycle, suggest reasons for the net effect of oceanic processes on the carbon content of the atmosphere. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................(4)

(d)

Suggest how the quantities of carbon dioxide released by the combustion of fossil fuels could be reduced. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... ....................................................................................................................................(3) (Total 14 marks)

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3.

The table below shows the size of the populations, and the numbers and percentages of the population that are infected with HIV, in five southern African countries. Country Population (thousands) Population aged 1549 (thousands) 20 982 786 795 1 000 468 HIV % of total infected population people with HIV (thousands) 4 200 290 160 240 130 13.3 10.5 18.2 % of adults with HIV % of female adults aged 1549 with HIV 54.8 51.2 53.1 54.2 51.5

South Africa Botswana Namibia Lesotho Swaziland

39 900 1 597 1 695 2 108 980

20.0 35.8 19.5 23.6 25.3

(a)

Complete the table by calculating the percentage of the total population with HIV in Namibia and Lesotho.(1)

(b)

Using the information in the table, explain the significance of the percentage of females aged 15 to 49 who are infected with HIV. ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................(2)

(c)

Suggest how the structure of the population of South Africa will change in the future. Explain your answer. ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................ ............................................................................................................................................(2) (Total 5 marks)

4.

Coral reefs are formed and maintained by very large numbers of simple animals called polyps. These polyps have single-celled algae (simple photosynthetic organisms) living inside their cells. It is thought that when the sea is too warm the relationship between the coral polyps and the algae breaks down, and the reef begins to look white (becomes bleached). If the sea temperature falls again within a few weeks then the coral polyps and the algae reunite. If it does not, then the coral polyps die. In 1998, 16% of the worlds coral reefs showed some bleaching. Half of these damaged reefs are now recovering. The Great Barrier Reef off the east coast of Australia has been badly bleached in the last few years. The average sea temperature on the reef has increased by 0.3 C in the last century. It is feared that southern and central sections of the Great Barrier Reef are likely to be severely affected by sea temperature rises in the next 20-40 years.

(a)

Name a method by which global sea temperatures can be monitored. .....................................................................................................................................(1)

(b)

Suggest how the algae normally help the coral polyps to survive. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

(c)

Some recovery in the Great Barrier Reef may be taking place at present. Suggest a possible explanation for this, other than change in sea temperature. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2) (Total 5 marks)

9

5.

The possible effects of global warming on the growth of Arctic shrubs were investigated using small portable greenhouses in which dwarf birch trees were grown. (a) Suggest three factors, other than temperature, which would be affected by enclosing a plot of land inside one of these greenhouses. 1 .................................................................................................................................. 2 .................................................................................................................................. 3 ..................................................................................................................................(3)

(b)

The diagram below shows the wood of one of the dwarf birch trees used in the experiment, as seen in transverse section under a microscope. Inorganic ions (fertiliser) were added to the soil while the tree was growing. The white arrows indicate the wood that was formed just before the fertiliser was added.

(i)

Name the method by which tree rings can be used to make deductions about the climate in the past. ...........................................................................................................................(1)

(ii)

Describe the change in growth following the addition of the fertiliser. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2)

(c)

Describe a technique which could be used to provide evidence that dwarf birch became more abundant 9000 years ago during an earlier period of global warming. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

...........................................................................................................................

(d)

Explain why a large increase in growth of trees may help to reduce the amount of global warming in future. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

11

(e)

Explain why an increase in the temperature of the soil (such as that due to global warming) would affect the decay of plant material in Arctic soils. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2) (Total 12 marks)

6.

The graph below shows changes in the biomass of trees during 240 years at a site undergoing 1 primary succession. Biomass was measured in tonnes per hectare (tonnes ha ). 3 5 0

3 0 0 B i o m a s s / t o n n e s h a 2 5 0 H 2 1 1 5 0 0 5 0 0 0 T i m e 0 0 0 4 0 s i n c e 8 0 s u 1 2 0 c c e s s i o 1 n b 6 e g 0 a n 2 / y 0 0 e a S W A p e m r u i l l o l d e r l o c e w c k s p r u c

(a)

Using the information in the graph, explain the meaning of the term succession. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

(b)

Describe the changes in the total biomass of the trees between 0 and 240 years. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(3)

(c)

Suggest why hemlock spruce is not present until 160 years after the start of the succession. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2) (Total 7 marks)

7.

(a) Describe a technique for determining the abundance of a named organism in a habitat that you have studied. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(4)

13

(b)

Mussels are animals found on rocky seashores. They are enclosed in two hard shells that can be clamped together very tightly. Adult mussels attach themselves firmly to the rocks and do not move around.

Ecoscene/Kevin King

A study was carried out to investigate the distribution of mussels on a rocky shore that has a freshwater stream running across it into the sea. The sea level rises and falls twice every day, between low water level A and high water level B. The sketch map below shows the shore between the low water level and the high water level, the freshwater stream and the six sites where the adult mussels were sampled.

The numbers of mussels found at each of the sites are shown in the table below. Site Number of mussels 1 3 2 5 3 15 4 22 5 20 6 2

(i)

Describe how the freshwater stream affects the distribution of the mussels. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2)

15

(ii)

Suggest two possible reasons for this distribution. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2)

(c)

Mussels are preyed upon by marine snails called dog whelks. A dog whelk crawls on to a mussel and takes one or two days to make a hole in the shell before it can eat the mussel inside.

Life sizeEcoscene/Chinch Gryniewicz

The numbers of dog whelks found at each of the sites are shown in the table below. Site Number of dog whelks 1 7 2 8 3 1 4 0 5 0 6 4

Suggest how the abiotic and biotic factors referred to in this question determine the distribution of the dog whelks on this seashore. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(3) (Total 11 marks)

17

8.

Measurements were made of the rate of energy flow in an ecosystem. The results are shown in the table below. Energy/ kJ m yr Energy fixed by photosynthesis Energy used in plant respiration Energy in new biomass of primary consumers 1.9 10 1.1 10 0.1 104 2 1

4

4

(a)

(i) working.

Calculate the net primary productivity in this ecosystem. Show your

Answer ...............................(2)

(ii)

Use the information in the table and your answer from (a)(i) to calculate the percentage efficiency of energy transfer from the plants to the primary consumers. Show your working.

Answer ...............................(2)

(b)

Give two reasons why not all of the energy fixed by the plants can be used to form biomass in the consumers. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2) (Total 6 marks)

9.

Wiithin Lake Washington, two distinct populations of salmon are evolving. The populations live in different areas of the lake and breed at different times of the year.

(a)

Explain why there is likely to be little transfer of genes between the two populations...................................................................................................................................... .....................................................................................................................................(1)

(b)

Explain how natural selection could result in the two populations becoming separate species. You should answer this question in continuous prose. (Allow one lined page).(7)

(c)

Suggest reasons why some people might not accept that species have arisen by the process of evolution.19

..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2) (Total 10 marks)

10.

The digestive processes of ruminant animals produce the gases methane and carbon dioxide. A study was carried out in Virginia, USA, to determine the methane and carbon dioxide emissions from cattle and sheep. The results of this study are shown in Figure 1 below. Figure 1 Table showing the emissions of methane and carbon dioxide from cattle and sheep in 1990 and 1996. Methane emissions 1 /tonnes year 1990 Beef cattle Dairy cattle Sheep Total % Increase 45 897 11 537 976 58 410 1996 52 626 10 108 672 63 406 8.6 Carbon dioxide 1 emissions/tonnes year 1990 126 217 31 727 2 628 160 572 1996 144 723 29 144 1 848 175 715

Both methane and carbon dioxide are greenhouse gases. Greenhouse gases vary in their potential warming effect. Figure 2 shows the global warming potential (GWP) of greenhouse gases relative to carbon dioxide.

Figure 2 Table comparing the global warming potential of four greenhouse gases. Greenhouse gas Carbon dioxide Methane Nitrous oxide CFC-11 Global Warming Potential (GWP) 1 21 206 3400

The percentage contribution of the different greenhouse gases to global warming has changed since 1880. These changes are shown in Figure 3. Figure 3 Pie charts showing the percentage contribution of different greenhouse gases to global warming. ( a ) 1 8 8 e r 0 1 9 7 9 ( b O ) t h 1 9 8 0 1 9 8 9

O t h N i t r o u s o x i d e s C F C s

e r

N i t r o u s o x i d e s C F C s C a r b o n d i o x i d e

M

e t h

a n

e C d

a r b o n i o x i d e

M

e t h

a n

e

(a)

Describe how cellulose in grass is digested in a ruminant animal. (3)

(b)

Using the data in Figure 1, calculate the percentage increase in the carbon dioxide emissions between 1990 and 1996. Show your working.

Answer ..............................(2)

21

(c)

Describe the changes in the emissions of methane and carbon dioxide between 1990 and 1996 as shown in Figure 1. Suggest reasons for these changes. (3)

(d)

The digestive processes of ruminant animals are not the only sources of methane and carbon dioxide in the atmosphere. State one other source of each of these gases in the atmosphere. Methane ........................................................................................................................ Carbon dioxide .............................................................................................................(2)

(e)

Explain the importance of greenhouse gases in the atmosphere and explain how a change in the concentration of these gases can lead to global warming. (3)

(f)

Using the information provided in Figure 2, explain how an increase in methane concentration in the atmosphere can have more effect than the same increase in carbon dioxide concentration. (2)

(g)

Carbon dioxide emissions increased after 1980. (i) Explain why the percentage contribution of carbon dioxide to global warming decreased as shown in Figure 3. (1)

(ii)

Explain how human activities could have been responsible for the changes since 1980 in methane, CFCs and nitrous oxides, as shown in Figure 3. (3) (Total 19 marks)

23

11.

(a)

Explain the meaning of the term speciation.

(2)

(b)

Using suitable examples, explain how sympatric speciation differs from allopatric speciation. (4) (Total 6 marks)

12.

There is widespread concern about the possible effects of human activities on global warming. (a) State two sources of evidence that global warming has been increasing over the past 150 years. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

(b)

Dinosaurs became extinct about 65 million years ago, possibly because of climate change resulting from the impact of a meteorite with the Earth. (i) Suggest how this impact might have caused the extinction of the dinosaurs. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)

(ii)

Give one alternative explanation that has been proposed by reputable biologists to explain the mass extinction of the dinosaurs. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2)

(c)

Climate change could mean extinction for many of Britains rare species of plants and animals. Suggest how rare species which do not become extinct may be affected by global warming. ..................................................................................................................................... .....................................................................................................................................(1)

25

(d)

Recent global warming might be the result of an increase in greenhouse gases in the atmosphere, related to the burning of fossil fuels by human activity since the Industrial Revolution. (i) Name two greenhouse gases other than carbon dioxide. 1 ........................................................................................................................ 2 ........................................................................................................................(2)

(ii)

Give one explanation for recent global warming other than burning fossil fuel. ........................................................................................................................... ...........................................................................................................................(1) (Total 11 marks)

13.

A student investigated the decomposition of leaves from a sweet chestnut tree. In November 1988, she placed an equal number of leaves in nylon bags with three different mesh sizes. The bags were then buried in garden soil. A fourth sample was placed in a mesh bag and suspended in the air. She examined the bags at intervals of six months and made estimates of the percentage of leaves that remained before reburying the bags. Her results are shown in Figure 1. Figure 1 The percentage of sweet chestnut leaves remaining in nylon bags of differing mesh size over a period of two and a half years. Percentage of sweet chestnut leaves remaining in the bags Sample 0.05 mm mesh bag in soil 1 mm mesh bag in soil 5 mm mesh bag in soil 0.05 mm mesh bag in air November 1988 100 100 100 100 May 1989 62 62 33 96 November 1989 60 38 10 92 May 1990 51 30 10 88 November 1990 42 30 10 84 May 1991 38 29 10 80

In another investigation, the nitrogen content of leaves from six species of tree was measured. Some fresh leaves from these trees were then placed in separate nylon bags with a 5 mm mesh and buried in garden soil in July. The bags were examined after four months and the percentage of the leaves remaining was recorded. The results of this investigation are shown in Figure 2. Figure 2 A scattergraph showing the relationship between the percentage of leaves remaining after four months and the nitrogen content of the leaves. 1 0 9 8 7a 6s 5n n 4 3 2 1 0 0 0 C P i n e 0 g0 e 0 a f t e r 0g t h s 0 0 0 0 0 0 N h B e r r y i r c h S w e e t C O h Se sy t c n a u m t a k o r e

P e r c e n t o f l e a v e r e m a i n i f o u r m o

. 5 i t r o g

1 e n c o n

1

. 5 t e n

2 t o f l e a v e s / %

(a)

(i) Using the information in Figure 1, compare the breakdown of the sweet chestnut leaves in the four bags between November 1988 and May 1991. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................(4)

27

(ii)

Suggest an explanation for the differences that you have described in (a)(i). ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................(2)

(b)

Using the information in Figure 2, describe the relationship between the nitrogen content of the leaves and the decomposition of the leaves. Suggest a reason for this relationship. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................................(2)

(c)

Coniferous forests in Northern Europe have long cold winters and short warm summers. Tropical rain forests are found in the hot and wet regions of the world. Coniferous forests have a thick layer of pine needles (leaves) lying on the forest floor. Tropical rain forests have relatively few leaves lying on the forest floor. Suggest reasons for this difference. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................................(3)

(d)

The organic nitrogen in fallen leaves is eventually converted into nitrates. Describe the role of soil microorganisms in this process. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................................(3) (Total 14 marks)

14.

The diagram below shows a simplified carbon cycle.

(a)

Each box represents a process. Write the name of the process in each of the boxes A, B, C and D.(2)

29

(b)

With reference to an example, explain what is meant by the term carbon sink. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ......................................................................................................................................(2)

(c)

(i) The increase in the concentration of carbon dioxide in the atmosphere has been linked to global warming. Explain what is meant by the term global warming. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................(2)

(ii)

Name two gases, other than carbon dioxide, which are thought to contribute to global warming. 1. ............................................................................................................................ 2. ............................................................................................................................(2) (Total 8 marks)

15.

The Isthmus of Panama is a strip of land that separates the Pacific Ocean from the Atlantic Ocean in Central America. The map below shows the Isthmus of Panama.

The pictures below show two species of fish known as wrasse.

Blue-headed wrasse (Thallassoma bifasciatum)

Rainbow wrasse (Thallassoma lucasanum)

31

The blue-headed wrasse is found in the coral reefs on the Atlantic side of the isthmus and the rainbow wrasse is found in the reefs on the Pacific side of the isthmus. It has been shown that both of the species are descended from a common ancestral population that was split as the isthmus formed. (a) Explain why the blue-headed wrasse and the rainbow wrasse are described as different species. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................................(2)

(b)

Suggest how analysis of DNA or proteins might be used to supply additional evidence that these species have descended from a common ancestor. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................................(2)

(c)

Explain how the splitting of the common ancestral population into an Atlantic population and a Pacific population have led to the formation of these two separate species. ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... ....................................................................................................................................... .......................................................................................................................................(5) (Total 9 marks)

16.

Changes in the global environment are investigated using remote sensing techniques. (a) Describe and explain what is meant by remote sensing. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(3)

33

(b)

Describe two kinds of data commonly collected by remote sensing which can be used by scientists studying climate change and its effects. ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

(c)

Techniques such as remote sensing have been available only in recent times. Information from dendochronology is usually limited to the past 1000 years. Apart from dendochronology, explain how scientists can investigate ecological changes over the past 12 000 years. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(4) (Total 9 marks)

17.

The diagram below summarises the carbon cycle. C i n a r b o n d t h e a t m i o x i d o s p h e e r e C B B D U s e d a s a m i n a p o w e r p r o d u c i n g e e c a y f ui c e r l o s t a t i l e c t r e d b b e s o n i c i t y y

F

o

s s i l

f u

e l As

P

l a n

t

b

i o

m

a s s

(a)

(i)

Name the processes A, B and C.

A ....................................................................................................................... B ....................................................................................................................... C .......................................................................................................................(2)

(ii)

Suggest a type of plant biomass that is used as a source of energy in some power stations as an alternative to fossil fuels. ...........................................................................................................................(1)

(b)

The use of biomass is considered to be sustainable whereas using fossil fuels is not sustainable. (i) State the meaning of sustainable. ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(1)

35

(ii)

Suggest why using plant biomass to generate electricity is thought to be more sustainable than using fossil fuel. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)

(c)

The diagram below shows an experiment to test the hypothesis that carbon dioxide is a greenhouse gas. E l e c t r i c a l c o n n e c t i o n s

T e m p e r a t u p r o b e s

r e

A t m a i r

o

s p

h

e r i c G l a s s b o t t l e s

A i r e n r i c h e d w c a r b o n d i o x i d e s o d a - w a t e r s y p

i t f h o

Name two pieces of equipment not shown in the diagram that you would need to complete the experiment. ..................................................................................................................................... .....................................................................................................................................(2)

(d)

Some scientists think that global warming will increase the rate of decay of dead biomass. (i) Suggest why global warming might increase the rate of decay. ........................................................................................................................... ...........................................................................................................................(1)

(ii)

Explain one reason why an increase in the rate of decay might increase the rate of global warming even more. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2) (Total 12 marks)

18.

A model ecosystem was set up in an aquarium. Organisms from three trophic levels were introduced and left until their population sizes were fairly constant. All of the organisms were then collected and the total biomass of each species was measured. The energy content per gram of the biomass was then measured. The table below summarises the data collected. Total biomass collected / g Species A Species B Species C 3000 80 140 Energy content per gram / kJ 0.5 1.5 0.1 Total energy from biomass / kJ 1500

(a)

(i) Complete the table by calculating the total energy from biomass of species B and C.(1)

37

(ii)

Calculate the total energy from biomass for species C as a percentage of that found for species B. Show your working.

Answer ....................................(2)

(b)

Explain how the data above support the hypothesis that species C is a secondary consumer. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(3) (Total 6 marks)

19.

A study of plant species near a sandy shore was carried out. The table below shows some of the data collected. Sites were sampled at a range of distances inland from a reference point on the beach Site number Distance from reference point / m Dead organic matter in soil / % Number of plant species found 1 20 0.4 1 2 80 0.5 1 3 250 0.9 8 4 500 2.8 16 5 650 6.4 7 6 1800 23.4 2

Each site represents a stage in the succession from bare sand to a climax community.

(a)

(i) Describe the changes in the percentage of dead organic matter and number of plant species as the distance from the reference point increases. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2)

(ii)

Suggest how changes in the percentage of dead organic matter in the soil could account for the changes in the number of plant species. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(4)

39

(b)

Explain what is meant by a climax community. ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

(c)

Another way to study plant succession is to measure changes in the percentage cover of plant species. Describe how you could measure percentage cover of a plant species in a site you have studied. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2) (Total 10 marks)

20.

A group of students carried out an investigation to determine the energy flow in a rainforest food chain. They collected invertebrate animals from trees, identified them and placed them in the appropriate trophic level. For each trophic level the animals were counted, weighed and the energy content determined. Using their data and other sources of information the students produced a diagram to show the energy flow along the food chain. The diagram is shown in Figure 1. Figure 1 S 2 0 03

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Some farmers clear plots of rainforest to use for crops. The trees are felled and then burnt. This practice is called slash and burn. The soil is left covered in ash, which is rich in nutrients. However, the nutrients are soon used up by the growing crops. Within two or three years the plot is abandoned and the farmer moves on to a new plot.

41

The abandoned plot is colonised by tree species and eventually the land is covered by secondary rainforest. The sequence of events is shown in Figure 2. This figure also shows that the total biomass of the rainforest trees is made up of leaves, stems and branches, roots and leaf litter. These components of the biomass change as the rainforest is cleared, farmed and then abandoned. Figure 2 P r i m a r y r a i n f o r e s Ft S S e c o n d a r y r a i n f o r e s t 1 0 t d o y n e a r s 2 e d 5 y e a r s

a r m

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t 0 0 0 0 1 5 1 5 0 0 0 0 2 5 5 5 0 0 0 0 0 3 5 7 5 0 0 5 0 0

l i t t e 4r 0

The biomass components are shown in million tonnes per hectare. (a) Define the term net primary production (NPP). ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

(b)

(i) Explain why only a small percentage of the light energy falling onto a leaf is converted into chemical energy. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2)

(ii)

Explain why only 10% of the energy locked up in the secondary consumers is transferred to the tertiary consumers. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)

(c)

The energy shown entering the decomposers in Figure 1, is much greater than that entering all of the consumers. Suggest an explanation for this difference. ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(1)

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(d)

(i) Using Figure 2, compare the components of the biomass of the primary rainforest with those of the secondary rainforest after 25 years. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)

(ii)

Using all of the information provided, suggest why slash and burn farming is considered to be unsustainable. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)

(e)

Suggest how the biodiversity of the surrounding rainforest could be changed by the practice of slash and burn. Give reasons for your answer. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(4) (Total 18 marks)

21.

An investigation was carried out into the effect of grazing by rabbits in an area of grassland. In 1954 and 1957, the mean height of the vegetation was measured. In 1956 an outbreak of a disease greatly reduced the number of rabbits. The results are shown in the table below. 1954 Mean height of vegetation/cm 2.0 1957 11.5

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(a)

Describe and explain the effect of the decrease in the number of rabbits on the mean height of the vegetation. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

(b)

A grazed grassland is a plagioclimax community, (i) Explain what is meant by the term plagioclimax. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2)

(ii)

Describe how an area of grazed grassland could develop into a woodland community. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(4) (Total 8 marks)

22.

Samuel Wilberforce, a bishop of Oxford in the 19th century, was a fierce critic of Darwins theory of evolution by natural selection. (a) Explain why Wilberforce might have been so strongly opposed to the theory of evolution by natural selection. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(3)

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One argument that Wilberforce used was that no new species had been seen to arise. Even breeds of dog that had been prevented from cross breeding for many generations remained the same species. If two breeds of dog are allowed to interbreed they produce fertile offspring showing a variety of intermediate characteristics (mongrels). (b) Describe how interbreeding of dog breeds can result in mongrel dogs. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2)

(c)

Explain why Wilberforces example of dog breeds does not show that Darwins theory of evolution by natural selection is incorrect. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2) (Total 7 marks)

23.

(a) The table below shows some data obtained from studies on seaweed on a rocky shore. The species are listed in the order down the shore that they are normally found. Seaweeds on the upper shore may be out of the sea, and exposed to the air for many days at a time. Some scientists suggested that seaweeds on the upper shore retain water better than seaweeds on the lower shore. Cell wall thickness / m Water loss on drying out for fixed time / % 85 70 80 83 88 Recovery of normal metabolism after drying out and then rewetting / % 95 49 20 0 0

Upper Shore

Pelvetia canaliculata Fucus spiralis Fucus vesiculosus Fucus serratus

1.2 1.47 0.69 0.42 0.28

Lower Shore (near sea)

Laminaria digitata

(i)

Explain why these data do not support the hypothesis that seaweed species growing high on the shore will retain water better than seaweed species growing lower on the shore. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2)

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(ii)

Suggest an explanation, supported by the data, that could account for this distribution of seaweeds. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)

The upper shore experiences a wider range of temperatures since it spends time exposed to the air, and it can reach much higher temperatures than seawater. Another study was carried out to investigate the effects of temperature on the activity of rocky shore snails. The temperature at which 50% became inactive was measured for 5 species of snail and the data are given below. The rate of water loss on exposure to the air was also measured Littorina littorea Temperature of inactivity / C Water loss / % body mass per day 46.0 Littorina saxatilis 45.0 Calliostoma 34.5 Littorina obtusata 44.0 Littorina neritoides 46.3

5.35

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8.35

3.7

(b)

Suggest one species that you would expect to find more frequently on the upper shore, and one species that you would expect to be limited to the lower shore, giving a reason for each of your answers. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(4)

(c)

Suggest two biotic factors that might affect the distribution of organisms in the rocky shore studied above. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... .....................................................................................................................................(2) (Total 11 marks)

24.

The periwinkle (Littorina littorea) is a small marine snail that feeds on algae (seaweeds) as shown in Figure 1 below. It prefers to eat fast-growing, short-lived green algae such as Enteromorpha rather than tough, long-lived red algae such as Chondrus. Figure 1 Periwinkle (Littorina littorea) feeding on algae.

If these two algae are growing in the same rock pool, the more rapid growth of Enteromorpha reduces the growth of Chondrus. However, periwinkles grazing on the Enteromorpha help to keep it under control and this allows Chondrus to grow.

51

A study was made of the feeding preferences of the periwinkle on rocky shores and how these affected the growth of Enteromorpha and Chondrus. An ecologist studied the percentage cover of algae in three rock pools. The density of periwinkles in the three rock pools was: Rock pool A Rock pool B Rock pool C 100 per m 200 per m 0 per m2 2 2

At the start of the study she removed all of the periwinkles from Rock pool B and placed them in Rock pool C which had none. She monitored the changes in the percentage cover of algae over a period of 28 months. Her results are shown in Figure 2. The effect of the density of the periwinkles on the diversity of the algae was also studied. The results are shown in Figure 3. Figure 2 R P e rc e n ta g e c o v e r o f a lg a e (% ) 1 8 6 4 2 0 0 0 0 0 0 0 2 4 T i m 6 e / 8 m 1 o 0 n 1 t h 2 s 1 0 E C n h t e r o o n d m r u o s r p h a o c k p o o l A

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Figure 3 Graph showing the change in the number of algal species with the increase in the density of periwinkles in rock pools N u m b e r o f a lg a l s p e c ie s 1 1 1 8 6 4 2 0 4 2 0

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(a)

State the terms that are used to describe the roles of the algae and periwinkles in a food chain. Algae ........................................................................................................................... Periwinkles ..................................................................................................................(2)

(b)

(i) Using Figure 2, describe the percentage cover of Enteromorpha and Chondrus in Rock pools B and C at the start of the study (Month 0). ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(2)

(ii)

Describe the changes in the percentage cover of Enteromorpha in Rock pools A, B and C. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ...........................................................................................................................(3)