19.1 Energy & Feeding Relationships

In the Arctic, snowy owls are predators of lemmings. The lemmings eat Arctic plants.

Draw the food chain for this Arctic ecosystem.

Fig. 1 shows changes in the populations of snowy owls and lemmings over a three year period.

Fig. 1

During the first 10 months of year 1, the lemming population increases slowly at first and then more rapidly.

Suggest why the rate of increase becomes greater.

[1]

Suggest why the lemming population falls during year 2.

[2]

Use Fig. 1 to describe and explain how changes in the lemming population affect the snowy owl population.

[3]

If all the snowy owls were removed from the Arctic ecosystem, suggest and explain what effect this would have on the lemming population in the following years.

[3]

Lemmings and snowy owls get their energy from the food they eat.

State the principal source of all the energy in this ecosystem.

[1]

Name the process that first traps this energy.

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Mangrove trees are hydrophytes because they grow in water.

Fig. 1 shows a young mangrove tree.

Fig. 1

Mangrove trees have many aerial roots and floating seeds.

Suggest how these adaptive features allow mangrove trees to survive in water.

Fig. 2 shows a food chain in a mangrove forest.

mangrove tree → fiddler crab → seagull

Fig. 2

Table 1 gives the number of organisms and their biomass in a mangrove forest.

Table 1

Estimate the biomass of one fiddler crab in grams.

Write your answer to two significant figures.

Show your working.

[2]

Sketch a pyramid of numbers, using the information in Table 1, for the food chain shown in Fig. 2.

Write the number of each trophic level on the appropriate part of your pyramid. 

[3]

Explain why the shape of a pyramid of biomass, for the information given in Table 1, would be different from the shape of your pyramid of numbers.

[4]

Wetlands are important ecosystems. Researchers studied the feeding relationships between the organisms in an area of wetland on the coast of Texas.

Fig. 1 shows part of the food web that they studied.

Fig. 1

Complete Table 1 by giving the name of one organism from the food web in Fig. 1 for each row.

Table 1

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The functioning of ecosystems relies on the cycling of nutrients.

Fig. 2 shows part of the nitrogen cycle.

Fig. 2

State the name of process A in Fig. 2 and give the type of organism that converts ammonium ions to nitrate ions.

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Describe how nitrate ions enter the roots of plants shown by arrow C on Fig. 2.

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State the name of the structure in plant cells where process D occurs.

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State the process that occurs at B.

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A pyramid of numbers for the wetland ecosystem showed that there were very large numbers of organisms at the base of the pyramid and very few at the top.

Explain why.

• Star grass is eaten by antelope species, such as topi and Thomson’s gazelle.
• Smaller animals such as mice and grasshoppers feed on red oat grass.
• Topi and Thomson’s gazelle are eaten by predators such as cheetahs, lions and serval cats.
• Grasshoppers and mice are eaten by serval cats and tawny eagles.
• Vultures feed on dead mammals.

Fig. 1 shows part of the food web for this ecosystem.

Fig. 1

Complete the food web by writing the names of the correct organisms in the boxes in Fig. 1.

Name the trophic level of the following species.

[1]

Topi

[1]

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[1]

[1]

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Explain why there are no more than four trophic levels in the food web shown in Fig. 1.

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Fish such as salmon can be reared intensively in fish farms. They are fed on high protein food made from animals. When eating this food, the fish are feeding as secondary consumers.

Describe the disadvantages of intensive farming, such as salmon farming, for producing human food.

Fig. 1 shows a simple food web.

Fig. 1

Table 1 shows some of the terms that can be used to describe the organisms in the food web in Fig. 1.

Place ticks (✓) in the boxes to show the terms that can be used to describe each organism.

Table 1

[3]

State the number of trophic levels in the food web in Fig. 1.

[1]

Identify one organism that feeds at more than one trophic level.

[1]

State the term used to describe an organism that gets its energy from dead or waste organic material.

[1]

State the principal source of energy for food webs.

[1]

Wetlands are important ecosystems. Researchers studied the feeding relationships between the organisms in an area of coastal wetland.

Fig. 1 shows part of the food web that they studied.

Fig. 1

Complete Table 1 by giving the name of one organism from the food web in Fig. 1 for each row.

Table 1

Extended only

The functioning of ecosystems relies on the cycling of nutrients.

Fig. 2 shows part of the nitrogen cycle.

Fig. 2

State the name of process A in Fig. 2 and give the type of organism that converts ammonium ions to nitrate ions.

[2]

Describe how the nitrate ions used in process C enter the roots of plants.

[3]

State the name of the structure in plant cells where process D occurs.

[1]

State the process that occurs at B.

[1]

Extended only

A pyramid of numbers for the wetland ecosystem showed that there were very large numbers of organisms at the base of the pyramid and very few at the top.

Explain why.

(i)

The sentences in the box describe the feeding relationships between four organisms. 

Use the information in the sentences to write a food chain containing these four organisms.

Do not draw pictures of the organisms.

[3]

State the principal source of energy for this food chain.

[1]

State the type of organism that gains its energy from dead organic material.

[1]

(i)

A species becomes endangered when it is at risk of extinction.

Explain two ways in which a species could become endangered.

[4]

State one way in which endangered species can be conserved.

[1]

Adaptive features are defined as the inherited features of an organism that increase its fitness.

State what is meant by fitness in this context.

Rodents are the most common mammals in many hot deserts.

Fig. 1 shows the lesser Egyptian jerboa, Jaculus jaculus, which lives in North Africa and the Middle East in areas that have high daytime temperatures and very little rainfall.

Fig. 1

Like many desert-living mammals, jerboas are active at night.

Suggest two features of J. jaculus that adapt it to each of the following challenges of living in desert ecosystems:

(i) very high daytime temperatures

1...............................

2...............................

[2]

(ii) very little or no light at night

1...............................

2...............................

[2]

A scientist studied communities in different parts of a desert and estimated the biomass of the organisms in each area.

He divided the organisms into four groups according to their roles in the food web as shown in Table 1.

Detritivores are animals that eat dead organisms or parts of organisms.

Table 1

Some of these results are shown as a pyramid of biomass in Fig. 2.

Fig. 2

Use the information in Table 1 to complete the pyramid of biomass in Fig. 2.

[2]

The scientist observed the detritivores and decided to include them with herbivores in this pyramid of biomass. 

Suggest what the scientist discovered about the detritivores that made him make this decision.

[1]

Explain why there are rarely more than four or five trophic levels in ecosystems.

[2]

Explain the advantages of presenting information about food webs as a pyramid of biomass and not as a pyramid of numbers.

[3]

Fig. 1 shows a pyramid of biomass and part of the carbon cycle.

Fig. 1

[1]

[1]

Some fungi and bacteria are decomposers

Define the term decomposer.

[1]

     Arrow X on Fig. 1 indicates the transfer of carbon from decomposers to the atmosphere. State the name of process X. 

[1]

Describe how human activities are affecting the carbon cycle.

Fig. 1 shows part of the carbon cycle.

Fig. 1

Identify the processes shown by arrows A, B and C on Fig. 1.

Choose words from the list.

(i)

On Fig. 1 draw one arrow to represent photosynthesis.

Label this arrow with a letter D.

[1]

On Fig. 1 draw one arrow to represent respiration.

Label this arrow with a letter E.

The concentration of carbon dioxide in the atmosphere is increasing.

Describe two possible causes of the increased carbon dioxide concentration in the atmosphere.  

[2]

State two adverse effects of the increase in carbon dioxide concentration in the atmosphere.

Carbon dioxide is a greenhouse gas.

State the name of one other greenhouse gas.

Fig. 1 shows a food chain that is found in the sea.

Fig. 1

State the name of the producer in this food chain.

[1]

Define the term producer.

State the name of the secondary consumer in this food chain.

[1]

State the name of the herbivore in this food chain.

[1]

State what the arrows in a food chain represent.

[1]

In some countries humans eat crabs.

Explain how the over-harvesting of crabs could affect the other organisms in the food chain shown in Fig. 1.