Trophic levels in an ecosystem

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Trophic Levels

Trophic levels describe the position of an organism in a food chain, food web or ecological pyramid.
Trophic levels are numbered starting at level 1 with plants and algae, and increase as you move along the food chain.
Level 1: Plants and algae make their own food and are called producers.
Level 2: Herbivores that eat plants/algae are called primary consumers.
Level 3: Carnivores that eat herbivores are called secondary consumers.
Level 4: Carnivores that eat other carnivores are called tertiary consumers.
Apex predators are carnivores with no predators and are at the top of the food chain.
Some organisms can occupy more than one trophic level in a food web if they eat both plants and animals (omnivores) or eat organisms from different levels.

Trophic levels describe the position of organisms in a food chain

Food Chains and Food Webs

A food chain shows the transfer of energy from one organism to the next, beginning with a producer.
The arrows in a food chain show the direction of energy transfer from one trophic level to the next.
A food web is a network of interconnected food chains and is a more realistic representation of feeding relationships in an ecosystem.
Food webs show interdependence – a change in one population can affect others in the web.
For example, if the population of earthworms decreases, the population of grass plants may increase (fewer are eaten), while populations of frogs and mice may decrease (they rely on earthworms as their only food source).
Consumers can be classed as primary, secondary, tertiary or quaternary according to their position in a food chain.

Energy is transferred from the sun and through the food chain

Decomposers

Decomposers break down dead plant and animal matter.
The two main groups of decomposers are bacteria and fungi.
Decomposers secrete digestive enzymes onto the surface of dead organisms.
These enzymes break down the dead matter into small soluble food molecules.
The small soluble molecules are then absorbed by the decomposers.
Decomposition releases organic nutrients back into the environment (e.g. soil), which are essential for the growth of plants (producers).
Decomposers are not assigned to a single trophic level.

Photographs of four different fungi growing on dead wood

Pyramids of Biomass

Biomass is the mass of living tissues (or recently dead tissues that have not yet been decomposed) that a plant or animal is made up of.
It is the dry mass of the organism – the mass without including all the water in the organism.
A pyramid of biomass shows the relative biomass at each trophic level in a food chain.
Trophic level 1 (producers) is always at the bottom of the pyramid, followed by primary consumers, then secondary consumers, and so on.
Pyramids of biomass are always pyramid-shaped because biomass always decreases as you move up through the trophic levels.
The width of each layer represents the relative biomass at that trophic level.
Pyramids of biomass provide a better idea of the quantity of plant or animal material at each level than pyramids of numbers, and are a better way of representing interdependence.

Pyramid of biomass in a terrestrial food chain

Transfer of Biomass

Energy flows from the Sun to the first trophic level (producers) in the form of light.
Producers convert light energy into chemical energy during photosynthesis, when they convert carbon dioxide and water into glucose and oxygen.
Producers use this glucose (during respiration) to produce their own biomass; biomass is a store of chemical energy.
When primary consumers eat producers, they break down the biomass (digestion) and use the chemical energy to increase or sustain their own biomass.
This transfer of chemical energy and biomass continues from one trophic level to the next as organisms eat one another.
Approximately only 10% of the biomass from each trophic level is transferred to the level above it.
This is why food chains rarely have more than five or six trophic levels – the total amount of biomass available eventually becomes too small to support another trophic level.

Losses of Biomass

Organisms rarely eat every part of the organism they consume – some biological material may be inedible (e.g. bones).
Not all ingested material is digested and absorbed; some is egested as faeces.
Some absorbed material is lost as waste: carbon dioxide and water are waste products of respiration.
Water and urea are waste products in urine, produced when proteins are broken down.
Energy is used for movement and to generate heat, so less is available to produce new biomass.
Energy is also used for metabolic processes.
Plants do not produce urine or faeces, so these cannot be given as ways plants lose biomass.

Calculating Efficiency of Biomass Transfer

The efficiency of biomass transfer between trophic levels can be calculated as a percentage or fraction of mass.
Use the equation: efficiency = (biomass transferred to next level ÷ biomass at previous level) × 100.
Divide the smaller number by the bigger one, then multiply by 100.
For example, if the producer has 10 000 kg of biomass and 8% is passed to the primary consumer, the primary consumer gains 800 kg.
If only 7% of that is passed to the secondary consumer, the secondary consumer gains 56 kg.
The efficiency of transfer affects the number of organisms that can be supported at each trophic level.

Human Impact and Food Production

Humans can affect food chains and food webs through overharvesting of food species and introducing foreign species to a habitat.
For example, increased catching of lobsters could reduce their population, affecting other organisms in the food web.
Modern farming methods such as keeping cattle indoors, limiting their movement, and controlling temperature improve the efficiency of biomass transfer from cattle to humans.
This is because less energy is used for movement and maintaining body temperature, so more biomass is available for growth.
Eating crops such as wheat and soya directly, rather than feeding them to cattle and then eating the cattle, is a more efficient way to feed the human population.
This is because energy and biomass are lost at each trophic level, so fewer people can be supported if humans eat higher up the food chain.

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1.Which of the following statements best defines a secondary consumer in a food chain?
Easy
- AA carnivore that eats a herbivore
- BA herbivore that eats a producer
- CA carnivore that also eats plants (an omnivore)
- DAn apex predator
2.Which of the following is the accepted way of demonstrating biomass in different trophic levels in an ecosystem?
Easy
- AA pyramid of numbers
- BA pyramid of biomass
- CA food web
- DA food chain
3.In a pyramid of biomass, what quantity does the width of each layer represent?
Medium
- AThe number of organisms at that trophic level
- BThe amount of energy at that trophic level
- CThe biomass at that trophic level
- DThe size of each individual organism
4.Which statement best explains why pyramids of biomass rarely contain more than five trophic levels?
Medium
- ABecause five levels allows greater biodiversity than eight or ten levels.
- BBecause an apex predator isn't eaten by anything else.
- CThere is a large loss of biomass at each trophic level so the food chain can only sustain a few apex predators.
- DBecause consumers in a food chain are usually connected to other food chains in a food web.
5.Which of the following are ways in which biomass is lost between trophic levels? (select all that apply)
Medium
- ANot all ingested material is absorbed; some is egested as faeces.
- BSome absorbed material is lost as carbon dioxide and water in respiration.
- CEnergy is used for movement and to generate heat.
- DBiomass is destroyed completely and leaves the ecosystem.
- EAll biomass is transferred to the next trophic level.
6.Decomposers occupy a single trophic level in a food chain.
Easy
True or false?
7.Match each trophic level with the correct description.
Medium
- Level 1
- Level 2
- Level 3
- Level 4
- Producers (plants and algae)
- Primary consumers (herbivores)
- Secondary consumers (carnivores that eat herbivores)
- Tertiary consumers (carnivores that eat other carnivores)
8.Place the following trophic levels in the correct order from bottom to top of a food chain.
Easy
- Producers
- Primary consumers
- Secondary consumers
- Tertiary consumers

更多題目

9.Which of the following organisms are producers? (select all that apply)
Medium
- AGrass
- BAlgae
- CRabbit
- DOak tree
- EFox
10.Match each trophic level with the correct organism type.
Medium
- Trophic level 1
- Trophic level 2
- Trophic level 3
- Trophic level 4
- Producer
- Primary consumer
- Secondary consumer
- Tertiary consumer
11.Place the following organisms in the correct order to form a food chain, starting with the producer.
Easy
- Grass
- Grasshopper
- Frog
- Snake
- Hawk
12.A food chain consists of phytoplankton, zooplankton, small fish, and snapper fish. Which trophic level does the small fish occupy?
Medium
- APrimary consumer
- BSecondary consumer
- CTertiary consumer
- DProducer
13.A pyramid of biomass is always pyramid-shaped.
Easy
True or false?
14.Which of the following is the correct unit for biomass in a pyramid of biomass?
Medium
- Akg/m²
- BJ/m²
- Ckg/m³
- Dg/m²
15.Which of the following are reasons why biomass is lost between trophic levels? (select all that apply)
Hard
- ANot all ingested material is digested and absorbed, some is egested as faeces
- BSome absorbed material is lost as waste products like carbon dioxide and water
- CEnergy is used for movement and generating heat
- DAll biomass is transferred to the next trophic level
- EOrganisms eat every part of the organism they consume
16.What is the role of decomposers in an ecosystem?
Medium
- AThey break down dead plant and animal matter, releasing nutrients back into the environment
- BThey produce their own food using photosynthesis
- CThey are primary consumers that eat producers
- DThey are apex predators that eat other animals
17.A marine food chain is: phytoplankton → zooplankton → small fish → snapper fish. The biomass of the phytoplankton is 5 400 kg/m² and the biomass of the snapper fish is 54 kg/m². Calculate the percentage of biomass transferred from the phytoplankton to the snapper fish, to 2 significant figures.
Medium
- A1.0%
- B10%
- C0.10%
- D54%
18.A student measures the biomass of organisms at each trophic level in a grassland food chain and records: grass 5800 kg/m², cattle 720 kg/m², humans 55 kg/m². Which of the following correctly describes how the width of each layer of a pyramid of biomass drawn from this data should change?
Medium
- AThe grass layer is widest and each layer above is narrower
- BThe human layer is widest because humans are largest
- CAll three layers are the same width
- DThe cattle layer is widest because cattle are heaviest
19.A fox eats a rabbit. Which of the following explain why not all of the rabbit's biomass becomes new fox biomass? (select all that apply)
Hard
- ASome of the rabbit is inedible, such as bones and fur
- BSome ingested material is egested as faeces
- CThe fox uses glucose in respiration, releasing carbon dioxide and water
- DThe fox converts all the rabbit's biomass directly into new fox biomass
- EThe fox passes on 90% of the rabbit's biomass to the next trophic level
20.A food web in a sea contains crabs, which eat mussels and small fish. The small fish eat zooplankton. If humans increase the number of lobsters caught in this part of the sea, and lobsters are predators of crabs, what is the most likely effect on the crab population?
Medium
- AThe crab population will increase because fewer crabs are eaten by lobsters
- BThe crab population will decrease because lobsters are their food source
- CThe crab population will stay exactly the same
- DThe crab population will increase because mussels will become more abundant
21.In a pyramid of biomass, the layer for trophic level 1 is at the bottom of the pyramid.
Easy
True or false?
22.A scientist measures the energy transferred to the next trophic level by each organism in a food chain over one year. The producer transfers 20 000 kJ, the primary consumer 2 000 kJ, the secondary consumer 200 kJ and the tertiary consumer 20 kJ. Which statement best explains why there is no fourth consumer in this food chain?
Hard
- AToo little energy remains to support another trophic level
- BThe tertiary consumer is an apex predator with no predators
- CThe producer cannot make enough glucose for more levels
- DThere is not enough biodiversity to support more levels
23.Match each term to the correct description.
Medium
- Producer
- Primary consumer
- Decomposer
- Makes its own food using light energy
- A herbivore that eats a producer
- Breaks down dead plant and animal matter
24.A student is given the following food chain: Oak tree → Blue tit → Sparrowhawk. The biomass of the oak tree is 12 000 kg/m² and the biomass of the blue tits is 960 kg/m². Which calculation correctly works out the percentage of the oak tree's biomass that is present in the blue tits?
Medium
- A(960 ÷ 12 000) × 100
- B(12 000 ÷ 960) × 100
- C(12 000 − 960) ÷ 12 000 × 100
- D(960 ÷ 12 000) ÷ 100
25.A student is measuring the biomass at each trophic level in a freshwater pond so that they can draw a pyramid of biomass. Which of the following steps would give valid, reliable data? (select all that apply)
Medium
- AMeasure the dry mass of the samples rather than the wet mass
- BCollect samples from several different points in the pond and calculate a mean
- CUse only the largest organism found at each trophic level as the sample
- DDry the samples in an oven before weighing them
- EEstimate the biomass by counting the number of organisms at each level
26.In a pyramid of biomass, the producer is always placed at the bottom of the pyramid.
Easy
True or false?
27.A student is asked to draw a pyramid of biomass for a food chain in which the producer is a large oak tree and the primary consumers are many small insects. Which statement explains why the pyramid of biomass will still be pyramid-shaped, even though there is only one producer?
Hard
- AThe single oak tree has a very large total biomass, which is greater than the total biomass of all the insects
- BThe oak tree is at a higher trophic level than the insects
- CThe insects have a greater total biomass because there are more of them
- DA pyramid of biomass can be any shape, so it does not matter
28.Match each term about biomass transfer to its correct description.
Medium
- Biomass
- Pyramid of biomass
- Efficiency of biomass transfer
- Dry mass
- The mass of living or recently dead tissue, measured without water
- A diagram showing the relative biomass at each trophic level, always pyramid-shaped
- The percentage of biomass passed from one trophic level to the next
- The mass of an organism after all its water has been removed
29.In a marine food chain, phytoplankton have a biomass of 5 400 kg/m². Only 10% of the biomass is transferred to each higher trophic level. The chain is: phytoplankton → zooplankton → small fish → snapper fish. What is the biomass of the snapper fish?
Hard
- A5.4 kg/m²
- B54 kg/m²
- C540 kg/m²
- D0.54 kg/m²
30.A student is investigating the efficiency of biomass transfer in a food chain. They measure the biomass of grass and the biomass of cattle in a field. Which of the following would reduce the reliability of their results? (select all that apply)
Hard
- ATaking samples from only one small area of the field
- BUsing wet mass instead of dry mass
- CMeasuring the biomass of all the grass in the field
- DTaking samples at different times of year and averaging
- ENot repeating the measurements
31.Which trophic level contains the producers in a food chain?
Easy
- ALevel 1
- BLevel 2
- CLevel 3
- DLevel 4
32.Which of the following best defines a herbivore?
Easy
- AAn animal that gets its energy by eating plants
- BAn animal that gets its energy by eating other animals
- CAn organism that makes its own organic nutrients using sunlight
- DAn organism that gets its energy from dead or waste organic material
33.Which of the following statements about trophic levels are correct? (select all that apply)
Medium
- ATrophic levels describe the position of an organism in a food chain, food web or ecological pyramid.
- BDecomposers occupy a single trophic level in a food chain.
- CApex predators are carnivores with no predators.
- DPrimary consumers are always carnivores.
- EProducers convert light energy into chemical energy.
34.A food chain always begins with a producer.
Easy
True or false?
35.Decomposers break down dead plant and animal matter by secreting enzymes into the environment.
Easy
True or false?
36.Pyramids of numbers are always pyramid-shaped.
Easy
True or false?
37.Which term describes an organism that gets its energy by feeding on other organisms?
Easy
- AConsumer
- BProducer
- CDecomposer
- DHerbivore
38.Which of the following best describes the role of decomposers in an ecosystem?
Medium
- AThey break down dead plant and animal matter, releasing nutrients back into the environment.
- BThey convert light energy into chemical energy during photosynthesis.
- CThey are the primary consumers in a food chain.
- DThey are apex predators with no natural predators.
39.What is the main role of producers in a food chain?
Easy
- ATo make their own food using energy from sunlight
- BTo eat other organisms to obtain energy
- CTo break down dead organic matter
- DTo act as apex predators
40.Which of the following are true about decomposers? (select all that apply)
Medium
- AThey include bacteria and fungi.
- BThey break down dead plant and animal material.
- CThey secrete digestive enzymes onto the surface of dead organisms.
- DThey are always primary consumers.
- EThey release organic nutrients back into the environment.
41.Select the correct word from each set of brackets to complete the passage accurately.
Easy
A pyramid of biomass shows layers that correspond to individual ____ levels. The highest level shows the biomass of ____ the ____ predators in a food ____.
42.In a food chain, 8% of the biomass of the producer is passed to the primary consumer. Of that, only 7% is passed onto the secondary consumer. The producer's biomass is 10,000 kg. Calculate the amount of biomass gained by the secondary consumer, in kg.
Medium
43.State the process by which decomposers absorb nutrients into their cells.
Easy
44.In a food chain, the biomass of grass is 5800 kg/m² and the biomass of cattle is 720 kg/m². Calculate the efficiency of biomass transfer from grass to cattle as a percentage. Give your answer to 2 significant figures.
Medium
45.Complete the passage about pyramids of biomass.
Easy
A pyramid of biomass shows layers that correspond to individual ____ levels. The highest level shows the biomass of ____ the apex predators in a food ____.
46.A food chain has a producer biomass of 25 000 kg/m². Using the typical value for biomass transfer between trophic levels, calculate the biomass that would be present in the primary consumer trophic level, in kg/m².
Medium
47.In a food chain, 8% of the producer's biomass is passed to the primary consumer. Of that, only 7% is passed to the secondary consumer. If the producer's biomass is 10 000 kg, calculate the biomass gained by the secondary consumer, in kg.
Hard
48.Complete the sentence about the units of biomass.
Easy
The units of biomass are given as kg/m². The m² part of this unit refers to the ____ over which the biomass was measured.
49.In a pyramid of biomass, what does the width of each layer represent?
Medium
50.Complete the sentence about trophic levels.
Easy
Trophic levels can be represented by numbers, starting at level ____ with plants and algae, which are called ____.
51.Complete the sentence about decomposers.
Easy
Decomposers break down dead plant and animal matter by secreting ____ into the environment; the small soluble food molecules then ____ into the microorganism.
52.Complete the sentence about energy flow in food chains.
Medium
Energy flows from the Sun to the first trophic level in the form of ____. Producers convert this into ____ energy during photosynthesis.
53.Explain the importance of decomposers in an ecosystem.
Hard
54.Explain why food chains rarely contain more than five trophic levels.
Hard
55.Modern farming methods keep cattle indoors, limit their movement and control the temperature of their surroundings. Explain why these methods improve the efficiency of biomass transfer from cattle to humans.
Hard
56.Explain why it is more efficient for humans to eat crops such as wheat and soya directly rather than feeding these crops to cattle and then eating the cattle.
Hard
57.A farmer keeps cattle indoors, limits their movement and controls the temperature of their surroundings. Explain how these methods improve the efficiency of biomass transfer from cattle to humans.
Hard
58.In a food chain, 8% of the biomass of the producer is passed to the primary consumer. Of that, only 7% is passed onto the secondary consumer. The producer's biomass is 10,000 kg. Calculate the amount of biomass gained by the secondary consumer, in kg.
Medium
- A56 kg
- B62 kg
- C50 kg
- D68 kg
59.In a food chain, the biomass of grass is 5800 kg/m² and the biomass of cattle is 720 kg/m². Calculate the efficiency of biomass transfer from grass to cattle as a percentage. Give your answer to 2 significant figures.
Medium
- A13.41 %
- B12.41 %
- C11.41 %
- D14.41 %
60.A food chain has a producer biomass of 25 000 kg/m². Using the typical value for biomass transfer between trophic levels, calculate the biomass that would be present in the primary consumer trophic level, in kg/m².
Medium
- A2750 kg/m²
- B2250 kg/m²
- C2500 kg/m²
- D3000 kg/m²
61.In a food chain, 8% of the producer's biomass is passed to the primary consumer. Of that, only 7% is passed to the secondary consumer. If the producer's biomass is 10 000 kg, calculate the biomass gained by the secondary consumer, in kg.
Hard
- A62 kg
- B68 kg
- C50 kg
- D56 kg

字卡

What is a trophic level?

A trophic level describes the position of an organism in a food chain, food web or ecological pyramid.

Which organisms occupy trophic level 1?

Producers, such as plants and algae, occupy trophic level 1.

What is a producer?

A producer is an organism that makes its own food, usually by photosynthesis, using energy from sunlight.

What is a primary consumer?

A primary consumer is a herbivore that eats producers. It occupies trophic level 2.

What is a secondary consumer?

A secondary consumer is a carnivore that eats herbivores (primary consumers). It occupies trophic level 3.

What is a tertiary consumer?

A tertiary consumer is a carnivore that eats other carnivores. It occupies trophic level 4.

What is an apex predator?

An apex predator is a carnivore at the top of a food chain with no predators of its own.

What is a decomposer?

A decomposer is an organism that gets its energy from dead or waste organic material, breaking it down.

How do decomposers break down dead material?

Decomposers secrete digestive enzymes onto the dead material, breaking it into small soluble food molecules which are then absorbed.

What are the two main groups of decomposers?

Bacteria and fungi are the two main groups of decomposers.

What is biomass?

Biomass is the mass of living tissues, or recently dead tissues that have not yet decomposed, usually measured as dry mass.

What does a pyramid of biomass show?

A pyramid of biomass shows the relative biomass at each trophic level in a food chain.

Why is a pyramid of biomass always pyramid-shaped?

Biomass always decreases as you move up the trophic levels, so each level is narrower than the one below.

What does the width of each layer in a pyramid of biomass represent?

The width of each layer represents the relative biomass at that trophic level.

Approximately what percentage of biomass is transferred from one trophic level to the next?

Approximately 10% of biomass is transferred from one trophic level to the next.

Why do food chains rarely have more than five or six trophic levels?

There is a large loss of biomass at each trophic level, so the total biomass available eventually becomes too small to support another level.

Give two ways in which biomass is lost between trophic levels.

Not all ingested material is absorbed (some is egested as faeces); some absorbed material is lost as waste such as carbon dioxide and water in respiration, and water and urea in urine.

How is biomass lost through respiration?

Glucose is used in respiration to provide energy for movement and keeping warm, producing carbon dioxide and water as waste, so less biomass is available to the next trophic level.

How do you calculate the efficiency of biomass transfer?

Efficiency = (biomass transferred to next level ÷ biomass at previous level) × 100.

In the food chain grass → rabbit → fox, the grass has 500 kg/m² and the rabbit has 50 kg/m². Calculate the efficiency of biomass transfer from grass to rabbit.

Efficiency = (50 ÷ 500) × 100 = 10%.

What is the role of a producer in a food chain?

Producers make their own food by photosynthesis, converting light energy into chemical energy stored in glucose, which is used to build biomass.

What is a food web?

A food web is a network of interconnected food chains showing the feeding relationships in an ecosystem.

Why can an animal occupy more than one trophic level in a food web?

An animal can be an omnivore or a predator that eats organisms from different trophic levels, so it can belong to more than one level.

Why is a pyramid of biomass a better representation of a food chain than a pyramid of numbers?

A pyramid of biomass shows the mass of living material at each level, giving a better idea of the quantity of material and interdependence, whereas a pyramid of numbers can be any shape and does not account for organism size.

Why do farmers keep cattle indoors, limit their movement and control the temperature?

These methods reduce energy lost through movement and heat, so more biomass is transferred to the next trophic level (humans), improving efficiency of food production.

Why would eating crops directly, rather than feeding them to cattle and then eating the cattle, feed more people?

Energy and biomass are lost at each trophic level, so eating crops directly avoids the losses that occur when crops are fed to cattle, making food production more efficient.

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