Food webs and ecosystems

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What is a food web?

A food web is the natural interconnection of food chains, showing 'what-eats-what' in an ecological community.
It is a simplified illustration of feeding pathways that link an ecosystem into a unified system of exchange.
Food webs map trophic links (feeding connections) between species or functional groups.
Food chains are linear, non-cyclic feeding pathways nested within a food web.

Trophic levels

Organisms are grouped into trophic levels based on their position in the food web.
Basal species (e.g., plants, algae) form the first trophic level; they are autotrophs that produce their own food.
Primary consumers (herbivores) eat producers; secondary consumers (carnivores) eat herbivores; tertiary consumers eat other carnivores.
Apex predators are at the top level with no natural predators.
Omnivores feed on more than one trophic level, causing energy to flow through multiple pathways.

Autotrophs and heterotrophs

Autotrophs (e.g., plants, cyanobacteria) produce biomass energy via photosynthesis or chemosynthesis.
Heterotrophs (e.g., animals, fungi) consume organic matter for energy and nutrients.
Some organisms (e.g., carnivorous plants) are mixotrophs, acting as both autotrophs and heterotrophs.

Energy flow in ecosystems

Energy flows through a food web from producers to consumers and decomposers.
Only about 10% of energy at one trophic level is transferred to the next; the rest is lost as heat or used for metabolism.
This energy loss limits the number of trophic levels in an ecosystem (usually 4–5).

Abiotic and biotic factors

Biotic factors are living components (plants, animals, bacteria) that interact in the food web.
Abiotic factors are non-living physical and chemical components (sunlight, temperature, water, soil) that affect the ecosystem.
Changes in abiotic factors (e.g., drought) can alter food web structure and population sizes.

Impact of changes on food webs

Removing a species (e.g., a predator or prey) can cause cascading effects throughout the food web.
Habitat destruction reduces available resources, leading to population declines or extinctions.
Introducing a new species can disrupt existing feeding relationships and outcompete native species.

Decomposers and detritivores

Decomposers (bacteria, fungi) break down dead organic matter, releasing nutrients back into the ecosystem.
Detritivores (e.g., earthworms, millipedes) consume detritus and help in decomposition.
Decomposers are essential for nutrient cycling and are often included as a basal or separate trophic group.

Food web models and limitations

Food webs are simplified representations that often aggregate many species into trophic species (functional groups).
Ecologists use mathematical models to study food web dynamics and network properties.
Real ecosystems are more complex; food webs may omit parasites, microbes, or other important interactions.

Energy pyramid showing trophic levels and energy transfer (only ~10% passes to the next level).

A simple food web showing feeding relationships among grassland organisms.

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1.What is the original source of energy for most food webs?
Easy
- AThe Sun
- BPlants
- CHerbivores
- DDecomposers
2.Which of the following is an abiotic factor in an ecosystem?
Easy
- ATemperature
- BGrass
- CRabbit
- DFungi
3.In a food chain, which trophic level do primary consumers occupy?
Easy
- ASecond trophic level
- BFirst trophic level
- CThird trophic level
- DFourth trophic level
4.Which of the following statements about food webs is correct?
Easy
- AFood webs show only one feeding pathway in an ecosystem.
- BFood webs are made up of interconnected food chains.
- CFood webs do not include decomposers.
- DFood webs only include animals.
5.What would most likely happen to the population of rabbits if all the foxes in a food web were removed?
Medium
- AThe rabbit population would initially increase, then may decrease due to food shortage.
- BThe rabbit population would decrease immediately.
- CThe rabbit population would remain unchanged.
- DThe rabbit population would become extinct.
6.Which of the following organisms is a decomposer?
Easy
- AFungi
- BGrass
- CRabbit
- DFox
7.In an energy pyramid, which trophic level has the greatest amount of energy?
Easy
- AProducers
- BPrimary consumers
- CSecondary consumers
- DTertiary consumers
8.In the energy pyramid shown, which level represents the organisms that obtain energy directly from the producers?
Easy
- APrimary consumers
- BProducers
- CSecondary consumers
- DTertiary consumers

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9.A student sets up two sealed containers with grass, snails, and soil. Container A is placed in sunlight, container B in darkness. After one week, which container is likely to have the highest oxygen concentration?
Medium
- AContainer A
- BContainer B
- CBoth have the same oxygen concentration
- DNeither container has any oxygen
10.Which of the following best describes the role of detritivores in a food web?
Easy
- AThey break down dead material and return nutrients to the soil.
- BThey are autotrophs that produce their own food.
- CThey are top predators that feed on all trophic levels.
- DThey are primary consumers that feed on producers.
11.In a food web, if a pesticide that does not break down easily is sprayed on plants, which organism is likely to have the highest concentration of the pesticide?
Medium
- ATop predator
- BProducer
- CPrimary consumer
- DDecomposer
12.Which of the following is an example of a mixotroph?
Medium
- ACarnivorous plant
- BGrass
- CRabbit
- DFungus
13.In a grassland ecosystem, a food chain consists of grass → grasshopper → lizard → hawk. If a pesticide that accumulates in body tissues is applied to the grass, which organism would be expected to have the highest concentration of pesticide?
Medium
- AGrass
- BGrasshopper
- CLizard
- DHawk
14.A student measures the biomass of organisms in a pond ecosystem. The results are: algae 5000 g, small fish 500 g, large fish 50 g, heron 5 g. Which statement best explains these values?
Medium
- AAlgae reproduce faster than fish.
- BEnergy is lost at each trophic level, so less biomass can be supported.
- CHerons eat only the smallest fish.
- DLarge fish are more efficient at converting food into biomass.
15.In a food web, if the population of a top predator declines sharply, which of the following is the most likely immediate effect on the ecosystem?
Medium
- AIncrease in the population of its prey, leading to overgrazing of producers
- BDecrease in the population of its prey due to reduced predation pressure
- CIncrease in biodiversity as new species fill the niche
- DNo change because other predators will compensate
16.Which of the following is an example of an abiotic factor that affects a food web?
Easy
- ANumber of predators
- BAvailability of sunlight
- CDisease in prey population
- DType of plants present
17.The diagram shows an energy pyramid. If the producers contain 10,000 kJ of energy, approximately how much energy is available to the tertiary consumers?
Medium
- A10 kJ
- B100 kJ
- C1000 kJ
- D10,000 kJ
18.In the energy pyramid shown, which trophic level contains the organisms that obtain energy directly from the producers?
Easy
- ATertiary consumers
- BSecondary consumers
- CPrimary consumers
- DProducers
19.A scientist constructs a food web for a forest and notes that many species have the same predators and prey. These species are grouped together as a single node in the web. What is this node called?
Hard
- ATrophic species
- BEcological niche
- CPopulation
- DCommunity
20.In a food web, which of the following is an example of a detritivore?
Easy
- AEarthworm
- BRabbit
- CFox
- DHawk
21.Which of the following best describes the role of a mixotroph in a food web?
Medium
- AAn organism that can obtain energy both by photosynthesis and by consuming other organisms
- BAn organism that feeds on both plants and animals
- CAn organism that decomposes dead matter
- DAn organism that is both predator and prey
22.Which of the following is a basal species in a food web?
Easy
- AA top predator
- BAn autotroph
- CA secondary consumer
- DAn omnivore
23.In a food web, if a species is removed, which of the following is most likely to happen to the number of trophic links per consumer?
Hard
- AIt will increase
- BIt will decrease
- CIt will remain the same
- DIt will become zero
24.A food web has 10 species and 20 feeding links. What is the connectance of this food web?
Hard
- A0.2
- B2
- C0.5
- D20
25.In an investigation of a grassland ecosystem, a student uses a quadrat to estimate the population of daisies. Which of the following is the most important reason for using random sampling when placing the quadrats?
Medium
- ATo ensure that every part of the field has an equal chance of being sampled
- BTo make the experiment easier to carry out
- CTo obtain the largest possible sample size
- DTo avoid sampling areas with no daisies
26.A student investigates the effect of temperature on the rate of decomposition of leaf litter by soil microorganisms. Which of the following variables should be kept constant during the experiment?
Medium
- AThe temperature of the incubator
- BThe mass of leaf litter in each container
- CThe number of microorganisms present
- DThe oxygen concentration in the containers
27.The diagram shows a food web. Which of the following would be classified as a basal species in this web?
Easy
- AA top predator
- BA primary consumer
- CA producer
- DA decomposer
28.In a food web, if the population of a top predator increases, what is the most likely short-term effect on the population of primary consumers?
Medium
- AIt will increase because there are more predators
- BIt will decrease because secondary consumers will increase
- CIt will remain unchanged
- DIt will increase because of more food available
29.A student sets up two sealed containers with grass, snails, and soil. Container A is placed in sunlight, container B in darkness. After one week, which container would likely have more oxygen?
Medium
- AContainer A
- BContainer B
- CBoth would have the same amount
- DNeither would have any oxygen
30.In a food web, if the number of trophic links per consumer is used to measure connectance, which of the following would increase connectance?
Hard
- AAn increase in the number of predators that each consumer has
- BAn increase in the number of prey species each consumer eats
- CA decrease in the total number of species in the web
- DA decrease in the number of feeding links
31.A food web has 12 species and 30 feeding links. What is the connectance of this food web?
Medium
- A0.4
- B2.5
- C30
- D12
32.The table below shows the biomass (kg) of organisms in a grassland ecosystem. Which statement is correct? Organism | Biomass (kg) Grass | 5000 Rabbits | 500 Foxes | 50 Wolves | 5
Medium
- AThe biomass of rabbits is 10% of the grass biomass.
- BThe biomass of foxes is 10% of the rabbit biomass.
- CThe biomass of wolves is 10% of the fox biomass.
- DThe biomass of grass is 10% of the total biomass.
33.Which of the following is an example of a chemolithotroph?
Medium
- AA green plant
- BA sulfur bacterium living in a hot spring
- CA rabbit
- DA mushroom
34.In a food web, which of the following is considered a basal species?
Medium
- AA top predator
- BA species that feeds on other consumers
- CA species with no prey in the web
- DAn omnivore that feeds on multiple trophic levels
35.A student investigates the effect of temperature on decomposition of leaf litter. Which variable should be kept constant?
Medium
- ATemperature
- BMass of leaf litter
- CNumber of decomposers
- DBoth mass of leaf litter and number of decomposers
36.In a food web, which of the following is a basal species?
Easy
- AA plant that produces its own food
- BA herbivore that eats grass
- CA carnivore that eats herbivores
- DA decomposer that breaks down dead matter
37.A student sets up two sealed containers with grass, snails, and soil. Container A is placed in sunlight, container B in darkness. After one week, which container is likely to have a higher concentration of carbon dioxide?
Medium
- AContainer A
- BContainer B
- CBoth containers have the same concentration
- DNeither container has carbon dioxide
38.The table below shows the biomass (kg) of organisms in a grassland ecosystem. Which statement is correct? Organism | Biomass (kg) Grass | 5000 Rabbits | 500 Foxes | 50 Hawks | 5
Medium
- AThe total biomass of producers is less than that of primary consumers
- BThe biomass of secondary consumers is greater than that of primary consumers
- CThe biomass decreases at each trophic level
- DThe biomass of hawks is greater than that of foxes
39.A student investigates the effect of temperature on the rate of decomposition of leaf litter by soil microorganisms. Which of the following variables should be kept constant?
Easy
- ATemperature
- BType of leaf litter
- CNumber of microorganisms
- DTime of day
40.Which of the following is an abiotic factor that affects a food web?
Easy
- APredation
- BTemperature
- CCompetition
- DDisease
41.What is the term for the graphical representation of feeding relationships in an ecological community?
Easy
- AFood chain
- BFood web
- CEnergy pyramid
- DTrophic level
42.Which of the following is an autotroph?
Easy
- ARabbit
- BFox
- CGrass
- DMushroom
43.A food chain is a linear feeding pathway, while a food web is a network of interconnected food chains.
Easy
True or false?
44.Decomposers are considered autotrophs because they break down dead organic matter.
Easy
True or false?
45.Which of the following can be considered basal species in a food web? (Select all that apply.)
Medium
- AAutotrophs
- BSaprophytic detritivores
- CTop predators
- DHerbivores
- EDecomposing organic material with associated microorganisms
46.Match each term with its correct definition.
Medium
- Autotroph
- Heterotroph
- Mixotroph
- Consumes rather than produces biomass energy
- Produces biomass energy by photosynthesis or chemosynthesis
- Can obtain energy both from photosynthesis and from consuming organic matter
47.Arrange the following trophic levels in order from lowest to highest (bottom to top) in a typical energy pyramid.
Easy
- Primary consumers
- Producers
- Tertiary consumers
- Secondary consumers
48.Match each term with its correct description.
Medium
- Autotroph
- Heterotroph
- Decomposer
- Mixotroph
- Produces its own food using sunlight or chemicals
- Obtains energy by consuming other organisms
- Breaks down dead organic matter
- Can obtain energy through both photosynthesis and consuming organic matter
49.Arrange the following trophic levels in order from the base (bottom) to the top of an energy pyramid.
Easy
- Tertiary consumers
- Primary consumers
- Producers
- Secondary consumers
50.Which of the following are examples of abiotic factors that can affect a food web? (Select all that apply.)
Medium
- ATemperature
- BSunlight
- CPredators
- DSoil pH
- EDecomposers
51.Complete the sentence.
Easy
In a food web, the feeding connections are called ____ links.
52.What is the term for the position an organism occupies in a food web, such as autotroph or heterotroph?
Easy
53.What is the term for a species that has no predators in a food web?
Medium

Ghi chú ôn tập

## Food Webs and Ecosystems ### Key Concepts - **Food web**: A graphical representation of feeding relationships (who eats whom) in an ecological community. - **Food chain**: A linear, noncyclic feeding pathway from a base species to a top consumer. - **Trophic level**: Position in the food web (e.g., autotrophs, heterotrophs). ### Trophic Levels - **Autotrophs (producers)**: Produce biomass energy via photosynthesis or chemosynthesis. Example: plants, cyanobacteria. - **Heterotrophs (consumers)**: Obtain energy by consuming other organisms. Types: herbivores, carnivores, scavengers, parasites. - **Mixotrophs**: Organisms that can be both autotrophic and heterotrophic (e.g., carnivorous plants). - **Decomposers**: Break down dead organic matter (e.g., bacteria, fungi). ### Food Web Structure - **Basal species**: No prey; include autotrophs and detritivores. - **Top predators**: No natural predators (apex predators). - **Trophic links**: Feeding connections; connectance = number of links per consumer. - **Trophic species**: Functional groups with same predators and prey. ### Energy Flow - Energy flows from autotrophs to heterotrophs through feeding. - Only about 10% of energy transfers between trophic levels (energy pyramid). ### Predicting Changes - Removing a species can disrupt the web (e.g., loss of a predator may increase prey, affecting plants). - Habitat destruction reduces biodiversity and alters food webs. ### Key Terms - **Autotroph**: Organism that produces its own food. - **Heterotroph**: Organism that consumes others for energy. - **Trophic level**: Position in food chain. - **Food web**: Network of interconnected food chains. - **Decomposer**: Organism that breaks down dead matter.

Autotroph: An organism that produces its own food using sunlight or chemical energy (e.g., plants, algae).
Heterotroph: An organism that obtains energy by consuming other organisms (e.g., animals, fungi).
Trophic level: The position an organism occupies in a food chain or web (e.g., producer, primary consumer).
Food web: A network of interconnected food chains showing feeding relationships in an ecosystem.
Food chain: A linear sequence of organisms where each is eaten by the next in line.
Decomposer: An organism that breaks down dead organic matter, recycling nutrients (e.g., bacteria, fungi).
Producer: Another term for autotroph; an organism that makes its own food.
Consumer: An organism that eats other organisms; heterotroph.
Apex predator: A predator at the top of a food web with no natural predators.
Biomass: The total mass of living organisms in a given area or volume.

Thẻ ghi nhớ

What is a food web?

A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community.

What is a trophic level?

A trophic level is the position an organism occupies in a food web, broadly classifying organisms as autotrophs or heterotrophs.

What are autotrophs?

Autotrophs are organisms that produce their own biomass energy, either by photosynthesis (capturing sunlight) or chemosynthesis (oxidizing inorganic compounds).

What are heterotrophs?

Heterotrophs are organisms that obtain organic matter by feeding on autotrophs or other heterotrophs; they consume rather than produce biomass energy.

What are mixotrophs?

Mixotrophs are organisms (e.g., carnivorous plants) that can act as both autotrophs and heterotrophs, obtaining organic matter from non-atmospheric sources in addition to photosynthesis.

What are the main types of consumer-resource interactions?

The main types are herbivory, carnivory, scavenging, and parasitism.

Who pioneered the concept of food cycles and food chains?

Charles Elton pioneered the concept of food cycles, food chains, and food size in his 1927 book 'Animal Ecology'.

What did Raymond Lindeman emphasize in his 1942 paper on trophic dynamics?

Lindeman emphasized the important role of decomposer organisms in a trophic system of classification.

What is a trophic species?

A trophic species is a functional group of species that have the same predators and prey in a food web.

What are basal species in a food web?

Basal species are those without prey; they can be autotrophs or saprophytic detritivores (decomposers).

What is a trophic link?

A trophic link is a feeding connection in a food web, representing who eats whom.

What is food web connectance?

Connectance is the number of trophic links per consumer in a food web.

How are food chains related to food webs?

Food chains are linear, noncyclic feeding pathways nested within the trophic links of food webs.

What are apex predators?

Apex predators are top-level organisms that no other species kills directly for food resource needs.

What are omnivores in a food web?

Omnivores are intermediate-level organisms that feed on more than one trophic level, causing energy to flow through multiple pathways.

What is the role of decomposers in a food web?

Decomposers break down dead organic matter and recycle nutrients, forming an important part of the basal species in some food webs.

How do ecologists use food web models?

Ecologists use quantitative models of trophic dynamics to measure and test patterns in food web structure, such as scaling laws relating predator-prey linkages to species richness.

What is the difference between a food web and a food chain?

A food web is a complex network of interconnected food chains, while a food chain is a single linear pathway of energy flow.

What abiotic factors affect ecosystems?

Abiotic factors include sunlight, temperature, water, soil, and nutrients; they influence the types and numbers of organisms in an ecosystem.

What biotic factors affect ecosystems?

Biotic factors include all living organisms and their interactions, such as predation, competition, and symbiosis.

How might removing a species from a food web impact the ecosystem?

Removing a species can disrupt energy flow, cause population changes in other species (e.g., prey increase or predator decline), and potentially lead to ecosystem instability.

How does habitat destruction affect food webs?

Habitat destruction reduces or eliminates food sources and shelter, leading to population declines, loss of biodiversity, and disruption of trophic interactions.

What is an example of a chemolithotroph?

The sulfur bacterium Thiobacillus, which lives in hot sulfur springs and obtains energy by oxidizing inorganic compounds.

What did Charles Darwin contribute to the concept of food webs?

Darwin used terms like 'entangled bank', 'web of life', and 'web of complex relations', and noted the role of earthworms in decomposition.

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