Food chains and webs

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Lesson notes

Food Chains

A **food chain** shows what eats what in a linear sequence.
Example: grass → grasshopper → bird → fox.
**Producers** make their own food through **photosynthesis** (e.g., grass, lettuce).
**Primary consumers** eat producers (herbivores).
**Secondary consumers** eat primary consumers.
**Tertiary consumers** eat secondary consumers.

Key Definitions

**Herbivore**: eats only plants.
**Carnivore**: eats other animals.
**Omnivore**: eats both plants and animals.
**Predator**: an organism that eats another organism.
**Prey**: the organism that a predator eats.

Food Webs

A **food web** contains many interconnected food chains.
It shows the complex feeding relationships in an ecosystem.
If one part of the web is affected, it can affect other parts.
Example: if carrots die, rabbit population may decrease due to less food.

Energy Flow

Energy flows from producers to consumers along food chains.
Only about 10% of energy is passed to the next trophic level.
The rest is lost as heat, waste, or used for life processes.
**Energy pyramids** show the decreasing energy at each level.

Energy pyramid showing trophic levels and energy loss.

Slides

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Practice questions

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1.What is a producer in a food chain?
Easy
- AAn organism that makes its own food through photosynthesis
- BAn animal that eats plants
- CAn animal that eats other animals
- DAn organism that breaks down dead matter
2.What is a herbivore?
Easy
- AAn animal that eats only plants
- BAn animal that eats other animals
- CAn animal that eats both plants and animals
- DAn organism that makes its own food
3.In a food chain: grass → rabbit → fox, what is the secondary consumer?
Medium
- AFox
- BRabbit
- CGrass
- DGrass and rabbit
4.In a food web, if all the rabbits died, what would most likely happen to the fox population?
Medium
- ADecrease because they have less food
- BIncrease because there is more grass
- CStay the same
- DIncrease because rabbits are competitors
5.Which of the following is always a carnivore?
Hard
- ATertiary consumer
- BPrimary consumer
- CHerbivore
- DProducer
6.What is the role of a primary consumer in a food chain?
Medium
- AIt eats the producer
- BIt eats the secondary consumer
- CIt makes its own food
- DIt breaks down dead organisms
7.Which term describes an animal that eats both plants and animals?
Easy
- AOmnivore
- BHerbivore
- CCarnivore
- DProducer
8.In the food chain: lettuce → slug → sparrow → hawk, what is the prey of the hawk?
Medium
- ASparrow
- BSlug
- CLettuce
- DHawk

More questions

9.If most of the slugs in a food web (lettuce → slug → sparrow) died, what would happen to the lettuce population?
Medium
- AIncrease because fewer slugs eat it
- BDecrease because sparrows eat more lettuce
- CStay the same
- DDecrease because slugs decompose into fertilizer
10.Which of the following best describes a food web?
Hard
- AMany food chains linked together
- BA single path of energy flow
- CA diagram showing only producers
- DA list of all predators in an ecosystem
11.What does the arrow in a food chain represent?
Easy
- AFlow of energy from one organism to another
- BDirection of movement
- CWhich organism is bigger
- DWhich organism is faster
12.In an energy pyramid, which trophic level has the most energy?
Medium
- AProducers
- BPrimary consumers
- CSecondary consumers
- DTertiary consumers
13.In a food chain, what is the role of a secondary consumer?
Easy
- AAn animal that eats the primary consumer
- BAn animal that eats the producer
- CAn organism that makes its own food
- DAn animal that eats only plants
14.Which of the following is an example of a producer?
Easy
- AGrass
- BRabbit
- CFox
- DHawk
15.In the food chain: lettuce → slug → sparrow → hawk, what is the tertiary consumer?
Medium
- AHawk
- BSparrow
- CSlug
- DLettuce
16.In a food chain, grass → grasshopper → frog → snake, which organism is the secondary consumer?
Medium
- Agrass
- Bgrasshopper
- Cfrog
- Dsnake
17.What is the role of a producer in a food chain?
Easy
- AIt eats other organisms.
- BIt makes its own food through photosynthesis.
- CIt breaks down dead organisms.
- DIt is always an animal.
18.In the food chain: lettuce → slug → sparrow → hawk, what is the prey of the sparrow?
Medium
- Alettuce
- Bslug
- Csparrow
- Dhawk
19.A student sets up a model ecosystem with two food chains: grass → rabbit → fox and grass → mouse → fox. If a disease kills all the mice, what is the most likely effect on the fox population?
Hard
- AThe fox population will increase because there is less competition for grass.
- BThe fox population will decrease because they lose a food source.
- CThe fox population will remain unchanged because they can eat rabbits.
- DThe fox population will first decrease then increase.
20.In an experiment, a scientist measures the number of organisms at each trophic level in a grassland ecosystem. She finds 1000 grass plants, 200 rabbits, 20 foxes, and 1 eagle. Which statement best explains the decreasing numbers?
Hard
- AEnergy is lost at each trophic level, so fewer organisms can be supported.
- BHigher trophic levels require more space.
- CPredators are less efficient at reproducing.
- DThe grass plants are the smallest organisms.
21.Which of the following is an omnivore?
Medium
- AFox that eats rabbits
- BRabbit that eats grass
- CBear that eats berries and fish
- DHawk that eats sparrows
22.In a food web, a plant is eaten by a caterpillar, which is eaten by a bird, which is eaten by a cat. The cat is a:
Medium
- Aprimary consumer
- Bsecondary consumer
- Ctertiary consumer
- Dproducer
23.A student investigates a pond food web: algae → water flea → small fish → large fish. Which statement about this food web is correct?
Hard
- AAlgae are primary consumers.
- BWater fleas are producers.
- CSmall fish are secondary consumers.
- DLarge fish are primary consumers.
24.Which of the following correctly describes a food chain?
Medium
- AA single path of energy flow through an ecosystem
- BA network of interconnected food chains
- CA diagram showing only producers
- DA list of all organisms in an area
25.In a food chain: grass → rabbit → fox, what would be the effect on the grass if the fox population decreases?
Hard
- AThe grass population would increase because fewer rabbits are eaten.
- BThe grass population would decrease because more rabbits eat it.
- CThe grass population would stay the same.
- DThe grass population would first increase then decrease.
26.In the food chain: grass → grasshopper → frog → snake, what is the secondary consumer?
Easy
- AFrog
- BGrasshopper
- CSnake
- DGrass
27.In the food chain: lettuce → slug → sparrow → hawk, what would happen to the lettuce population if most of the slugs died?
Medium
- AIt would increase
- BIt would decrease
- CIt would stay the same
- DIt would first decrease then increase
28.What does an arrow in a food chain represent?
Easy
- AThe direction of energy flow (eaten by)
- BThe direction of movement
- CThe size of the organism
- DThe number of organisms
29.In the food web: grass → rabbit → fox and grass → mouse → fox, if a disease kills all the mice, what is the most likely effect on the fox population?
Medium
- AIt will decrease because foxes lose a food source
- BIt will increase because foxes eat more rabbits
- CIt will stay the same
- DIt will first increase then decrease
30.In an experiment, a scientist measures the number of organisms at each trophic level in a grassland ecosystem. She finds 1000 grass plants, 200 rabbits, and 20 foxes. Which statement is correct?
Hard
- AThe number of organisms decreases at higher trophic levels
- BThe number of organisms increases at higher trophic levels
- CThe number of organisms is the same at all levels
- DThe number of organisms is highest for secondary consumers
31.In a food chain, what is meant by a 'producer'?
Easy
- AAn organism that makes its own food through photosynthesis
- BAn organism that eats other organisms
- CAn organism that breaks down dead material
- DAn organism that eats only plants
32.Which of the following is a herbivore?
Easy
- ARabbit
- BFox
- CHawk
- DSnake
33.In the food chain: lettuce → slug → sparrow → hawk, what is the secondary consumer?
Medium
- ASparrow
- BSlug
- CHawk
- DLettuce
34.In a food web, a scientist observes that the number of caterpillars has increased dramatically. Which of the following is most likely to happen as a result?
Medium
- AThe number of birds (that eat caterpillars) will increase.
- BThe number of grass plants (producers) will increase.
- CThe number of foxes (top predators) will decrease.
- DThe number of rabbits (herbivores) will increase.
35.A student sets up two model ecosystems in sealed jars. Jar A contains grass, rabbits, and foxes. Jar B contains grass, rabbits, foxes, and decomposers. After six months, which jar is more likely to have a stable ecosystem?
Hard
- AJar A, because there are fewer organisms competing for resources.
- BJar B, because decomposers recycle nutrients back into the soil.
- CJar A, because decomposers would consume too many rabbits.
- DJar B, because decomposers provide food for the foxes.
36.In an experiment, a scientist measures the biomass at each trophic level in a grassland ecosystem. The results show that the biomass of grass is 10,000 kg, the biomass of rabbits is 1,000 kg, and the biomass of foxes is 100 kg. What is the approximate efficiency of energy transfer from the grass to the rabbits?
Medium
- A1%
- B10%
- C90%
- D100%
37.Which of the following is an example of a food chain?
Easy
- ASun → grass → rabbit → fox
- BFox → rabbit → grass → sun
- CGrass → rabbit → fox → sun
- DRabbit → grass → fox → sun
38.In a food web, a pesticide is applied that kills all the insects. Which of the following is the most likely long-term effect on the ecosystem?
Hard
- AThe number of producers will increase because there are fewer herbivores.
- BThe number of top predators will increase because they have less competition.
- CThe number of herbivorous mammals will decrease because they rely on insects for food.
- DThe number of decomposers will increase because there will be more dead insects.
39.What is the role of decomposers in a food web?
Easy
- AThey produce food for other organisms.
- BThey break down dead organisms and return nutrients to the soil.
- CThey eat primary consumers.
- DThey convert sunlight into chemical energy.
40.A student constructs a food web: grass → rabbit → fox, and grass → mouse → fox. If a disease kills all the rabbits, what is the most likely effect on the fox population?
Medium
- AThe fox population will increase because there are more mice.
- BThe fox population will decrease because it loses a food source.
- CThe fox population will remain the same because it can eat grass.
- DThe fox population will increase because there is less competition.

Revision notes

## Food Chains and Webs - **Food chain**: shows what eats what (e.g., grass → grasshopper → ...). - **Food web**: many food chains linked together; more realistic. ### Key Definitions - **Producer**: organism that makes its own food via **photosynthesis**. - **Primary consumer**: eats producer. - **Secondary consumer**: eats primary consumer. - **Tertiary consumer**: eats secondary consumer. - **Herbivore**: eats only plants. - **Carnivore**: eats other animals. - **Omnivore**: eats both plants and animals. - **Predator**: organism that eats another. - **Prey**: organism that is eaten. ### Example Food Chain Grass → Grasshopper → Frog → Snake → Hawk - Producer: grass - Primary consumer: grasshopper - Secondary consumer: frog - Tertiary consumer: snake - Apex predator: hawk ### Example Food Web Lettuce → Slug → Sparrow → Hawk Carrot → Rabbit → Fox - If carrots die → fewer rabbits. - If slugs die → sparrows have less food → sparrow population may decrease → lettuce population may increase (fewer slugs eating it). ### Key Points - Changes in one population affect others in the web. - Know the roles: producer, consumer levels, herbivore/carnivore/omnivore, predator/prey.

Producer: Organisms that make their own food through photosynthesis.
Primary consumer: Animal that eats the producer.
Secondary consumer: Animal that eats the primary consumer.
Tertiary consumer: Animal that eats the secondary consumer.
Herbivore: Animal that eats only plants.
Carnivore: Animal that eats other animals.
Omnivore: Animal that eats both plants and animals.
Predator: An organism that eats another organism.
Prey: The organism that a predator eats.

Flashcards

What is a food chain?

A food chain is a way of showing what eats what.

What is a producer?

An organism that makes its own food through photosynthesis.

What is a primary consumer?

An animal that eats the producer.

What is a secondary consumer?

An animal that eats the primary consumer.

What is a tertiary consumer?

An animal that eats the secondary consumer.

What is a herbivore?

An animal that eats only plants.

What is a carnivore?

An animal that eats other animals.

What is an omnivore?

An animal that eats both plants and animals.

What is a predator?

An organism that eats another organism.

What is prey?

The organism that a predator eats.

What is a food web?

A food web contains lots of food chains linked together.

In a food chain, what is the role of grass?

Grass is a producer, making its own food through photosynthesis.

In a food chain, what is a grasshopper?

A grasshopper is a primary consumer (herbivore) that eats grass.

In a food chain, what is a frog?

A frog is a secondary consumer that eats the grasshopper.

In a food chain, what is a snake?

A snake is a tertiary consumer that eats the frog.

In a food chain, what is a hawk?

A hawk is a quaternary consumer that eats the snake.

If all carrots in a food web died, what would happen to the rabbit population?

There would be fewer rabbits because they would have less food to eat.

In the food web, what is the producer?

Lettuce (or carrot, depending on the web).

In the food web, what is the secondary consumer?

The sparrow (or frog, depending on the chain).

What is the prey of the hawk?

The snake (or sparrow, depending on the chain).

What is the predator of the slug?

The sparrow (or thrush, depending on the web).

If most of the slugs died, what would happen to the sparrow population?

The sparrow population would decrease because they have less food.

If most of the slugs died, what would happen to the lettuce population?

The lettuce population would increase because fewer slugs are eating it.

Name a primary consumer from the food web.

Rabbit (or slug, grasshopper).

Name the predators of a rabbit.

Fox and hawk.

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