Food chains and food webs

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Notas de aula

Big idea: who eats what, and where the energy goes

Big idea (key concept): Relationships. Living things in an ecosystem depend on each other. What happens to one organism affects others.
Related concept: Energy. The links between organisms are really links for passing energy along, starting with the Sun.
Global context: Globalization and sustainability. People are part of food webs too. Fishing, farming and invasive species change food webs around the world, so understanding them helps us look after the planet.
Producers make their own food. Plants and algae use light energy to make sugars by photosynthesis.
Consumers cannot make their own food, so they get energy by eating other organisms.
Decomposers, such as fungi and many bacteria, break down dead plants, dead animals and waste, and return nutrients to the soil.

Decomposers return nutrients to the soil

Reading a food chain

A food chain shows the feeding links between organisms, for example: Sun → grass → mouse → owl.
Each arrow means ‘gives energy to’. It points from the organism that is eaten to the organism that eats it.
A food chain always starts with a producer, because only producers can capture the energy in sunlight.
Animals that eat only plants are herbivores. Animals that eat only other animals are carnivores. Animals that eat both are omnivores.
In grass → mouse → owl, the grass is the producer, the mouse is the primary consumer and the owl is the secondary consumer.

A food chain

Predators, prey and trophic levels

A predator hunts and eats other animals. The animal it eats is its prey.
A trophic level is a feeding step in a chain. Level 1 is the producer, level 2 is the primary consumer, level 3 is the secondary consumer, and so on.
In grass → grasshopper → frog → python → eagle, the frog is a secondary consumer, the python is a tertiary consumer and the eagle is a quaternary consumer.
An animal at the top of a food chain, with no natural predators, is an apex predator.
One animal can be in more than one trophic level. A python that eats a frog is a tertiary consumer, but a python that eats a mouse that ate grass is a secondary consumer.

Trophic levels

Food webs and what happens when one organism is removed

Most animals eat more than one thing, and are eaten by more than one thing. Many food chains linked together make a food web.
A food web is a better model of an ecosystem than a single chain because it shows all the links, not just one path.
If one organism is removed, the organisms that ate it lose a food source and may decrease. The organisms it used to eat may increase because fewer are being eaten.
These changes can spread through the web, so organisms that are not directly linked can still be affected.
Sustainability: if too many large fish are caught, the small fish they eat can increase, and this can unbalance the whole food web. Careful fishing limits help protect it.

A food web shows the interdependence of organisms

Energy along a food chain

The original source of energy for almost all food chains is the Sun. Producers capture a small part of it.
At each step, only about 10% (one tenth) of the energy is passed on to the next level. This is a rough rule: the real figure varies.
The rest is lost. Some is released as heat when organisms respire, some is used for movement, and some is in waste or in parts that are not eaten, such as bones.
Because so much energy is lost at each step, there is less and less energy available higher up the chain. This is why food chains rarely have more than four or five links.
It is also why top predators are few in number: there is not enough energy to support many of them.

Energy loss along a food chain

Think like a scientist: investigating a food web in the field

Scientists cannot count every animal in a meadow, so they take samples. A quadrat is a square frame placed on the ground; you count the organisms inside it.
Place quadrats randomly so you do not choose the easy places, and use many quadrats, then calculate a mean.
Inquiry task: plan an investigation to find out whether grass length affects the number of grasshoppers. The independent variable is grass length and the dependent variable is the number of grasshoppers per quadrat.
Control other variables: same size of quadrat, same time of day, same weather, and the same field.
Evaluate: Would one quadrat be enough? What could make your results less reliable? How could you improve the method?

Quadrat sampling in an ecosystem

Slides

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CADASTRE-SE — GRÁTIS ENTRAR

Questões de prática

Prévia grátis — 8 de 54 perguntas. Cadastre-se para ver todas.

1.What is a producer?
Easy
- AAn animal that eats plants as its food
- BAn organism that makes its own food from light
- CAn organism that breaks down dead matter
- DAn animal that hunts other animals for food
2.Which of these is a producer?
Easy
- AAn oak tree
- BA mushroom
- CA fox
- DA rabbit
3.What is a consumer?
Easy
- AAn organism that makes food from sunlight
- BAn organism that lives only in water and soil
- CAn organism that breaks down dead plants
- DAn organism that gets energy by eating others
4.What does an arrow in a food chain show?
Easy
- AWhich organism is bigger
- BWhich organism eats the other, pointing from eater to food
- CThe direction energy flows, from the eaten organism to the eater
- DWhich organism lives the longest
5.In the food chain grass → rabbit → fox, which organism is the primary consumer?
Easy
- AThe fox
- BThe rabbit
- CThe Sun
- DThe grass
6.In the food chain grass → rabbit → fox, what is the fox?
Easy
- AA secondary consumer
- BA decomposer
- CA primary consumer
- DA producer
7.What is the original source of energy for almost all food chains?
Easy
- AThe soil
- BWater
- CPlants
- DThe Sun
8.What is a predator?
Easy
- AAn animal that eats only plants
- BAn animal that is hunted by other animals
- CAn animal that hunts and eats other animals
- DAn animal that feeds on dead matter

Mais perguntas

9.What is prey?
Easy
- AA plant that is eaten by animals
- BAn animal that is hunted by a predator
- CAn animal that feeds on dead matter
- DAn animal that hunts other animals
10.What is a herbivore?
Easy
- AAn animal that eats only plants
- BAn animal that eats only other animals
- CAn animal that eats both plants and animals
- DA plant that makes its own food
11.Which of these is an omnivore?
Easy
- AA lion
- BA cow
- CA rabbit
- DA human
12.What do decomposers do?
Easy
- AMake their food using sunlight
- BHunt other animals for food
- CBreak down dead matter and waste
- DEat only living plants
13.In a food chain, arrows point from the predator to its prey.
Easy
True or false?
14.Every food chain begins with a producer.
Easy
True or false?
15.A food web is made up of many food chains linked together.
Easy
True or false?
16.Match each role to an example from the food chain grass → rabbit → fox.
Easy
- Producer
- Primary consumer
- Secondary consumer
- Rabbit
- Fox
- Grass
17.Put these in the order the energy flows along the food chain.
Easy
- Rabbit
- Fox
- The Sun
- Grass
18.Complete the sentence.
Easy
An animal that eats only plants is called a ____.
19.Complete the sentence.
Easy
A ____ is an animal that hunts and kills other animals for food.
20.Complete the sentence.
Easy
Organisms that break down dead plants and animals are called ____.
21.Why do food chains nearly always start with a plant or another producer?
Medium
- APlants are the biggest living things in an ecosystem
- BOnly producers can capture the energy in sunlight
- CAnimals cannot eat each other until later
- DPlants are found in almost every habitat
22.In the food chain algae → water flea → minnow → heron, which organism is the tertiary consumer?
Medium
- AThe heron
- BThe water flea
- CThe minnow
- DThe algae
23.Which of these is a correct food chain?
Medium
- ARabbit → grass → fox
- BFox → rabbit → grass
- CFox → grass → rabbit
- DGrass → rabbit → fox
24.Why is a food web a better model of an ecosystem than a single food chain?
Medium
- AIt shows the size of each animal
- BIt shows only the top predators in it
- CIt shows organisms have several food sources
- DIt shows how much each animal weighs
25.In a meadow, grass is eaten by rabbits, mice and grasshoppers. Frogs eat grasshoppers. Foxes eat rabbits and mice. Snakes eat frogs and mice. Hawks eat snakes. If all the frogs were removed, which organism would most likely increase first?
Medium
- AThe grass
- BThe grasshoppers
- CThe hawks
- DThe foxes
26.Why do food chains rarely have more than five links?
Medium
- AEnergy is lost at each step, leaving too little
- BPlants cannot support more than four animals
- CPredators get too big to catch their prey
- DDecomposers eat the top predator first
27.About what fraction of the energy in one trophic level is passed on to the next?
Medium
- AAbout one half
- BAlmost all of it
- CNone of it
- DAbout one tenth
28.Which of these is one way energy is lost from a food chain?
Medium
- AEnergy turning back into sunlight
- BEnergy being passed to the producer
- CHeat released when organisms respire
- DEnergy being made by the consumer
29.What is an apex predator?
Medium
- AAn animal that eats only plants and fruit
- BAn animal at the top with no natural predators
- CThe first animal in any food chain
- DAn animal that feeds on dead matter
30.Which statement about decomposers is correct?
Medium
- AThey return nutrients from dead matter to the soil
- BThey are always the top of the food chain
- CThey make food using sunlight
- DThey only eat living animals
31.People catch nearly all the large fish in a part of the sea. What is most likely to happen to the smaller fish they eat?
Medium
- AThey will decrease because they have no food
- BNothing will change
- CThey will all become predators
- DThey will increase because fewer are eaten
32.In a meadow, grass is eaten by rabbits, mice and grasshoppers. Frogs eat grasshoppers. Foxes eat rabbits and mice. Snakes eat frogs and mice. Hawks eat snakes. Which of these are primary consumers in the meadow? (select all that apply)
Medium
- ARabbits
- BMice
- CGrasshoppers
- DFrogs
- EHawks
33.Which of these are producers? (select all that apply)
Medium
- AAn oak tree
- BSeaweed
- CA mushroom
- DA shark
- EAlgae
34.Energy is passed along a food chain without any being lost.
Medium
True or false?
35.Match each word to its meaning.
Medium
- Predator
- Prey
- Herbivore
- Carnivore
- Is hunted and eaten
- Eats only plants
- Eats only other animals
- Hunts and eats other animals
36.Put these organisms in order from trophic level 1 upwards.
Medium
- Small fish
- Seal
- Phytoplankton
- Zooplankton
37.Complete the sentence.
Medium
Many food chains that overlap and link together make a food ____.
38.A field of grass holds 10 000 kJ of energy. Assume exactly 10% of the energy passes on at each step in the chain grass → rabbit → fox. How much energy passes to the fox?
Medium
39.A student wants to find out whether grass length affects how many grasshoppers live there. What is the dependent variable?
Medium
- AThe length of the grass
- BThe size of the quadrat
- CThe number of grasshoppers
- DThe time of day
40.In the same investigation, which of these should be kept the same to make it a fair test?
Medium
- AThe length of the grass
- BThe size of the quadrat
- CThe number of grasshoppers
- DThe height of the student
41.
In a pond, small fish eat snails and snails eat pondweed. A class counts the organisms every two weeks.
Week Small fish Snails Pondweed cover (%)
0 10 200 40
2 20 150 55
4 30 90 70
As the number of small fish increased, what happened to the number of snails?
Medium
- AIt decreased
- BIt increased
- CIt stayed the same
- DIt doubled
42.
In a pond, small fish eat snails and snails eat pondweed. A class counts the organisms every two weeks.
Week Small fish Snails Pondweed cover (%)
0 10 200 40
2 20 150 55
4 30 90 70
By how many did the number of snails fall between week 0 and week 4?
Medium
43.Write a food chain with four organisms. Label the producer and the primary, secondary and tertiary consumers, and say what the arrows mean.
Medium
44.In a meadow, grass is eaten by rabbits, mice and grasshoppers. Frogs eat grasshoppers. Foxes eat rabbits and mice. Snakes eat frogs and mice. Hawks eat snakes. If all the frogs were removed, which organism loses one of its two food sources?
Hard
- AThe rabbits
- BThe hawks
- CThe foxes
- DThe snakes
45.
In a pond, small fish eat snails and snails eat pondweed. A class counts the organisms every two weeks.
Week Small fish Snails Pondweed cover (%)
0 10 200 40
2 20 150 55
4 30 90 70
Which conclusion is best supported by the data?
Hard
- ASnails eat the small fish, so fish increased
- BPondweed eats snails, so the snails fell
- CMore fish led to fewer snails and more pondweed
- DFish and snails both increased over four weeks
46.A student counts grasshoppers in one quadrat in long grass (8) and one quadrat in short grass (3). Why is this not enough to conclude that long grass has more grasshoppers?
Hard
- AQuadrats always give the same answer
- BOne sample might be chance; many are needed
- CGrasshoppers cannot be counted
- DLong grass should not be sampled
47.Why is there less energy available to animals at the top of a food chain?
Hard
- AEnergy is lost at every step, so less is passed on
- BTop predators eat much less food than others
- CThe Sun gives less energy to top predators
- DEnergy is stored in the producers for ever
48.Which of these are ways energy is lost between one trophic level and the next? (select all that apply)
Hard
- AHeat from respiration
- BEnergy used for movement
- CParts not eaten, such as bones
- DPhotosynthesis in the consumer
- EEnergy passing down to the producer
49.Removing one organism from a food web can affect organisms that do not eat it and are not eaten by it.
Hard
True or false?
50.In a meadow, grass is eaten by rabbits, mice and grasshoppers. Frogs eat grasshoppers. Foxes eat rabbits and mice. Snakes eat frogs and mice. Hawks eat snakes. Match each organism that is removed to its most likely first effect.
Hard
- Grasshoppers removed
- Foxes removed
- Grass removed
- Rabbits are eaten less, so increase
- Rabbits, mice and grasshoppers lose their food
- Frogs lose a food source
51.A fishing fleet removes most of the large predator fish from part of the ocean. What is the best description of the risk?
Hard
- ANothing will change as fish are replaced
- BAll the smaller fish will die out
- CThe predator fish will get more food
- DThe food web may become unbalanced
52.In a meadow, grass is eaten by rabbits, mice and grasshoppers. Frogs eat grasshoppers. Foxes eat rabbits and mice. Snakes eat frogs and mice. Hawks eat snakes. Predict what would happen to the grass if all the frogs were removed, and explain your answer.
Hard
53.Explain why there are usually no more than four or five links in a food chain.
Hard
54.Plan an investigation to find out whether grass length affects the number of grasshoppers. Include what you will change, what you will measure, two things you will control and how you will make your results reliable.
Hard

Resumos de revisão

## The big idea - Organisms in an ecosystem depend on each other (**Relationships**) and energy passes between them (**Energy**). ## Roles - **Producers** make food using light. **Consumers** eat other organisms: **primary**, **secondary**, **tertiary**. **Decomposers** break down dead matter. - A **predator** hunts **prey**. **Herbivores** eat plants, **carnivores** eat animals, **omnivores** eat both. ## Chains and webs - A **food chain** starts with a producer. **Arrows** point in the direction energy flows, from eaten to eater. - A **food web** is many chains linked together. Removing one organism can change the numbers of others. ## Energy - Energy starts with the **Sun**. Only about **10%** passes to the next level. The rest is lost as heat, movement and waste, so chains are short. ## Investigating - Use **quadrats**, place them randomly, use many and calculate a mean. Change one variable, measure one, control the rest.

Producer: An organism that makes its own food, usually by photosynthesis.
Consumer: An organism that gets energy by eating other organisms.
Decomposer: An organism that breaks down dead matter and returns nutrients to the soil.
Food chain: A line of organisms showing who eats whom and the direction energy flows.
Food web: Many food chains linked together.
Predator: An animal that hunts and eats other animals.
Prey: An animal that is hunted and eaten by a predator.
Herbivore: An animal that eats only plants.
Carnivore: An animal that eats only other animals.
Omnivore: An animal that eats both plants and animals.
Trophic level: A feeding step in a food chain, such as producer or primary consumer.
Apex predator: An animal at the top of a food chain with no natural predators.
Quadrat: A square frame used to sample and count organisms in an area.

Flashcards

What is a producer?

An organism that makes its own food using light energy, such as a plant or alga.

What is a consumer?

An organism that gets energy by eating other organisms.

What do decomposers do?

Break down dead plants, dead animals and waste, returning nutrients to the soil.

What does an arrow in a food chain mean?

Energy flows from the organism that is eaten to the one that eats it.

What must every food chain start with?

A producer, which captures the Sun's energy.

In grass → rabbit → fox, name the primary and secondary consumers.

Primary consumer: rabbit. Secondary consumer: fox.

What is a predator? What is prey?

A predator hunts and eats other animals; prey is the animal that is hunted.

What is an apex predator?

An animal at the top of the food chain with no natural predators.

Herbivore, carnivore, omnivore: what does each eat?

Herbivore: plants only. Carnivore: animals only. Omnivore: both.

What is a food web?

Many food chains linked together, showing that organisms have several food sources and predators.

What happens to the predators' prey if a predator is removed?

The prey are eaten less, so their numbers may increase.

What happens to a predator if its main prey is removed?

It loses a food source, so its numbers may decrease.

What is the original source of energy in a food chain?

The Sun.

How much energy passes on to the next trophic level?

About 10% (one tenth). The rest is lost as heat, movement and waste.

Why are food chains short?

So much energy is lost at each step that there is too little left to support many more links.

What is a quadrat and how do you use it well?

A square frame for counting organisms. Place many randomly and calculate a mean.

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CADASTRE-SE — GRÁTIS ENTRAR

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Em breve

Week	Small fish	Snails	Pondweed cover (%)
0	10	200	40
2	20	150	55
4	30	90	70

Week	Small fish	Snails	Pondweed cover (%)
0	10	200	40
2	20	150	55
4	30	90	70

Week	Small fish	Snails	Pondweed cover (%)
0	10	200	40
2	20	150	55
4	30	90	70