Teaching sequence

Work through this resource material in the following sequence:

10 minutes

Part A: Activating prior knowledge

20 minutes

Part B: What are food chains and food webs?

30 minutes

Part C: How fragile are food webs?

45 minutes

Part D: How do humans impact marine food webs?

15 minutes

Reflection

Learning intentions:

Students will:

understand the difference between a food web and a food chain
understand how each species in a food web is integral to the health of the whole web
recognise how food webs can be used to help us understand the health of marine environments.

Success criteria:

Students can:

explain the difference between food webs and food chains
identify the trophic levels of food webs
undertake research online
produce a scientific poster.

Part A: Activating prior knowledge

Step 1

Break the class into small groups. Assign each group with three of the following terms and invite them to come up with a definition (WITHOUT looking up the answers). Give the groups three minutes to come up with their definitions. Groups can record their definitions in their workbooks or on the Student Worksheet.

Once complete, invite each group to share their definitions. You can use the definitions below to provide correction or clarity. Students should update their definitions in their workbook or on the Student Worksheet.

Producer
Producers are organisms that make their own food (also known as autotrophs). They get their energy from chemicals or the sun and are able to convert this energy into food. Plants are the most common type of producers. Through photosynthesis, green plants are able to convert sunlight and water into food. Producers are at the beginning of the food chain; they produce and provide nutrients and compounds for other organisms in the food chain.
Consumer
Consumers are organisms that need to eat food to obtain their energy (also known as a heterotroph). Consumers often eat other organisms or organic matter.
Decomposer
Decomposers are organisms who feed on dead or decaying material, and in doing so perform the natural process of decomposition. Examples of decomposers include fungi and bacteria.
Herbivore
An animal that feeds on plants.
Carnivore
An animal that feeds on other animals.
Omnivore
An animal that feeds on both plants and other animals.
Predators
An animal that naturally preys on other animals.
Food chain
A way of representing one series of relationships within a food web by showing links between producers and consumers.
Food web
A way of graphically showing all the interconnecting food chains within an ecological community.

Part B: What are food chains and food webs?

Step 1

Begin this activity by distributing the Food Chains and Food Webs Factsheet to your students (also available on the Student Worksheet under Resources). Invite students to read the factsheet, and once complete, work through the information on the sheet together to ensure all content is understood.

Step 2

Next, invite students to form pairs and distribute a copy of the Marine Food Web Activity sheet to each pair. Students are to work together and use their existing knowledge of the ocean to complete the food web, adding in arrows that show the direction of the flow of energy within the web.

This is a relatively complex web. if you have time, you could also allow groups to undertake the research necessary to complete the web.

In addition, invite students to find an example of each of the following in their food web and add labels accordingly:

Producer
Consumer
Carnivore
Herbivore
Omnivore

Explain to students that decomposers exist in every food chain and web, and on every trophic level. They are mainly bacteria that work to break down dead animal and plant matter. Converting these materials into forms that can be re-used as nutrients by phytoplankton and other organisms. There are no decomposers represented visually in this food web.

Once complete, invite pairs to swap their food web with another pair. Distribute or display the Marine Food Web - With Answers image to the class and invite each pair to add corrections to the food webs they are checking.

Remind students to be kind, specific and helpful when providing their feedback.

Tips for providing feedback

Be kind - It can be hard to share your ideas with others, so remain kind and supportive.
Be specific - Be clear about what you think and why. Rather than saying, ‘I like the colours, ’ say something like ‘, I like the ways those colours help create a mood that supports your message.
Be helpful - Try not to say what is strong or weak, but also make suggestions about how things could be improved.

Ask students to return food webs to the original pairs.

Step 3

Now explain to students that all organisms in all ecosystems are part of a food chain and a food web. Distribute or display the Trophic Levels Factsheet to students and lead them through the image using the text below (image also available on the Student Worksheet under Resources):

In marine food webs, the primary producers (at the bottom of the food chain) are organisms like phytoplankton and seaweed, those species that convert sunlight into energy through photosynthesis. Zooplankton are primary consumers, eating the phytoplankton and seaweed. At the next stage up are the first level carnivores, such as the juvenile stages of fish and jellyfish, and small fish, seastars and crustaceans. The second level carnivore consumers are at the next level, and include larger fish. The third level carnivorous consumers include organisms like squid, while the top level carnivores include sharks, dolphins and albatross.

Step 4

Finally, facilitate a class discussion about keeping a food web healthy. Use the guiding questions below:

What might happen if one of the species in the food web suddenly disappeared?
Why might a species disappear?
Would it be worse if a producer or consumer disappeared?
What might happen if an introduced species becomes part of the marine ecosystem?
What sorts of things might upset the balance of a food web?
How can we keep the marine food web healthy?

Part C: How fragile are food webs?

Preparation

Print a copy of the Antarctic Organisms Cards on A3 paper and cut out each card. You will need a ball of string.

Step 1

Take the class to an open space outside of the classroom. Explain to students that we are going to create an example of an Antarctic food web.

Step 2

Give each student one of the cut out organisms cards – if you have more students than cards, ask extra students to observe. Invite students to stand in a circle displaying their card.

Step 3

Tell students that the string will represent the connections between plants and animals in the food web. Explain that you will represent the sun and that all energy initially comes from the sun.

Pass the ball of string to the student holding the ‘Herbivorous phytoplankton’ card and state that you are giving them energy to grow. The student holding the Herbivorous phytoplankton card should hold onto the section of the string and pass the ball of string onto the organism (or organisms) that they eat. This continues until everyone is holding onto a piece of the string. Some plants or animals may have more than one connection, but everyone should be part of the web.

Step 4

While all the students are still holding onto the string, read out the following scenario:

A ship carrying herbicides and pesticides for farming struck an iceberg and sank while passing through Antarctic waters. Some of pesticides and herbicides leaked into the waters around the Antarctic. While these chemicals are designed to control insects on land, they can also harm some of the organisms in the waters around Antarctica, particularly the phytoplankton which suffers catastrophic and immediate decline and is virtually wiped out.

Ask the students representing phytoplankton to let go of the string and bob down. Then explain to students that all the organisms affected by the phytoplankton dying out must also let go of the string and kneel down. Continue the process until all the organisms affected have all dropped the string and knelt down.

Step 5

Engage students in a discussion around this activity. Consider the following questions in your discussion:

What happens to the web when one organism suffers a decline in numbers?
Which types of organisms are most affected (e.g. producers, consumers, predators, etc?) Why do you think this is?
Imagining that this was a one-off event, what do you think would happen to this ecosystem in the long term?
What did this activity make you realise about the fragility of food webs?

Head back inside for the next part of the lesson.

Part D: How do humans impact marine food webs?

Step 1

Now explain that marine ecosystems are increasingly under threat from human behaviour, even though most human activity takes place on land. Share the following clips from Blue that describe the ways that three marine animals are being affected by humans. As they watch, invite students to take notes of anything that is interesting or surprising, and of anything that they think relates to food chains or webs.

For the love of sharks (https://vimeo.com/1056609005/fd59bf4c92)

Importance of marine turtles (https://vimeo.com/1056609220/37e6d8c08f)

Unsustainable fishing (https://vimeo.com/1056608479/d7c167898e)

Once complete, invite students to share some of their observations with the class. Consider the following questions:

What did you find most interesting or surprising?
What would you like to know more about?
What things did you see that you think relate to food chains or food webs?

Step 2

Now break the class into three, six or nine (or other multiples of three) small groups or pairs and assign each group with one of the following animals so that each animal is assigned an equal number of times:

Shark
Marine turtle
Tuna

Each group needs to select one particular species of this animal and create a poster describing the food chain for this animal.

Encourage students to select a common or well-known species to ensure there is plenty of information about this species for students to work with.

The food chain should be annotated to include the following (also available on the Student Worksheet):

The names of the organisms in the food chain
One interesting or surprising feature about each organism in the food chain
The flow of energy
Existing and potential threats to this food chain (e.g. human impacts like overfishing, ghost nets, shark-finning, climate change, etc.)
What action needs to be taken to limit the impacts on this food chain.

Students should undertake research online or use the factsheets below (also available on the Student Worksheet):

For students conducting research online, share the following sources (also available on the Student Worksheet):

Blue The Film - Explore

Step 3

Once complete, invite students to form new groups in order to share their learning. Each new grouping should be made up of one group that looked at sharks, one that looked at turtles and one that looked at tuna. Each person representing a marine animal needs to share what they found with the rest of the new grouping.

Ensure that the new concepts are learned in a self-guided manner by encouraging students to take their own notes about the other animals and food chains, and to ask clarifying questions about the animals and food chains being shared.

Reflection

Invite students to work independently to answer the following reflection questions:

How does thinking about ecosystems in terms of food webs and chains help you understand the relationships between organisms?
How was the information presented in this lesson connected to what you already knew?
What is still challenging for you in terms of food chains and food webs?
What would you still like to know more about?

Take it further

Invite students to apply their learning in a real-world context by participating in the Social Action lesson of this unit.

Blue - Ocean Food Chains and Food Webs

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Summary

Learning intentions:

Students will:

Success criteria:

Students can:

Lesson guides and printables

Lesson Details

Skills

Curriculum Mapping

Resources Required

UN Sustainable Development Goals

Additional Info

Related Professional Learning

In this lesson