Teaching Sequence

20 minutes – Part A: Recyclable Vs Recycled
15 minutes – Part B: Investigation – Plastic Usage
20 minutes – Part C: Calculating costs
15 minutes – Reflection: Is it enough to just recycle?

Work through this resource material in the following sequence:

Part A: Recyclable Vs Recycled

Note: The main idea for this lesson is based on the Thought Starter: Is it enough to just recycle plastic bottles? Students will come back to this idea during the reflection, so try to repeat this question several times throughout the lesson to keep this idea fresh in students' minds.

Step 1.

Introduce the topic for this lesson by inviting students to read the 'The Role Of Recycled Plastics In Closing The Loop' Article to learn about plastic water bottles made from 100% recycled material.

Step 2.

Invite students to consider the question:

What is the difference between a ‘recycled’ and a ‘recyclable’ plastic water bottle?

Students can answer the question using the space provided on the Student Worksheet.

Step 3.

Now direct students to look at this Global Plastic Production Graph and predict how much plastic was produced in 2020. Students may estimate this figure, extrapolate using the graph, or use a calculation – see below:

Ensure all students understand the workings for this calculation before moving onto the next step.

Step 4.

Once complete, invite students to read the quote below (also on the Student Worksheet) and use the figures in the quote to make predictions regarding recycling and recycled plastic bottles (students can record their ideas on Table 1 of the Student Worksheet). Students will need to choose a percentage for ‘fewer than half’ and use their estimate from Step 3. See below:

Example: Using 382 million tonnes as the approximate value for 2020

Approximate amount of plastic that was recycled in 2020.

Approximate amount of recycled plastic that was used to make new plastic bottles, in 2020.

382 x 50%
382 x 0.5
= 191

Less than 185 million tonnes will be recycled.

191 x 7%
191 x 0.07
= 13.37

Less than 13.37 million tonnes will be made into new bottles.

Now ask students to use their value from this table to work out the percentage of total plastic produced that could be recycled into new plastic water bottles.

Part B: Investigation – Plastic Usage

Step 1.

In this section, students will be asked to survey a random sample of 15 people about their usage of plastic bottles over the course of a week. Students may record their findings on Table 2 of the Student Worksheet. Ensure that students who are being surveyed reflect their entire usage within a week (e.g. at school, home, work, etc.).

Step 2.

Direct students to work out the averages at the bottom of the table.

Rule for finding an average: sum of all scores/number of students surveyed (15)

Optional discussion: From this point on you may choose to discuss differences in sample populations. If you would like to consider this idea, make the following adjustments to your lesson:

Engage students in a brief discussion on ‘random’ samples. For example, you could pose the question: Why would choosing a purely random selection of 15 people (admittedly this is extremely difficult to achieve) produce better results than choosing 15 people that you know?
Allow students to survey 15 people of their own choosing which will produce different outcomes for most students, particularly if there are any outliers in the sample.
Encourage students to share their results with each other to see differences.
Discuss how the differences in averages in Part B may lead to very different outcomes in Part C. Use contrasting student examples to guide you.
Plan your lesson so that students can conduct their survey either before class (in preparation for the activity) or over the course of two lessons. This will help to make the sample groups random.

Part C: Calculating the differences

Note: During this section students will be using the average values from their survey to calculate the weight of plastic used and associated energy costs.

Step 1. Calculating the weight

If you are able to collect sample bottles of each size range then you can ask students to weigh each bottle on a set of scales and use these figures in their calculations (students can record their findings on Table 3 of the Student Worksheet). Otherwise, provide students with the approximate values listed below:

Approximate weight of PET plastic bottles
250 mL	330 mL	600 mL	1.5 L	2 L
6.4 g	14.3 g *	19.7 g	32.6 g	36.7 g *

Sources:

https://www.researchgate.net/figure/Average-and-median-weight-of-plastic-Bottlestbl1_324151712
http://www.petresin.org/news_didyouknow.asp
*This is extrapolated by applying a logarithmic trendline (with an R² value of 0.98) to the previous values.

Ask students to use the weight of each bottle type and their averages from Part B to calculate the weight of plastic used in a week, a year and 10 years. They will also need to convert these figures to kilograms. Students can record their results on Table 4 of the Student Worksheet.

See the example below for all working out:

*Example only*
Size of bottle	250 mL	330 mL	600 mL	1.5 L	2 L
Average weight per week: Average x weight	6 250ml bottles Working: 6 x 6.4	2 330ml bottles Working: 2 x 14.3	1 600ml bottle Working: 1 x 19.7	0 1.5L bottles Working: None	1 2L bottle Working: 1 x 36.7
Average weight per week: Average x weight	= 38.4	= 28.6	= 19.7	= 0	= 36.7
Average weight per year: Weekly weight x 52	Working: 38.4 x 52	Working: 28.6 x 52	Working: 19.7 x 52	Working:	Working: 36.7 x 52
	= 1996.8	= 1487.2	= 1024.4	= 0	= 1908.4
1996.8 + 1487.2 + 1024.4 + 1908.4 Total weight of plastic bottles used in a year: 6416.8 g
6416.8 / 1000 = 6.4168 Total weight of plastic bottles used in a year: 6.4 kg

How many kilograms of plastic will be used in 10 years?

6.4 x 10 = 64 kg

Step 2. Calculating energy costs:

Students will now need to use their calculated weights to work out the manufacturing costs if the plastic is made from raw materials or recycled plastic. Direct students to Table 5 on their Student Worksheet (below) for the costs per kilogram.

Example only
Plastic made from raw materials uses approximately 22 kWh per kg	Plastic made from recycled plastic uses approximately 17 kWh per kg
Working out: 64 x 22 = 1408	Working out: 64 x 17 = 1088
Energy cost: 1408 kWh	Energy cost: 1088 kWh

Sources: (slide 16) Converted from MJ to kWh

https://lbre.stanford.edu/pssistanford-recycling/frequently-asked-questions/frequently-asked-questions-benefits-recycling

Now ask students to graph these values using a vertical bar graph or grid (example below):

The y-axis will show the kWh.
The x-axis will show the two categories – plastic made from raw materials, plastic made from recycled materials.

Reflection

Now that students have completed the investigation, encourage them to think about what their findings actually mean. Prompt them through the following steps to help them collate their ideas (also available on the Student Worksheet):

Ask students to reflect on the energy cost of producing plastic bottles. Discuss how the environment may be affected by producing plastic bottles. Ask students to share their thoughts with a peer and list their ideas.
Remind students of the difference between the terms recycled and recyclable. Ask them to reflect on the outcomes of their investigation and explain the differences between using plastic made from recycled and raw materials.
Now ask students to decide: Is it enough to just recycle plastic bottles? Allow students to discuss their ideas with the class or a peer, and challenge them to give justified reasons for making their decision.

Differentiated Learning

Extension – This lesson could be extended by reducing the amount of scaffolding and teacher direction. High ability students or extension classes may not need as much teacher guidance and may enjoy completing the lesson at their own pace. This activity could also be extended by evaluating samples (as outlined in Part B) and/or by writing a short report which addresses the claim “It is OK to use plastic bottles so long as you recycled them”.

Provisions for Learning Support – Depending on support requirements, students requiring learning support could work in a pair or group or receive additional scaffolding. The lesson could also be shortened by investigating the use of just one bottle size (e.g. 600 mL only).

Take Action

To conclude this investigation ask students to think about ways that they might be able to help. Direct students to read the quote below (source) and then ‘send a message’ to average Australians about the usage of plastic bottles. Encourage students to be creative with this task and consider allowing students to use electronic devices or other media to complete this activity.

Teacher Reflection

Take this opportunity to reflect on your own teaching:

What did you learn about your teaching today?
What worked well?
What didn't work so well?
What would you share?
Where to next?
How are you going to get there?

The information and statistics included in this document are approximate and have been simplified for educational/illustrative purposes. They should not be relied upon for any other purpose.

Visy Education - Drastic Plastic Usage

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