Human Impact Whats in a Tomato

What’s in a Tomato? Understanding our human impact on the environment:
This lesson plan demonstrates the use of research, experimental design, writing and critical thinking
skills by exploring linkages between tomato diversity and human impacts on the (food) environment.
Subject/Course: Environmental Sciences: SVN3E
Grade Level: Grade 11
Topic: The impact of human activities on the environment
Specific Curriculum Expectations Met:
A1.1 Formulate relevant scientific questions about observed relationships, ideas, problems or issues,
make informed predictions and or formulate educated hypothesis to focus inquiries
A1.6 Compile accurate data from laboratory and other sources and organize and record the data,
using appropriate formats, including tables, flow charts, graphs and or diagrams
A1.8 Synthesize, analyze, interpret and evaluate qualitative and or quantitative data to determine
whether the evidence supports or refutes the initial prediction or hypothesis and whether it is
consistent with scientific theory; identify sources of bias and or error and suggest improvements to
the inquiry to reduce the likelihood of error
A1.10 draw conclusions based on inquiry results and research findings and justify their conclusions
with reference to scientific knowledge.
B1. Analyse selected current environmental problems in terms of the role human activities have
played in creating or perpetuating them, and propose possible solutions to one such problem;
B2.1 use appropriate terminology relating to the environmental impact of human activity, including,
but not limited to: carbon footprint, carbon neutral, biodegradable, biodiversity, carrying capacity,
sustainability, and invasive and native species.
B3.4 explain the concept of a “carbon footprint” and how it is used to measure the impact on the
environment of a range of human activities
Required Resources:
Total of 4 tomatoes halves: 2 tomatoes halves from 2 different, locally grown in Ontario tomatoes and 2
tomatoes from 2 different imported tomatoes (Mexico, US)
1 plastic knife
1 ruler
1 measurement table (see below)
1 diagram of tomato cross section (see below)
Paper Towel
Michelle is shopping at a No Frills grocery store and is looking to buy some fresh tomatoes for tomato
and cheese sandwiches. She notices a few choices when it comes to buying tomatoes. She can purchase 1
locally grown in Ontario tomato for $1.50 or 2 tomatoes imported from Mexico for $1.00. Michelle
decides to purchases both types and returns home to make her sandwiches.
As she begins to slice each tomato, she observes a difference between the two. The insides of the Ontario
tomato (e.g. columella, septa) appear more red in colour; feels less firm; was easier to slice; and the
tomato skin wall (e.g. pericarp wall) is less thick compared to the Mexican tomato. Mexican tomatoes
appear more pale on the inside; feels more firm; and was harder to slice. Michelle also decides to taste a
slice of each tomato and discovers that the imported tomato had less taste compared to the local tomato.
Stricken by curiosity, Michelle takes both tomato slices to her high school’s science club, and seeks
assistance from a group of interested environmental science and biology students. She asks for the
students’ help in understanding the difference between the two tomatoes. She mentions that she is
especially curious about the difference in each tomato’s skin wall.
Working in smaller groups as part of the science club, you are asked to conduct the following
investigation to help Michelle better understand the differences in tomato types.
Activity and Answer Key:
Part 1: Investigating differences
1) Watch the Story of Food as an introduction to the activity:
2) Before proceeding with any dissection, discuss with your group and generate a hypothesis
regarding the difference in the tomato skin wall. Either your group believes that there is a
difference in the skin wall of the imported vs. local tomato or your group believes there is no
difference and what Michelle witnessed was a coincidence. (A1.1)
Ho: The pericarp wall in imported tomatoes (Mexico, US) will be thicker in diameter compared to
those in local Ontario grown tomatoes.
Ha: There is no difference in the diameter thickness of the pericarp wall of imported or locally
Ontario grown tomatoes
3) n/a
4) With each tomato slice, measure the tomato’s pericarp wall in three different places (as shown in
Figure 1). Record each measurement you take for each slice sample (using Table 1). When
finished, calculate the sample’s average skin wall diameter. Record this average value in Table 1.
Be sure to add the unit measurements into your table as well. (A1.6)
Table 1: Tomato pericarp wall measurements, with example
Tomato Sample Measurement Measurement
Local 1
Local 2
Imported 1
Imported 2
Check the average calculations
5) Using the data that you’ve generated in Table 1, defend whether it supports or refutes your
group’s original hypothesis described in step 1. (A1.8)
Either the data (average calculations) supports that imported tomatoes have greater pericarp walls
or that there is no relationship between tomato origin and pericarp wall. Some students (although
rare) may find that local tomatoes have thicker pericarp walls. In this case, consider the student’s
rationale as to why the opposite happened.
Part 2: Relating differences
Answer the following questions by identifying key findings from the above reading. In some cases, you
will need to compare your results from Part 1 and interpret this with key findings from the above reading.
1) Explain why tomatoes are an essential ingredient for a healthy diet. (A1.6)
Tomatoes are: rich in Vitamin A (for good eyesight, sexual reproductive health and body growth),
Vitamin C (disease prevention, stress control, heal cuts and wounds), potassium, phosphorus,
iron, calcium, and lyocpene (shown to suppress cancer).
2) How have tomatoes changed over the last 50 years? (A1.6)
Today’s fresh tomato contains 30.7% less vitamin A;16.9% less vitamin C; 61.5% less calcium
(required to maintain strong bones and teeth); 11.1% less phosphorus; 9% less potassium; 7.97%
less niacin; 10% less iron and 1% less thiamine than its 1963 counterpart.
Fat (lipid) content in tomato has increased by 65 percent since 1963, and sodium has increased
upward of 200 percent.
3) What are some commonalities between the scientists and processing tomato experts’ desired traits
in an ideal tomato? (A1.6)
Firmness, in terms of thickness and hardness of the outer pericarp wall (which provides the
ability to withstand pressure and between 25 000 and 50 000 pounds of weight when
bouncing along in a truck during shipment, thus increasing yield (in pounds per acre))
Firmness, provides the ability to withstand rough handling during mechanical harvesting
Resistance to disease
Heat tolerance
4) In Pawlick’s chapter one, he claims there is a connection between the thickness of a tomato skin
wall and the tomato being imported. Can you explain why imported tomatoes have thicker skin
walls compared to local tomatoes? (A1.6)
Identified in both scientist and processing experts, firmness, in terms of thickness and
hardness of the outer pericarp wall is desired in tomatoes, especially imported, since they
need to withstand 25 000 to 50 000 pounds of weight when bouncing along a truck during
shipment, or withstanding rough handling during mechanical harvesting
Thicker tomatoes are desired because they more likely will survive transportation and
harvesting, whereas local tomatoes do not have to travel as far and so no need for thickness
5) Are your findings from Part 1 supported by Pawlick’s claim identified in question 4? If not, can
you explain reasons why you didn’t observe this claim in your results from Part 1? (A1.6)
Findings from part 1 should support Pawlick’s claim that imported tomatoes have a thicker
pericarp wall.
If findings do not support this, assess student’s explanation. Several factors include: mixing
of the tomato samples (on student’s part), local grown tomatoes are of the same genetic type,
local grown tomatoes are not actually local grown but imported and masked as being locally
grown (e.g. this is very typical of produce purchased from farmer markets early in the
season), difference in timing of the tomatoes (e.g. very ripe in season local tomatoes vs.
picked before ready/ripe imported tomatoes)
6) Having conducting this experiment, what explanation should you be able to provide to Michelle
regarding the differences between the pericarp wall in both tomatoes? (A1.8) (A1.10)
Locally grown tomatoes stay on the vine for much longer, allowing them to ripen naturally,
which gives flavour. These tomatoes do not have thick pericarp walls as it is not in their
genetic make up.
Imported tomatoes are selected for their thick pericarp wall characteristic, which takes away
from flavour since this is not what they’re bred for. Imported tomatoes are picked earlier
(while still green and not yet ripe) and sprayed with ethylene gas, a naturally produced gas, to
speed up ripening during transportation.
Part 3: Interpreting Differences
To answer the questions in this section, you will need to consider key findings from chapter one and think
broadly (e.g. in relation to the environment, which includes humans).
1) Assuming that your data from Part 1 supported the claim that imported tomatoes have thicker
pericarp walls, can you explain how humans have played a key role in the dominance of these
selected tomato types in supermarkets. (B1)
Consumers demand/expect tomatoes to be fresh year round
Supermarkets address/meet this need by imported from US/Mexico during winter months
This has skewed the desire for certain tomatoes (that have more desirable traits) over other
types of tomatoes and explains why only 5 of approximately 5000 tomato varieties are
commonly found in supermarkets.
2) Chapter one mentions that southern US states and Mexico are primarily tomato producers year
round, while southern Ontario only has a presence during summer months. US and Mexico’s
dominance is related to its climate and large scale greenhouse production systems. How might
these large scale greenhouses influence water use (and other environmental problems, if any) in
some of these southern regions? (B1)
In some southern regions such as California, fresh water is a scarce resource that may not be
efficiently used for large scale agricultural production
Use of scarce freshwater resources in warm or desert like regions reduces water availability
for humans and other ecosystems (e.g. aquatic ecosystems), creating water starved conditions.
This is exacerbated during drought-like conditions.
As a result, water may be piped in from other regions or over pumped from groundwater
resources. A piped waterline is associated with huge environmental costs (e.g. land lost to
development) and over extraction of groundwater aquifers may collapse the aquifer/land
Water may also be trucked in but at the costs of transportation, oil/gas needed as well as
carbon/ greenhouse gas emissions
3) Because of Ontario’s colder climate, we cannot grow our own tomatoes during winter months.
Instead, we import our tomatoes from the US and Mexico. Can you explain some environmental
problems that result from the constant transportation of tomatoes into food supermarkets in
Canada? (B1)
use of scarce crude oil and long distance transportation creates carbon and greenhouse gas
emissions which contributes to climate change
large scale food production in southern regions may degrade soil quality from
pesticide/chemical use to protect crops. Use of these chemicals may run off into water
sources and pollute the water
over breeding due to selection of more desirable tomatoes ideal for shipping, reduces the
diversity (biodiversity) of our food availability, which can influence the amount of nutrients
that we receive, influencing human health
food packaging (non recyclable plastic food containers) that store the tomatoes create
unnecessary waste
4) What is a carbon footprint and how does the everyday transportation of tomatoes from
international areas affect our carbon footprint, in terms of annual carbon emission produced?
Assume that the daily distance from California or Mexico to Ontario is 5000km and that the car
fuel efficiency is 1km/L. Assume that local grown tomatoes travel a daily distance of 50km with
the same car fuel efficiency rate previously described. Graph the differences in terms of annual
carbon produced and discuss. (B2.1) (B3.4)
Carbon footprint is a measure of how much carbon or greenhouse gas emissions we produced
as a result of our daily activities/lifestyle choices
By choosing to purchase imported over local, we create a larger carbon footprint as a
family/community/city/province etc.
The more transportation, especially from international destinations, the larger the footprint, as
shown below in the graph
Annual carbon emissions produced (kgC/year) per year from
imported and local tomatoes
Imported Tomates from
Local Tomato from
Tomato Source
Additional Teacher Notes:
- SVN 3E students may find Pawlick’s reading a bit difficult. If this is the case, the teacher can
synthesis Pawlick’s reading into a PowerPoint presentation or a 1-2 page summary.
Nemose. 2011. Solanum lycopersicum, tomato. Retrieved Jan 11, 2011 from:
Pawlick, T. 2006. The End of Food. Greystone Books. Vancouver, BC, Canada. 265pp.
USC Canada. 2011. The Story of Food. Retrieved Jan 11, 2011 from:
For more information, please contact:
Jason Tran, OAC Liaison Officer, University of Guelph
[email protected]
519-924-4120 ext. 56812