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F2.2 · Investigate environmental factors affecting plant growth

Learn to investigate environmental factors affecting plant growth through clear examples and targeted practice.

Ontario Grade 11 Biology

Plants: Anatomy, Growth, and Function

A Grade 11 inquiry lesson for Ontario Biology expectation F2.2

A plant on a sunny windowsill may look different from one kept in a dim corner. That difference raises a biological question: could light have affected their growth? In Grade 10 science, you learned to ask testable questions, identify variables, and collect observations. This lesson uses those inquiry skills to investigate how environmental conditions relate to plant growth. An environmental factor is a condition outside an organism that may affect it. Examples include light, water, temperature, and the amount of available space. The aim is not to assume that one factor explains every difference. It is to design a careful test and decide what the evidence supports.

What you will learn

Identify environmental factors that can affect plant growth.
Plan a fair investigation that tests one environmental factor.
Use observations and measurements to describe a pattern without overstating what it shows.
Recognize limits in an investigation and suggest a reasonable improvement.

1. From an SNC2D inquiry to a plant question

A plant is a living system made of cells. Its visible growth depends on the conditions around it. Growth can be described in several ways, such as a change in height, the number of leaves, or the appearance of new growth. Choose a measure that fits the question and can be recorded consistently.

Suppose a class notices that seedlings near a window appear taller than seedlings farther away. This is an observation: a recorded or noticed pattern. It does not, by itself, show that light caused the difference. The plants might also have received different amounts of water, or they may have started at different sizes.

A testable question names a factor and an outcome. For example: How does the daily duration of light affect the height of seedlings over a set period? The factor deliberately changed is the independent variable. The outcome measured is the dependent variable. Conditions kept the same are controlled variables. Keeping other relevant conditions alike helps make the comparison fair.

A pattern is not automatically proof of a cause.
Name the environmental factor and the growth measure in the question.
Change one main factor while keeping other relevant conditions alike.

2. Structure the investigation before collecting evidence

Use similar seedlings of the same kind and, as far as possible, a similar starting size. Assign them to groups that receive different levels of the factor being tested. For a light investigation, the groups might receive different planned durations of light. Keep the type and amount of water, growing medium, container size, temperature, and measurement schedule as similar as possible.

A growing medium is the material that supports the plant and holds water around its roots. Use the same kind and amount in every container. Label each group clearly. Decide in advance when and how the growth measure will be recorded. For height, use the same measuring method and reference point each time.

More than one plant in each group can help show whether a result is shared across plants or is unusual for one plant. Repeat measurements at planned times when the investigation allows. Record observations honestly, including unexpected results. Do not change the method for only one group partway through.

A results table can separate the plan from the finding. It also makes clear which conditions are being compared. The entries below are a planning template, not experimental results.

The independent variable is the factor deliberately changed.
The dependent variable is the outcome measured.
Controlled variables are conditions kept alike for a fair comparison.

3. Read evidence carefully

After collecting observations, compare the groups using the measure chosen in advance. A table or graph can help reveal a pattern. For example, one group may show a greater increase in height than another. Report what the records show, including variation among plants, rather than selecting only the result that fits an expectation.

An explanatory model is an idea used to explain an observed pattern. If seedlings receiving more light show a different growth pattern, light may be one explanation. The investigation supports that explanation only to the extent that the groups were comparable and the measurements were consistent. It does not establish that light was the only influence in every setting.

Environmental factors can also interact in practical ways. A plant receiving more light may need its water conditions monitored carefully so that groups remain comparable. The investigation must still test the chosen factor fairly; changing several conditions together makes it hard to tell which one is linked to the outcome.

A conclusion should answer the original question and refer to the evidence. It should also state a limitation. A limitation is a feature of the investigation that restricts how confidently or broadly its result can be used. Examples include few plants, a short observation period, or difficulty keeping conditions identical.

Describe the observed pattern before offering an explanation.
Use only the evidence collected to support a conclusion.
A limitation narrows what can be concluded; it does not make the observations useless.

4. Improve the test and communicate the conclusion

A strong investigation has a clear question, a consistent procedure, and records that another student could understand. If results differ widely within a group, check whether starting sizes or conditions differed. A next investigation might use more plants or a longer planned observation period, if time and resources permit.

Do not claim that a result applies to all plants or all environments from a small classroom test. A careful conclusion is specific: it describes the plants and conditions tested, names the observed pattern, and notes a relevant limitation. This keeps the claim proportional to the evidence.

When planning, ask: What factor will change? What growth measure will be recorded? Which conditions must stay alike? When and how will measurements be taken? What could limit the conclusion? These questions connect the Grade 10 inquiry skills of controlling variables and recording observations to a biological investigation of plant growth.

Plan how to measure before starting.
Keep conclusions specific to the plants and conditions investigated.
Use limitations to guide a realistic improvement.

Planning a fair plant-growth investigation

Investigation part	Example for a light test
Question	How does daily light duration relate to seedling height?
Factor changed	Planned daily light duration
Outcome measured	Seedling height recorded with the same method
Conditions kept alike	Seedling type, growing medium, container, water plan, and temperature
Evidence to record	Measurements for each group at planned times
Possible limitation	Few plants or a short observation period

Worked example

Planning a light investigation

A class wants to test whether daily light duration is associated with seedling growth. Identify the variables and a fair comparison plan.

Define the comparison
Use groups of similar seedlings and give the groups different planned durations of light. The daily light duration is the independent variable because it is the factor deliberately changed.
Choose the outcome
Record seedling height at the same planned times using the same method. Height is the dependent variable because it is the measured outcome. A class could instead choose another clear growth measure, but it should decide before the test.
Keep conditions comparable
Use the same kind of growing medium, container size, water plan, and temperature as far as possible. This reduces alternative explanations for any difference between groups.
State a cautious conclusion
If the groups show different height patterns, report that pattern for these seedlings under these conditions. Do not claim that light duration alone explains every difference unless the investigation supports that claim.

Answer: The independent variable is daily light duration. The dependent variable is the chosen growth measure, such as height. Keep other relevant conditions alike, record measurements consistently, and conclude only what the evidence supports.

Check: If one group also receives more water, the comparison no longer isolates light duration as clearly.

Worked example

Investigating water availability

A student proposes giving one group of seedlings a planned lower amount of water than another group. How can the student make the question and evidence more useful?

Make the question testable
Name the water condition and the growth outcome. For example, ask how the planned amount of water affects the number of new leaves over a specified observation period.
Control other conditions
Use similar seedlings and keep light, growing medium, containers, and temperature as alike as possible. Otherwise, a difference in leaves could be linked to another changed condition.
Record evidence consistently
Count leaves using the same rule at each planned observation. Record the groups separately and include all plants, rather than reporting only the plants that fit the expected pattern.
Limit the claim
A difference in the recorded outcome is evidence of a pattern under the tested conditions. It does not automatically establish the best water plan for every plant or growing environment.

Answer: A useful investigation clearly defines the water condition, measures one chosen growth outcome consistently, controls other relevant conditions, and limits its conclusion to the tested seedlings and conditions.

Check: The student should not change light exposure between groups while testing water, because that would introduce another possible explanation.

Worked example

Interpreting an unexpected pattern

In a planned investigation, the group receiving more light does not show greater height than the other group. What should the class do with this result?

Check the record
Confirm that measurements were made at the planned times and with the same method. Check that the group labels and observations were recorded correctly.
Describe, do not replace, the result
Report that the measured heights did not show the expected greater-height pattern in the higher-light group. Do not remove valid observations simply because they were unexpected.
Review possible limits
Consider whether starting sizes or controlled conditions differed, and whether the observation period was sufficient to show a clear pattern. These are questions to investigate, not reasons to invent a different result.
Plan a next step
If a condition was not kept comparable, improve the procedure and repeat the test if appropriate. If the method was followed, the result still answers what happened under those tested conditions, even if it does not match the prediction.

Answer: Keep and report the result accurately. Check the method, identify limits that could affect interpretation, and make a specific improvement or follow-up plan without claiming that the unexpected observation is an error.

Check: An unexpected result is evidence to assess, not a result to discard automatically.

Common mistakes and how to avoid them

Concluding that light caused a difference because two groups looked different.

Correction: Check whether other conditions differed. Describe the pattern and make a causal claim only as strongly as the investigation supports.

Changing water, light, and temperature at the same time.

Correction: Test one main factor at a time when the goal is to investigate its relationship to growth. Keep other relevant conditions alike.

Recording only the plants that match the prediction.

Correction: Record all observations using the planned method. Unexpected results are part of the evidence.

Claiming that a small test gives the best conditions for every plant.

Correction: State which plants and conditions were tested, and identify limits on how broadly the result can be applied.

Lesson summary

Environmental conditions such as light, water, temperature, and available space may affect plant growth.
A fair investigation changes one main factor, measures a clear growth outcome, and keeps other relevant conditions alike.
Observations show what happened; an explanatory model suggests why it may have happened.
Conclusions should match the evidence and acknowledge limitations.

Check your understanding

Question 1

A student changes light duration and measures the number of leaves. Which is the dependent variable?

Daily light duration
Number of leaves
Container size
Seedling type

Show answer and explanation

Number of leaves

The number of leaves is the outcome being measured, so it is the dependent variable.

Question 2

Two groups receive different amounts of water, but one also receives more light. What is the main problem?

There is no measured outcome.
The test has changed more than one relevant condition.
The observation must be incorrect.
The groups cannot be compared in any way.

Show answer and explanation

The test has changed more than one relevant condition.

Because light also differs, it is harder to tell whether a growth difference is linked to water, light, or both.

Question 3

A small class investigation finds a growth difference between two groups. Which conclusion is most careful?

The tested condition caused the same result in every plant species.
The result proves that no other factor affects plant growth.
The groups showed a difference under the conditions tested; more evidence may be needed for a broader claim.
The result should be removed if it does not match the prediction.

Show answer and explanation

The groups showed a difference under the conditions tested; more evidence may be needed for a broader claim.

This conclusion reports the observed comparison and limits its scope to the tested conditions.

Key terms

Environmental factor: A condition outside an organism that may affect it, such as light, water, or temperature.
Independent variable: The factor deliberately changed in an investigation.
Dependent variable: The outcome measured in an investigation.
Controlled variable: A condition kept alike so it is less likely to explain differences between groups.
Observation: Information noticed or recorded using a planned method.
Limitation: A feature of an investigation that restricts what can be concluded from its evidence.

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About this lesson and its review

Published by DoAssignment. This reviewed lesson follows Ontario Grade 11 Biology (SBI3U), expectation F2.2. It is a study resource, not an official curriculum publication.

Before publication, content is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability. Errors can still occur, so corrections are welcomed.

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