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Effects of cigarette smoke on the growth of plants

Effects of cigarette smoke on the growth of plants

Introduction: (Initial Observation)

To beautify our surroundings and breathe a little easier, we usually include several living plants in our home and work spaces. Plants are beautiful and work as air cleaners and make our indoor environments more pleasant for living and working.

While plants cleanup the air, remove carbon dioxide and produce oxygen, they may also be subject to harmful affects of some pollutants such as cigarette smoke

Cigarette smoke is produced by combustion of some organic material, so there is increased carbon dioxide over a limited area. This is good for the plants and can increase their growth if there is sufficient light.

The smoke particles that we see, however, are particulate pollution which can possibly coat the leaf surface, reducing photosynthesis. These particulates can also clog stomata pores, reducing gas exchange in the leaf. These effects are bad for plants. Cigarette smoke, and some other smokes, also contain tar which may clog stomata pores.

This project is aimed to discover the overall affect of cigarette smoke on plant growth.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about what you want to investigate. Read books, magazines or ask professionals who might know in order to learn about the effect or area of study. Keep track of where you got your information from.
You may search the Internet to find about any previous research on this subject. Some students have already worked on this project and have posted a brief report on the Internet. It seems that all such reports have only one intension and that is to prove that cigarette smoke is harmful to both plants and human. None of these project reports indicated a thorough investigation by the reporter.

When you search the Internet for this subject use keywords such as “cigarette smoke + plant”, “smoke + plant”. Following link shows a sample report.


Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to discover the effects of cigarette smoke on plants growth.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable for this project is the cigarette smoke presence or absence.

Dependent variables are growth conditions such as plant height, number of leaves, color of leaves and size of leaves.

Controlled variables are temperature, light, water, soil, nutrients and all other plant growth conditions. We control such values and keep them constant among different test groups to make sure that any change in plant growth is not caused by these variables.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

My hypothesis is that cigarette smoke has no negative effect on plant growth. My hypothesis is based on my gathered information and the fact that carbon dioxide can increase the plant growth and other organic material in smoke such as tar are themselves plant material.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”


In this experiment we test two groups of 10 plants for the effects of cigarette smoke. To do this we expose one group to the cigarette smoke and keep the other group away from smoke as control.

We do this experiment outdoor to avoid having cigarette smoke indoors.

Build a Smoker Box

The hardest part of this project is being exposed to cigarette smoke. To make it easier on ourselves we build a cigarette smoker. The cigarette smoker on the right is made of a plastic container, a 5 volts cooling fan (used for computer processor) and a 6 volts battery. It creates suction that we need for smoking.

The plastic container lead has at least two holes. One big hole for fan and another small hole for cigarette.

You can make more cigarette holes if you wish so all cigarettes will burn together. The fan mounted over the larger hole will blow out the air. This creates a partial vacuum so the air will be sucked in from other hole where you have the cigarette. This simulates smoking cigarette by people. You may construct your smoker with longer wires so the battery can stay outside. In this way you can turn off the fan after all cigarettes are fully burned. This will also let you to stop the fan before the cigarette filters burns.


  1. Get twenty small ceramic flower pots.
  2. Prepare a mixture of potting soil and top soil (Enough for all flower pots)
  3. Fill up all the pots with the soil mixture that you just made.
  4. Place one bean seed in the center of each pot and push it down exactly one inch.
  5. Add some water to all plants.
  6. Make two clear plastic boxes using clear Plexiglas with estimated size of 10 x 15 x 10 inches. You may use any other clear container for this purpose. For example a glass aquarium can be good. Also you can make a wooden frame and then cover it with a sheet of clear plastic. The main purpose of this plastic is to keep the cigarette smoke inside and avoid polluting your environment. Whatever you do make sure that both containers are identical and both containers have an opening for outside air to enter.
  7. Place 10 of the flower pots in first green house and label the green house with “CONTROL”.
  8. Place 10 of the flower pots in the second green house and label the green house with “SMOKE”.
  9. Place a smoker box in the “SMOKE” green house.
  10. Water the plants and measure the height and count the number of leaves every day for approximately one months. This will also give a chance to the plants to get fresh air for about 1 hour a day.
  11. Light up the smoker with 5 cigarette each day after watering and recording your observations.

Make a graph:

You may make a bar graph to visually present your results. Make two vertical bars. One for the group with cigarette smoke and the other for the group without cigarette smoke. Write the name of the groups under the bars.

The height of each bar will be the average plant growth or plant height for the group it represents. If you see other noticeable differences such as the number of leaves or the number of flowers, you may also make similar data tables and similar graphs for those as well.

Materials and Equipment:

  1. Potting soil
  2. Top soil
  3. Small ceramic flower pots
  4. Bean seeds
  5. Water
  6. smoker assembly
  7. small green house that you make using Plexiglas

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Compile your data and use it to draw a conclusion and answer the following questions.

What was the average height of plants exposed to cigarette smoke and how was it different from your control group that was not exposed to cigarette smoke?

What was the average number of leaves on plants exposed to cigarette smoke and how was it different from your control group?

What was the average size of leaves in each group?

How different are the color of leaves in each group?

Compare general appearance of plants in two groups.


You will need to calculate the average height of plants in each group.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Following is a sample conclusion, but don’t trust it. Do your own experiment and get your own results.

When my project was completed, I found that my hypothesis was partially correct. In my exposed plants, fewer new leaves had grown compared to my controls. The height of the plants, however, did not seem to differ much, which contradicted my hypothesis. I believe that the reason the height of plants were similar was because the normal plants had leaves which made the stems make a spiral shape instead of a straight line as the other group of plants did. The group of plants exposed to smoke had less weight of leaves, therefore was much more likely to grow in a straight line. Thus, the difference in the number of leaves between two groups of plants had probably affected the height of plants as well.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


Visit your local library and find any information that you can get related to your project. You may not find a book or magazine article directly related to the effect of cigarette smoke on plants; however you may easily find books and articles about cigarette smoke or health effects of cigarette. You will also be able to find books and articles related to air pollution and its effect on plants and animals. What you find may be specifically targeting an especial type of pollution that has nothing to do with cigarette; then it is your job to relate them. After all cigarette is a plant product and an organic matter. Many of the byproducts of smoking cigarette must be similar to burning other plants and organic material.

Finally you may use books related to plant biology and botany for more information on material that are good or are hazardous to plants.