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Plant Growth; How does the hours of sunlight effect plant growth?

Plant Growth; How does the hours of sunlight effect plant growth?

Introduction: (Initial Observation)

In summer time, days are long and we have more hours of sunlight. In winter however the days are short and we only get a few hors of sunlight each day. Do you think that this has any affect on plants life? Is it what causes autumn and falling leaves and finally leafless and almost lifeless trees. Of course cold weather and other factors may also be involved, but it is good if we be able to see how does the hours of sunlight affect a 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 the affect of sunlight on plant growth. 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.

Plants must have light to manufacture food and grow. Light retards stem growth, but promotes leaf expansion. The sunshine helps the plants make their own food. And the leaves take the air into the plants. Air, water, sunshine, and soil help the plants grow. If plants do not get sunlight, they cannot produce chlorophyll and they will lose their green color and eventually die. If plants lack any of the other things they need to grow and make their own energy and food, they will die.

Green plants need these things in order to grow and make their own energy and food:

  • Water
  • Nutrients
  • Light energy
  • Carbon Dioxide
  • Chlorophyll

Chlorophyll is the chemical that makes plants green.

Question/ Purpose:

The purpose of this project is to see the effect of sun light on plants and to find out how does the hours of sunlight affect the plant growth?

Identify Variables:

We change the hours of sunlight (hours that plant is exposed to sunlight) to see how does it affect the plant growth. So the hours of sunlight is our independent variable and plant growth is our dependent variable.


My hypothesis is that a few hours (about 4 hours) of sunlight is enough for the plant growth. I think excess hours of exposure to sunlight is not beneficial. However very low hours of sunlight can hurt some plants and stop it’s growth. This probably depends on the specific plants.

Experiment Design:

In the first experiment we want to see how effective is sunlight for the general health of a plant. To do that we get a sample plant and somehow we place a part of this plant such as a leaf or a few leaves in the dark. That can be a dark box or dark paper. This is the details:

Experiment 1:

  • Take the black construction paper and cut out 4 square or oval pieces. Cover up 2 leaves on the healthy green plant with the black construction paper pieces, one on top of the leaf and one piece on the bottom of the leaf. Secure the papers on the leaf with paper clips.
  • Look at your leaves to make sure that the entire leaf area on top and on the bottom is covered up and won’t be able to get any sunlight.
  • After a week, remove the paper clips and pieces of black construction paper. What do the leaves look like? What color are they? What do you think happened?
  • Leave the plants on the windowsill or table top for another week. Water the plants when needed. Watch the leaves and see what happens to them when they are able to get sunlight again.

Now that we know plants need sunlight, let’s try another experiment to see the effect of hours of sunlight on plant growth.

Experiment 2:

From a bag of lima beans, select 20 large, almost identical beans, Take 4 plates and place 5 beans in each plate. Number the plates from 1 to 4. Pure some water in each place and cover them with cloth. Add water as needed daily to keep the cloth moist, but don’t submerge the beans entirely in water. After a few days, you should see a little sprout coming out of each beans. Remove the cloths from plates as germination continues for a few days till the first leaf appears. Now you need to control the amount of sunlight each plate gets. Take 4 brown paper bags and place them upside down on each plate. Allow plate number one to have 2 hours of sunlight, then cover it with the bag for the rest of the day. Allow plate number two to get 4 hours, plate number three with 6 hours and plate number four with 8 hours of sun light every day. Continue exposing the plates to different hours of sunlight for two weeks and at the end, remove the paper bags and observe all the beans in all plates.

How do they differ from each other ? What plate has the best or tallest or greenest beans leaves ? What do you think happened.

Record he result in the following table by placing an X in appropriate boxes.

Plate # 1 Plate # 2 Plate # 3 Plate # 4
Most leafy
Best Lima plants

Also measure the height of plants once a week and record the results in a table like this. You can use this table to draw a graph or chart.

Plant height after one week Plant height after two weeks Plant height after three weeks Plant height after four weeks
2 hours sunlight
4 hours sunlight
6 hours sunlight
8 hours sunlight

Notes: If you live in a warm area or it is the summer time, you can do this experiment outside. But if it is cold out, do your experiment in a warm green house or next to a well lit window that gets lots of sunlight.

Materials and Equipment:

Experiment A

  1. A green plant with healthy green leaves
  2. Paper clips
  3. Black construction paper

Experiment B

  1. Lima beans
  2. Brown paper bags
  3. Plates
  4. Cloth
  5. Water

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.

Experiment A results: When you cover the leaves with black construction paper, leaves do not receive sunlight therefore, they can not make Chlorophyll, the green color. As a result, the green color fades away and leave may fall off. Once you place the plant close to window where it can get some sunlight, with little bit of water every day, it begins making the green color and looks healthy again.

Experiment B results: Plates with most sunlight has the best lima leaves.


Does the result of your experiment support your hypothesis? Write your conclusion.

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.

Plants are the only things on earth that turn sunlight into food. They do it through a process called photosynthesis. Photosynthesis means to “put together using light”. Plants use sunlight to turn carbon dioxide from the air, and water into food. Plants need all of these to remain healthy. When the plant gets enough of these things, it produces a simple sugar, which it uses immediately or stores in a converted form of starch. We don’t know exactly how this happens. But we do know that chlorophyll, the green substance in plants, helps it to occur. Without chlorophyll plants can’t make food and without sunlight, there can’t be chlorophyll to make food.


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.

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.

Why plants needs chlorophyll and what is photosynthesis?

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.

Experiment A: If the leaves are not fully covered or the clip is not tight, the leaves may get some light and make a little bit of color. The stress, pressure or weight of leaf covering may also have some affects. We must try to minimize any pressure to the plant.

Experiment A: All plates need to be kept close to each other and be at the same temperature. Air movement should be allowed from bottom of bags and water quantity should be identical for all plates.