Factors Affecting Plant Growth Lab

Lab for Biology on plants (Tropisms)

Factors Affecting Plant Growth


Problem: What is the effect of an external factor on the growth of plants?


External Factor: Light (Phototropism)

Hypothesis: the direction of the light rays hitting the plant determines the direction of growth

Experimental Plan:

1.) We will test our hypothesis by putting our plant beside a window as there is directional light unlike ceiling lights. Then we will see if the deviation of the plant changed by measuring the angle with a protractor.

2.) We will place the Plant beside a window to see if it bends towards it.


1.) Collect materials needed for this lab.(Beans/seeds, water bottles, water, tissues ,ruler, Window light).

2.) Cut out the first 5 cm of the water bottle. Now you have two pieces, the top and the bottom.

3.) Take about 10 tissues and roll them up, place them in the bottom half of the water bottle.

4.) Place the beans/seeds on the sides of the water bottle ( not in the middle!) so they can grow properly.

5.) Soak the tissues so the beans have moisture to germinate. Do not overwater!

6.) Then, put the top part of the water bottle on and let it sit for 7 days beside a window. Check on it each day and measure the deviation and length it grew to see if its attracted to the light.

7.) After each 7 days, measure and observe the growth of your plant.

8.) Create a chart of your observations to conclude your research.

Checking The Plan

1.) a.) Our independent variable is the light.

b.) Our dependant variable is the plant as it is affected by the light..                                                                                                                                         c.) Our control variable is the other plant that is not receiving light

2.)We will set 2 plants, One beside a window and another in a dark room with no light.

3.) We will see and measure the length difference between the plant with no light and the plant with light.

 Data and Observation

Day Number

Length (cm)

Angle of Deviation toward light


0.0 cm

0 degrees


0.5 cm

5 degrees


2.5 cm

17 degrees


7.3 cm

24 degrees


12 cm

32 degrees


15 cm

43 degrees


17 cm

52 degrees




1.)  Our plant grew best beside the window as there was lots of light so it could produce its own food and grow taller. However, the one in the dark room barely grew and eventually died as it could not make food due to no light.

2.) Our plant did not grow under no light because plants are autotrophs. Without light they cannot photosynthesize and can’t create their own food. Eventually they die.

3.) Yes, our results support our hypothesis because our plant grew towards the light and grew taller than a plant without light.

Conclude and Apply

My advice to farmers is to first of all plant their crops in a greenhouse. Greenhouses absorb the most amount of light which is beneficial to the plant for growing and photosynthesizing. I would also make the light only come from the top of the house since the plants are attracted to the light hitting it. Since the light is at the top, the plants will grow in that direction and won’t start curving.


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