Date: 14th March, 2014
Form 2 Science: Responses of plants towards light, water and gravity.
Just like us, plants respond to various stimuli. The growth response of plants in a particular direction
(towards or away from stimuli) is called tropism.
The types of tropism are as follows:
1.
2.
3.
4.
Phototropism: Movement or growth of plants in response to light
Geotropism: Movement or growth of tips of roots and shoots in response to gravity
Hydrotropism: Movement or growth of plants in response to water
Thigmotropism: Movement or growth of plants in response to touch or contact stimuli
Plant responses can be positive or negative. A positive response is when the plant moves toward or in
the direction of the stimulus. A negative response is when a plant moves away from the stimulus.
What you need to do:
Plan and carry out an investigation to study the responses of green bean seedlings towards light, gravity
or water. Choose one stimulus to investigate and write the aim, problem statement, hypothesis,
variables and steps, and draw your observations for your experiment in your exercise book.
Some suggestions are provided below:
1. To study phototropism, a shoebox (or any box) or egg carton can be used. All boxes or container
used should have just one small window. If your box is big enough, you might want to create a
maze to see if the germinating plant can find the light.
2. To study geotropism, a paper plate can be used. Seedlings can be taped to the plate in various
positions; there should be some positioned such that the roots come out from the top or sides.
3. To study hydrotropism, wire mesh that fits in a box can be used. Alternatively, straws arranged
criss-cross in a box, leaving some space at the bottom where wet cotton can be placed at one
corner can be used. Straws should be arranged such that the holes are small enough to support
seedlings.
Reminders:
If you are investigating plant’s response towards light and gravity, remember that the seedlings need
water. To avoid a mess while watering, you can use a straw to water the seedlings.