4. Discussion

Key findings

We found that most seeds followed our hypothesis and that it grew towards the direction of gravity. In just one day, the seeds were able to change their direction of root growth drastically. According to the graph above for experiment 1 and 2, the results show that on the 3^rd day where the CD case was rotated 90˚, the angles of the root changed a lot towards the direction of gravity, resulting in big change of angles. The results of the first experiment are that the total length of the roots of all 30 seeds is 165.1cm which makes the average of length of roots of the first experiment to be 5.50cm while the result of the total angle of the roots for all 30 seeds is 2749˚ which also makes the average of the angle of growth of roots to be 91.6˚.  Meanwhile for the second experiment, the results of the second experiment of the total length of roots of all 30 seeds is 179.9cm which makes the average of the length of roots in the second experiment to be 6 cm corrected to 3 significant figures while the total angle of the roots of all 30 seeds is 3260˚ which makes the average of the angle of roots in second experiment to be 109˚ corrected to 3 significant figures. Therefore, the total length of roots of all 30 seeds in the two experiments is 345 cm, which makes the average of the length of roots for both experiments to be 5.75cm. Adding on, the total angle of the roots of all 30 seeds in the two experiment is 6009˚ which shows that the average of the angle of the roots in both experiments to be 100.15˚.   Most of the seeds germinated and the success rate is high even though some of the seeds did not germinate and a small number did not follow our hypothesis. The roots of the green bean changed direction quite fast when the direction of gravity changed. The direction of gravitational pull then affects the seeds by speeding up the rate of growth of roots.

Explanation of key findings

The roots followed the direction of gravity. The plant responded to gravity via auxin, which is a chemical used to promote growth in the plant, to the roots so the roots grew faster the shoot. Plant roots detect gravity by using special cells in their roots called statocytes. These cells contain small bodies called statoliths that sink to the bottom of the cells in response to gravity. The process that plants utilise to determine the direction of gravity using statoliths is similar to dropping a rock to determine which way is down. The statocyte cell will sense where the statoliths touch the inside of the cell and in this way the cell will recognise which way is down. The statocyte communicates this information to other parts of the root through a process called signal transduction. Transduction means that information is converted from one form to another, and the signal being sent is chemical. All biological systems use signal transduction constantly. The information is sent from the statocytes to cells in the root tip, and in this way the root tip "learns" which way is down and grows in that direction.

     Roots also will change direction when a plant is tipped on its side. Auxin concentrates on the lower sides of the roots and inhibits the elongation of root cells. As a result, root cells on the upper side of the root grow longer, turning the roots downward into soil and away from the light. Roots also will change direction when they encounter a dense object, such as a rock. In these cases, auxin concentrates on the lower side of the roots, enabling the roots to change direction and find a way around the rock so that normal growth can resume. An good example of the theory of the roots changing direction is in our project. Within a short time of 2 days, some of our seeds germinated a grew long roots of up to 4 cm. This phenomenon mostly appeared in the 5th and 6th set-up, which is rotated 90 degrees every 2 days.

Evaluation of hypothesis

     The hypothesis is correct because the plants we used in this project responded to gravity change. The plants responded to gravity due to gravitropism. During the experiment, it was observed that most of the green bean seeds germinated and grew towards the direction of gravity, telling us that the hypothesis would be mostly true. Also, plant roots are known to contain auxin, a chemical that allows for the direction of root growth and plant growth to change according to the environment.

Areas for improvement
There are 5 areas for improvement, which are:

1. Instead of using CD cases, we could have used frames of wood.

2. Instead of using the green bean seeds, we can use an alternative such as radish seeds to observe how it responds in the same environment.

3. We can tweak the experiment a little by changing the CD cases into transparent vases that has the ability to grow bigger and more challenging plants.

4. Also, we could have used newer or bought more CD cases instead of using the same CD cases from the first experiment for the second experiment

5. Instead of using petri dishes to hold the CD cases, we should have used something bigger such as pie plates to hold the CD case easier as the CD case can fall off the petri dish quite easily.