Experiment: Plant Sensitivity.

Aim: To observe phototropism and geotropism in plants.

Apparatus: a cardboard box with one sided illumination; two Petri dishes with sprouted seedlings; a clinostat with seedlings on it and another Petri dish with seedlings.

Method:Phototropism.

1. Two Petri dishes with seedlings growing in them were placed in a cardboard box as shown in the diagram. One of the Petri dishes was placed in the part that had absolute darkness and the other one was placed in the partition that had one sided illumination.

2. These were left and watered for a few days.3. The shoots were observed after a few days.

Geotropism

1. Some seedlings were pinned onto the cork of the clinostat.2. Some other seedlings were planted in a Petri dish.3. Both the clinostat and the Petri dish were left vertical.4. The clinostat was switched on.5. Both seedlings were watered and left for a few days.6. After a few days the shoots were observed.

Precautions:1. It was made sure that all the seedlings were watered every two days2. It was made sure that the seedlings of the phototropisms experiments

were not exposed too much to light, but only for watering.3. It was made sure that the phototropism box was tightly closed so that no

light enters expect from the small hole on one side.4. It was made sure that while watering the seedlings on the clinostat, no

water was spilled on the mechanism that could cause electric shock.

Results:Phototropism:

1. The seedlings that were growing in the dark side kept growing straight up.

2. The seedlings that were growing in the one sided illuminated partition turned towards the light.

Geotropism:1. The shoots that grew on the clinostat kept growing horizontally.2. The shoots that grew in the vertical Petri dish grew upwards.

Conclusions:(Write your own conclusions why the seedlings and shoots grew as they did. In your write up you can explain in terms of auxins – light – gravity – plant sensitivity. Why is it important for plants to respond in such ways to the different stimuli? )