our knowledge.
- What do we call the action of kicking a foot ball?
Kicking of a foot ball is a voluntary action’ These actions are within our control.
- How is the knee jerk action takes place?
In the knee jerk action a nerve pathway was involved.
v) Do you think most of the functions in our body go about in an involuntary manner? Why ? Why not ?
Most of our body functions are done without the involvement of our knowledge. For example, heart beating, respiration, digestion, etc., are the involuntary actions which are carried by our body.
Activity – 4
Touch the leaves of Mimosa pudica (athipathi, touch me not) plant and observe the response of leaves.
- Are they folding?
When the leaves of Mimosa are touched the leaves get folding. Touching the leaves is the stimulus and folding is the response.
- In which direction the folding of the leaves take place?
The folding of the leaves take place inward direction.
- Give some examples of situations in plants responding to a certain stimulus.
Examples: The sun flower turning to the direction of sun, the bending response of the plant when it is kept in the dark. Some of leaves of the trees opens at the day time and closes after sun set.
Phototropism of stem and geotropism of roots, hydrotropism of roots of plants growing towards water and thigmotropism where the creepers like cucumber, bitter – gourd takes the help of tendrils and wind around the support are some of the examples of response to stimulus in plants.
Activity – 5
Take a glass jar and fill with soil. Sow a bean seed near the wall of the jar. After 4 – 5 days you will notice seed germination. Keep the jar under the sun. Observe how root and shoot grows. Then tilt the glass jar and keep the plant horizontally. Observe the direction of the root and shoot growth for more than a week.
- Does the shoot take a horizontal tilt after a week?
After a week the shoot takes a horizontal tilt.
- Which side of the shoot may have grown more and which side less to bring about this effect?
The shoot grown more towards the light and less where light is not falling.
- Do you find any difference in the shape of epidermal cells?
The straight portions of the epidermal cells shows no bending but the bending portions of epidermal cells shows bending.
- Who performed experiments on phototropism?
Charles Darwin and his son Francis Darwin performed some experiments on phototropism.
- What did they do in their experiment?
Charles Darwin and his son Francis Darwin performed experiments on phototropism. They covered the terminal portion of the tip of stem (coleoptile) with a cylinder of metal foil. Exposed the plant to light coming from the side.
- What did they observe by that experiment?
They observed that the bending towards the light (characteristic) of the seedling did not occur. If light was permitted to penetrate the cylinder bending occurred normally.
- What did Charles Darwin and his son Francis Darwin state on their experiment?
They stated that when seedlings are freely exposed to a lateral light some ‘influence’ is transmitted from upper to the lower part causing the material to bend.
- What are the experiments of F.W. Went and how did he succeeded in separating ‘influence’ from the plant?
F.W. Went cut off coleoptile tips from oat seedlings. He placed the tips on a slice of agar and left them for about an hour.
He then cut agar into small blocks and placed a block on one side each stump of the decapitated plants. They were kept in the dark during the entire experiment. Within one hour he observed a distinct bending away from the side on which agar block was placed.
- How did Went come to know about auxin?
Went interpreted these experiments as showing that the coleoptile tip exerted it’s effect by means of chemical stimulus rather than a physical stimulus such as an electrical impulse.
This chemical stimulus came to be known as auxin. In this way the first plant hormone auxin was discovered by F.W. Went.
- What is the meaning of auxin in Greek?
The Greek word auxin means to increase.