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Activity 7 : “Interaction and coordination: Tropisms”

Videoclip projection: "Tropisms"

a) Read and translate the text before watching the video.

b) Watch the videoclip with the help of the transcription next to it.

c) Answer the questions.

a) Read and translate this text before watching the video.

Tropisms

Growth in plants reflects the way in which they interact with the environment.

Phototropism

If we place a strong light on one side of this fuchsia plant, the plant will grow towards it. This is called a phototropic response. But what controls such response?

If the tip (=punta) of a plant is protected from the light by using a small cap, the plant will continue to grow upward. This suggests that there's something at the tip of the plant that controls the direction of growth.

If we place this fuchsia plant on its side, it quickly recovers its orientation and grows upward. But is the plant responding to light, or to gravity?

Geotropism

These pea seeds are germinating in the dark, yet the roots are going down and shoots (=brotes) are going up. The roots and shoots must be responding to gravity, but in different ways. The roots are said to be positively geotropic, and the shoots negatively geotropic.

Why does a plant move if they don't have a nervous system or endocrine system?

It is probable that all of these growth responses are due in some part to a hormone or auxin (=auxina) called indole acetic acid, or IAA. One theory states that a light-sensing mechanism in the tip of a fuchsia plant promotes the active transport of hormones to the shaded part of the stem (=tallo). This action produces cell growth and elongation in this area. The result is a curvature which orientates the plant towards the light.

Experience: What happens if I remove the tip of the plant?

By removing the growing tip which controls auxin distribution and therefore apical dominance, lateral buds can grow.

… and why do leaves fall from trees?

An important hormone in deciduous plants is abscisic acid, which controls leaf fall, thereby protecting the plant from adverse seasonal conditions.

b) Watch the videoclip with the help of the transcription next to it.

Growth in plants reflects the way in which they interact with the environment.

If we place a strong light on one side of this fuchsia plant, the plant will grow towards it. This is called a phototropic response. But what controls such response?

If the tip of a plant is protected from the light by using a small cap, the plant will continue to grow upward. This suggests that there's something at the tip of the plant that controls the direction of growth.

If we place this fuchsia plant on its side, it quickly recovers its orientation and grows upward. But is the plant responding to light, or to gravity?

These pea seeds are germinating in the dark, yet the roots are going down and shoots are going up. The roots and shoots must be responding to gravity, but in different ways. The roots are said to be positively geotropic, and the shoots negatively geotropic.

It is probable that all of these growth responses are due in some part to the auxin indole acetic acid, or IAA. One theory states that a light-sensing mechanism in the tip of a fuchsia plant promotes the active transport of IAA molecules to the shaded part of the stem. This action produces cell growth and elongation in this area. The result is a curvature which orientates the plant towards the light.

A gravity-sensing mechanism in the shoots tip triggers a similar migration of IAA molecules, producing growth in the stem, which orientates the plant from a horizontal position back to a vertical position.

The growth substance IAA also appears to have a role in maintaining apical dominance.

By removing the growing tip which controls auxin distribution and therefore apical dominance, lateral buds can grow.
 
An important hormone in deciduous plants is abscisic acid, which controls leaf fall, thereby protecting the plant from adverse seasonal conditions.

c) Answer these questions:

1.- Where is the control centre for the growth response of the plant?

2.- How can a plant move if they don't have a nervous system or endocrine system?

3.- What happens if we remove the tip of the plant?

4.- Why do leaves fall from trees?

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