Question Video: Predicting the Result of an Experiment Investigating Auxins in Plants | Nagwa Question Video: Predicting the Result of an Experiment Investigating Auxins in Plants | Nagwa

Question Video: Predicting the Result of an Experiment Investigating Auxins in Plants Biology • Third Year of Secondary School

Join Nagwa Classes

Attend live Biology sessions on Nagwa Classes to learn more about this topic from an expert teacher!

In an experiment investigating hormonal control in plants, two young plant shoots are taken and the tips of both are removed. In experiment 1, the cut section of a shoot is covered with a block of permeable gelatin. In experiment 2, the cut section of a shoot is covered with a layer of impermeable mica. Then, the tips are placed back on the shoots and they are left to grow for a week in the presence of a light source. In which experiment would you expect the shoot to bend toward the light?

02:47

Video Transcript

In an experiment investigating hormonal control in plants, two young plant shoots are taken and the tips of both are removed. In experiment one, the cut section of a shoot is covered with a block of permeable gelatin. In experiment two, the cut section of a shoot is covered with a layer of impermeable mica. Then, the tips are placed back on the shoots and they are left to grow for a week in the presence of a light source. In which experiment would you expect the shoot to bend toward the light?

Hormones are chemical messengers that travel throughout an organism’s body to cause a particular effect. Auxins are a group of plant hormones that can control cell elongation among their many other functions. Auxins are influenced by light, which allows them to stimulate directional growth in response to a light stimulus through a process called phototropism.

Let’s look more closely at how auxins work. Auxins are usually produced in cells at the tip of a plant shoot and diffuse down the plant from cell to cell. When a light source is arriving from one side, auxins usually accumulate in the cells on the shaded side of the shoot, causing these cells to elongate comparatively more than the cells on the illuminated side of the shoot. The asymmetrical cell elongation results in the plant bending, or curving, toward the light source. This allows the photosynthetic cells, which are mostly found in the leaves and shoots of plants, to access more light for photosynthesis so that they are able to produce sugars at a faster rate.

Now that we understand how plants grow in response to light, let’s think about the proposed experiment in the question. We know that auxins are made in the tip of the shoot and diffuse downward through the plant. The question tells us that the gelatin placed between the tip and the rest of the shoot in experiment one is permeable. If permeable gelatin separates the shoot tip from the rest of the plant, the auxins that are produced in the shoot tip will still diffuse down through the gelatin and influence directional growth in the same manner as without the gelatin present.

However, we are told that the mica which is placed between the tip and the rest of the shoot in experiment two is impermeable. If the impermeable mica is placed between the tip of the shoot and the rest of the plant, the auxins produced in the shoot tip cannot diffuse through it and therefore cannot access the cells lower down in the shoot. This means that they cannot affect directional growth. So phototropism does not occur and the plant will likely not grow at all. This means that we can deduce the experiment in which the shoot would be expected to bend toward light and therefore the correct answer to this question. We would only expect the shoot to bend toward the light source in experiment one.

Join Nagwa Classes

Attend live sessions on Nagwa Classes to boost your learning with guidance and advice from an expert teacher!

  • Interactive Sessions
  • Chat & Messaging
  • Realistic Exam Questions

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy