RESULTS & DISCUSSION

PLANT 1

When the cut section of the shoot is covered with a block of permeable gelatin, the gelatin forms a barrier between the shoot tip and the rest of the plant. Despite being a barrier, the gelatin allows the passage of substances, including auxins. Because of its permeable nature, the auxins produced in the shoot tip can freely diffuse down through the gelatin and exert their influence on directional growth, just as if the gelatin were not present. Consequently, phototropism, the bending of the shoot towards the light source occur.

PLANT 2

When the cut section of the shoot is covered with impermeable mica, the mica layer acts as a barrier that prevents the diffusion of auxins produced in the shoot tip. As a result, the auxins are unable to reach the cells lower down in the shoot. Without the presence of auxins in these cells, their ability to stimulate directional growth is impaired. As a consequence, the plant does not exhibit phototropism and is unlikely to show a significant growth response to the light source.

The experiment described investigates the hormonal control in plants, specifically focusing on the role of auxins in phototropism, the process by which plants bend or curve towards a light source. Two young plant shoots are taken, and the tips of both shoots are removed. In experiment one, the cut section of a shoot is covered with a block of permeable gelatin, while in experiment two, the cut section is covered with a layer of impermeable mica. The tips are then placed back on the shoots, and the plants are left to grow for a week in the presence of a light source. The question asks which experiment would result in the shoot bending toward the light. Based on our understanding of auxin's role in phototropism, we can analyze the expected outcomes of each experiment. Auxins, which are plant hormones responsible for various functions, including cell elongation, are produced in the cells at the tip of a plant shoot. They diffuse down the plant from cell to cell. When a light source is present, auxins tend to accumulate in the cells on the shaded side of the shoot, causing those cells to elongate more than the cells on the illuminated side. This asymmetrical cell elongation results in the plant bending or curving toward the light source, enabling the photosynthetic cells to access more light for efficient photosynthesis.

WHY DOES THE PLANT RESPOND TO THE AUXIN IN SUCH A WAY?

In the described experiment, the application of the growth regulator, specifically auxins, plays a crucial role in the plant's response to the light source. Auxins are responsible for regulating various aspects of plant growth and development, including cell elongation. They are primarily produced in the cells located at the tip of a plant shoot, known as the apical meristem.

When a plant is exposed to light, auxins tend to accumulate in higher concentrations on the shaded side of the shoot. This differential distribution of auxins leads to asymmetrical cell elongation. The cells on the shaded side receive a higher concentration of auxins, which stimulates their elongation or growth. As a result, these cells elongate more than the cells on the illuminated side, causing the shoot to bend or curve toward the light source.

In experiment one, the cut section of the shoot is covered with a block of permeable gelatin:
- The permeable gelatin allows the diffusion of auxins through its structure.
- The auxins produced in the apical meristem can freely diffuse through the gelatin and move towards the rest of the shoot.
- As a result, the auxins can still accumulate on the shaded side of the shoot, causing the cells on that side to elongate more, resulting in the shoot bending towards the light source.
In experiment two, the cut section of the shoot is covered with a layer of impermeable mica:
- The impermeable mica acts as a barrier that prevents the diffusion of auxins from the apical meristem to the rest of the shoot.
- As a result, the auxins produced in the apical meristem cannot diffuse through the mica layer and reach the shaded side of the shoot.
- Without the accumulation of auxins on the shaded side, there is no asymmetrical cell elongation, and therefore the shoot does not bend towards the light source.

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Therefore, based on our understanding of auxins' role in phototropism, it can be expected that experiment one, where the cut section of the shoot is covered with permeable gelatin, would result in the shoot bending towards the light source. In contrast, experiment two, where the cut section is covered with impermeable mica, would not induce phototropism, as the auxins cannot reach the shaded side of the shoot.

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