Which of the following movements in plants is due to the increased concentration of auxin?

Options

A. Movement of shoot towards the source of light.
B. Nyctinasty
C. Movement of sunflower towards sun
D. All of the above.

Answer

To solve the question "Which of the following movements in plants is due to the increased concentration of auxin?", we can follow these steps:

### Step 1: Understand the Role of Auxin
Auxins are a class of plant hormones that play a crucial role in growth and development. They are primarily involved in cell elongation, which affects how plants respond to environmental stimuli.

**Hint:** Remember that auxins promote cell elongation, especially on the side of the plant that is away from the light.

### Step 2: Analyze the Options Given
Let's evaluate each option provided in the question:

1. **Movement of the shoot towards the source of light**: This movement is known as phototropism. When light is detected, auxins accumulate on the shaded side of the plant, causing those cells to elongate more than the cells on the light-exposed side. This results in the shoot bending towards the light.

**Hint:** Think about how plants grow towards light and how auxins facilitate this process.

2. **Nastic movements (like Nyctinasty)**: These movements are not dependent on the direction of a stimulus but rather occur in response to environmental changes, such as light and temperature. They do not involve auxin concentration changes.

**Hint:** Nastic movements are more about internal rhythms rather than growth direction influenced by auxins.

3. **Movement of the sunflower towards the sun**: This is another example of phototropism, similar to the first option. However, the question specifically asks for the movement due to increased auxin concentration, which is more directly related to the shoot's response to light rather than a general movement of the flower head.

**Hint:** Consider how sunflowers track the sun and whether this is directly linked to auxin.

4. **All of the above**: Since not all options are correct, this cannot be the answer.

**Hint:** If one or more options are incorrect, then "all of the above" cannot be the right choice.

### Step 3: Conclusion
After analyzing the options, the correct answer is **Movement of the shoot towards the source of light** (Option 1), as this movement is directly influenced by the increased concentration of auxin on the shaded side of the plant.

**Final Answer:** Option 1 - Movement of the shoot towards the source of light.