What causes a green plant exposed to the light on only one side, to bend toward the source of light as it grows 

Options

A. Auxin accumulated on the shaded side stimulating greater cell elongation there
B. Green plants need light to perform photosysnthesis
C. Green plants seek light because they are phototropic
D. Light stimulates plant cells on the lighted side to grow faster

Answer

To understand why a green plant bends toward a light source when exposed to light from only one side, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding Phototropism**:
- Phototropism is the growth response of a plant to light. When a plant is exposed to light from one direction, it will bend toward the light source.

**Hint**: Remember that phototropism refers specifically to how plants respond to light.

2. **Role of Auxins**:
- Auxins are plant hormones that play a crucial role in regulating plant growth. They are primarily produced at the tips of shoots and roots.

**Hint**: Auxins are essential for growth regulation in plants, particularly in response to environmental stimuli.

3. **Unilateral Illumination**:
- When light falls on one side of the plant (unilateral illumination), auxins will accumulate on the shaded side of the plant. This happens because auxins move away from the light.

**Hint**: Think about how light affects the distribution of hormones in the plant.

4. **Cell Elongation**:
- The accumulation of auxins on the shaded side stimulates greater cell elongation on that side compared to the side exposed to light. This differential growth causes the plant to bend toward the light source.

**Hint**: Consider how differences in cell growth on either side of the plant lead to bending.

5. **Resulting Bend Toward Light**:
- As the cells on the shaded side elongate more than those on the light-exposed side, the plant bends toward the light source. This bending allows the plant to maximize its exposure to light, which is crucial for photosynthesis.

**Hint**: Visualize the bending process as a result of uneven growth on both sides of the plant.

### Conclusion:
The bending of a green plant toward a light source when exposed to light on only one side is primarily due to the accumulation of auxins on the shaded side, leading to greater cell elongation on that side, resulting in the plant bending toward the light.