Dicot leaf shows differential colouration between the two surfaces because of

Options

A. Undifferentiated mesophyll
B. Presence of upper palisade and lower spongy parenchyma
C. Presence of upper spongy and lower palisade parenchyma
D. Presence of spongy parenchyma only

Answer

To answer the question "Dicot leaf shows differential coloration between the two surfaces because of", we will analyze the options based on the structure of a dicot leaf and the arrangement of its tissues.

### Step-by-Step Solution:

1. **Understanding Leaf Structure**:
- A dicot leaf typically has two distinct surfaces: the upper surface (adaxial) and the lower surface (abaxial).
- The leaf is composed of various types of tissues, including epidermis, mesophyll (which includes palisade and spongy parenchyma), and vascular tissues.

2. **Identifying Mesophyll Types**:
- The mesophyll is divided into two main types:
- **Palisade Parenchyma**: Located just beneath the upper epidermis, these cells are elongated and tightly packed. They contain a high concentration of chlorophyll, making this region appear darker green.
- **Spongy Parenchyma**: Found beneath the palisade layer, these cells are loosely arranged with air spaces. They contain fewer chlorophylls, resulting in a lighter green coloration.

3. **Differential Coloration**:
- The differential coloration between the two surfaces of the leaf is primarily due to the presence of these two types of mesophyll.
- The **adaxial surface** (upper side) has a higher concentration of chlorophyll due to the palisade parenchyma, making it appear darker green.
- The **abaxial surface** (lower side) has the spongy parenchyma, which has a lower chlorophyll concentration, leading to a lighter green color.

4. **Effects of Sunlight Exposure**:
- The adaxial surface is more exposed to sunlight, which enhances chlorophyll production in the palisade parenchyma. This contributes to the darker green coloration of the upper surface.
- Conversely, the abaxial surface is less exposed to direct sunlight, resulting in a comparatively lighter coloration.

5. **Conclusion**:
- The differential coloration between the two surfaces of the dicot leaf is due to the presence of the **upper palisade and lower spongy parenchyma**.

### Final Answer:
The correct option is: **presence of upper palisade and lower spongy parenchyma**.