`C_4` plants are most efficient plants to tropical climate and

Options

A. Shows photorespiration
B. have large number of Chloroplasts and thick walls of bundle sheath cells
C. From 4-C organic acids in bundle sheath cell
D. Perform primary `CO_2` fixation in bundle sheath cells

Answer

### Step-by-Step Solution:

1. **Understanding C4 Plants**: C4 plants are adapted to tropical climates and are known for their efficiency in photosynthesis, particularly in conditions where CO2 concentration is low and temperatures are high.

2. **Key Characteristics**:
- C4 plants have a specialized leaf anatomy known as Kranz anatomy. This includes two types of cells: mesophyll cells and bundle-sheath cells.
- Bundle-sheath cells surround the vascular bundles and are characterized by thick cell walls and a high number of chloroplasts.

3. **Photosynthesis Process**:
- In C4 plants, the primary fixation of CO2 occurs in the mesophyll cells, not in the bundle-sheath cells.
- The enzyme phosphoenolpyruvate carboxylase (PEP carboxylase) in mesophyll cells captures CO2 and converts it into a 4-carbon compound (C4 acid).

4. **Transport of C4 Acid**:
- The C4 acid produced in mesophyll cells is then transported to the bundle-sheath cells.
- Within the bundle-sheath cells, the C4 acid is converted into a 3-carbon compound (C3 acid) which enters the Calvin cycle for further processing.

5. **Photorespiration**:
- C4 plants are designed to minimize photorespiration, a wasteful process that occurs in plants when oxygen competes with CO2 for the active site of the enzyme RuBisCO.
- Due to the high concentration of CO2 in the bundle-sheath cells, C4 plants effectively prevent photorespiration.

6. **Conclusion**:
- The correct characteristics of C4 plants include having a large number of chloroplasts and thick walls in bundle-sheath cells, and the primary CO2 fixation occurs in mesophyll cells, not bundle-sheath cells.

### Final Answer:
The most efficient plants for tropical climates are C4 plants, which have a specialized leaf anatomy (Kranz anatomy), perform primary CO2 fixation in mesophyll cells, and minimize photorespiration.