Introduction:
C3 and C4 plants are two different types of photosynthetic pathways found in plants. C3 plants are the most common type and include many familiar plant species, while C4 plants are found in hot and arid regions. C4 plants are considered more photosynthetically efficient compared to C3 plants due to several reasons.

Explanation:
1. More chloroplasts:
C4 plants have a higher number of chloroplasts compared to C3 plants. Chloroplasts are the organelles responsible for photosynthesis, and they contain the pigment chlorophyll, which captures sunlight. Therefore, the increased number of chloroplasts in C4 plants enhances their ability to capture and utilize light energy efficiently.

2. CO2 compensation point:
The CO2 compensation point refers to the concentration of carbon dioxide (CO2) at which the rate of photosynthesis equals the rate of respiration. C4 plants have a higher CO2 compensation point compared to C3 plants. This means that C4 plants can continue photosynthesizing at lower CO2 concentrations, such as those found in hot and dry environments. This ability allows C4 plants to thrive in conditions where C3 plants would struggle.

3. CO2 efflux prevention:
The statement that CO2 efflux is not prevented in C4 plants is incorrect. In fact, C4 plants have evolved mechanisms to minimize CO2 efflux. They use a specialized enzyme called phosphoenolpyruvate carboxylase (PEP carboxylase) to initially fix CO2 into a four-carbon compound called oxaloacetate in the mesophyll cells. This prevents the loss of CO2 through photorespiration, which is a wasteful process in C3 plants.

4. CO2 recycling:
The CO2 generated during photorespiration in C3 plants is not efficiently recycled, leading to a loss of carbon and energy. In contrast, C4 plants can trap and recycle CO2 through the action of PEP carboxylase. The four-carbon compound produced in the mesophyll cells is transported to bundle sheath cells, where it releases CO2 for use in the Calvin cycle. This efficient recycling minimizes the loss of CO2 and enhances the overall photosynthetic efficiency of C4 plants.

Conclusion:
In conclusion, C4 plants are photosynthetically more efficient than C3 plants due to their higher number of chloroplasts, higher CO2 compensation point, prevention of CO2 efflux, and efficient recycling of CO2 through PEP carboxylase. These adaptations allow C4 plants to thrive in hot and arid environments where C3 plants would struggle.

C₄ plants are photosynthetically more efficient than C₃ plants because C4 plant contain two types of chloroplast i.e., bundle sheath chloroplast and mesophyll chloroplast. So such plants operate a dicarboxylic acid cycle in addition to Calvin cycle. CO₂ acceptor molecule (PEP) is present in large bundle sheath cell which has higher efficiency in picking up CO₂. Thus, photosynthesis continues even at low CO₂ concentration and the rate of photorespiration is also negligible.