What is the Difference Between C3 and C4 Plants?

The main difference between C3 and C4 plants lies in the dark reaction of photosynthesis. C3 plants use the C3 pathway or Calvin cycle for this process, while C4 plants use the C4 pathway or Hatch-Slack Pathway. Here are the key differences between C3 and C4 plants:

1. First Stable Intermediate Product: In C3 plants, the first stable intermediate product is a 3-carbon acid (phosphoglyceric acid), while in C4 plants, it is a 4-carbon acid (oxaloacetate).
2. Photorespiration: C3 plants are more prone to photorespiration, which occurs when rubisco, the primary photosynthetic enzyme, reacts with oxygen instead of carbon dioxide. This leads to a loss of energy and decreased efficiency in hot and dry environments. C4 plants, on the other hand, have adapted to reduce photorespiration by concentrating carbon dioxide in bundle sheath cells around rubisco, effectively removing its contact with oxygen.
3. Leaf Anatomy and Chloroplast Types: C3 plants exhibit only granal chloroplasts, while C4 plants exhibit both granal and agranal types of chloroplasts. C4 plants possess kranz anatomy, which allows for the separation of carbon dioxide fixation and rubisco, reducing photorespiration.
4. Water Efficiency: C4 plants have higher water efficiency than C3 plants. For every CO2 molecule fixed, C4 plants release 277 molecules of water, while C3 plants release 833 molecules of water.
5. Abundance and Environment: C3 plants are more abundant in nature, accounting for approximately 95% of plants on Earth. They are commonly found in cool and wet areas. C4 plants make up about 3% of vascular plants and are dominant in hot, dry environments.

In summary, C3 and C4 plants differ in the dark reaction of photosynthesis, with C4 plants having evolved adaptations to reduce photorespiration and increase water efficiency in hot and dry environments.

Comparative Table: C3 vs C4 Plants

The main differences between C3 and C4 plants are related to their photosynthetic pathways, leaf anatomy, and the type of chloroplasts they exhibit. Here is a table summarizing the differences between C3 and C4 plants:

C3 plants are more common in temperate climates, while C4 plants are found in tropical climates. C3 plants exhibit only granal chloroplasts, whereas C4 plants exhibit both granal and agranal chloroplasts. Carbon dioxide fixation occurs only once in C3 plants, while it occurs twice in C4 plants. C3 plants have a lower photosynthetic efficiency compared to C4 plants due to the absence of photorespiration in C4 plants.