Difference Between C3 And C4 Plants, Pathway and Examples

Difference Between C3 and C4 Plants:  All plants rely on sunlight as their primary energy source for survival. This energy is harnessed through the process of photosynthesis, where "photo" refers to light. Photosynthesis is a complex pathway that plants use to convert atmospheric carbon into sugar (carbohydrate) molecules. These resultant products serve as the fundamental energy source for all plant species.

Plants can be broadly categorized into two types: C3 and C4 plants. These represent distinct photosynthetic pathways utilized by plants to fix carbon dioxide. This discussion provides a brief overview highlighting the differences between these two plant types.

 C4 plants exhibit greater photosynthetic efficiency, particularly in conditions characterized by high light intensity, elevated temperatures, and limited water availability. As a result, they are predominant in arid and tropical regions. Conversely, C3 plants are more widespread and adaptable to a broader range of environmental conditions. The detailed difference between C3 and C4 plants are provided below.

Difference Between C3 and C4 Plants Overview

C3 plants are characterized by their utilization of the C3 pathway in photosynthesis, employing the Calvin cycle during the dark phase. C3 plants' leaves, unlike C4 plants', lack Kranz anatomy. Photosynthesis in C3 plants occurs only when the stomata are open. It is worth noting that approximately 95% of shrubs, trees, and plants are classified as C3 plants.

C4 plants, on the other hand, are distinguished by their reliance on the C4 pathway, also known as the Hatch-Slack pathway, in the dark reaction of photosynthesis. The leaves of these plants have Kranz anatomy, and their chloroplasts are dimorphic. C4 plants are in the minority, accounting for about 5% of all plant species on Earth. Examining the difference between C3 and C4 plants reveals significant differences in their photosynthetic processes.

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Difference Between C3 and C4 Plants

The fundamental difference between C3 and C4 plants lies in the differing products synthesized during the absorption of carbon dioxide for photosynthesis from sunlight and its subsequent conversion to glucose. Photosynthetic plants in the C3 pathway produce a 3-carbon acid or 3-phosphoglyceric acid (PGA) as their initial product during carbon dioxide fixation. Plants in the Hatch and Slack or C4 pathway, on the other hand, generate oxaloacetic acid or a 4-carbon compound as their primary product before entering the C3 pathway.

Plants that use the CAM (crassulacean acid metabolism) pathway have a different photosynthetic strategy. Plants in this pathway capture solar energy during the day and use it at night to assimilate or fix carbon dioxide. These differences represent a general difference between C3 and C4 plants, with potential variations among specific plant species.

C3 Plants 

C3 plants are characterized by the three-carbon compound 3-phosphoglycerate being the first product of the Calvin cycle. Also known as temperate plants, these organisms undergo direct carbon dioxide reduction in the chloroplast. C3 plants can have both annual and perennial life cycles and are notably rich in proteins. Examples of C3 plants include wheat, oats, rye, and orchardgrass.

C3 plants fix carbon through the C3 cycle, converting carbon dioxide into 3-carbon sugars. This process allows plants to transform the 3-carbon compounds into nucleotides, amino acids, and complex sugars, such as starches. Carbon fixation is a vital process that contributes significantly to the creation of organic matter.

The C3 cycle, or Calvin cycle, stores energy for plants over an extended period. The Calvin cycle is a light-independent reaction in photosynthesis that is powered by ATP and NADPH generated in the light-dependent reactions. The Calvin cycle removes greenhouse gases from the atmosphere by converting carbon dioxide into usable forms, such as proteins, sugars, lipids, and nucleotides. The C3 cycle also contributes to the foundation of the food chain by storing sugars that plants and animals can utilize.

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C4 Plants

C4 plants use a distinct carbon-cycling mechanism to convert carbon dioxide into four-carbon sugar compounds before entering the C3 or Calvin cycle. This adaptation makes them highly productive in hot and arid climates. Notable examples of C4 plants consumed by humans include pineapple, maize, and sugarcane.

In environments with elevated temperatures, photorespiration is decreased, outweighing the ATP required for the transport of CO2 from mesophyll cells to bundle-sheath cells. The C4 pathway is used by only 3% of vascular plants. The name C4 comes from the four-carbon compound oxaloacetate produced during this pathway. Plants using the C4 photosynthetic pathway, such as maize, sugarcane, and many grass species, fix CO2 into a four-carbon compound before transferring it to the Calvin cycle.

C4 plants are more efficient at photosynthesis under high light and heat, making them well-suited to hot climates. This adaptation also reduces water loss through transpiration. C4 plants are commonly found in tropical and subtropical regions, as well as in areas with high light intensity and temperature.

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