Question

\(\mathrm{C}_{4}\) plants are also known as (a) Hatch and Slack type (b) Calvin type (c) Calvin and Bassham type (d) Emerson type

Short answer

The correct answer is (a) Hatch and Slack type.

Step-by-step solution

Understand the different types of plants

There are different types of plants based on their photosynthetic processes. C3, C4, and CAM plants are distinguished by the paths that they use to fix carbon, in the process of photosynthesis.

Comparing the given options

Comparing the given options is a way to check which terminology aligns with what we know about C4 plants. Calvin Cycle is a term associated with C3 plants, not C4, while CAM plants undergo Crassulacean Acid Metabolism. The Emerson Effect is about the quantum efficiency of photosynthesis and doesn't refer to specific plant types.

Determine the correct term for C4 plants

It is known that C4 plants undergo a unique process of carbon fixation that seeks to efficiently prevent photorespiration. This process was first explained by Marshall Davidson Hatch and Charles Roger Slack, thus C4 plants are known as Hatch and Slack type.

Key concepts

Hatch and Slack pathway

The Hatch and Slack pathway is named after researchers Marshall Davidson Hatch and Charles Roger Slack. Both scientists made significant contributions to understanding the special process that occurs in C4 plants to optimize photosynthesis.
Unlike the typical pathway seen in most photosynthetic organisms (C3 plants), C4 plants utilize a mechanism that effectively concentrates carbon dioxide in their leaf cells.
This helps them reduce photorespiration, which is a wasteful process where oxygen is fixed instead of carbon dioxide.

• The key players in this pathway are specialized leaf cells known as mesophyll and bundle-sheath cells.
• Initially, carbon dioxide is captured in the mesophyll cells.
• The CO2 is then converted into a four-carbon compound, typically oxaloacetate.
• This compound travels to the bundle-sheath cells, where it releases CO2 for use in the Calvin Cycle.

In this way, the pathway enhances the efficiency of photosynthesis, especially in hot and dry conditions, by minimizing energy loss.

carbon fixation

Carbon fixation is a fundamental process in photosynthesis where carbon dioxide is captured from the atmosphere and converted into an organic compound.
This is essential as it forms the building blocks for the growth of plants and ultimately feeds the entire food chain.

• In C3 plants, carbon fixation occurs directly in the Calvin Cycle, where CO2 is fixed by the enzyme RuBisCO.
• C4 plants use a more effective carbon fixation strategy by first capturing CO2 into four-carbon compounds to prevent photorespiration.
• CAM plants fix carbon dioxide at night, storing it for daytime photosynthesis.

This process is crucial because it allows plants to obtain the carbon necessary for producing sugars and other organic molecules needed for growth and development.

photorespiration

Photorespiration is a process that occurs when the enzyme RuBisCO binds to oxygen instead of carbon dioxide during the Calvin Cycle.
This leads to the generation of a toxic compound, which the plant then needs to recycle, using energy and organic carbon substrates, making it a costly process.

• It happens more frequently at higher temperatures, when stomata close to prevent water loss, reducing CO2 intake.
• C3 plants are significantly affected by photorespiration, often leading to a decrease in photosynthetic efficiency.
• C4 and CAM plants have developed methods to minimize photorespiration, making them more efficient under these conditions.

Understanding photorespiration is important as it impacts plant productivity, especially in climates where water is scarce and temperatures are high.

C3 plants

C3 plants are the most common type of plants and make up about 85% of the plant species on Earth.
Their name comes from the 3-carbon molecule, 3-phosphoglycerate, which is the first stable product of carbon fixation by RuBisCO in the Calvin Cycle.

• The majority of crops, such as rice and wheat, are C3 plants.
• They thrive in cool, wet, and temperate climates where photorespiration is less of an issue.

However, in hot and dry environments, C3 plants can struggle due to increased rates of photorespiration, leading to energy inefficiencies and lower biomass production compared to C4 and CAM plants. This is partly due to their inability to concentrate carbon dioxide in their leaves.

CAM plants

CAM (Crassulacean Acid Metabolism) plants are adapted to survive in arid environments where water conservation is critical.
These plants fix carbon dioxide at night, storing it in the form of organic acids to be used during the day for photosynthesis.
This nighttime fixation ensures that their stomata can remain closed during the hottest parts of the day to reduce water loss while still performing photosynthesis.

• Common examples include succulents like cacti and certain orchids.
• This adaptation allows these plants to conserve water and thrive in challenging conditions.
• CAM plants exhibit a high water-use efficiency, which makes them particularly suited to desert habitats.

By employing CAM photosynthesis, these plants can maintain productivity and competitive advantage in habitats where other plant types would struggle.