Problem 133 - Objective Biology for NEET

Question

Select the incorrect statement from the following: (a) At high intensities, both \(\mathrm{C}_{3}\) and \(\mathrm{C}_{4}\) plants shows increase in the rate of photosynthesis by increasing \(\mathrm{CO}_{2}\) concentration. (b) \(\mathrm{C}_{4}\) plants shows saturation at \(360 \mu \mathrm{l} / \mathrm{L}\). (c) \(\mathrm{C}_{3}\) plant shows saturation beyond \(450 \mu \mathrm{l} / \mathrm{L}\). (d) Productivity of tomatoes and ball papers cannot be increased by enriching environment by \(\mathrm{CO}_{2}\)

Step-by-Step Solution

Answer

Option D is the incorrect statement.

Step 1: Analyzing Option A

At high intensities, both \(\mathrm{C}_{3}\) and \(\mathrm{C}_{4}\) plants show an increase in the rate of photosynthesis by increasing \(\mathrm{CO}_{2}\) concentration. This is a correct statement as both types of plants will indeed increase their photosynthesis rates when \(\mathrm{CO}_{2}\) concentration is elevated.

Step 2: Analyzing Option B

\(\mathrm{C}_{4}\) plants show saturation at $360 \mu \mathrm{l} / \mathrm{L}$. This is also a correct statement as \(\mathrm{C}_{4}\) plants have been known to reach photosynthesis saturation at this \(\mathrm{CO}_{2}\) concentration level.

Step 3: Analyzing Option C

\(\mathrm{C}_{3}\) plants show saturation beyond $450 \mu \mathrm{l} / \mathrm{L}$. This is a true statement because \(\mathrm{C}_{3}\) plants, unlike \(\mathrm{C}_{4}\) plants, reach saturation at a higher \(\mathrm{CO}_{2}\) concentration due to their different photosynthesis process.

Step 4: Analyzing Option D

Productivity of tomatoes and bell peppers cannot be increased by enriching environment by \(\mathrm{CO}_{2}\). This is an incorrect statement. Most plants, including tomatoes and bell peppers, can increase their productivity when the \(\mathrm{CO}_{2}\) levels in their environment are increased.

Key Concepts

C3 and C4 Plants

Understanding the difference between C3 and C4 plants is crucial to comprehend their photosynthetic behavior and response to environmental changes. C3 plants, named after the three-carbon compound they first form during the photosynthesis process, utilize the Calvin cycle to fix carbon dioxide (CO2). This process is less efficient under high temperatures and light intensities, as well as low CO2 concentrations, due to a phenomenon called photorespiration.

In contrast, C4 plants have evolved a specialized mechanism that effectively concentrates CO2 in certain cells, thus minimizing photorespiration and making the process more efficient, particularly in hot, dry climates. The first stable product they form is a four-carbon compound, hence the name C4. Maize and sugarcane are typical examples of C4 plants.

While both types of plants experience increased photosynthesis rates with elevated CO2 levels, C4 plants usually show a saturation point at lower CO2 concentrations than C3 plants because of their CO2-concentrating mechanism.

Photosynthesis CO2 Enrichment

CO2 enrichment leverages the dependency of photosynthesis on carbon dioxide availability. By increasing CO2 concentration, plants can typically increase their rate of photosynthesis, which can lead to enhanced growth and productivity. This is especially true in controlled environments such as greenhouses, where CO2 levels can be manipulated.

However, there is a limit to this benefit, known as the photosynthesis saturation point. Beyond this point, additional CO2 will not lead to significant increases in photosynthesis rates because the enzymes responsible for carbon fixation are already working at maximum capacity. The exact saturation point varies between C3 and C4 plants, due to their distinct photosynthetic pathways.

Therefore, in practical applications, CO2 enrichment must be managed carefully to ensure plant growth is actually being promoted without wasting resources or causing possible harm due to excessive CO2 concentrations.

Plant Productivity

Plant productivity is a measure of the efficiency with which plants can convert light, water, CO2, and nutrients into biomass. Enhancing this productivity is a key goal in both agriculture and horticulture, as it leads to greater yields of crops and better growth of ornamental plants.

One of the proven methods to boost plant productivity is CO2 enrichment, which stimulates photosynthesis and, consequently, plant growth. However, it's crucial to understand that not all plants exhibit the same response to increased CO2. Factors such as plant species, climate, water availability, and nutrient levels all play a role in determining how much productivity will increase with higher CO2 levels. For instance, C3 plants often see more benefit from CO2 enrichment than C4 plants, because their rate of photosynthesis is more sensitive to changes in CO2 concentration.

Importantly, despite the general benefits of CO2 enrichment, overdoing it can be counterproductive. As stated in the exercise solution, even plants like tomatoes and bell peppers that can thrive with additional CO2, will not benefit from concentrations beyond their respective saturation points.