Which one of the following gases is reported to retard photosynthesis ?
(a) CO
(b) CFCs
(c) CO2
(d)

Q: Why doesn't CO retard photosynthesis?

Carbon Monoxide is highly toxic to animals because it binds to hemoglobin in the blood. Since plants do not have hemoglobin, CO largely ignores them and doesn't significantly affect photosynthesis at typical pollution levels.

Q: Doesn't CO2 cause global warming? Why isn't it the answer?

While CO2 is indeed a major greenhouse gas responsible for global warming, it is also the primary raw material for photosynthesis. An increase in CO2 can actually increase the rate of photosynthesis, a phenomenon known as the CO2 fertilization effect.

Q: How exactly does NO2 damage the leaves?

NO2 enters the leaves through tiny pores called stomata. Once inside, it dissolves in the cellular water to form nitrous and nitric acids. These acids lower the pH and physically damage the cell membranes and chloroplasts.

Q: Do CFCs affect plants?

CFCs are known for depleting the ozone layer in the stratosphere, which allows more harmful UV radiation to reach the Earth. While excessive UV can harm plants, CFCs themselves do not directly retard photosynthesis at the ground level like NO2 does.

Q: Is NO2 the only gas that damages plants?

No, other tropospheric gases like Sulfur Dioxide (SO2) and ground-level Ozone (O3) are also highly toxic to plants. They can cause severe leaf damage and significantly retard the rate of photosynthesis.

Question

Which one of the following gases is reported to retard photosynthesis ?

Options:

(A) CO

(B) CFCs

(C) CO_2

(D) NO_2

Sigma Percentile · Accepted Answer

### The Green Engine: Photosynthesis

Imagine a plant as a microscopic factory. Its primary job is to take in carbon dioxide from the air, absorb sunlight, and produce life-sustaining oxygen and glucose. This miraculous process is called photosynthesis. It is the foundation of almost all life on Earth. But what happens when this factory is attacked by toxic invaders?

### The Culprits: Analyzing the Options

In our atmosphere, human activities have introduced several foreign gases. Let's look at the suspects provided in the question:

- **Carbon Monoxide ($CO$):** Highly toxic to humans because it binds to hemoglobin, but plants don't have blood. It largely ignores them.
- **Chlorofluorocarbons (CFCs):** These are notorious for destroying the ozone layer high up in the stratosphere, but they don't directly choke plants at the ground level.
- **Carbon Dioxide ($CO_2$):** This is actually plant food! An increase in $CO_2$ generally boosts photosynthesis, not retards it.
- **Nitrogen Dioxide ($NO_2$):** A reddish-brown gas emitted from vehicle exhausts and industrial chimneys. This is our prime suspect.

### The Attack of Nitrogen Dioxide

When $NO_2$ levels rise in the lower atmosphere, the gas enters the plant leaves through tiny pores called stomata. Once inside, it dissolves in the cellular water to form destructive acids. This chemical assault damages the delicate cellular structure of the leaves, causing lesions and brown spots—a condition known as chlorosis or necrosis.

Because the solar panels of the plant (the leaves) are physically damaged, their ability to capture sunlight and process $CO_2$ drops drastically. **Therefore, higher concentrations of $NO_2$ directly damage plant leaves and severely retard the rate of photosynthesis.**

### The Bigger Picture

Understanding this helps us see why air pollution isn't just a human health issue; it's an ecological crisis. $NO_2$ doesn't just stop at damaging leaves; it also reacts with water vapor to form acid rain, further degrading the soil and aquatic ecosystems. Protecting our air means protecting the very plants that give us the oxygen we breathe.

Animated Solution for Chemistry - Environmental Chemistry: Which one of the following gases is reported to retard photosynthesis ?

Select Answer:

Visualized Solution

$Photosynthesis Overview$

$Atmospheric Pollutants$

$Role of NO_{2}$

$Effect of NO_{2} on Plants$

$Retardation of Photosynthesis$

$Conclusion$

$The Way Forward$

The Sigma Insight: Atmospheric Pollution

The Green Engine

The Culprits

The Attack of Nitrogen Dioxide

The Bigger Picture

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