Let's understand the process of photosynthesis in green plants and identify the gas released.

Understanding Photosynthesis in Green Plants

Photosynthesis is a vital process carried out by green plants, algae, and some bacteria. It's how they convert light energy into chemical energy in the form of glucose (sugar).

This process uses simple inorganic substances from the environment to create organic food compounds. The key inputs for photosynthesis are:

• Carbon dioxide (absorbed from the atmosphere through small pores called stomata)
• Water (absorbed from the soil through the roots)
• Light energy (captured by chlorophyll, the green pigment in chloroplasts)

The main products of photosynthesis are:

• Glucose (used by the plant for energy or stored)
• Oxygen (released into the atmosphere)

The Chemical Equation of Photosynthesis

The overall chemical equation for photosynthesis is often written as:

\(6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Light Energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2\)

Here:

• \(6\text{CO}_2\) represents six molecules of carbon dioxide.
• \(6\text{H}_2\text{O}\) represents six molecules of water.
• \( \text{C}_6\text{H}_{12}\text{O}_6 \) represents one molecule of glucose (sugar).
• \(6\text{O}_2\) represents six molecules of oxygen.

This equation clearly shows that carbon dioxide and water are consumed, light energy is used, and glucose and oxygen are produced.

Gas Released During Photosynthesis

Based on the process and the chemical equation, one of the main products released by green plants during photosynthesis is oxygen. This oxygen is released into the atmosphere, which is essential for the respiration of most living organisms, including animals and humans.

Analyzing the Options

Let's look at the given options in the context of photosynthesis:

1. Oxygen: As discussed, oxygen is a key gaseous product released during photosynthesis.
2. Nitrogen: Nitrogen is an important element for plant growth and is absorbed by plants from the soil, usually in the form of nitrates or ammonium. It is not directly involved as a gas released during photosynthesis.
3. Carbon-dioxide: Carbon dioxide is a reactant, meaning it is taken in by plants during photosynthesis, not released.
4. Water-vapour: Plants release water in the form of water vapour through a process called transpiration, which is different from photosynthesis. While transpiration often occurs simultaneously with photosynthesis (as stomata are open for \(\text{CO}_2\) uptake), water vapour is not a direct product of the photosynthetic reaction itself in the same way oxygen is.

Therefore, the gas released by the green plants specifically as a product of photosynthesis is oxygen.

Photosynthesis Inputs and Outputs Summary

Revision Table: Key Aspects of Photosynthesis

Additional Information on Photosynthesis

Understanding photosynthesis involves knowing a few more details:

• Chloroplasts: These are organelles within plant cells where photosynthesis takes place. They contain chlorophyll.
• Chlorophyll: The green pigment that captures light energy needed for the reaction.
• Stomata: Small pores on the surface of leaves, primarily on the underside, that regulate gas exchange (\(\text{CO}_2\) intake and \(\text{O}_2\) and water vapour release).
• Light-Dependent Reactions: The first stage of photosynthesis where light energy is absorbed to create ATP and NADPH (energy carriers) and water is split, releasing oxygen.
• Light-Independent Reactions (Calvin Cycle): The second stage where ATP and NADPH are used to convert carbon dioxide into glucose. This stage doesn't directly require light but uses products from the light-dependent reactions.

The release of oxygen occurs specifically during the light-dependent reactions when water molecules are split (photolysis). This makes oxygen a direct byproduct of using water and light energy in the initial steps of photosynthesis.